Greg Loeb, Department of Entomology
Cornell AgriTech, Cornell University
New York State Agricultural Experiment Station, Geneva NY 14456
As of this writing (May 22, 2024), degree day accumulations since Jan 1 are somewhat advanced compared to the last few years. Related, there was significant freeze damage to tender shoots on Long Island and Lake Erie regions at the end of April. ields will be likely be down in these areas; amount varying by cultivar and severity of damage. For vines with reduced yield due to freeze damage, you might see greater damage to clusters by some direct pests, such as grape berry moth, as they concentrate on fewer clusters. For vines with lower crop load but otherwise have adequate to excessive canopy growth, freeze damage will likely exaggerate canopy growth. Under such circumstances, the vines should be able to tolerate higher levels of damage from leaf feeing pests like grape leafhoppers or Japanese beetles. However, if it’s a less vigorous vineyard with low vine size, controlling leaf feeding insects presents an opportunity to increase vine size and future productivity.
My goals for this review are to 1) review the main arthropod pests to keep in mind as the season progresses, including new invasive insects that pose a risk to grapes, 2) provide some basic background on biology and ecology that helps in understanding different approaches to management, 3) summarize results from recent research, and 4) provide an update on changes in chemical control options. I want to acknowledge and thank the extension educators out in the grape growing regions of New York and Pennsylvania for their assistance and input for this review. Let me get started by highlighting changes in the NY and Pennsylvania Grape Guidelines for 2024, which should be coming out soon.
Update from NY and Pennsylvania Grape Guidelines and other chemical news
As has been the case the last few years, there are only a few, relatively minor changes to insecticides and miticides available for use on grapes in the 2024 grape guidelines. To my knowledge, there has not been any insecticides with new active ingredients labeled for grapes this past year. We have been running some efficacy trials for new chemistry targeting grape berry moth and also vinegar flies the past few years. It has looked pretty good on berry moth. At some point, I expect it will get a grape label, although the company is prioritizing some other crops initially. There is another diamide insecticide (Shenzi 700 WP, EPA # 70506-609, UPL) with the same active ingredient that is in Altacor [chlorantraniliprole]. Relevant pest insects on the label include gape berry moth, climbing cutworm, and Japanese beetle. As is true for other diamides, Shenzi is not allowed for use on grapes on Long Island. The only other note I wanted to make on “new” insecticides is that the neonicotinoid Assail [acetamiprid] has an SC formulation labeled for use on grapes. Actually, this was first registered in 2021, but I missed it and it is not in the guidelines. It pretty much has the same pests on the grape label as the SG formulation.
Mentioning neonicotinoids reminded me to briefly comment on the new NY State legislation (Birds and Bees Protection Act) recently signed into law that places restrictions on the use of products containing neonicotinoid active ingredients in order to reduce impact on pollinators. The new law will not impact grape production. It is mainly targeting use of neonicotinoids in seed treatments for field crops and also in turf. Restrictions will be phased in over the next several years, with the potential for waivers.
Finally, I did want to highlight some new information on the likelihood that at least populations of grape berry moth in western NY have developed resistance to the pyrethroid insecticide Danitol 2.4 EC [fenpropathrin]. We have been testing the efficacy of a number of different insecticides against grape berry moth at CLEREL in Portland, NY over the past several years and have included Danitol as a standard. Danitol has been providing less and less control of GBM over time relative to unsprayed vines. In 2023 we ran a large trial comparing efficacy of a number of labeled insecticide classes against GBM and found that Danitol provided no control whereas all the other products, including other pyrethroid insecticides like Mustang Maxx [zeta cypermethrin], Brigade [bifenthrin] and Baythroid [cyfluthrin], were reasonably effective suggesting this is a resistance issue for Danitol specifically. Note that we have only tested GBM in the area of CLEREL so we don’t know how widespread of an issue this is. Based on some informal surveys, NY and PA growers do not use much Danitol for GBM, but it is something to pay attention to if you are still using it for GBM.
Update on Spotted Lanternfly
Spotted lanternfly (SLF) has continued to spread out from its area of first detection in Pennsylvania. The NYS IPM program has been regularly updating the reported distribution map for SLF and you can go to this link to see the latest update. Native to parts of Asia, this phloem-feeding planthopper was first discovered in the USA in the fall of 2014 in Berks County, PA. It can build to very large numbers and feed on ornamental plants, native perennials, fruit trees and grapes. Indeed, in the quarantine zone in PA, grapes are the most negatively impacted crop. SLF has now also been causing economic damage to grapes in Virginia and New Jersey and late in the 2022 field season SLF was found on vines in a commercial vineyard in NY (Hudson Valley region) at low numbers. In 2023, SLF did not cause economic damage to any commercial vineyards in NY, though over time, we do expect populations to continue to build and presenting an increasing risk for grapes. SLF has not been detected on grapes in other grape growing regions of NY but is getting close on Long Island (found in Suffolk County), Finger Lakes (established population in Monroe County) and Lake Erie (established population in Buffalo). Given the rate of movement of SLF observed over the past several years, we will likely get more reports of infestations in NY vineyards this growing season, though predicting exactly where is challenging. Importantly, it takes a few years for populations to build in the surrounding landscape before they begin cause economic damage in vineyards. However, it’s prudent for NY growers (and PA growers outside the quarantine zone) to be on the alert and continue educating themselves on where to look for, and how to identify SLF immatures and adults, where to report findings, and management alternatives.
NYS Agriculture and Markets is leading NY’s SLF efforts, working closely with USDA APHIS and Cornell (NYS IPM program, NE IPM program). NY growers can find more information on identification of SLF, signs of infestation, and reporting at NYS Ag & Mkts web site at https://agriculture.ny.gov/spottedlanternfly , along with the NYSIPM web site indicated above. There is also a wealth of information put together by the PA extension team on SLF (see https://extension.psu.edu/spotted-lanternfly). Check out this short video on SLF produced by Lake Erie Regional Grape Program Leader Jennifer Phillips Russo. PSU entomologists have also prepared an extension publication (updated late in 2023) specific to managing SLF in vineyards at this link (https://extension.psu.edu/spotted-lanternfly-management-in-vineyards).
As a quick reminder on the life cycle of SLF, it has only one generation per year. It overwinters in the egg stage. Egg masses are laid on all sorts of surfaces (trees, brick walls, carts, trailers, etc.) in late summer (see Fig. 1), starting in August and continuing late into the fall. The eggs hatch in the spring, about the time this newsletter gets circulated. The nymphs feed on various host plants, including grapes, but many other plant species, and they move around quite a bit. Especially early in the invasion, most SLF are found in the landscape outside the vineyard. SLF become adults in later summer (see Fig. 2).
SLF nymphs and adults feed on many different wild plants as they develop and mature, but they clearly perform better and can lay more eggs when feeding on the invasive tree of heaven (TOH, Alianthus altissima). New infestations of SLF are most often first discovered associated with TOH. Penn State Extension has put together an informative fact sheet on how to identify TOH (https://extension.psu.edu/tree-of-heaven). For grape growing regions in NY and PA that do not yet have SLF, it would be beneficial to start scouting, especially emphasizing looking for SLF on or near your vineyards. Hans Walter-Peterson, Dr. Terry Bates, and myself were funded by NYW&G Foundation to develop educational materials and mapping tools connected with MyEV (spatial mapping tool, efficient vineyard, see https://www.efficientvineyard.com/) to assist growers with identification of TOH and mapping its location on or near their vineyard blocks. We have also developed a factsheet on distinguishing TOH from look alike species black walnut and staghorn sumac which can be linked to here.
