Category: Pest Management

Corn Stunt: A New Disease and a New Insect Vector for New York State

Gary C. Bergstrom

School of Integrative Plant Science, Plant Pathology and Plant-Microbe Biology Section, Cornell University, Ithaca, NY 14853

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The presence of the corn stunt spiroplasma was confirmed in corn fields in four non-contiguous New York Counties (Erie, Jefferson, Monroe, and Yates) in October 2024.  The causal agent of corn stunt, Spiroplasma kunkelii, belongs to a specialized class of bacteria known as mollicutes which also includes phytoplasmas. Spiroplasma cells lack walls, and they have a short, spiral shape. They live an obligate lifestyle, i.e., they survive and reproduce only in living leafhopper hosts and in the phloem sieve elements of specific plant hosts. The pathogen that causes corn stunt is transmitted by the corn leafhopper, Dalbulus maidis, also not documented previously in New York (Figure 1). That status changed this October as individuals of D. maidis were caught on a yellow sticky trap in Jefferson County. One captured leafhopper was confirmed by molecular tests to be infected by S. kunkelii. This is the first documentation of the corn leafhopper and of S. kunkelii in both corn leaves and corn leafhoppers in New York.

Figure 1. Corn leafhopper
Figure 1. Corn leafhopper, Dalbulus maidis, the insect vector of corn stunt spiroplasma, is characterized by two prominent dark dots between its eyes and a deeply imbedded V-pattern on its upper thorax. Photo courtesy of Dr. Ashleigh Faris, Oklahoma State University.

How is the spiroplasma transmitted and spread?

The corn leafhopper, D. maidis, can acquire spiroplasma through its probing mouthparts in less than an hour of feeding in phloem tissues of infected corn plants, but it can take up to two weeks of spiroplasma replication in the leafhopper’s body before the insect can then transmit the spiroplasma into the phloem of healthy corn plants. Symptoms don’t generally appear until about a month after plants have been infected. The most severe symptoms are the result of infection at early corn growth stages (from VE to V8). An infected leafhopper can transmit spiroplasma to many nearby plants and can also be blown by air currents and deposited into distant corn fields.

Where did the leafhopper and spiroplasma in New York come from?

Corn stunt is a disease complex first described nearly 80 years ago in the Rio Grande Valley of Texas. Spiroplasma kunkelii is the principal pathogen causing corn stunt. However, other pathogens, either alone or in combination, also can cause corn stunt; these pathogens include the maize bushy stunt phytoplasma, the maize rayado fino virus, and the maize striate mosaic virus. Leaf samples from New York have been archived for later testing for these additional pathogens. Over past decades, there have been observations of corn stunt symptoms in several southern and eastern states but epidemics of corn stunt with well documented isolation of S. kunkelii have been primarily in Texas, Florida, and California. In recent years, corn stunt has occurred as a yield-reducing disease primarily in Mexico, Central and South America, particularly in Argentina and Brazil. The principal vector, the corn leafhopper, can be transported long distances by air currents and carries the pathogen within it. While there is no direct proof, it is very likely that long-distance atmospheric transport of the corn leafhopper into the Midwest and Northeast in 2024 was aided by storm systems that moved north from southern states.

What are the symptoms of corn stunt?

Corn stunt symptoms present similarly to other stresses in corn, including drought, soil compaction, and phosphorous deficiency. Leaf blades and sheathes can show white or yellow stripes (loss of chlorophyl) or red or purple streaks (anthocyanin pigments) and plants may show premature senescence (but without stalk rot) (Figure 2). Corn stunt varies from several common stressors in that plants can show significant stunting and ear abnormalities such as poorly filled ears, no ears or multiple ears at the same node. Symptoms may appear in patches within a field or across larger portions of a field.

red streaked corn leaves infected with corn stunt
Figure 2. Corn plants testing positive for corn stunt spiroplasma showed stunting, leaf reddening, and abnormal ears in (A) Erie County and (B) Jefferson County, New York near the end of the 2024 growing season.

How was corn stunt detected in New York?

From conference calls with my field crop pathology counterparts in southern and corn belt states this summer, I became aware that, in association with stunted and discolored corn plants, corn stunt and corn leafhopper were being observed further north of their usual ranges in 2024. Yet, I thought that New York was at a sufficiently northern latitude to avoid these problems. I credit a very observant agronomy specialist, Rafaela Aguiar with Kreher Family Farms, for noticing unusual symptoms in field corn in Erie County in late summer. Rafaela, a native of Brazil and with previous agronomic experience in South America, thought the symptoms resembled corn stunt which she had seen in South America. Though I was skeptical, it turned out that Rafaela was correct. We initially collected samples of symptomatic plants (Figure 2A) from three Erie County fields and sent them to the Diagnostic Lab at Oklahoma State University. Two of the three fields came back as strongly positive for the corn stunt spiroplasma. In a race against corn harvest and frost, samples were then collected from corn in other counties where similar symptoms had been reported. Samples from Jefferson, Monroe, and Yates Counties were also positive (Figure 2B). I suggest that, given more time for scouting in October, corn stunt may have been diagnosed in many more corn fields in New York this year.

What does this mean for future corn production in New York?

Documentation of the pathogen and its insect vector in New York in 2024 demonstrated that corn stunt could occur in New York in future growing seasons. And if spiroplasma-infected corn leafhoppers arrive at earlier corn growth stages, significant yield losses could result.  Then again, the atmospheric pathways that carried corn leafhoppers to New York in 2024 might not be repeated for several years. Many presume that the corn leafhopper will not overwinter as far north as New York, but, with climate change, that may be proven incorrect.  There is much that we don’t know. Cornell University, Cornell Cooperative Extension, and the New York State Integrated Pest Management Program have committed to participate in a Corn Stunt Working Group of plant pathologists and entomologists in states affected by corn stunt and corn leafhopper. One aim of the group is to deploy a common protocol to monitor the corn leafhopper during the 2025 growing season. Also, the Cornell Plant Disease Diagnostic Clinic is gearing up to offer a molecular test for corn stunt spiroplasma in 2025.

