Scaffolds 2024 Digest: Week 12
This post is a text digest of the Scaffolds Podcast. To listen to the original episode, visit the following link: Scaffolds Podcast on Spotify
On this week’s episode of Scaffolds, I talked to Anna Wunsch about apple viruses. Kerik gives us an update on Apple Blotch and Marsonnina, and Anna gives us our state of the state update on degree day accumulation and trap captures.
Monique Interviews Anna Wunsch
Monique: Okay, so today I’m here with Anna Wunsch. Anna did a master’s degree with Dr. Mark Fuchs and is now working as a research support specialist in his lab. And today we’re going to talk about viruses in Apple. So welcome, Anna.
Anna Wunsch: Great. Thank you so much for having me.
Monique: I’m super excited to learn more about viruses in apple. So when you were doing this work, what were the specific questions you were looking to answer?
Anna Wunsch: Yeah. So viruses in apples can tend to be a little bit poorly understood. I know when we think about apple diseases, the main players, of course, are bacterial and fungal, like fire blight and apple scab. But viruses infect apples as well, and the infections they cause can be a little less obvious. So the big players in the apple virus world, the most prevalent viruses, tend to cause latent infections, meaning that they don’t cause obvious symptoms on most of the commercial cultivars that are being grown today. So that means that you could walk out into your orchard and trees may be infected, but you wouldn’t be able to tell by looking at them.
Monique: When you were looking for viruses, were you targeting any certain varieties or any certain stage of apples? And do we have any idea how the viruses are getting into the apples?
Anna Wunsch: Yeah. So, well, first of all, just to back up viruses of apples, there are a few really prevalent ones that are kind of globally distributed. So we have them really prevalently in New York. And those, particularly the three that are most prevalent, I tend to refer to as the big three, those are apple stem pitting virus, ASPV, apple chlorotic leaf spot virus, or ACLSV, and apple stem grooving virus, or ASGV. And what’s interesting about these viruses is that they are all known only to be graft transmissible, which means that they don’t have any insect vectors that are transmitting them from one plant to another. They’re also not mechanically transmitted. These are just being transmitted from one tree to another through grafting or budding or other vegetative propagation methods. So as trees and planting material have been distributed across the globe over the past, you know, 100, 200 years, those viruses in that material have been transported around the globe as well, and so now a lot of them can be found everywhere that apples are grown. So once a tree is infected with a virus, that virus can be found throughout all of its tissues, from the roots, the leaves, and we found even the fruits, including the peel and the flesh and even the seeds.
Monique: So I guess my main question is, okay, so there’s these viruses, and they may be in the plant material, but what are the symptoms to look out for? I know you said they’re not super obvious, but are there any characteristic symptoms of any of those big three that would be worth looking out for?
Anna Wunsch: So, unfortunately, no, the big three on the commercial cultivars that most people are growing won’t cause any noticeable symptoms. And so really, the way that these infections manifest are a little bit more subtle. So this would be like smaller decreases in productivity and yield over an orchard’s lifespan. So unless you have an adjacent block of the same scion-rootstock of the same age that’s uninfected, you wouldn’t have a good reference to compare that yield. But the way that in a lab, scientists are able to determine whether a tree or other planting material is infected is either through a laboratory test or through biological indexing on certain apple species or cultivars that do show obvious symptoms. So, for example, there’s a crab apple species that is often used as an indicator species to which planting material can be grafted and that will show characteristic symptoms.
Monique: So what about trying to avoid planting trees with viruses? Are there any good strategies for New York growers to avoid planting trees with viruses?
Anna Wunsch: Yeah, absolutely. So, as I mentioned, because the source of viruses, in apples and pear trees is almost exclusively from infected planting material, that’s infected root stocks or infected scions, the most important management strategy is to avoid infected material in the first place. So sourcing certified material when possible, and always sourcing material from a reputable nursery. And then the good news is that because viruses of apple and pear are, for the most part, not transmitted by insect vectors, they’re not going to spread within an orchard if they are there. So in terms of a certification program, New York Department of Ag and Markets does offer a virus tested plant material certification program, both for grape and for apple. And what that means is this program is nursery focused. So nurseries will bring in virus tested clean budwood or scion and rootstock material from sources that are part of the National Clean Plant Network. And these are like the cleanest of the clean. A lot of this material originates from tissue culture material, and then this material is bulked up by nurseries, and those material in those increased blocks is tested on a rolling basis to ensure it’s virus negative. And that material can be available through nurseries, though at this point, the number of nurseries participating in the apple certification program is pretty small.