SLF uses their sucking mouthparts to feed on plant phloem. They process a lot of phloem to extract needed nutrients, eliminating copious amounts of liquid out their rear ends. This sugary excrement is a great resource for sooty mold, which is commonly associated with SLF infestations. In terms of damage to grapevines, with sufficient numbers, their feeding stresses the vine. Although we do not yet have good estimates on the economic threshold for SLF, we do think it takes a good number of them (> 15 or 20 adults per vine) to cause economic injury. It takes many more nymphs to cause economic injury compared to adults, although that can occur in heavily infested areas. Much of the damage to grapevines appears to be caused by the adults, however, which repeatedly migrate into vineyards from the outside around harvest and into the postharvest, potentially building to large numbers and greatly stressing vines. Of course, vine age and health, soil fertility, cultivar, etc. will influence the relationship between SLF density and vine damage. An additional potential way adult SLF could cause economic damage for juice grapes is through being collected with the grapes by the machine harvester and delivered to the processing plant where they could present significant contamination issues. There is basically no observational or experimental data available at this time to evaluate how significant a risk this represents. As part of a new USDA SCRI (Specialty Crops Research Initiative) currently under review, we hope to begin research on this risk and potential management tactics.
Several insecticides with different modes of action are labeled on grape for controlling SLF (some require a 2ee label exemption in NY) and they are generally effective. Labeled insecticides are listed in the grape management guidelines under spotted lanternfly. We also have developed a quick guide that lists insecticides labeled for use on grapes in NY for SLF, along with information on efficacy, restrictions, etc, which is available through the NYS IPM web site (https://cornell.app.box.com/s/vvjw2hy84obrmtoe7bhzj2vyz2k6wwm8). The insecticides we have available for SLF are generally effective in killing either the nymphal and/or adult stage. The big challenge in areas where SLF populations are high, however, is the repeated movement of adults from the surrounding landscape into the vineyards thereby requiring repeated control applications.
Review of key arthropod pests
Unlike the situation with grape diseases, where there is a clear big 4 or 5, for arthropods there is one key pest (grape berry moth) that is widespread and causes serious damage most years and then a dozen or more pests that can create major problems but typically vary in abundance and pest potential from season to season and place to place. It’s clearly a challenge to be able to recognize all of these potential pests and/or their symptoms and be familiar with different management options. Hopefully this review will be of use in this regard. I will focus on the grape pests that have a moderate to large potential to cause economic injury as we progress through the field season. For the sake of completeness, I am including information that is pretty much a repeat from previous years. However, pay particular attention to updated information on grape berry moth and vinegar flies and sour rot based on recent research.
More details on control measures can be found in the New York and Pennsylvania Pest Management Guidelines for Grapes: 2024. The guidelines should be out before we get too far into the season. For greater focus on organic options, refer to the online organic grape guide at https://ecommons.cornell.edu/handle/1813/42888.3. Before applying any chemical control measure make sure to read the label, taking into account things like mode of action (IRAC code), potential for phytotoxicity, labeled pests, re-entry and days to harvest intervals, effects of pH, compatibility with other pesticides, seasonal and per application restrictions, and impact on beneficials. The IRAC code categorizes active ingredients by how they mechanistically impact the arthropod. To reduce the risk of some species developing resistance to a particular active ingredient, its prudent, where possible, to rotate among different modes of action. Also keep in mind that in NY, the pest needs to be on the registered product label to be used, unless a 2(ee) exemption has been approved and is in hand. This extra requirement is not the case in PA and most other states.
Arthropods are generally detectable in the field before they cause economic injury. Moreover, most insecticides and miticides work as eradicants as opposed to preventative agents. They can be quite expensive and some are harsh on beneficial insects and mites and there is the risk of pests developing resistance. Because of all these factors, it is advisable to monitor pest densities and only apply control measures when economically justified.
Budswell to Bloom
Steely Beetle (grape flea beetle) and Climbing Cutworm
The steely beetle (small, shiny black or dark blue in color) overwinters as adults and become active as temperatures increase in the spring. A fact sheet on steely beetle can be found at https://ecommons.cornell.edu/bitstream/handle/1813/43101/grape-flea-beetle-FS-NYSIPM. pdf?sequence=1&isAllowed=y. They feed on swollen buds prior to budbreak with the potential of causing considerable damage under the right conditions; specifically when we get a prolonged swollen bud stage. We are past this stage so normally there would be no further threat until next season. However, because of recent freeze damage in some areas, secondary buds will push and they could be vulnerable to adult steely beetles. Look for damage from steely beetle along the edges of the vineyard. After budbreak the adult steely beetle is no longer a threat. Although steely beetle larvae will feed on grape leaves later in the early summer, this damage is not economically important. Climbing cutworm (fact sheet at https://ecommons.cornell.edu/bitstream/handle/1813/43085/climbing- cutworms-FS-NYSIPM.pdf?sequence=1&isAllowed=y) refers to larvae of several species of Noctuid moths that cause a similar type of damage as steely beetle. Larvae hide during the day in the leaf litter or grass below the vine and then climb up into the vine to feed on buds and very young shoots on warm evenings. Grass under the vine may increase problems from cutworms. Use about 2% bud damage from either species as a threshold for treatment. Some hybrids with fruitful secondary buds that tend to overcrop can probably handle higher damage levels. There are several effective, broad-spectrum, insecticides labeled for steely beetle and climbing cutworm in grapes. Rather than providing a complete list here, I refer you to the guidelines.
Soft Scales and Mealybugs
Soft scales and mealybugs are sucking insects that spend part of their life-cycle on the canes or the trunk and part on leaves or fruit. At high densities they can reduce vine vigor or contaminate grape clusters with their sugary excrement, which supports the development of sooty mold. However, the major concern with soft scales and mealybugs in our area relates to their potential to vector viruses that cause grape leafroll disease. This is a serious disease of V. vinifera grapevines (a fact sheet on leafroll is available at https://ecommons.cornell.edu/bitstream/handle/1813/43103/grape-leafroll-FS- NYSIPM.pdf?sequence=1&isAllowed=y). Soft scales and mealybugs are able to vector grape leafroll disease even at low densities. Indeed, the more we look, the more vineyard sites we find that have either soft scales or grape mealybug or both types at low densities. Soft scales in our area overwinter on canes as large immatures or young adults. At this stage they vary in shape and color but are typically brown or gray and look like bumps or large scales on the canes. They have limited ability to move at this stage. As the spring progresses they complete development, mate and begin laying eggs (mid-May to early-June), often many hundreds to over a thousand per female. The eggs hatch into mobile crawlers that disperse out on to the foliage to feed. The significant species of soft scales found on grapes in our area (lecanium scale, cottony maple scale) have just one generation per year. As they mature during the season, they move back to the canes to overwinter.
Grape mealybug in our area predominantly overwinters on canes or trunks as crawlers (first immature stage after hatching from eggs) near their egg sack, moving out from trunk wood to first or second year wood in spring (at budswell, see Fig 3). These crawlers like to hide under loose or cracked bark; look where one-year canes have been bent over trellis wire. As they become adults, they move back to the trunk region to lay eggs (around mid-June). The first instar crawlers (summer generation) are observed around the beginning of July. These crawlers go on to mature, being found on various tissue including clusters. As they become adults, they migrate back to the trunk regions to lay eggs (mid-August), which mostly hatch and then spend the winter as first instar crawlers. Working with Dr. Marc Fuchs, virologist at AgriTech, we have documented that grape leafroll disease has increased within a vineyard over time in several different vineyard blocks in the Finger Lakes indicating that insect vectors are likely responsible. Note that the virus is not passed on to the eggs from the female.
The newly hatched crawler must acquire the virus when it feeds to be able to transmit to it. Once acquired from an infected plant, if the insect moves on to an uninfected vine before it molts, it can spread the disease. Since crawlers are the most active stage of both mealybugs and soft scale, they are the most likely stage to spread the disease. Our research has shown that overwintering crawlers in November were generally not infected with grape leafroll associated viruses (GLRaV) even though they were present on infected vines. However, we discovered that in April/early May the now overwintered crawlers were infected at high levels (>70%) suggesting they had fed on the vine and acquired the virus sometime between late fall and late April prior to budbreak. We hypothesize that the crawlers may be particularly important in spreading the virus within a vineyard during the spring since there is little or no foliage to impede movement from vine to vine.