How will the corn stunt disease complex be managed?

Awareness and accurate diagnosis of corn stunt and regional monitoring for corn leafhopper are necessary first steps in managing this complex. Based on limited observations in 2024, it appears that corn stunt could cause significant yield reductions under New York corn growing conditions. Plant breeding is the long-term solution to prevent corn yield losses. Hybrids with moderate resistance to the spiroplasma and / or the leafhopper have been deployed in Latin American countries to manage the corn stunt complex. International companies that sell seed in the U.S. as well as Latin America are aware of which germplasms are most promising for incorporation into hybrids for northern temperate areas such as ours. I do not expect much choice of resistance in northern hybrids in 2025. Management of corn leafhopper populations with insecticides at corn vegetative stages to reduce corn stunt deserves further investigation. My principal advice to New York growers in 2025 is to plant corn at the earliest recommended date to avoid arrival of leafhoppers at the most vulnerable plant stages for infection by spiroplasma.

Acknowledgements:

I gratefully acknowledge agronomist Rafaela Aguiar of Kreher Family Farms for her keen observation of corn stunt symptoms and her continuing cooperation. Colleagues Michael Stanyard (Cornell Cooperative Extension Northwest New York Dairy, Livestock, and Field Crops Program) and Michael Hunter (New York State Integrated Pest Management Program) were instrumental in collecting corn leaf samples and leafhoppers from additional sites in New York. Identification of corn leafhopper and corn stunt spiroplasma would not have been possible without the expert help of colleagues at Oklahoma State University including professors Maira Duffeck and Ashleigh Faris, and diagnostician Jennifer Olson.

References:

Faris, A.M. and M. Duffeck. 2024. Corn leafhopper leads to corn stunt disease across Oklahoma – August 12, 2024. Oklahoma State University Extension News, EPP23-17.

Klaudt, J. 2004. Corn leafhoppers carrying corn stunt make first-time appearance in Kansas. Kansas State University Research and Extension News Release – October 16, 2024.

Redinbaugh, M.G. 2016. Diseases caused by mollicutes. Pages 16-19 in: Compendium of Corn Diseases (Fourth Edition), ed. G.P. Munkvold and D.G. White. APS Press, St. Paul, MN.

 

 

 

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What’s in a Net? Citizen Scientists Sweep Alfalfa Fields for Pests and Predators

Ashley Bound1, Emily Anderson2, Erik Smith1

 1CCE Central NY Dairy, Livestock, and Field Crops Team
2CCE Chenango County 

Introduction

Potato leafhopper (PLH) is a major pest to alfalfa crops across the US and in Central New York. It causes damage to young plants and successive regrowth, resulting in a decrease in overall quality with the potential to cause financial losses to farmers. With funding from the Chobani Community Impact Fund and leadership from the Central New York Dairy, Livestock, and Field Crops (CCE CNYDLFC) regional team and Cornell Cooperative Extension of Chenango County (CCE Chenango), local Future Farmers of America (FFA) chapters worked together during the 2023 growing season to inform farmers about PLH population dynamics in their fields. The goal of this project was to monitor alfalfa fields for PLH, inform farmers if and when PLH populations had reached the action threshold (the population at which a farmer would want to take action to prevent economic loss) and gain a better understanding of the populations of potential insect predators of PLH through the growing season. In the process, community members of different ages and backgrounds had the opportunity to come together to gain hands-on experience with agriculture in the region, share skills and unique perspectives, connect with farmers, and participate in a local citizen science project.

Alfalfa is a good source of protein for livestock and a high-yielding crop for silage, hay, and pasture, and is an essential component of Total Mixed Rations on most dairy farms. Alfalfa is also useful in crop rotations because its root systems help improve soil structure and, as a legume, it is able to fix nitrogen from the atmosphere.

One of alfalfa’s most common pests in New York is potato leafhopper (Empoasca fabae) (PLH) (Fig. 1). Heavy PLH pressure can result in the reduction of stand quality and the loss of nutritional value, and it can impact the availability of successive cuttings. PLH is found across much of the eastern half of the United States and is a pest of many different crops, including clovers, potatoes, soybeans, and apples. At ¼  in, the small PLH can cause big problems. It feeds by using its straw-like mouthparts to extract sap from plants. While taking nutrients from the plant, the PLH also secretes a toxic saliva, which reduces the plant’s ability to photosynthesize. Leaves of infected plants will begin to yellow; this is known as “hopper burn” (Fig. 2).

Potato leaf hopper
Figure 1. A potato Leafhopper adult is about ¼ inches in length (Ken Wise)
hopper burn on alfalfa
Figure 2. Hopper burn, PLH-damaged alfalfa (NYSIPM)

Potato leafhopper management

PLH pressure in alfalfa fields is commonly addressed in two ways: spraying the field with a pesticide to reduce PLH numbers or harvesting the field early. Costs and benefits exist between both options, but often the decision relies on the timing of the upcoming harvest.

Advising between when to cut and when to spray pesticides can help the farmer reduce the cost of pesticides, fuel, and labor used while also maintaining the value of the alfalfa stand.

Farmers and pest scouts use large canvas sweep nets to sample PLH populations in alfalfa fields (Fig. 3). If the field has high PLH numbers, but the farmer is within one week of harvesting the field anyway, it would be more cost-effective to cut the field early. Cutting early allows the farmer to prevent further damage caused by PLH and maintain the quality of the alfalfa without unnecessarily expending time, fuel, and product by spraying with a pesticide. On the other hand, if the field is more than one week away from harvest and PLH numbers are high, it would make more economic sense to treat the field with an insecticide to provide the alfalfa more time to mature without PLH damage, since a low-yield harvest would have low economic value.

It is unclear whether PLH populations are predated upon by other insects or spiders to a degree that would affect alfalfa yield loss. Several species are reported to feed on PLH, but PLH are considered too fast to be captured by most predators. Still, insecticide applications intended to manage PLH would potentially affect other insects in the field, including those predating on pea aphid, another summertime insect pest of alfalfa that can cause yield loss in rare cases where populations get out of hand.

