Scaffolds 2024 Digest: Week 16
On this week’s episode of Scaffolds, I talked to Doctor David Crowder. If you remember, a couple episodes ago, I was talking about some papers from his lab on woolly apple aphid. Well, I finally got him on the podcast, and we discuss a decision aid support tool that he directs for the Washington State tree fruit industry. It was a really fun and interesting conversation, and I think the tool is worth checking out. It is linked in the show notes. After that conversation, we hear from Kerik about powdery mildew. And then, last but not least, we have our state of the state update on degree day accumulation and trap captures.
Monique Interviews Dr. David Crowder
Okay, so today I’m here with Doctor David Crowder. He is an associate professor of entomology at Washington State University, where his lab works on applied insect ecology. Hello, Doctor Crowder.
David: Hello, Monique. How’s it going?
Monique: It is going well. It’s so fun to have someone from Washington state with us today. And so we actually decided that we were going to have a conversation about the decision support tool that you developed for the Washington State tree fruit industry. And so first, I’d like you to explain a little bit about what a decision support tool is.
David: Well, a decision support tool, in my mind, could be anything that we try to use to help farmers, producers, or other partners in agriculture industry make decisions to help their operations be more profitable and sustainable. In our case, our decision aid system, what we call it, is an online platform that uses weather data and runs those weather data through a series of models to kind of deliver real time information to farmers on what’s going on in their farm and provide forecasts as well to help them make decisions about insects, pathogens, horticultural disorders, other factors such as that.
Monique: So it sounds similar to Cornell’s NEWA. Do you guys have, like, weather stations and stuff?
David: It is similar in a way to NEWA. We have a different platform than, than you all do. But yes, we have a network of over 250 weather stations in Washington state. We also have a nationwide grid of weather networks, and we can run what we call virtual weather stations pretty much anywhere in the country. We have focused on the Pacific Northwest, but we also work up in, in Canada and down into California and some other, we’re expanding into some other states in the midwest. So we do have a network of physical weather stations that are pulling in data on temperature, precipitation, solar radiation, other weather variables very similarly to NEWA, we run those data. And I know you mentioned that you give out degree day information on your podcast. So we have over 45 different models in the tree fruit system, about 30 of them are phenological models, everything from bloom of different types of apples and pears, blueberry. We have a lot of different insect models for things like codling moth, obliquebanded leafroller, navel orange worm, apple maggot. And then we also run models of things such as fire blight, powdery mildew disease. We have models for sunburn, and we even have models for beneficial species, such as how active will honeybees be on your orchard today? How active will your natural enemies be? And so we’re trying to give out a lot of different information to growers to help them make decisions by integrating weather data through models.
Monique: I’m assuming that you focused a lot on the insect side of that development, being that that’s your expertise. So what are your thoughts about the current state of models being used with really changing weather patterns? What are you guys seeing in Washington state?
David: Well, first off, I would like to say that I am by far not the only person that has created this system. I took over as the director in 2021, but the development of the models in Washington has been going on since the early 2000s, really. And I think Washington was one of the first states, really, that tried to get growers to use these degree day tools to really help manage their orchards. Now, in, in terms of your question, I think phenology models are very accurate, and I think they can tend to be very stable over time. It’s not an insect trait that evolves that rapidly or that quickly. And so climate change may affect the phenology of the insects as they adapt over time, but it’s not something that we really worry about on the year to year. But what is important, I think, is that the weather is very different from year to year. And that’s something that we’re trying to convey to the growers, that the, the actual phenological stages of the insects might be very different in 2024 than in 2023. And as an example, in 2023, we had one of the coldest springs that we’ve actually had in a long time in Washington. But then in the month of May, we had one of the warmest Mays that we’ve ever had. And so our codling moth, which is one of our main insect pests, a lot of the growers were thinking, hey, this is going to be really delayed based on the weather they were getting through April. And if we weren’t running these forecasts in May, that telling them, hey, things are going to really ramp up in May, this is going to be kind of a quicker May than you’ve ever had in the past, they may not have been ready to get their management actions in place in 2024. We’ve had more of a middle ground year, but we actually like to give growers data not only on what’s going on this year, but we tell them how this year compares to the last five years. They can get forecasts up to 42 days in advance. And so I think with our system, we’re not thinking about climate change as much as how do you adapt to the year to year variability in weather, which obviously is changing more and more due to climate change. But our phenology models in general tend to be fairly stable from year to year. The final point I will make, though, and I’ve seen this in other decision aid systems, and it’s something that we’ve tried to avoid, is that we’ve really made a focus on having models that have been developed and validated in the Pacific Northwest. I see other decision aid sites where maybe we’re in the Pacific Northwest, but we’re running a model that was developed in Europe and never validated in our local kind of environment. And I think those models can get you into trouble if you just assume that population of an insect is completely static across its entire range. So every model that we do have on our site has been locally validated with data collected in Pacific Northwest orchards to make sure that we’re not making an error in saying transferring one of your models from New York to the Pacific Northwest, but it’s not going to work.