An important question is whether insecticides targeting the insect vector can be used to slow the spread of leafroll disease within a vineyard? Experiments conducted over the past several years suggest that using an effective insecticide against grape mealybug, such as Movento [spirotetramat], can slow the spread to some degree. The results were not overwhelming, however, and disappeared the year after we stopped applying Movento. It is possible that combining effective chemical control of the vector with rogueing out infected vines may suppress or stop the spread
of the disease. We tested this idea at a vineyard in the Finger Lakes over a six year study from 2016-2021. We had four treatments (with replication): rogue out leafroll infected vines and the two neighbor vines on either side within a row (the recommended approach when disease incidence is below 25%), treat vines with insecticide (split applications of Movento, 6.25 fl oz/A at about bloom and 6.25 fl oz/A one month later), rogue and treat with insecticide, or do nothing (control). We documented excellent control of mealybugs in plots treated with insecticide (Fig 4). The impact on leafroll disease is more complicated. Over time rogueing greatly reduced the number of new infected vines to virtually zero. We see a similar pattern for rogueing plus insecticide. A careful examination of the data from this experiment indicates that the strategy of removing two vines on either side of an infected vine, something referred to as spatial rogueing, is justified, for at least several seasons. Interestingly, and somewhat surprising, controlling the vector (grape mealybug) without rogueing had little impact on spread of leafroll (see Fig 5). Under higher mealybug populations it is possible that treating them with insecticide, in combination with rogueing, would be beneficial in controlling disease and perhaps more effective than rogueing alone.
There are multiple insecticides labeled for use against grape mealybug. Fewer options are labeled for soft scale. See Grape Pest Management Guidelines for a full listing. For both pests, there are two times during the season where non-systemic chemical control is most effective: in the spring at or just prior to budbreak targeting the overwintering stage of the insect and during the growing season right after egg hatch targeting the crawler stage (first instar immature). A delayed dormant oil application has been shown to be effective in controlling soft scale in other crops and I would expect it would work in grapes, though I have not specifically tested this. The oil smothers the soft scale, which are often out on the canes where they are exposed. Delayed dormant oil was not particularly effective against grape mealybug in our trials, however. We believe that is because the overwintering mealybug crawlers are protected under loose bark on the trunk.
As indicated above, during the growing season the systemic insecticide Movento [spirotetramat] has been very effective in controlling grape mealybug in our trials (2 applications, 6.25 fl oz/A per application, 30 days apart). As a reminder, spirotetramat is also one of the active ingredients in Senstar. Both the Movento label and Senstar label for grapes now include suppression of European fruit lecanium scale. The neonicotinoid insecticides Admire Pro [imidacloprid] and Platinum [thiamethoxam] (not allowed on Long Island), when applied through a drip system and therefore systemic throughout the vine, are effective against grape mealybugs. Admire Pro (when applied via drip to soil) also includes European fruit lecanium scale on the label.
For contact insecticides, it’s important to target the mobile crawler stage (stage after hatching from the egg) since the crawlers actively move around the vine and are more likely to get exposed to the insecticide residue. The question is how to time egg hatch? Right now we don’t have a validated degree-day model to predict this timing. A number of years ago, however, we did obtain some initial estimates and found egg hatch for grape mealybug occurred at around 800 DD (starting Jan 1, base 50 F) which that year was around July 1 while we observed the first crawlers of soft scale insects at around 650 DD (starting Jan 1, base 50 F) which that year was third week of June. If you do have soft scale insects or mealybugs in your vineyard, one thing you can do is check the status of eggs underneath soft scale (mostly on canes) or adult grape mealybug females (under loose bark on trunk wood). With a hand lens you should readily be able to see the eggs and crawlers if present.
During the growing season carbaryl is labeled for European fruit lecanium and an insect growth regulator called Applaud [buprofezin] is labeled for both soft scale and mealybugs. Note that Applaud is not legal to use on Long Island. Another insecticide labeled for lecanium scale on grapes is Knack [pyriproxyfen, the same active ingredient combined with spirotetramat in Senstar], an insect growth regulator. Knack is allowed on Long Island.
Plant bugs
There are at least two species of plant bugs that have the potential to cause significant damage to grapes prior to bloom: banded grape bug and Lygocoris bug. These insects are only a threat up to bloom. Both species overwinter as eggs, presumably on grape canes, emerging as nymphs shortly after budbreak to 5 inch shoot growth. The banded grape bug (BGB) nymph is greenish to brown in color with black and white banded antennae (see Fig. 6). Nymphs of Lygocoris are pale green with thin antennae and
about half the size of BGB. Nymphs of both species can cause serious economic damage by feeding on young clusters (buds, pedicel and rachis) prior to flowering. Adults, which appear close to bloom, do not cause economic damage and for at least one of the species (BGB), become predaceous on small arthropods. There is only one generation per season. Monitor for nymphs by examining flower buds on approximately 100 shoots along the edge and interior of vineyard blocks. A video demonstrating scouting techniques for banded grape bug can be found at https://www.youtube.com/watch?v=FrEJ6IJB_is. These plant bugs are sporadic from year to year and from vineyard to vineyard; most vineyards will not require treatment. If present at relatively low numbers (1 nymph per 10 shoots), they can cause significant yield reductions and hence it is worth the time to check. Pay particular attention to vineyard edges. Remember, though, by the time you reach bloom, it is too late to treat. There are several insecticides labeled for use against banded grape bug (Imidan [phosmet], Danitol 2.4 EC [fenpropathrin], Assail 30 SG [acetamiprid] and Cyclaniliprole + Acetamiprid 130 SL).
Grape Plume Moth
This is another potential pest of grapes that overwinters as eggs in canes and emerges shortly after budbreak. Larvae typically web together young leaves or shoot tips and leaves to form a protective chamber from which they feed (Fig. 7). Research indicates 1) that damage tends to be concentrated on the vineyard edge near woods and 2) that it takes quite a few plume moth larvae to cause economic damage. For Niagara grapes we were unable to detect a statistical effect on vines with 20% infested shoots compared to control vines. Nevertheless, the trend was for reduced yield associated with high plume moth infestations (>20%). For higher value cultivars a somewhat lower threshold would be appropriate. Treatment of plume moth can be tricky for several reasons. First, the larvae develop very quickly and often have reached the pupal stage before you even recognize there is a problem. Second, larvae inside their leaf shelters are protected from insecticides. For these reasons, it’s important to monitor and treat for plume moth early in the season (before 10 inch shoot stage) using sufficient water to achieve good coverage. Danitol is the only insecticide labeled for use against grape plume moth in NY (2(ee) recommendation). Dipel can be used in PA, as well as some other insecticides labeled for use on grapes.
Grape Cane Gallmaker
The grape cane gallmaker is a beetle in the weevil family. You can find a fact sheet on GCG at https://ecommons.cornell.edu/bitstream/handle/1813/43098/grape-cane-gallmaker-FS-NYSIPM. pdf?sequence=1&isAllowed=y. The adult is quite small (less than
¼” or 3 mm long) and reddish brown in color (Fig. 8). Adults overwinter in debris on the ground and become active in Spring. Egg-laying occurs in May and June when shoots are between 5” to 20” (25 to 50 cm) in length. The female weevil 
hollows out a small cavity along the shoot just above a node and places a single egg. She fills the cavity with frass and then goes on to create additional cavities along the shoot (up to 14). Only the first has an egg, although other adults may join in such that you can find more than one gall with a larva per shoot. In response to the adult weevil feeding damage, the vine forms a gall (swelling) around each of the cavities (Fig 9). The egg hatches and the larva feeds on grape tissue that forms around the cavity, emerging as an adult later in the summer. The galls typically do not kill the shoot but can create areas of mechanical weakness that can lead to breakage (Fig 10). And if numerous enough, galls can truncate shoot growth.
Grape cane gallmaker is considered a minor pest, generally not requiring control. However, there have been increasing reports of extensive galling on grapevines of several different cultivars in the Finger Lakes region, especially around Keuka Lake, but also Seneca Lake, to the extent that chemical control may be warranted. Insecticides should target the adult stage during May and June. In severe situations, multiple applications, starting at 2-4 inch shoot growth, may be necessary to get things under control. There are a limited number of products labeled for grape cane gallmaker including Danitol, Baythroid, and Leverage.