 What is considered a high PLH number?

Table 1. Economic thresholds of PLH in non-PLH-resistant alfalfa (adapted from Cornell Guide for Integrated Field Crop Management)

Height of Alfalfa (in) Max PLH/Sweep
<3 0.2
3-7 0.5
8-10 1
11-14 2
15+ 2*

* No action needed if within 1 week of cutting, and consider cutting early.

For Example…

If the stand of alfalfa is 21 in. tall and the average number of PLH per sweep was 2.5, then the action threshold has been reached, and it would make sense to cut the stand early to prevent further damage because it is likely within one week of harvest.

However, if the alfalfa in the field is only 10 in. tall and an average of 1.5 PLH were found per sweep, the field should instead be managed with an insecticide application to prevent further PLH damage, since the next cutting will not happen within the next week.

If the alfalfa height is 20 in., but the average number of PLH per sweep was only 1.2, then the action threshold was not reached, and no action would be warranted for the field.

Methods

To help our extension staff collect data and provide management recommendations to local farmers, nine area youth groups including seven FFA chapters were provided with sweep nets, insect identification guides, and a comprehensive insect identification textbook, all of which they could keep at the end of the project. In-person training sessions and data sheets were also provided by CCE staff.

Data collection was performed with a standard 15-inch-diameter insect sweep net (Fig. 3). Participants swept the net a total of 10 times back and forth in a swinging motion while walking forward – each swing counting as one sweep – and at the end of the 10 sweeps, the number of insects in the net was recorded. In addition to PLH, participants also recorded seven types of predators that are known to feed on PLH and other insect pests. These included hoverfly larvae (Fig. 4), ladybugs and ladybug larvae (Fig. 5), lacewing larvae, damsel bugs, assassin bugs, minute pirate bugs, and spiders (including harvestmen, also known as daddy longlegs).

sweep net
Figure 3. Sweep net (Gemplers)
Hoverfly larva and aphids
Figure 4. Hoverfly larva feeding on an aphid (Kerri Wixted)
Ladybug larva
Figure 5. Ladybug larva (Cornell University)

This process was repeated for a total of three – five sets of sweeps, or 30-50 total sweeps per field. Fields were typically re-sampled weekly through the growing season, except immediately following harvest.

After counting the numbers of pests and predators and averaging those values across all sweeps, alfalfa height was recorded so that a determination could be made as to whether that field reached the threshold for management using the established economic thresholds (Table 1).

Results and Discussion

With four FFA chapters and one local youth group participating through the duration of the project, we were able to monitor PLH in 21 alfalfa fields on 13 farms in 5 counties over 12 weeks from June to August, when alfalfa crops are at highest risk of PLH and when producers are most likely to invest in insecticidal sprays to salvage yield.

Across all fields and sampling dates, 1,951 PLH and 1,291 insect predators were recorded (Table 2). This does not include many other insects that were also observed in our sweep nets, like horse flies, deer flies, bees, aphids, and parasitoid wasps. The two most common insects sampled were aphids and several species of parasitoid wasps. Aphid populations seldom reach damaging levels in alfalfa, and these species of wasp parasitize other insects, primarily aphids in this setting.

Table 2. Total PLH and selected predators observed across all fields and dates

table 2

Out of 126 sampling efforts, the action threshold was reached only 10 times (7.9%). Of those 10 times, applying a short-residual insecticide was the most economical management strategy in five cases, while early harvest was recommended the other five times. This meant that it was only economical to spray in 3.97% of cases. Only eight fields of the 21 monitored during the growing season reached threshold at least once (38% of fields). Five of those eight were fields where early harvest was recommended due to being within one week of planned harvest. Interestingly, of the three fields where sprays were recommended due to reaching threshold more than a week from harvest, two were in this situation more than once during the season (twice each). This means that only very few fields experienced consistently high PLH pressure. These fields will be monitored in 2024 to see if these trends continue, or whether 2023 was unique. Without question, PLH populations can vary wildly between growing seasons due to their migratory nature, so more observation will be needed to see how different fields experience PLH pressure over time.

Predators outnumbered PLH in our sweeps until mid-July, and again after mid-August (Fig. 6). We know that the predators we recorded have been reported by others to feed on PLH, but we do not have a good understanding of how well they may be able to control PLH populations. But if they are, and if 2023 was a typical year for these species, there appears to be a period of about 5 weeks in the middle of summer that may be the highest risk for yield loss due to PLH infestation and potential yield loss. Alfalfa weevil is an important pest of alfalfa through late-June, and these predators may be exploiting this pest before PLH populations increase.

figure 6 bar graph
Figure 6. Insect population dynamics in Central NY alfalfa fields in 2023

Forage crops are unique because they are harvested multiple times per year, allowing for a partial reset of local pest populations with each harvest. But while the recommended short-residual sprays do not have extended activity directly, their effects can extend through the growing season if used incorrectly. Spraying without scouting to verify whether action thresholds have been reached, and spraying when pests are below economic thresholds not only wastes money in the short-term, but puts important insect diversity at risk. Not only non-target insects like pollinators, but also predators that may be feeding on PLH, alfalfa weevil, and aphids and preventing their populations from reducing forage yield and quality.

Potato leafhopper-resistant alfalfa varieties exist, and the economic thresholds of these varieties can be double, to nearly 10x the level of traditional alfalfa. If PLH-resistant varieties were used in this study, the economic threshold would have been reached no more than three times, all in different fields. For resistant varieties with economic thresholds higher than 3x the standard varieties, no fields in our study would have reached the economic threshold. However, farmers usually prioritize digestibility or other desired traits over pest resistance when choosing an alfalfa variety (these traits are not stackable with current varieties), so most alfalfa grown in NY is not PLH-resistant.