Monique: Is there any incentive to get more nurseries to participate or is there some reason why they aren’t?
Anna Wunsch: Yes, we would love to have more nurseries participating in this program. There was a more extensive certification program in New York a few decades ago, but that petered out and now we’re sort of in a ramp up stage trying to get more nurseries to participate. I think many growers have gone decades without having access to certified material and now maybe don’t see a reason to go out of their way to look for certified material because they’ve become used to growing material that hasn’t been able to be certified. But I think as more nurseries participate, there will be more access for growers to get this certified material, and I’m hoping it will catch on because that’s really our only management strategy for eliminating viruses from orchards.
Monique: So I have one last question. Do you think now that we are growing everything high density, do you think that that has an impact on the effect of these viruses compared to on standard sized trees?
Anna Wunsch: Yeah, I think that there’s a lot that we don’t understand yet about high density plantings, and especially that there are a lot of scion and rootstock combinations being planted right now that maybe haven’t been tested really extensively. And we don’t know a lot about how individual latent viruses or combinations and co-infections of those viruses might impact those trees. So, for example, we know that some cultivars are more sensitive to viruses than others or particular viruses, but we don’t know sometimes how like a combination of those viruses might impact a new scion cultivar and rootstock combination. And we also know that in high density orchards, these trees tend to be just under a lot more stress, generally because they’re packed together, competing more for water and nutrients, and they’re often pushed to crop, you know, pretty early in their lifespan.
Monique: Okay, this is all very fascinating. So, I’m hoping growers listening to this will consider getting clean plant material, especially because it’s a, it’s a good long term investment. So thank you so much for joining us today, Anna.
Anna Wunsch: Yeah, thank you so much for having me.
State of the State with Dr. Anna Wallis
Anna: And now for the state of the state, your weekly roundup of phenology and degree day accumulations from major fruit production regions of the state. I’m Anna Wallis with the New York State IPM program at Cornell, and as usual, the information I’ll be sharing has been aggregated from the regional specialists around the state.
Over the past week, and right now we’re moving through a little bit of a cooler trend across most of the state, but forecasts predict that we will be moving out of that pretty soon. We’ve had cooler temperatures, with highs only in the sixties at the end of last week and over the weekend. It’s also been wetter, with as much as an inch and a half of rain recorded mostly at the end of last week, and up to an inch of rain in some locations on Sunday, although that’s been pretty site specific and NEWA stations are reporting pretty different accumulations depending on location. The NOAA Climate Prediction center, 6-to-10 and 8-to-14 day outlooks are predicting a big change back to much, much warmer and slightly drier than average conditions. So pay attention to irrigation, especially for young, high density trees, over the next couple of weeks.
Looking at phenology across the state now, we continue to be well ahead of the degree day averages, the 15 and 30 year averages across the state. Again, because of the early spring and warm trend earlier in the season, despite the cool weather last week. Now that the thinning window is finished, where return bloom sprays are going on, we’re thinking about that at this time. In the Hudson Valley, apples are continuing to size in many locations. We’re looking at 30 or more millimeters in diameter, of course, depending on variety, location, and the thinning that was done. Cherries are starting to color really nicely, particularly in earlier varieties. And peaches and nectarines are continuing to size and color. Strawberry harvest, looking at small fruits, is in full swing. So that is continuing at this time in Western New York, in the Lake Ontario, and similarly in the Capital Region, we’re just slightly behind, that fruit is also beyond 30 mm in many locations. And in the Champlain valley, again, just a little bit behind and approaching 20 mm or more in many locations.
Now looking at upcoming pest events, plum curculio continues to be active in unmanaged areas. We’re seeing feeding on fruitlets that can sometimes look like a little feeding mark surrounded by a red halo. Across the state, we’ve passed the period of this insect moving into orchards. Usually that happens from petal fall until approximately 308 degree days base 50 after petal fall, and so we’ve passed that across the state.