Monique: Yeah, I think we have a big issue with that on the east coast, where the New York models are being used in the Southeast, and it’s just a totally different environment with very different climatic variables.
David: Yes. And even in the Pacific Northwest, you know, we have a standard phenology model for the codling moth, but it is affected both by elevation and latitude. So if we were going to run our system, say, down in Utah, which is a question we’ve been asked, we would have to make some corrections, directions to the model, and we have to make some small tweaks to the model, even to run it up in Canada. So, you know, the models are not different populations or metapopulations of insects will have slightly different phenology. And I think you can run into trouble if you transfer things from one place to another kind of willy nilly.
Monique: So what do those model alterations look like? And in terms of validating, when you say validate the model, and in what way are they validated?
David: So I think the most common thing that we have to adjust to make a model transferable from one area to another is whether or not there’s a biofix and when that biofix is actually occurring. So a biofix is, you know, as your listeners probably know, a biological event where kind of we start counting the degree days. And in the case of the codling moth, we have a pretty important measurement of when the first generation of adults start flying or when that first generation of eggs start being laid. And so we’ve seen that along elevational and latitude gradients, that those, that degree day threshold where we need to start counting, where the population really starts developing, can change a little bit, that the more southern latitudes, we see things happening a little bit earlier along the degree day spectrum. In terms of validation, there’s a couple different ways that you can build these phenology models. I think a very traditional way is to use laboratory assays of insects that are measured how fast they develop at different temperatures in the lab or greenhouse setting, and then kind of build a model based on how fast we think it takes to get from one stage to the other in terms of heat units. And then you have to go out, ideally in orchards or other field settings that are unmanaged because, you know, management can obviously make it difficult to measure the population development and collect data on when those stages are out there. So phenology models are actually quite intensive. You know, there’s a fairly standard way to build them. But in terms of management, you might have to have a grad student or a postdoc out there four or five days a week collecting data and all the different stages of the insects that are in the orchards and trying to fit that up to the model you’ve built based on lab data. The other way that we do it is we collect long term sampling data from many, many different orchards that are provided to us by, in many cases, commercial partners that are running tens of thousands of acres and have hundreds or thousands of traps out there. And they feed us data on the insects that they’re collecting, the different stages. And then we try to match up those data to the weather data that we have at those sites and build a phenology model kind of based on field sampling data.
Monique: So amongst the insects, which models do you think are the most important? Is it really just the internal laps, or do you guys have other models that you think are something that is regularly dependent on.
David: On the insect side, I think it’s the leps, mostly in tree fruits. In Washington, it’s codling moth. It’s obliquebanded leaf roller as well. We also have a western cherry fruit fly, which seems to be a pretty important model in pears. A couple years ago, we, along with colleagues in Wenatchee, which is one of our experimental stations that’s owned by Washington State University, there was the development of a pear psylla model, and that is by far the most critical model in pears. And so apples, it’s definitely the leps and the fruit fly. And then pear psylla has become really a critical model because that’s an insect that growers spend upwards of $1,500 an acre to control in Washington state.