The partnership between CCE Chenango, the CNYDLFC regional team, and FFA chapters was instrumental to the project’s geographic reach and success. Through this partnership, young people in the community were able to aid farmers while learning about local agriculture, entomology, Integrated Pest Management, and the natural diversity that can be found on farms. While many of the young people involved with this project either lived on farms or were otherwise related to farmers, this was an enriching experience that gave them a better understanding of how crops are produced, and how farmers and CCE work together to make informed management decisions.

Additional Resources

Acknowledgments

This project was made possible by Chobani through the Chobani Community Impact Fund and relied on leadership and participation from the Central New York Dairy, Livestock, and Field Crops team; Cornell Cooperative Extension of Chenango County; high school members of the local Future Farmers of America chapters; and each landowner that generously allowed sweeping to occur on their fields. The authors thank Joe Lawrence (PRO-DAIRY) and Ken Wise (NYSIPM) for reviewing the article. For questions, contact Erik Smith, erik.smith@cornell.edu.

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Soybean cyst nematode in soybeans and dry beans: new research and renewed sampling efforts in 2022

E. Smith1, M. Zuefle2, X. Wang3, K. Wise2, J. Degni1, A. Gabriel1, M. Hunter1, J. Miller1, K. O’Neil1, M. Stanyard1, G. Bergstrom4

1Cornell Cooperative Extension, 2New York State Integrated Pest Management, 3United States Department of Agriculture – Agricultural Research Service, 4Cornell University

Soybean cyst nematode (SCN) is a plant parasitic roundworm and is the most damaging pest of soybean crops worldwide. Yield losses can reach 30% before above-ground symptoms manifest, leaving growers unaware that they have an infestation until it’s too late. With soybean prices the highest they’ve been in a decade, this translates to a loss of more than $13,000 per fifty acres in a field that would otherwise produce a yield of 55 bu/acre. We are only now beginning to understand the spread and damaging effect of SCN on dry bean crops, for which financial losses would almost certainly be greater due to their higher value.

In addition to legume crops, SCN can infest and reproduce on several weed species such as chickweed, purslane, clover, pokeweed, and common mullein. Overwintering SCN eggs hatch in spring when soil temperatures reach approximately 50°F (10°C). Females colonize roots to feed, eventually allowing the lower half of their bodies to protrude through the root wall and become visible as small white cysts (Figure 1). Eventually, the female dies and the cyst dries, hardens, and darkens in color, concealing up to 400 eggs. While we can expect at least three generations of SCN each growing season, these cysts can survive for years in the soil until the right conditions allow them to hatch. Because of their hardiness, longevity, and their relatively broad host range, once a field has been infested with SCN is it considered impossible to eradicate. SCN cysts can spread via wind, soil, water, tires and farm equipment, contaminated seeds or plants, and through birds or other animals.

soybean roots with nematode cysts
Figure 1. Soybean cyst nematode cysts on soybean roots. Photo: Craig Grau, University of Wisconsin

This is an extremely hardy and pernicious pest, but populations can be managed using an integrated approach including scouting, soil sampling, host resistance, and crop rotation. The first step is of course scouting and identification using soil sampling.

If SCN infestation is not known in a field, the roots of symptomatic plants (stunting or premature yellowing compared with the surrounding crop) may be inspected for cysts (Figure 1). Otherwise, soil samples should be collected near harvest or just after. Samples should be taken from the root zone in field entrances and sections of the field that showed stunting or premature yellowing/death compared with the surrounding crop (Figure 2). If a field is known to have an SCN infestation, soil samples should be taken across the field in a zig-zag or grid pattern because SCN infestations are unevenly distributed.

soybeans dried by SCN with healthy surrounding crop
Figure 2. Soybeans infested with SCN drying down prematurely compared with the surrounding crop. Photo: Erik Smith, Cornell Cooperative Extension

From 2017 to 2020, 134 soybean and dry bean fields in 42 counties were sampled for SCN, yielding positive samples in 30 counties (SCN+). In 2021, further testing revealed 6 more counties with infestations (Table 1, Figure 3).

Table 1. Soybean cyst nematode sampling results in 2021.

Fields tested Fields SCN+ Counties sampled Counties SCN+ New SCN+ counties
98 30a 37 15 6b

aMostly low populations (<500 eggs/cup of soil). Moderate egg counts (500-10,000 eggs/cup) were found in Western NY, the North Country, and the Southern Tier (no geographic trend).

bBroome, Genesee, Oneida, Schenectady (not previously sampled), Tioga, and Yates (not previously sampled).

NYS map
Figure 3. Counties with known infestations of soybean cyst nematode (red), counties that have been sampled but have not yielded positive samples (green), and counties that have not been sampled (gray).

To scout for damage and sample soil more efficiently, researchers from New York State IPM are investigating the effectiveness of using soil electrical conductivity (EC) mapping technology. Soil EC mapping can determine field distribution for many nematode species but has not been tested on SCN. Nematode population density, if present, has a strong positive correlation with the proportion of sand in the soil because of increased mobility in looser, sandier soils. EC measurements can be used to detect the variability in sand content in a field and thereby create a map of areas with higher likelihood of SCN. This map is then used to target soil sampling to those areas. Preliminary data collected in 2021 using an EC machine shows there is variation in SCN distribution within fields. Results from 2022 (funded by the NY Dry Bean Industry) will be used to seek additional funding to expand our mapping, and to utilize existing EC maps from growers of dry beans, soybeans, and snap beans to further validate this approach.

While we have many SCN-resistant soybean varieties, the majority (>95%) are derived from a single resistant cultivar, PI 88788. The extensive use of this cultivar in soybean breeding has led to the emergence of SCN populations that can overcome PI 88788-type resistance. For example, recent SCN surveys conducted in major soybean producing states including Missouri and Minnesota all reported an increased level of adaptation to PI 88788-type resistance. In contrast with our current soybean varieties, SCN field populations exhibit great genetic diversity. During the fall of 2022, researchers from the USDA-ARS will be collecting soil samples to conduct a comprehensive study on SCN distribution, density, and virulence phenotypes across New York state. Regular monitoring of SCN densities and virulence phenotypes is essential for developing effective management plans based on the use of resistant cultivars.