Rose Chafer
Rose chafer is a beetle in the same Family (Scarabaeidae) as
the Japanese Beetle. Rose chafer adults feed on a variety of host plants (e.g., roses, tree fruit, small fruit, etc.) but in our area the preferred host is grape. Although rose chafers are not a widespread problem, in some vineyards in the Lake Erie Region, these beetles can cause significant crop loss in vineyard blocks where they occur. Vineyard blocks with sandy soils (particularly sandy sites from the lake front to just south of Route 5 in North East, Pennsylvania) have the most persistent problem with this pest. I have also seen spotty problems on sandy knolls in some blocks in the grape belt. Every year in early June (about 7-10 days before bloom) in the Lake Erie Region, large numbers of rose chafer beetles emerge from the soil at the same time and begin mating and feeding extensively on tender flower clusters. Beetles will also feed on grape leaves but over the years I have only seen minimal injury on Concord leaves. Feeding continues to occur in vineyards for about a 3-week period. Fortunately, there is only 1 generation per year. Adult beetles are about ½ inch long, have a light brown-tan body coloration and long, spiny legs (Fig. 11). Females prefer laying eggs in grassy areas with sandy soils. Rose chafer grubs are C-shaped and have a white body with a brown head capsule. They are similar in appearance to Japanese beetle grubs. These larvae feed on roots of grasses, weeds and other plants during the summer. Vineyards with a history of this pest or blocks with sandy soils should begin scouting about 10 days before bloom. Scouting for this pest should be conducted daily, if possible, but at a minimum of 3 times/week and should continue for about 2 weeks after bloom. Infested areas can lose extensive numbers of flower clusters if beetles are not detected early and treated. Research from Ohio State recommends an insecticide application if a threshold of 2 beetles per vine is reached. Blocks with high populations of rose chafers may require a second insecticide application. Insecticides for management of rose chafer listed in the guidelines include Assail, Danitol and Sevin.
Bloom to Mid-season
Grape Berry Moth
Grape berry moth (GBM) is familiar to most grape growers in our region. Despite this familiarity, managing this pest is still challenging, especially late in the growing season. Part of the key to successful management of GBM is having a good understanding of its phenology (timing of the different stages of its life cycle), combined with scouting and use of the Grape Berry Moth Degree Day Model found on NEWA, so that management actions are properly timed. Of course, getting good spr ay coverage on fruit is also critical, which can be a challenge in itself, especially later in the season for cultivars with dense canopies like Concord.
GBM has several flights during the growing season (3-4) starting around bloom and continuing, in some years, well into September. A temperature-driven phenology model has been developed for GBM, using bloom date of wild grapes as the starting point for accumulating degree days (biofix), that helps predict timing of egg-laying associated with these flights. Knowing when most eggs are laid is important for effective chemical control since insecticides mostly target the young larvae before they have a chance to enter the berry where they are well protected. The GBM phenology model is available to growers through the Network for Environment and Weather Applications (NEWA) web site (http://newa.cornell.edu/) along with management guidelines. The GBM model is most useful for timing the second and third flights of the season, but less helpful for timing subsequent flights. Part of the reason is that by late season, the flight period becomes less synchronous and more spread out such that eggs are being laid continually. Therefore, we are recommending growers use the phenology model to time the second and third flights but beyond that, in warm years and for high-risk sites, growers should continue spraying on a 7 to 10 day rotation until about mid-September when egg laying pretty much stops.
At any given date, the model will provide the degree-day accumulations from the biofix, a forecast of accumulation over the next several days, and pest management advice based on current degree day accumulations. For example, as accumulation gets close to 810 degree days (the estimated degree days required to develop from an egg to an egg-laying female moth), the program notes that this is approaching the peak of the second GBM flight and you are advised to apply an insecticide at near 810 for a high risk site and to scout for damage for low or intermediate risk sites. The NEWA forecast makes a distinction between insecticides that need to be consumed (e.g. Altacor [chlorantraniliprole], Intrepid [methoxyfenozide]) where the timing should be close to 810 degree days and those that work mostly through contact (e.g. Brigade, Danitol, Baythroid, Sevin) where timing should be between 810 and 850. It’s important for both intermediate and high-risk vineyards for the second and third generations to scout for damage. The timing of scouting should be just prior to predicted peak flight and initiation of egg- laying (810 degree-days after biofix for second generation and 1620 degree-days after biofix for third generation). If it were easy to see GBM eggs, then the scouting could be helpful for timing insecticide applications. However, it is very difficult to scout for eggs. Therefore, the purpose of the scouting is to get a handle on potential damage levels and whether you are exceeding economic thresholds. For Concord grapes, if the percent of clusters that show some GBM damage to berries is <6% at second flight and <15% at third flight, then a treatment is not recommended. These levels can be used as a guide for wine grapes. However, for high value vinifera cultivars, especially cultivars with tight clusters prone to fruit rots, the thresholds should be lower. Note that for super high-risk sites where GBM damage can be extreme, we do recommend a spray at the traditional 10-day postbloom period that targets offspring of the first flight of the season. For most vineyard sites, though, the 10-day postbloom spray does not provide much benefit.
It is becoming more common to hear about situations where growers are seeing unexpected levels of grape berry moth damage late in the growing season (September and into October). This is part of a larger concern that growers are not getting good control of grape berry moth in some regions, especially in the Lake Erie Grape Belt. There are several possible explanations which are not necessarily mutually exclusive. One possibility is that GBM has developed resistance to some of the most commonly used insecticides resulting in higher overall populations. As noted above under chemical news, we have been investigating this issue over the past several years at CLEREL. In 2023, we conducted a large field trial assessing the efficacy of a number of different insecticides labeled for use against GBM in NY across several different active ingredients. Our results are summarized in Table 1. Danitol 2.4 EC did not provide any control of GBM damage in this trial which is consistent with what we have been seeing in previous years. Although we have not done the careful laboratory-based research to quantify the level of resistance or the mechanisms involved, I feel confident in the conclusion that at least populations of GBM in the area around CLEREL have become resistant to Danitol. I don’t know if GBM in other grape growing regions of NY are also resistant, but its worth being aware of the potential. On the positive side, the other pyrethroids included in this trial did provide reasonably good control as did products based on other modes of action such as Intrepid (growth regulator), Delegate (spinosyn), and Altacor (diamide). In this trial, Delegate was particularly effective.
A second hypothesis is that the NEWA GBM phenology model is no longer accurately predicting peak GBM egg laying, especially for later generations. For example, it’s possible that 810 degree days to develop between an egg and an egg-laying female is no longer appropriate. The GBM phenology model was developed over 20 years ago and perhaps it needs re-evaluation. We plan to use UV light traps at CLEREL this field season to collect adult GBM and determine if peak flights are still lining up well with degree day predictions.
A third hypothesis, related to the second one, is that the conditions triggering diapause has changed such that pupae are entering diapause later than our current estimate of early August. Recall that diapause allows the pupal stage to better survive harsh winter conditions and that diapause is induced when eggs or very young larvae are exposed to shortening day length (under 14 hours, around the start of August). If GBM starts requiring shorter day length to induce diapause, this would result in more adults flying and laying eggs later in the fall than has occurred in the past.
As we delve into some of these explanations for why we are not achieving as good of control of GBM as in the past, I would recommend still using the NEWA GBM model, with monitoring, for the second and third flights. Beyond the third flight, especially for high-risk sites, my recommendation is to use a 7-10 day rotation of insecticides, paying attention to label restrictions such as days to harvest. There are many options available for chemical control of GBM. See New York and Pennsylvania Pest Management Guidelines for Grapes for a full listing. The most commonly used products are the pyrethroids (Danitol, Brigade (including several generic products with the active ingredient bifenthrin), Baythroid, Mustang Maxx, Hero). Pyrethroids are broad-spectrum and will kill a number of other insect pests, as well as beneficial insects. Leverage and Brigadier both include a pyrethroid that provides control of GBM and a neonicotinoid that provides good control of sucking insects like leafhoppers (see below). I would shy away from Danitol for GBM control given our recent efficacy trial results. Other broad-spectrum insecticides labeled on grapes for GBM include Sevin and Avaunt (carbamate class) and Imidan (organophosphate class).