Monique: So have there been any differences in the development of that model, since that’s for a hemipteran or a piercing sucking insect with a different type of life cycle? Were there any nuances or differences in developing that model versus one for lepidopterans?
David: I think, you know, with Codling moth, they have fairly discrete generations. We’ve also developed a model for a Colorado potato beetle. This is in another system, but, you know, that’s an insect that has really, really discrete generations. Pear psylla is, as well as other insects that are faster developing, like aphids, have really overlapping generations in a lot of cases. And, you know, the overall process is the same, but it can be a little bit tricky. You know, if you’re building a model that has an insect with very discrete generations, with one where everything is overlapping, that the modeling techniques and the types of distributions that you use are slightly different, but overall, the process is fairly standard, I would say, you know, in all these cases, these phenology models, we’re only using temperature data. So, you know, they’re fairly process driven models, fairly straightforward. I think the actual models on our system that are the more out of the box are things like for honeybees or other diseases where there’s a lot more weather factors that are actually driving the dynamics of the populations.
Monique: So, one final question. Do you think we’ll ever get a model for woolly apple aphid?
David: We might. I mean, they are a tricky insect, as you know. I think because of how they kind of cluster together, it can be really difficult to even see the different life stages that they’re emerging. You know, with woolly apple aphid, as with some of our other aphids, the place to start might be just assuming that they just have one kind of continuous, long generation. I know that’s not the case, but they’re reproducing so much that the model that might be important for woolly apple aphid is just when do they really start colonizing the orchards? When do they start coming out of the root layer? When might you need to start making some of those first treatments? You know, in many of our models, I think the most important thing to just tell the growers is, like, when is that population starting its development? Because they’re going to be spraying throughout the year for the insect. And our goal is not to eliminate all the insecticide sprays. It’s to eliminate the superfluous ones. And the superfluous ones are often occurring early in the season where, you know, a grower is spraying to try to prevent risk, but the insect is not even active. And so, you know, they’re completely wasting their active ingredient or at the end of the year, when the population either has stopped developing or it’s reached a point where it’s not doing damage anymore. So I think an enterprising student or lab could definitely develop a model for woolly apple aphid. You know, in our area, it’s more of a secondary pest. And so that hasn’t been the main focus. But I think you can develop a phenology model for just about anything if you put your mind to it.
Monique: Well, that is some inspiring advice for the development of that model. So thanks so much for chatting with us today, Dave.
David: No, thanks for having me. It was a pleasure.
State of the State with Dr. Anna Wallis
And now for the state of the state, your weekly roundup of phenology and degree day accumulations from the major fruit production regions of the state. As always, I’m Anna Wallis with the New York State IPM program at Cornell, and I’ll be sharing information aggregated from the regional specialists and my own observations.
Over the past week and the holiday weekend, we had some extremely hot, humid conditions across the state, with highs in the 80’s in most locations and overnight lows remaining in the 60’s. Heat advisories were issued in many places in the Hudson Valley and in some other locations across the state, with a real feel up into the upper 90’s in a lot of places. This is just a friendly reminder to stay hydrated, keep replenishing electrolytes, and be looking out for your crews and for each other during these heat waves. There was some sporadic rainfall again this week, ranging from 0 to 1 inch of accumulated precipitation, according to NEWA weather stations this past week. Again, most of that was in sporadic storms over the end of last week over the holiday. So if you were looking for some fireworks, we hope that you got to see them. The US drought monitor, which is a product that you can see online, has a great map showing abnormally dry to drought conditions across the country in the northeast. We don’t have any regions that are at risk at this time, although we have a couple of pockets that are considered abnormally dry, so we’ll continue watching that and providing updates. We’ll also include a link to that tool in the show notes looking at the forecast for the next couple of weeks, it’s unfortunately not looking like this weather is going to let up anytime soon. Heat and scattered storms are in the forecast for the rest of this week, with a high pressure front moving in bringing more storms again at the beginning of next week, potentially moving in as early as Sunday evening. Both the 6 to 10 and 8 to 14 day outlooks in the NOAA Climate Prediction Center are predicting a lot, lot hotter weather than normal for the next few weeks, with wetter than average conditions as well. The long term forecast for the rest of the season over the months of July, August, and September is also predicting hotter than average and wetter than average weather.