Oriental fruit moth OFM flight is ending or continuing to taper; Codling moth flight continues. We have a similar biofix for the Hudson Valley as well as Geneva and some locations in western New York. For most of those places, it was approximately the week of May 13, and in the Champlain Valley a week, about, after that. So this insect, we would typically target the larvae with our first insecticide application at approximately 200 to 250 degree days base 50 since the biofix. Right now, early this week in the Hudson Valley in western New York, we’re at about approximately 400 to 500 degree days since that biofix. The second application targeting larvae should go on at about 10 to 14 days after that first application. And again, the Champlain Valley is just about a week behind that.
Oblique banded leaf roller trap captures continue in many locations this week. This is the second week of trap captures or sustained trap capture at the Hudson Valley Research Lab this week, in earlier locations, we’ve had earlier trap captures of this insect. You should monitor growing terminals at about 600 to 700 degree days base 43 after the biofix, and you can see if there is larval activity in those growing terminals and use that to determine whether you should make an insecticide application targeting this insect. In orchards with a history of really severe or heavy pressure and infestation, an insecticide can go on targeting young larvae, and that’s typically at 350 degree days base 43 after that biofix, followed up with a second spray 10 to 14 days later.
I also want to mention apple maggot. It feels a little bit early, usually we use the guidance of putting traps into the orchard at the beginning of July in many places in the state. But everything this year seems to be a little bit early, and so we’re starting to put our apple maggot sticky coated red plastic spheres in the orchard this week. Also, in other parts of the northeast, we’ve had reports of apple maggot trap captures as early as mid June over the past couple of years. So it’s a good idea to be thinking about getting your traps ready for apple maggot at this time.
We’ve continued to see aphid activity, both green and red apple aphid. We see leaf curling and feeding on terminals. Rosy apple aphid can turn the leaves sort of pink and very easy to spot, so that’s a good thing to be looking for. Woolly apple aphid continues to be active. This is pretty location dependent, but we’re seeing the wool and aphids active on both old pruning cuts as well as moving to the axles of the leaves at this point. And we’re seeing them pretty active on root suckers. So you can be looking at all those locations.
We’ve had more reports of leaf hopper and mullein plant bugs across Western New York and the Hudson Valley this week, so be looking out for those insects. We’ve continued to see some sawfly damage, which can look like a circular sort of scar going around the fruit, but it can also look like feeding and very wet frass from small fruitlets, which can be very easily confused with internal lep feeding. So be looking for those insects.
It’s a little bit early to be seeing codling moth damage at this point, so it’s unlikely that that would be the cause of any internal fruit feeding, but you can look for the insects to be able to determine what is causing it.
San Jose scale crawlers should be emerging around this time. So if you are monitoring for this insect using double sided sticky tape wrapped around the branch of a tree near an active infestation, you should be seeing those crawlers now.
Mite activity both European red mite and two spotted spider mite, we expect to be taking place at this time, especially with the very warm, dry, and potentially dusty conditions, we can see these populations exacerbated so it’s a good idea to be monitoring for this insect. During the month of June, we use a threshold of two and a half mites per leaf, which means you’ll take a sequential sample starting with 20 leaves. And if two and a half mites are present on a leaf, it’s called positive. So, you’ll do that for each of the leaves and then determine how many leaves were positive for mite presence. And next, you’ll use the chart in the Cornell guidelines to determine whether you’re above or below threshold for some kind of management. And so that would be a miticide to treat for European red mite or two spotted spider mite.
Apple leaf curling midge is a somewhat new insect in many places throughout the state. We’ve seen this insect for a couple of weeks now, both in western New York and in the Champlain Valley in particular. It starts with really curled, tightly curled sort of hardened leaves. And if you uncurl them, you can see the nymphs that turn bright orange before they pupate and drop to the ground. So you can be monitoring for that insect now.
Dogwood borer, we have detected some borers and clear winged moths flying in a few locations throughout the state. It’s important to get a good identification on this insect. Dogwood borer can be very similar to peach tree and lesser peach tree borer, so make sure you’re looking very carefully for identifying those clear winged moths.