There are several additional, more narrow-spectrum, materials registered for use against GBM. Dipel, Biobit, Deliver, and BT Now are organic options that have been around for a number of years. The toxin produced by the Bacillis thuringiensis (Bt) bacteria is specific to Lepidoptera. We have found that 2 applications of Bt per GBM generation improves efficacy. Use sufficient water to achieve good coverage of fruit since the larvae must consume the Bt as they enter the berry for it to be effective. Good coverage is an issue for all the GBM materials. Delegate is another fairly selective material that is effective. The insect growth regulator Intrepid has proven quite effective and has been in use on grapes in many states for nearly 20 years. Relatively recently New York grape growers are allowed to use Intrepid for GBM management through a Special Local Needs label (but not for use in Nassau and Suffolk Counties). A copy of the SLN label, and the Intrepid label, must be in the possession of the applicator if Intrepid is applied in NYS. Intrepid is a selective material active against the larvae and eggs of many species of Lepidoptera including GBM. Intrepid has fairly long residual activity and is an excellent choice for the second generation treatment in July as it may provide some control of the overlapping third generation as well. Finally, several anthranilic diamide insecticides (diamides) have been labeled for use on grapes for GBM (also not allowed on Long Island) in the last several years (Altacor WG, Altacor Evo, Shenzi, Verdepryn 100 SL, Cyclaniliprole 50 SL, Voliam Flexi WG [chlorantraniliprole + thiamethoxam]). These materials are pretty selective for Lepidoptera such as GBM and have pretty good residual activity. Similar to Intrepid, Delegate, and Bt, they work best when ingested by the first instar (recently hatched) larvae as they try to move into the fruit.
Mating disruption involves the release of the synthetic version of the sex pheromone that a species uses to locate mates. The synthetic pheromone interferes with mating thereby reducing the amount of egg-laying. Mating disruption has been successfully used for a number of different insect pests of fruit crops, especially Lepidopteran pests where females release a specific-specific pheromone that attracts males for potential mating. There is a mating disruption product for GBM (Isomate-GBM plus) although it is no longer available for sale in NY or PA. The company was not making sufficient sales to justify continuing to market their product. It is still being sold and used in Canada. Several of us tested Isomate-GBM plus in NY, PA and MI in mostly concord vineyard blocks a few years ago with mixed results. In general, mating disruption works best when used over larger acreage (area-wide disruption).
Grape Leafhoppers
There is a suite of leafhoppers that feed on grapes. TheEastern grape leafhopper Erythroneura comes (pale white in summer) mainly feeds on native cultivars like Concord (see fact sheet at https://ecommons.cornell.edu/handle/1813/43102 ))
while several additional species feed on V. vinifera and interspecific hybrids including E. bistrata/vitifex, E. vitis, E. vulnerata, and E. tricinta. All these Erythroneura leafhoppers have similar life-cycles. They overwinter as adults and become active as temperatures warm up in the spring. They move on to grapes after budbreak, mate and begin laying eggs around bloom. There is one full generation during the summer and a partial second. In warm years there is a potential for a nearly full second generation of nymphs and adults. Both nymphs and adults cause similar damage; removal of leaf cell contents using sucking mouthparts causing white stippling (Fig 12). Hence, moderate densities can reduce photosynthesis, ripening and yields. Severity of damage is increased in dry years, assuming irrigation is not available. Sampling for leafhoppers corresponds to sampling for grape berry moth. At the immediate post bloom period sucker shoots should be examined for evidence of stippling (white dots on leaves caused by leafhopper feeding). If you see stippling throughout the vineyard block an insecticide treatment is recommended. The next sampling period for leafhoppers is mid-July and focuses on abundance of first generation nymphs. Check leaves at the basal part of shoots (leaves 3 through 7) for leafhopper nymphs or damage, on multiple shoots and multiple vines located in the exterior and interior of the vineyard. Use a threshold of 5 nymphs per leaf. The third time for sampling for leafhoppers should occur in late August. This focuses on nymphs of the second generation. Follow a similar sampling protocol as used at the end of July, using a threshold of 10 nymphs per leaf. Note if you have made previous applications of insecticides for leafhopper (or broad-spectrum insecticide for GBM), it is very unlikely that it will be necessary to treat for grape leafhoppers in late August. If you do not observe much stippling it is not necessary to more carefully sample for leafhopper nymphs.
There is a modified approach to monitoring grape leafhopper based on the presence or absence of a certain amount of stippling of leaves (as depicted in a photograph on the scouting form) as the key to determining whether a leaf was “damaged” by leafhopper. If you scout for leafhoppers in July while scouting for GBM you can head off any problems. At least in Concord, we have not seen where it has been a problem late in the season if it was not above threshold in July.
There are several choices of pesticides to use against leafhoppers. Sevin, or other carbaryl products, was a standard for many years and is likely still effective except in isolated pockets of Concord and other native grapes around the Finger Lakes where we have observed control failures suggesting emergence of resistance. There are many effective alternatives to Sevin (see New York and Pennsylvania Pest Management Guidelines for Grapes for a full listing).
Potato Leafhopper
The potato leafhopper is quite distinct from grape leafhoppers discussed above. One big difference is that potato leafhopper originates each year from the southeastern US (it cannot successfully overwinter in upstate NY or PA) while grape leafhoppers are year-round residents to our area. The overwintered, winged adults ride north on warm fronts and usually arrive in our area sometime after bloom. When and where they arrive is not very predictable and some years are worse than others. Generally, though, we begin seeing signs of damage in early part of June. Potato leafhopper tends to arrive on Long Island before the Finger Lakes or Lake Erie regions. Vineyards adjacent to alfalfa sometimes get an infestation of potato leafhopper right after the alfalfa is cut. The adult potato leafhopper is iridescent green and wedge-shaped while the nymph is usually green and moves sideway in a unique crab-like manner when disturbed. Instead of feeding on cell contents of leaves like grape leafhoppers, potato leafhopper adults and nymphs use their sucking mouthparts to tap into the phloem vessels of a number of different species of plants including grapes. In the process of feeding, they introduce saliva into the plant that causes, to varying degrees, distorted leaf and shoot development (Fig. 13). Some cultivars of vinifera grapes seem particularly sensitive as does the French-American hybrid Cayuga White, but Labrusca cultivars also show symptoms. Feeding symptoms in grapes include leaves with yellow margins (more reddish for red Vinifera grapes) that cup downward. Often these symptoms are noticed before the leafhoppers themselves.
Potato leafhopper is a sporadic pest, although it can be serious in some places and some years. We currently do not have good estimates for an economic threshold. We do know that shoots will recover from feeding damage once the leafhoppers are removed. Several insecticides are registered for its control in grapes including Sevin, Danitol, Leverage, Assail, Admire Pro, Actara (not for use on Long Island), and Applaud (not for use on Long Island). Note that products containing imidacloprid are considered restricted use pesticides in NY (not PA). Potato leafhopper is fairly mobile, and it may require several treatments over the season as new infestations occur.
Grape Phylloxera
Grape phylloxera is an aphid-like insect with a complex life cycle that causes galls on either leaves or roots. There is a wide range in susceptibility of grape varieties to both gall types. Leaf galls are in the shape of pouches or invaginations and can contain several adults and hundreds of eggs or immature stages (Fig. 14). Leaf-galls first appear at low densities on the third or fourth leaf, probably originating from overwintered eggs on canes. The crawlers from these first generation galls disperse out to shoot tips and initiate more galls starting around the end of June or beginning of July. These second generation galls tend to be more noticeable. At high densities, leaf galls can cause reduced photosynthesis. Labrusca-type grapes and vinifera grapes tend to get few if any leaf galls. Some hybrid grapes, such as Baco Noir, Seyval, and Aurora, can become heavily infested with leaf galls.