With the current infestation levels in NY, crop rotation is our most valuable management tool. Rotating out of soybeans for even one year can reduce SCN populations by 50% or more. Continuing to rotate crops allows us to keep populations low, reducing the likelihood that growers will have to resort to more costly management strategies.

Please contact your local Cornell Cooperative Extension agent if you would like your field(s) to be sampled for SCN. This year, the NY Corn and Soybean Growers Association (NYCSGA) is providing funding for up to 75 soybean fields to be tested, while the NY Dry Bean Industry is funding EC mapping of three dry bean fields and nine soil samples per field (27 total samples). With continued scouting, soil sampling, and race-typing by Cornell University, USDA-ARS, and NYSIPM, New York’s soybean and dry bean growers are in position to continue making the best management decisions for this pest.

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Are Persistent Biocontrol Nematodes (Entomopathogenic) for the control of Corn Rootworm an economic benefit for your NY farm?

Elson Shields and Tony Testa, Dept of Entomology, Cornell University, Ithaca, NY

Research in NY has shown that corn rootworm can be controlled for multiple growing seasons with a single application of native persistent biocontrol nematodes, known also as Entomopathogenic nematodes.  On NY farms with a good crop rotation between corn and other crops, research shows biocontrol nematodes can be used to replace the more costly GMO-rootworm traited corn.  On NY farms where GMO-rootworm traits are failing, the addition of biocontrol nematodes to the field as an additional management tool restores the yield to the pre-rootworm damage level and targets the resistant rootworm larvae who have survived the toxin in the plant but should not be used alone.  In fields which are long-term continuous corn, biocontrol nematodes should only be utilized with corn containing rootworm traits because these two different modes of mortality for rootworm reduces the long-term selection for resistance.

What are Biocontrol Nematodes?

Biocontrol nematodes are microscopic round worms in the soil which only attack insects in the soil or on the soil surface.  Biocontrol nematodes are different from the plant parasitic nematodes which attack crops.  The biocontrol nematodes discussed here are native to our Northern New York (NNY) soil where they were original collected.  The nematode insect infective stage (called the Infective Juvenile or IJ) moves about in the soil in search of insect hosts, finding the insect using CO2 gradients and other chemical attractants.  When an insect host is located, the IJ enters the insect through a breathing opening called a spiracle and enters the insect body cavity.  Once inside, the nematode releases a bacteria which kills the insect.  The nematodes then molt to adults and produce offspring on the nutrition provided by the dead insect.  When the insect resources are consumed, a new set of IJs are released into the soil to search for additional insect hosts.  An average sized insect larvae will produce between 100,000 and 200,000 new IJs.

What do these biocontrol nematodes attack?

This entire technology was developed to reduce snout beetle (ASB) populations to sub-economic levels in NNY.  ASB is costly to the dairy farmer, commonly killing alfalfa stands in a single year.  To date, more than 150 NNY farms have applied biocontrol nematodes to >25,000 acres to successfully reduce snout beetle to a sub-economic level and increase stand life back to 3-5 years.

Corn Rootworm:  During the research developing the use of native persistent biocontrol nematodes to reduce ASB populations in NNY to sub-economic levels, it was discovered that biocontrol nematodes applied in alfalfa for snout beetle control also carryover to attack corn rootworm when the field is rotated to corn.  Biocontrol nematodes completely compatible with all of the Bt-RW traits, killing the Bt toxin survivors,.  Research has shown that after 4 years of corn, the populations of biocontrol nematodes in the field are high enough to attack alfalfa soil insects when the field is rotated back to alfalfa.

Wireworm and White grubs:  Since NY alfalfa culture usually incorporates grass into the mix, NY fields usually have a population of wireworms and native white grubs in the field when the field is rotated to corn.  Often, these insects then cause stand problems in 1st year corn.  If the field has been inoculated with biocontrol nematodes for control of either snout beetle or rootworm, the biocontrol nematodes also attack these insects and reduce their impact on seedling corn when rotated to corn.

Does the soil type influence the species of biocontrol nematode applied?

NY research data indicates a mix of biocontrol nematode species gives better control of soil insects than a single species alone.  The reason for these results is each nematode species has a preferred section of the soil profile where it is most effective.  For example, Steinernema carpocapsae prefers the top 2-3” of the soil profile and dominates this region.  If S. carpocapsae is the only nematode used, insect larvae below the 2” level escape attack.  The addition of a second nematode species which prefers the low portions of the soil profile compliments the presence of S. carpocapsae and gives more complete control of soil insects throughout the plant root zone.  In sandier soils, the top 2” often become too dry for a biocontrol nematode to move and attack insect larvae.  In these soils, a nematode species mix which include S. carpocapsae would be ineffective and requires a different mix of nematode species.

Our recommendations for biocontrol nematode species mixes for soil types:

Clay loam – silt loam soils:  S. carpocapsae + S. feltiae

Sandy loams – sand soils:  S. feltiae + Heterorhabditis bacteriophora.

What are the differences between the entomopathogenic (biocontrol) nematodes purchased on the web from the Persistent NY strains mentioned here?

Biocontrol nematodes purchased from commercial sources have lost the ability to persist in the soil after application for a significant length of time.  Many commercial strains persist in the soil for only 7-30 days and require application timing to be closely match with the presence of their target host, requiring an annual reapplication.  In contrast, the NY persistent strains of Biocontrol Nematodes are carefully cultured to maintain their evolutionary ability to persist across hostile conditions such as the lack of available hosts and temperature extremes (dry soil conditions, winter).  Additionally, NY persistent strains are re-isolated from the field every two years so the nematode cultures do not become “Lab strains”, but remain adapted for NY agricultural soil conditions.  New York persistent strains are applied once and persist in the field for many years following application.  Not surprising because they were isolated from NY soils where they have evolved for a few million years.  If the NY persistent strains are cultured carelessly, they also quickly lose their ability to persist and are no better than the commercial strains purchased off the web.

How are biocontrol nematodes applied?

There are two major ways to apply biocontrol nematodes to NY fields.