Moving into some diseases, we’re continuing to get reports of fire blight strikes across the state, so be scouting for those mostly blossom blight, but soon to be shoot blight strikes showing up in orchards where it might have slipped through. Primary scab season is over at this point, but we are detecting abundant lesions in unmanaged blocks, and in a few managed blocks, we’ve seen a couple of breakthrough infections occur. So make sure you stay vigilant so you can stay on top of fungicide programs for that. Typically, you’d be looking for those olive green to darker brown, sort of fuzzy lesions as they first appear, and then they can become sort of sheet scab, which looks a little bit like black, sooty mold covering on a whole leaf surface. Powdery mildew continues to be pretty prevalent in most of the state. We expect that to continue with the really warm, dry conditions. More reports of rusts throughout the state is also taking place. So we’re seeing those bright orange lesions on leaves.
And as we move into the summer months, we’re starting to think more about the summer diseases. So that includes the sooty blotch and fly spec complex as well as summer fruit rots. And so with the early spring and the really wet conditions, we expect that there’s a lot of inoculum out there that could potentially cause infections. And so it’s going to be important to stay on top of your fungicide program.
Thinking about cherries and berries, we continue to have spotted wing drosophila trap captures in many parts of the state. First and sustained trap captures have been reported in many locations in the Hudson Valley and now in western New York and the Capital Region. This is the third week in a row that we’ve captured spotted wing drosophila in both Albany and Dutchess counties in the Hudson Valley and Capital Region, as well as Suffolk County on Long Island. Last week we had first trap captures reported in Clinton, Columbia, Schuyler, Washington and Ontario counties. And early this week we have reports of first trap captures in Wayne, Delaware and Tompkins County. This is a little bit earlier than usual, but not unexpected given the early wet spring conditions. Predominantly low numbers have been reported to this point, both on red sticky traps and in jar traps, but the populations can escalate really quickly after first trap captures, especially under humid warm conditions.
We have posted the quick guide for insecticides, updated for 2024 on the Cornell Fruit Resources page, and it’s important to be rotating your chemistries to maintain resistance management, especially for this insect that has so many generations within one season.
To stay on top of the latest updates, we encourage you to subscribe to our new blog, the Berry Pest monitoring network for berry growers, as well as other fruit growers such as cherry growers that would like to continue to get spotted winged drosophila updates. To do this, you should go to the new blog, which is included in the show notes, click on subscribe, which is on the right side of the page and then you will get another email and you’ll need to confirm your email for the duration of the 2024 season. We’ll continue to post updates about spotted winged drosophila on both blogs, both the spotted winged drosophila blog and the Berry Pest monitoring network blog, but we encourage everyone to move over to the new blog because that’s where the most up to date information will be in the future. Again, we’re doing that for a couple of reasons. The first is that we are monitoring additional pests in berries, so if you want updates on those pests, you can see that on the blog. In addition, we’re reporting more regionally to account for microclimates throughout the state rather than at the county level, and it’s making it a little bit easier for us to manage on the back end, which hopefully you won’t see at all, but it can make it more efficient for us to serve the industry.
And now here are the current degree days in the major fruit producing regions of the state. Throughout the season, we’re continuing to align this with information previously done by Art Agnello related to McIntosh phenology and degree days base 43 Fahrenheit as of Monday, June 10, Geneva was at 1191 degree days base 43; Highland, 1282; Clifton Park, 1256; Peru, 1002; Medina, 1172; Appleton North, 1043; Fairville 1113; and Williamson, 1116. The degree days and upcoming pest events from table 7.1.4 in the Cornell Guidelines are also posted in the show notes.
One final announcement, we have a second virtual orchard IPM scout training coming up on Tuesday, June 25, and this is a post bloom follow up to the first virtual orchard IPM scout training that we held in April. We’ll be broadcasting again from orchards live in our regions across New York state, going over a few insect pests and disease identification in the field, things that you can be looking for at this time in the season, so feel free to join us for that. There is a registration link in the show notes and that information will be shared in regional newsletters. If you missed the first one, the recording is on the New York State IPM YouTube website and you can watch that as well. Thanks.