Root galls are swellings on the root, sometimes showing a hook shape where the phylloxera feed at the elbow of the hook. Root galls likely reduce root growth, the uptake of nutrients and water, and can create sites for invasion of pathogenic fungi. Labrusca grapes will get root galls but these tend to be on smaller diameter, non-woody roots that may reduce vine vigor in some cases, but are not lethal. The roots of vinifera grapes are very susceptible to the root-form of phylloxera, including galls on larger, woody roots that can cause significant injury and even vine death. Indeed, most vinifera grapes grown in the eastern US are grown on phylloxera-resistant rootstock and this is the primary method for managing the root-form of phylloxera.
Motivated by the difficulties associated with needing to hill up around grafted vines each winter to protect some buds of the scion in the case of a severe winter, we have conducted research to test whether we can manage root-form phylloxera well enough with insecticides to allow the use of own rooted vinifera vines in some circumstances. I won’t go into details here, but we have shown, under on farm research conditions, that the insecticide Admire Pro, applied through a drip system, can greatly reduce phylloxera colonization of own-rooted vinifera over several years. I suspect that Movento, which is quite effective against grape phylloxera, could be used in a similar manner, though we have not explicitly tested it for this purpose. Overall, however, I generally would not recommend using own rooted vinifera in combination with insecticide for managing grape phylloxera. Using a good phylloxera resistant rootstock is a much safer way to go, although there might be very specific situations where own-rooted could make sense.
There are a couple of insecticides labeled for the control of leaf-form phylloxera, although we do not have a well-defined treatment threshold at this time. The neonicotinoid Assail (acetamiprid) and the pyrethroid Danitol (fenpropathrin) are labeled for the leaf-form of grape phylloxera as are the systemic insecticides Movento and Senstar. Soil applied Admire Pro is also systemic to the foliage and therefore will provide control of leaf-form phylloxera as well as some other sucking insects such as leafhoppers. Similarly, the neonicotinoid Platinum (cannot use on Long Island) is also labeled against grape phylloxera.
As noted above, imidacloprid applied through the soil (e.g. Admire Pro) is labeled for grape phylloxera as is Platinum and can provide some control of root phylloxera as well as leaf galls, especially when applied through a drip system. Movento, applied as a foliar spray, has also shown good efficacy on root- form phylloxera in our trials both with V. vinifera vines, but also with Concord. Recall that Concord and other native grapes are moderately susceptible to root galling phylloxera. Overall, our data indicate some benefit to using Movento on native grapes. There are a number of questions remaining, however, that warrant further study. How often does Movento need to be applied to maintain benefits? Can rates or number of applications be reduced while maintaining benefits? Will young vines benefit more or less from Movento compared to mature vines? What are the economics involved? To what extent will some of our hybrid grapes grown on their own roots benefit from Movento?
Grape Rootworm
Grape rootworm was a key pest of grapes in NY and surrounding areas in the early 1900s. Since the sixties, broad-spectrum insecticides targeting grape berry moth greatly reduced the impact of grape rootworm. However, with the use of more selective materials, and less use of insecticide overall in recent years, growers are observing more evidence of this pest, especially in the Lake Erie Region, but also in the Finger Lakes. Grape rootworm is a beetle in the Family Chrysomelidae (flea beetle family). You can find a fact sheet of grape rootworm at https://ecommons.cornell.edu/bitstream/ handle/1813/43105/grape-rootworm-FS-NYSIPM. pdf?sequence=1&isAllowed=y. The adult (Fig 15) feeds on leaf material, creating characteristic chain like
feeding damage (Fig 16). This damage is not economically significant but recognizing these symptoms can help in determining the start of adult emergence. The adults emerge over the middle part of the season, starting around bloom time. After an initial bout of leaf feeding, they mate and the females lay clusters of eggs on older canes, often under loose bark. The eggs hatch and the larvae drop to the ground where they work their way into the soil to find fine grape roots to feed on. Feeding damage by larger larvae cause reduced vine growth and vigor, increased vulnerability to stress, and reduced yields. Adults begin appearing in the Lake Erie region around or shortly after bloom (about 600 degree days, base 50 F) and peak around the third week of June (around 750 DD). Scouting for presence of adults is difficult as they are easily startled and will fall to the ground if disturbed. This behavior has been used to develop a scouting technique using a 2 foot square catching frame covered with a white cloth. To scout, place the catching frame under a vine and give the top wire a shake to dislodge adults. It is then easy to identify any grape rootworm that have fallen onto the catching frame. In terms of chemical control, it appears one well- timed insecticide is sufficient to greatly reduce adult populations. In the research trials, an insecticide applied as soon as scouting indicated the presence of adults provided season long control. In general, we recommend scouting for adult feeding damage around bloom for evidence of adult activity. Also, continue to follow email alerts from the regional grape programs. There are five different insecticides labeled to control grape rootworm: Sevin, Sniper (2ee), Danitol 2.4 EC (2ee), Leverage 360 (2ee), and Admire Pro (2ee). Keep in mind your grape berry moth management strategy when choosing a material for grape rootworm. Seasonal limits should be taken into consideration, so you do not find yourself without good options later in the season. Even though the adult stage does not cause significant damage to vines, it is the target of the insecticides to prevent egg laying and larval infestation. Adult female grape rootworm require a week or two of leaf feeding (pre- oviposition period) before they start to lay eggs. Hence, knowing when adults have emerged from the ground is critical to successful chemical control.
Spider Mites
There are two species of spider mites that attack grapes in the Eastern US; two-spotted spider mite (TSSM) and European red mite (ERM), but ERM typically is the more common. It is important to know the difference between the two species since some miticides are more effective against one than the other. Problems with spider mites tend to be more serious in hot and dry years and later in the season. An important difference between the two spider mite species is that ERM overwinters on grapes as eggs in bark crevices of older wood while TSSM overwinters as adult females, probably in ground cover. As the name indicates, ERM is reddish in color and lays red eggs (Fig. 17). Adult female TSSM tend to have large black spots on the top of the abdomen but this is pretty variable. TSSM eggs are clear to opaque. TSSM tends to stay on the bottom side of leaves and produces obvious webbing while ERM can be found on either side of the leaf and does not produce much webbing. Both species have the capacity to go through a number of generations during the season. However, we typically do not see significant populations and damage until mid to late summer. This is especially true of TSSM since they do not start on the vine.
Because of their small size, it is often difficult to know if you have mites. Foliar symptoms (bronzing of leaves, see Fig 18) are one clue, although if you have widespread, obvious symptoms then economic damage may already be occurring. The working threshold for spider mites (TSSM and ERM combined) in our area is 7 to 10 mites per leaf, although this will vary depending on health of the vineyard, crop load, value of the grape, etc. In summer, I suggest sampling at least 50 mid-shoot leaves from both the edge and the interior (25 leaves each) of a vineyard block, examining both sides of the leaf. A hand lens will be necessary to see the mites for most people. Even with a hand lens, it is challenging to count the mites. Thus, we recommend estimating the proportion of leaves infested with mites and use something like 50% infested as a treatment threshold. A leaf is considered infested if it has one or more spider mites. Remember to keep rough track of which species is most common.