Commercial Pesticide Sprayer:  Thousands of acres have been inoculated using slightly modified pesticide sprayers of all sizes from 30’ booms to 100+’ booms.  To use these sprayers, the following guidelines need to be followed.

    1.   A good washing of the sprayer (similar to changing pesticides)
    2.   All screens and filters removed (nematodes cannot pass through them)
    3.   Nozzle change to a stream type nozzle to shoot a concentrated stream of water to the soil surface through any vegetation.
    4.   50 gpa minimum
    5.   Application in the evening or under cloudy/rainy conditions (nematodes are sensitive to UV)

Liquid Dairy Manure:  This method was recently developed and offers some advantages over using a pesticide sprayer.  The biggest limitation is the time between adding the nematodes to the liquid manure and field application.  After adding the nematodes to the manure, the manure needs to be spread in the field within 20-30 minutes.  Longer intervals results in the nematodes dying from the lack of oxygen.

The advantages of using liquid dairy manure as the carrier are 1)  no extra trips over the field, 2)  can be applied any time of the day and 3)  no extra costs.

Application timing:

Biocontrol nematodes which are persistent, can be applied anytime during the growing season when soil temperatures are above 50 F.  Ideally, nematodes should be applied when there are host in the soil so they can immediately go to work and reproduce.  However, the NY persistent strains have the ability to sit and wait for months before needing to attack hosts and reproduce.  We request that no nematode applications be made after September 15th due to cooling soil temperatures and limited time to find hosts before winter.  Applications are made to the soil surface under conditions of low UV exposure (late in the day, rainy/overcast days, in cover crops where there is adequate ground shading).  Field tillage has no impact on biocontrol nematodes.  In addition, if nematodes are applied before field tillage, the movement of soil during tillage helps the nematodes redistribute throughout the field and help them fill in the gaps which may occur during application.

Where can I get Biocontrol Nematodes which are adapted to NY and will persist across growing seasons?

Currently, there are two sources to purchase biocontrol nematodes adapted to NY growing conditions with their persistent genes intact to persist across growing seasons (and winter) in NY.

    1.   Mary DeBeer, Moira, NY.  cell:  (518) 812-8565  email:  md12957@aol.com
    2.   Shields’ Lab, Cornell University:  Tony Testa  email:  at28@cornell.edu  cell: (607) 591-1493
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Seed Corn Maggot, Stand Losses and the Need for Insecticide Seed Treatments

Elson J. Shields, Entomology, Cornell University, Ithaca, NY

Seed corn maggot, Delia platura, (SCM) is the primary NY pest attacking large-seeded crops during germination.  These crops include corn, soybean and edible beans.  One of the difficulties in managing this pest is the unpredictability of the infestations, the lack of an insecticide rescue option and the lack of flexibility to compensate for crop stand losses.

SCM adult flies, looking similar to small house flies, are attracted to fields with high organic matter within the plant zone, and lay their eggs close to germinating crop seeds.  The newly hatched larvae attack and feed on the germinating seeds and young emerging plants.  In NY, the frequent use of animal manures and cover crops known as green manure crops increases the attractiveness of the fields to SCM.  The short and cool NY growing season encourages growers to plant their crops as early as possible to be able to harvest profitable yields.  This early planting of seeds into cold soils results in slow and delayed emergence which increases the window of vulnerability to SCM damage.  In these situations, stand losses can exceed 50% due to the attractiveness of the organic matter, resulting in a high level of eggs being laid around the germinating seeds.

Under NY growing conditions, measurable yield losses in corn start to occur between 10-20% stand losses.  The magnitude of the yield loss is dependent on the corn variety, degree-day maturity requirements and the subsequent growing conditions which influence the ability of the undamaged plants to compensate for the damaged plants.  Due to the short growing season in NY, the decision to replant the field is seldom an option due to the additional expense of replanting (ca. $130/ac) and the yield reductions associated with shorter season corn variety required to be planted for maturity to be completed before killing temperatures in the fall. Typically, if the surviving corn stand has less than a 40% stand loss, the resulting yield loss is less costly than the combined cost of replanting and yield decline associated with late planting.

2021 Field Study in Aurora, NY

A study was initiated to examine the impact of SCM and the necessity of insecticide seed treatments on corn grown under continuous corn culture with minimal organic matter and corn following a green manure cover crop with high organic matter.

Experimental design:

The continuous corn site had been planted to corn for 7 years prior to the 2021 growing season.  Previous corn crops had been harvested as grain and soil tillage was restricted to spring chisel plowing.  Crop residue was minimal and planting in 2021 was achieved using a 4-row no-till planter.  The cover crop site was planted to red clover in 2020 and the clover crop was retained as a green manure crop.  Prior to planting the cover crop site to corn, the clover was mowed, liquid dairy manure was applied to the surface and the soil was chisel plowed to prepare the seed bed for planting.  Planting in 2021 utilized a 4-row no-till planter.  Each area was planted on a weekly basis yielding 6 different sequential planting dates.  Each row of the 4-row planter contained a different treatment and the plots for each planting date were comprised of a single planter pass in the continuous corn and two planter passes in the cover crop site.  The following treatments were planted as single rows within each planter pass.  1)  conventional corn (non-Bt-RW) with no seed applied insecticide, 2) conventional corn (non-Bt-RW) with seed applied insecticide, 3)  Bt-RW corn with no seed applied insecticide and 4)  Bt-RW corn with seed applied insecticide.  Each planting date was replicated four times at each location.  Data collected included stand counts after the plants were V3-4 growth stage and excavation of the missing plants to document the reason for the missing plant.

Results:

Continuous corn site:

At the continuous corn site, the experimental design allowed 24 planting pairs (corn type x presence/absence of seed applied insecticide) for comparison and analysis.  Fourteen of the 24 planting pairs (58%) suffered stand losses in the untreated seed row from seed corn maggot ranging from 2% to 66% stand loss.  If the 10% stand loss/yield loss threshold is used, then nine of the 24 planting pairs (38%) indicated economic yield losses in the non-seed applied insecticide treatments. If 14% stand loss/yield loss threshold is used, then eight of the 24 pairs (33%) indicated economic yield losses in the non-seed applied insecticide treatments.   If the 20% stand loss threshold is used, then six of 24 (25%) planting pairs indicate economic losses in the non-seed applied insecticide treatments.  Four of the planting pairs had greater than 40% stand losses in the non-seed applied insecticide treatments.