And that’s all until next week.
| Phenological Stage | DD Accumulation |
| Silver tip | 58-106 |
| Green tip | 99-144 |
| Half-Inch Green | 150-201 |
| Tight Cluster | 206-257 |
| Pink | 267-316 |
| Bloom | 344-415 |
| Petal Fall | 439-523 |
| Phenology & DDs for NY NEWA Stations from 1/1 – 6/10 | |
| Station | DD Accumulation |
| Geneva | 1191 |
| Highland (HVRL) | 1282 |
| Clifton Park | 1156 |
| Peru (Forrence) | 1002 |
| Medina – Inland | 1172 |
| Appleton North – Lakeside | 1043 |
| Fairville (The Apple Shed) – Inland | 1113 |
| Williamson (DeMarree) – Lakeside | 1116 |
Phenology & DDs for NY NEWA Stations from 1/1 – 6/10
Station || Stage || DD 43F || Rainfall past week (in)
Geneva || fruit sizing || 1191 || 1.48
Highland (HVRL) || fruit sizing || 1282 || 0.72
Clifton Park || fruit sizing || 1156 || 0.97
Peru (Forrence) || fruit sizing || 1002 || 1.23
Medina – Inland || fruit sizing || 1172 || 1.6
Appleton North – Lake || fruit sizing || 1043 || 1.64
Fairville (The Apple Shed) – Inland || fruit sizing || 1113 || 1.7
Williamson (DeMarree) – Lake || fruit sizing || 1116 || 1.27
*all DDs Baskerville-Emin, B.E
Upcoming Pest Events
Pest/Phenology Event || DD Base 43˚F || Approx. Date
ERM Sample – 2.5 mites/leaf || 1-Jun
OBLR traps set out || 1-Jun
Black stem borer – 1st flight peak || 681 ± 170 || 1-Jun ± 9 days
RBLR – 1st flight ending || 753 ± 140 || 2-Jun ± 8 days
American plum borer – 1st flight peak || 784 ± 183 || 3-Jun ± 9 days
Codling moth – 1st flight peak || 768 ± 206 || 3-Jun ± 12 days
STLM – 1st flight ending || 813 ± 128 || 5-Jun ± 9 days
OBLR – 1st adult catch || 884 ± 90 || 9-Jun ± 6 days
OFM – 1st flight ending || 825* ± 126* || 12-Jun ± 8 days
Peachtree borer – 1st adult catch || 1032 ± 266 || 15-Jun ± 11 days
San Jose scale – 1st flight ending || 1039 ± 182 || 16-Jun ± 8 days
Black stem borer – 1st flight ending || 1056 ± 198 || 19-Jun ± 9 days
STLM – 2nd gen. 1st adult catch || 1063 ± 91 || 16-Jun ± 6 days
San Jose scale – 1st crawlers observed || 1124 ± 91 || 19-Jun ± 8 days
Dogwood borer – 1st adult catch || 964 ± 230 || 12-Jun ± 9 days
American plum borer – 1st flight ending || 1344 ± 144 || 29-Jun ± 7 days
Apple Maggot Traps Set Out (in orchard) || 1-Jul”
ERM Sample – 5.0 mites/leaf || 1-Jul
Comstock mealybug tape traps set out || July 1 (ENY), July 15 (WNY)
OFM – 2nd flight starting || 1180* ± 136* || 29-Jun ± 5 days
OBLR Summer Gen. 1st Sample || 10-Jul ± 5 days
STLM Summer Gen. 1st Sample || 9-Jul ± 7 days
RBLR – 2nd flight starting || 1367 ± 105 || 29-Jun ± 6 days
AM – 1st catch || 1509 ± 285 || 4-Jul ± 12 days
Lesser peachtree borer – peak catch || 1234 ± 470 || 25-Jun ± 19 days
STLM – 2nd flight peak || 1563 ± 207 || 6-Jul ± 8 days
Codling moth – 1st flight ending || 1557 ± 262 || 6-Jul ± 12 days
*Base temperature for OFM 45F
NEWA Help Desk Frequently Asked Questions and Table of Contents. https://help.nysipm.org/hc/en-us/categories/16994462926231-NEWA-Network-for-Environment-and-Weather-Applications
Quick Guide for Apple Insect Pests https://help.nysipm.org/hc/en-us/articles/23290226665751-NEWA-Quick-Guide-for-Apple-Insect-Pests
NY Tree Fruit Pest Monitoring Network
https://blogs.cornell.edu/treefruitpests/
Interested in collaborating and contributing trap capture data? Contact Anna Wallis aew232@cornell.edu
Berry Pest Monitoring Network – NEW Blog!
https://blogs.cornell.edu/berrypests/
Quick Guides for SWD Management
https://fruit.cornell.edu/spottedwing/management/
https://fruit.cornell.edu/spottedwing/
Virtual Orchard IPM Scout Training 2