There are several chemical options available for mite control in New York and
Pennsylvania: Vendex [fenbutatin-oxide], Agri-Mek plus several generics [abamectin], Nexter [pyridaben] (not on Long Island), Acramite [bifenazate], JMS Stylet Oil [aliphatic petroleum distillate], Zeal Miticide1 [etoxazole], Onager or Savey [hexythiazox], Danitol [fenpropathrin], Portal [fenpyroximate] and Nealta [cyfmetofen]. There is also a new miticide recently labeled for use on grapes, Magister SC [fenazaquin], in the same class of acaricides as Nexter, although it is allowed for use on grapes on Long Island. Read labels carefully. JMS Stylet Oil is not compatible with a number of other products including Captan, Vendex, and sulfur. Also, although Stylet Oil can help with mite problems, it is not likely to provide complete control in problem vineyards. Nexter is very effective against ERM but higher rates should be used for TSSM. It also provides some partial control of leafhoppers. Agri-Mek currently has TSSM on the label but not ERM, although in apples both species are on the label. Acramite includes both TSSM and ERM, although it calls for higher rates for ERM. Zeal miticide 1 includes both ERM and TSSM the label. Since Zeal miticide 1 affects eggs and immatures, it is advised to apply before populations reach damaging levels to give the material time to work. Similar advice can be applied to Onager, Savey and Portal. Danitol and Brigade and Hero (two-spotted only) are broad-spectrum pyrethroid insecticides that also have fairly good miticidal activity. Pyrethroids are hard on beneficial mites, however.
Spider mites are often thought of as a secondary pest. In other words, typically something must happen in the vineyard that disrupts their natural control by predators, particularly predatory mites, before their populations increase to damaging levels. Several broad-spectrum insecticides used in grapes, including Danitol, Brigade, Brigadier, Leverage, Baythroid and possibly Sevin can suppress predatory mites. Since Danitol and Brigade have miticidal activity they would not be expected to flare spider mites in the short term. However, in the past, spider mites have been quick to develop resistance to frequent use of pyrethroids. The other miticides (Vendex, Onager, Savey, Zeal, Acramite, Nealta, and Nexter) are generally pretty easy on natural enemies, although at high rates Nexter can negatively affect predatory mites. Overall, paying attention to conserving predatory mites can pay economic dividends since miticides are, in general, expensive.
Japanese Beetle
The adults (1/2 inch body, metallic green in color, Fig 19) seem to have a fondness for grape foliage, but also feed on a number of other plant species. Although the adults have broad diets, the larvae (Fig 20) feed principally on the roots of grasses. Hence, we often find the most significant problems with adult Japanese beetles in areas surrounded by an abundance of turf. The fact that most vineyards have sod row middles may exacerbate problems with adults. The adults emerge from the soil in mid-summer and begin feeding and then mating and egg-laying. The feeding damage caused by adults can be quite extensive, perhaps exceeding 10
or 20% of the foliage. Fortunately, mature grapes are fairly tolerant of this type of feeding at this time of the season. The exact amount is hard to nail down but it seems that up to 15 or 20% leaf damage has little impact on yield parameters. Note, though, that the actual impact of leaf feeding will depend on a number of factors including health and size of the vine and the cultivar. Moreover, if it is a high value cultivar then the economic injury level will be lower compared to a lower value cultivar. Young vines may be particularly vulnerable in that they have fewer reserves to draw upon to recover from damage. You should make a special effort to regularly monitor vines inside growth tubes for Japanese beetles and apply insecticides directly into the tubes if treatment is warranted. Grape cultivars do seem to vary in resistance to foliar feeding by Japanese beetle adults. Thick leaved native cultivars are the most resistant followed by hybrids and then V. vinifera.
There are several insecticides labeled for use against Japanese beetles on grapevines. These all are roughly similar in efficacy but they do vary in impact of beneficial arthropods like predatory mites. Also keep in mind that the adults are very mobile and can re-colonize a vineyard block after being treated with an insecticide. Regular monitoring of the situation is recommended.
Drosophila Fruit flies
Drosophila fruit flies (or vinegar flies) have generally been thought of more as a pest or nuisance in wine cellars but not so much as pests in vineyards. However, we now know that several species of vinegar flies can contribute to sour rot in wine grapes (see Fig. 21) for susceptible cultivars, especially when favorable environmental conditions exist. Favorable weather conditions include above average temperatures and precipitation after veraison. As you know, 2021 and 2018 were bad sour rot years in the eastern US. Not coincidently, in both years we had above average precipitation in August and September as well as somewhat above average temperatures. Although 2023 started off quite wet and we were concerned about sour rot risk, things dried out closer to harvest and overall, 2023 was not a bad year for sour rot.
Vinegar flies contribute to sour rot in two ways: by spreading microorganisms that help cause sour rot (acetic acid bacteria and yeast) and the activity of the larval stage exacerbates symptoms. The most common species of vinegar fly found associated with sour rot is Drosophila melanogaster but the relatively new invasive vinegar fly Spotted Wing Drosophila (SWD) (Drosophila suzukii) also directly contributes. Both species can become very abundant close to harvest.
Another important risk factor for sour rot is damage to fruit. We have both observational data and experimental data showing that berry damage by insects such as yellowjackets (see Fig. 22) or bird pecks and possibly grape berry moth (more work needed on berry moth), in the presence of vinegar flies, exacerbates sour rot, especially when weather conditions favor sour rot. Hence, minimizing berry damage after veraison is very important.
For managing sour rot in a year that has weather conditions conducive to high sour rot risk, we are currently recommending weekly insecticide control of vinegar flies, plus pesticides targeting the causal microbes (e.g., Oxidate), starting at about 12-15 Brix for susceptible wine cultivars. However, we have field data over two field seasons (2020, a low sour rot season, and 2021, a high sour rot season) suggesting that applying insecticide at around 12-15 Brix and one other time closer to harvest was as effective as weekly applications, so it’s possible weekly applications are not necessary.
In addition to costs of materials and labor associated with insecticide applications for sour rot, there is also concern about insecticide resistance. We now have good evidence that NY populations of D. melanogaster (and probably populations in other eastern US grape growing areas) show some level of resistance to three out of the four insecticide classes labeled for use on grapes for Drosophila fruit flies (a pyrethroid – Mustang Maxx, an organophosphate – Malathion, and a neonicotinoid – Assail) with only the spinosyn (Delegate) not showing clear evidence of resistance, although we have found a few populations that are showing worrying signs with regards to resistance to Delegate. This is based on testing field collected D. melanogaster in the lab against different concentrations of insecticide compared to a known susceptible D. melanogaster population. Although our laboratory evidence suggests significant levels of resistance to three insecticide classes, it’s important to note that this does not directly translate into field failure. Nevertheless, there is clearly a risk of resistance developing leading to control failures and therefore, it behooves the industry to manage the situation. This means applying insecticides for managing sour rot only when required by reducing risk factors including minimizing fruit injury from birds or insects such as yellowjackets, in order to reduce fly access to fruit, and rotating materials among different modes of action.
There are several different insecticides labeled for use on grapes for vinegar flies. Some of these specifically list spotted wing drosophila while others list vinegar flies more generally. A full list is included in the NY and PA Pest Management Guidelines for Grapes. Be cognizant of days to harvest restrictions (e.g., Danitol, has a 21 d DTH while Mustang Maxx has a 1 d DTH), target species and whether a 2ee is required (in NY). Given the concern with insecticide resistance to most of the products labeled for vinegar flies, we did conduct a field trial in 2023 testing efficacy of some biorational insecticides for controlling vinegar flies. Unfortunately, none of the products we tested significantly reduced the number of vinegar flies reared from ripe berries whereas Mustang Maxx did result in some reduction (Fig. 23). None of the biorational insecticides tested reduced sour rot compared to control treatment, but overall levels of sour rot were low in 2023.
Sour rot has been a focus of the grape entomology program and the grape plant pathology program, along with our grape extension colleagues, for a number of years now. We have definitely learned more about sour rot biology and the role insects, especially vinegar flies, play in disease development. We have also made progress in developing tactics for managing sour rot, although it’s a complex disease with a number of different risk factors that influence its severity and more research is needed. Moreover, it is probably best managed using multiple approaches.
Multicolored Asian Lady Beetle (MALB)
MALB was introduced into the US from Asia to help control aphid pests. It has spread to many areas in the southern and eastern US and into Ontario Canada and has generally been an effective biological control agent. However, it has the habit of moving into vineyards in the fall near harvest time (Fig. 24). When disturbed, the adult MALB releases a defensive chemical out of its joints (methoxypyrazines) that helps it ward off enemies. Unfortunately, the defensive chemical has a nasty taste and offensive odor at very low detection levels that gets carried into the juice and wine. Relatively low densities of MALB (10 per grape lug) can cause off-flavors in juice and wine.