Corn following cover crop site:

In the corn following cover crop site, the experimental design allowed 24 planting pairs (corn type x presence/absence of seed applied insecticide) for comparison and analysis.  Sixteen of the 24 planting pairs (66%) suffered stand losses in the untreated seed row from seed corn maggot ranging from 2% to 62% stand loss.  If the 10% stand loss/yield loss threshold is used, then 13 of the 24 planting pairs (54%) indicated economic yield losses in the non-seed applied insecticide treatments.  If 14% stand loss/yield loss threshold is used, then nine of the 24 pairs (38%) indicated economic yield losses in the non-seed applied insecticide treatments.  If the 20% stand loss threshold is used, then seven of 24 (29%) planting pairs indicate economic losses in the non-seed applied insecticide treatments.  Five of the planting pairs had greater than 40% stand losses in the non-seed applied insecticide treatments.

Discussion:

The following values were estimated for 2021 from three different regions of NY.  These values were estimated by regional experts.

Region                          Silage value (in field)                 Representative Yield                 Value/ac

NNY:                                         $40/ton                                    17 tons/ac                            $680

CNY                                          $38/ton                                    20 tons/ac                            $760

WNY:                                        $47/ton                                      20 tons/ac                            $940

In all three regions, a one-ton silage loss per acre in yield equals eight-times the cost of the insecticide seed treatment.  A one-ton reduction in silage is approximately 5% loss in yield which equals a $40 loss per acre.  If we use the estimate that 1%-5% yield losses began at a 10% stand loss ($8-$40 in lost silage), then it is economically beneficial for the farmer to utilize an insecticide seed treatment costing $5 per acre to prevent the loss.

Continuous Corn:

Research data collected in controlled studies during 2021 at the Cornell Musgrave Farm located in Aurora, NY shows that in continuous corn production, seed corn maggot economically damaged 38% of the non-insecticide seed treated plots ranging from 10% to 66% stand losses.  If we estimate a 10% stand loss equals a 1-5% yield loss, then the value loss to the farmer is $8-$40/acre.

The cost to the farmer to protect his yield loss with insecticide seed treatment is $5/acre and therefore it is economically viable to spend $5 per acre to protect yield losses ranging from $8 to $400 per acre on 38% of a farm’s acreage.  If we estimate a 20% stand loss results in a greater than 5% yield loss, then 25% of the fields will suffer losses greater than $40 per acre.  These losses would be economically devastating to a farmer, where the farm loses yield on 38% of their acreage ranging from $40/ac to $400/ac.  Since predicting which fields will be attacked by seed corn maggot prior to planting is difficult and imprecise, the prevention of yield losses ranging from $40-$400/ac on 25% of the acreage easily compensates and is economically justified for the cost of the insecticide seed treatment for all acres.

Corn following a Cover Crop:

Research data collected in controlled studies during 2021 at the Cornell Musgrave Farm located in Aurora, NY shows that in corn production following a cover crop, seed corn maggot economically damaged 54% of the non-insecticide seed treated plots ranging from 11% to 62% stand losses.

If we estimate a 10% stand loss equals a 1-5% yield loss, then the value loss to the farmer is $8-$40/acre.  The cost to the farmer to protect his yield loss with insecticide seed treatment is $5/acre and therefore it is economically viable to spend $5 per acre to protect yield losses ranging from $8 to $400 per acre on 54% of a farm’s acreage.  If we estimate a 20% stand loss results in a greater than 5% yield loss, then 33% of the fields will suffer losses greater than $40 per acre.  These losses would be economically devastating to a farmer, where the farm loses yield on 54% of their acreage ranging from $40/ac to $400/ac.  Since predicting which fields will be attacked by seed corn maggot prior to planting is difficult and imprecise, the prevention of yield losses ranging from $40-$400/ac on 33% of the acreage easily compensates and is economically justified for the $5 per acre cost of the insecticide seed treatment for all acres.

Conclusions:

This 2021 research data indicates the level of potential economic losses by NY corn farmers if seed applied insecticide is not available for use.  In NY, replanting after stand losses from SCM is not a viable economic option in most situations due to the short NY growing season.  The farmer is required to suffer yield losses due to reduced stand because replanting is seldom a viable economic option.

These data documents the increased risk of economic stand losses from SCM when the farmer plants corn after a cover crop/green manure crop, which is utilized in soil building and nutrient retention over the winter months.  These data also indicate why the attempts to have farmers adopt cover crops in the 1990’s, were not successful due to SCM related stand losses in the corn crop planted following the cover crop.  Adoption of cover crops to build soil health and nutrient retention was not successful until corn seed was treated with a seed-applied insecticide to prevent stand losses in cropping situations where SCM pressure was increased.  Given that conservation practices such as reduced tillage and planting cover crops to reduce erosion and runoff are not only encouraged but also incentivized in NY State, it is important to understand that in the absence of these seed protectants, farmers may revert to planting fewer cover crops to avoid losses to SCM.

We thank NY Farm Viability Institute, Cornell CALS and Cornell Agricultural Experiment Station for their research support for this ongoing study focused on identifying alternative management strategies for SCM.

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What is the true cost of Alfalfa Snout Beetle on your Farm?

Elson Shields, Department of Entomology – Cornell University

When alfalfa snout beetle (ASB) becomes fully established on your farm, its presence cost you $300-$600 per cow annually.  The higher producing dairies are hit harder than the lower producing dairies because the higher producing dairies are more reliant on their production of high quality alfalfa and grass forage to maintain their high milk production.  This is an unbelievable amount of loss caused by ASB and is ignored by many in the NNY Agribusiness community.