MALB is sporadic both in where it shows up during a given year and from year to year. Vineyards adjacent to soybeans in a year when soybean aphid is abundant may be more vulnerable. Pay attention to the newsletters of the regional grape extension programs as we get into harvest to see if and when MALB is turning up in vineyards. Then scout your vineyards before harvest. Late harvested varieties are usually the most vulnerable. The economic injury level for Concord grapes has been established at about 6 beetles per 10 pounds of fruit by National Grape Cooperative. For wine grapes, something in the range of 5 beetles per 25 clusters could result in off-flavors. There could be several different species of ladybugs in your vineyard but probably only MALB would be at high densities on the clusters. You can recognize MALB by the black markings directly behind the head that look like an M or W depending on which direction you look from. The color or number of spots is variable. The abundance of MALB appears to be closely tied to the abundance of soybean aphid and therefore vineyards adjacent to soybeans are at greater risk.
There are a few chemical approaches to managing MALB in New York: Mustang Maxx, Aza- Direct and Evergreen [natural pyrethrins]. Mustang Maxx has a 1 DTH restriction. Aza-Direct, which is based on the active ingredient azadirachtin from the neem tree, appears to have a repellent effect on MALB, based on trials by Roger Williams at Ohio State. Based on a trial a few years ago by Tim Weigle, Evergreen appears to have both toxic and repellent effects on MALB. Aza-Direct and Evergreen have no days to harvest restrictions. For Aza-Direct, pH in spray water should be 7 or less (optimum is 5.5 to 6.5). The neonicotinoid insecticide Venom [dinotefuran] has shown good efficacy against MALB (both toxic and repellent) in trials conducted by Rufus Isaacs at Michigan State University. It only has a 1 day to harvest restriction. Venom is labeled for use in PA but not NY. A 2(ee) label expansion for Admire Pro [imidacloprid] has also been approved for use in NY. Admire Pro has a zero day to harvest interval when applied to foliage. Imidacloprid has both toxic and repellent effects on MALB similar to Venom.
Bottom line comments
The bottom-line message for insect and mite pests is to regularly monitor your grapes. There is no guarantee that a particular pest will show up in a particular year or at a particular site. Moreover, you typically have time to react using an eradicant if a pest does reach sufficient densities to cause economic damage. Knowledge of what is present will lead to better management decisions. Also, for those of you who have experienced damage from the recent freeze event, be aware that for vineyards with adequate or excessive canopy, reduced yields will likely exacerbate this imbalance. For this situation, the vines likely will be able to handle more leaf feeding damage from insects such as leafhoppers, mites and Japanese beetle than with a large crop load. On the other hand, be aware that direct pests such as grape berry moth may be more concentrated on fewer clusters and require control.
During the period after budbreak to bloom plant bugs (banded grape bug and Lygocoris inconspicuous) represent the greatest insect risk for yield loss. Most vineyard blocks escape serious damage from plant bugs most years but every year I find sites with significant numbers that managers don’t know about. Monitor for the nymphs at about 7-10-inch stage, keying in on the flower buds. If you find more than one nymph per 10 clusters, consider an insecticide treatment such as Sevin or Danitol or Assail. Remember that only the nymphs cause significant damage. Treatments close to bloom are probably too late to do much good since most nymphs have completed development and become adults. Other than plant bugs, there are relatively few insect pests between budbreak to bloom period that can cause significant harm. For those sites where grape cane gallmaker has become problematic, this is the time period where control should be applied. Also, sites with sandy soils may experience damaging populations of rose chafer at around bloom time. The light-brown adult beetles feed on flowers and young clusters and can reduce yields. Grape rootworm also comes out around bloom or a little after. Adult beetles cause characteristic chain like feeding damage on lower leaves. It’s the larval stage that causes the significant injury, feeding on roots. Chemical control targets the adult stage.
Mid-summer to harvest is the time where insects and mites often create the most concern. On the top of the list is grape berry moth. Traditionally for high-risk sites we have recommended an insecticide during the postbloom period to kill first generation larvae. But except for super high-risk sites or high value varieties, our research indicates this postbloom spray is not useful. Focus should be on the second-generation and third-generation larvae in mid-summer and late summer and in warm years, late summer/early fall damage from a combination of third and fourth generation larvae. Timing of insecticides is important. Insecticides mostly target the egg and young larva before it penetrates the berry. Check out the temperature-based phenology forecast model available online at http://newa.cornell.edu/ (look under pest forecast models for grape berry moth). This model can help you better time the occurrence of grape berry moth flight activity for the second and third flights. It has not been as useful for timing late season GBM. In warm years and in high-risk sites, growers need to continue chemical control on a 7-to-10-day interval from mid-August to mid- September. Good coverage of the fruiting zone is essential.
Two other pests are worth mentioning for the mid-summer period. One is conspicuous and you probably will be tempted to spray for it even if it does not make economic sense to do so because the damage looks bad. I am speaking of Japanese beetle. Granted, these guys can do a lot of feeding during July. But remember that for a healthy vineyard, especially a vigorous one, the vines can probably handle conservatively 15% foliar damage. If you do need to treat, be aware of the potential for some insecticides to flare spider mites. Spider mite is the second pest I wanted to mention. They are actually not very conspicuous and, as a consequence, growers may miss them. Be on the lookout for yellowing or bronzing leaves and generally low thrift during the hot days of late July and August.
Toward harvest keep an eye out for multicolored asian lady beetle (MALB). This normally beneficial insect can become a pest at this time of year by congregating in the clusters at harvest. It has primarily been an issue for late harvested varieties. The adult beetle releases a noxious chemical when disturbed (such as by harvesting the fruit) and this can taint wine and juice. Their populations have been fairly low in recent years although we have seen exceptions, especially in areas where soybeans are also being grown. For late maturing cultivars it is essential that you monitor clusters for MALB close to harvest and take appropriate action if they are present. Keep an eye out for email alerts from your regional grape extension programs.
Spotted lanternfly has been a major concern for PA growers for a number of years and is becoming increasingly of concern to NY grape growers as it spreads out from PA. Adult SLF have the greatest potential to cause economic damage to grapes because of their large size and their mobility. Adults appear in our areas around August and start laying eggs in September. We do not have a good estimate of how many adults it takes to cause economic damage, but it is more than a few per vine. They tend to be more problematic on the edges of vineyards. Insecticides are generally effective, although they often need to be applied multiple times as waves of adults move into the vineyard. For areas that SLF has not yet been found in vineyards, start monitoring for them around the borders of your vineyard blocks, especially paying attention to tree of heaven, if present. Make sure you report anything suspicious.
The other late-season insect pests we have concerns about are fruit flies, both the regular vinegar flies and the new invasive spotted wing drosophila. Our concern centers on their role in promoting sour rot. Because sour rot can be devastating in a bad year, the temptation is to apply insecticides to control vinegar flies after about 12 or 13 Brix for susceptible cultivars. However, the development of insecticide resistance in D. melanogaster has changed the cost-benefit analysis and more than ever, it’s important to be judicious in their use as well as rotating among different insecticide classes. Be aware of risk factors such as above average rainfall in August coupled with warm temperatures and berry injury. Try to minimize berry injury as much as feasible.
In summary, there is a seasonality to pests and checking the electronic updates from your regional grape extension programs is an excellent way to stay on top of what you should be on the look out for during the season. Generally speaking, we have good chemical control options available for most arthropod pests if necessary. But be smart about using them. Pay attention to label restrictions and review recommendations in the pest management guidelines. Rotate among materials with different modes of action (see IRAC codes on labels) to reduce development of resistance. Be aware of consequences of your choice of pesticides on natural enemies and other beneficial arthropods. Most important, only use pesticides or other control options when it makes economic sense to do so (monitor and apply economic thresholds where available). If you have questions, contact your regional extension office or you can also contact me at my office (315-787-2345) in Geneva or through email at gme1@cornell.edu.