It takes about 10 years for alfalfa snout beetle to become fully established on individual farms after its initial invasion.  ASB damage is frequently missed and stand loss is often blamed on winter kill, until there is a massive migration of adults out of a field or someone uses a shovel to dig yellowed plants in the fall and finds the larvae.  ASB often kill out the alfalfa on the high spots in the field first, a symptom which should draw attention from the truck windshield driving past.  The best time to survey a field/farm for ASB is during October with a shovel to dig and examine yellowing alfalfa plants.  At this time of year, ASB larvae are large, white and easy to identify.

ASB is flightless and has a 2-year lifecycle, so movement around the farm is by walking or hitching rides on farm equipment.  The practice of cutting an infested alfalfa field and then moving to a non-infested field next to harvest is the most common way ASB is moved around the farm.  During 1st harvest, ASB adults can be easily observed on the harvesting equipment.  Over the 10 year period, ASB causes more fields to die out from “perceived winter kill”, resulting in less alfalfa to harvest and more required off-farm purchases of replacement protein, so the increasing costs of feeding the cows is spread out over the 10 year period and often overlooked.

The cost of alfalfa snout beetle to the dairy operation is two prong and can be broken down into two different areas.

1) The cost of forage loss from the field loss and the cost of replanting

Alfalfa is an expensive crop to plant with the required PH adjustment for yield, cost of the seed and the cost of land preparation required for good germination and plant stands (~$140/ac).  As a general rule in a NNY 3-cut system, the cost of establishing the crop are not covered with the on-farm production of protein until the beginning of the third crop year.  If farms cannot keep their alfalfa stands viable through the 3rd and 4th production years, the cost of establishing the stand outweighs the benefit of growing alfalfa. Depending on the speed that ASB eliminates the alfalfa stand, the alfalfa stand could be lost in a single year or over a 2-3 year period with grass filling in the open spaces.  In a NNY 3-cut-4-year rotation alfalfa production system, the cost of alfalfa snout beetle killing out the alfalfa stand ranges between $200 and $400 an acre.   In a NNY 4-cut-3-year, the cost of alfalfa snout beetle killing out the alfalfa stand ranges between $200 and $500 an acre.  These cost estimates are a combination of the loss of crop yield and the cost of re-establishment of the alfalfa field.

2)  The cost of purchasing off-farm protein to replace the alfalfa protein which is no longer available on the farm.

A more hidden cost of alfalfa snout beetle is the cost of the increased protein purchases to compensate for the lack of protein produced on the farm due to the loss of alfalfa from ASB damage.  The “off farm purchase protein costs” is directly impacted on the farm’s ability to manage the remaining grass in the field for high protein production. Below are presented various scenarios typical of NNY farms impacted by alfalfa field loss from ASB.

Table 1:  The cost of extra soy required in the diet when ASB impacts the production of alfalfa on the farm and causes widespread alfalfa stand losses.  Estimates are based on the diet of 30% forage and 70% corn silage.  While many farmers claim to produce higher quality grass, analysis of grass forage suggests that the 15% and 11% protein cover the common range of grass quality.

% Alfalfa in Stand 15% protein grass 11% protein grass
 100

(clear seeded)

100 cow dairy

 $9.30/cow/month

$112/cow/year

$11,200/year

 $16.80/cow/month

$201/cow/year

$20,100/year
 50:50

(alfalfa:grass)

100 cow dairy

 $4.70/cow/month

$56.40/cow/year

$5,600/year

 $8.40/cow/month

$100.80/cow/year

$8,400/year

***These estimates were provided by Michael Miller, W.H. Miner Institute and Everett Thomas, Oak Point Agronomics

In summary, the cost of additional purchases of soy protein once ASB becomes establish on the farm ranges from $4.70 to $16.80/cow/ month or $56.40 to $200 per cow/year Add to this the cost of losing alfalfa stands and spending money to replant the stands and the cost per cow increases another $200-$500 /year and the loss to the dairy from ASB is significant. In NY, the “rule of thumb” is that it requires 1 acre of forage to support 1 cow.  As a result, the cost per acre and cost per cow of forages are often used interchangeably in discussions. This is the reason that money making dairies become under severe financial pressure within 10 years of ASB moving onto the farm.

The Alfalfa Snout Beetle Solution:

Due to the long-term research support by the NNY dairy farmers, NNYADP, NYFVI, state of NY and Cornell University, ASB can be controlled on a farm for many years with a single application of native NY biocontrol nematodes (entomopathogenic) on each field.  The cost of this application is in the range of $40-$60 per acre.  The presence of ASB on your farm is costing you between $50-$200/year every year and the solution to ASB is a single expense of $40-$60; a one-time expense.  To date, nearly 28,000 acres of NNY ASB infested land has been treated for ASB located on >140 farms.  In those fields, alfalfa stand life has increased back to 4-6 years compared to the previous ASB ravaged 1-2 years.

NNY farmers who have initiated a program of applying biocontrol nematodes to your farm, please continue because it is saving/making you money to control ASB.  In addition, talk to your neighbor about controlling his ASB because your control would be better if your neighbor was not producing millions of ASB to flood into your alfalfa stands.

NNY farmers who have not applied biocontrol nematodes for ASB control are bleeding profits and are spending unnecessary scarce money on purchases of soy protein when they could be growing it themselves.  In addition, you are creating a problem for your neighbor who is trying to control this insect and you need to work with your neighbor to control ASB for both of your benefit.

For more information about ASB control with biocontrol nematodes contact:

Mike Hunter, CCE Field Crops Specialist, Phone (315) 788-8450, ext. 266, Email:  meh27@cornell.edu

Kitty O’Neal, CCE Field Crops and Soil Specialist, Phone 315 379 9192 ext 253, Email:  kitty.oneil@cornell.edu

Joe Lawrence, CCE Dairy Forage Systems Specialist, Phone 315-778-4814, Email:  jrl65@cornell.edu

To Purchase Biocontrol Nematodes for your farm, Contact:

Mary DeBeer, Moira, NY, Phone:  (518) 812 – 8565, Email:  md12957@aol.com

 

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