Looking at phenology across the state, we are near terminal bud set on apples in most locations. We said this last week, but we’re still seeing some new growth in some places and varieties, especially after all the rain. But looking at close to terminal bud set in most varieties now, again, it’s a really compressed growth season, so we’re seeing really similar phenology across the state. Fruit is continuing to color and size very well across the state. Most people are focusing on cover sprays in between the wet weather and storms of last week and then again expected this week and next week, the Hudson Valley continues to be a little bit ahead of other regions. Apples are sizing extremely well depending on variety, location and thinning that was done. Cherries continue harvesting, with early plums also beginning harvest. Peaches and nectarines are sizing very well and early harvest on the earliest varieties is just beginning. Blueberries, raspberries, and other berries are also beginning to harvest, with earlier varieties harvesting now. In the past week or two, we’re beginning to see marginal chlorosis in Honeycrisp leaves, which is an anomaly to this variety and doesn’t indicate any poor health. It’s something we’re very familiar with as Honeycrisp growers, but it’s always a good reminder to me that this is the time of year to be taking leaf foliar samples if you’re going to be doing that this year. Also a good time to be doing the peel SAP analysis if you’re participating in that program.
Looking at some upcoming pest events. Oriental fruit moth we’re seeing the second generation peak egg hatch in Hudson Valley and western New York. So it’s time for a cover spray if you haven’t had one in the past 10 to 14 days. In the Champlain valley, the first flight is beginning, but may be a little bit early for an insecticide targeting egg hatch at this time. For codling moth, we continue to see damage in unmanaged areas. Remember that codling moth prefers to feed on the seeds, so you’ll see tunneling from the side of the fruit or the calyx end directly to the seeds, where they prefer to feed on the high source of nutrition that the seeds provide. In the Hudson Valley the biofix for the first generation was May 6 in Highland and accumulated degree days base 50 since that biofix is 1250 at this time. So the NEWA prediction model is forecasting the second generation of moths are continuing emergence. In western New York and the Champlain valley we’re seeing flight taper for the second generation. Remember, if you had good control of the first generation, you should see less pressure in the second generation. Your first insecticide application should be targeting larvae at 200 to 250 degree days base 50 after the first catch or biofix for either generation. For obliquebanded leafroller trap captures continue but taper in most places across the state. This week we are continuing to see terminal and fruit feeding in unmanaged locations, so you can be looking for rolling and webbing of those youngest leaves. Also, fruit feeding just on the skin or under the skin. Look especially in the tops of the canopies and inside compact fruit clusters where they like to hide out of. We typically recommend monitoring growth terminals at 600 to 700 degree days base 43 after the biofix or the first capture in your orchard.
Apple maggot trap captures are also continuing across the state this week. In most locations those trap captures remain fairly low, but in some areas they are reaching above threshold. So continue to be monitoring at your location to know if you have pressure. This is a fairly sporadic pest where we know that there is very high pressure and high trap captures in some locations but not in others. Remember that the recommended threshold for management is five flies per trap for baited traps. So those traps are the red spheres that are coated in tangle foot or the sticky material, and then the bait is sort of a pear essence or an ammonium acetate lure that can be purchased to accompany those traps.
We are continuing to see some mite outbreaks, both European red mite and two spotted spider mite outbreaks in some locations, mostly owing to the very hot weather. They’re particularly prone to outbreaks in hot, dry, dusty weather. Now that we’ve moved into July, if you’re sampling and scouting for mites, your threshold for presence absence on a leaf is 5 mites per leaf. Instructions and a chart for sequential sampling of mites is available in the Cornell guidelines.
A few other pests that we’re continuing to see include woolly apple aphid. We see active colonies increasing and moving to leaf axils at this point in the season. We’re also seeing continued activity by Japanese beetle, stink bugs, and brown marmorated stink bugs, as well as apple leaf curling midge in a few isolated locations.
Looking at some diseases, we continue to get a few reports of fire blight, but it continues to be relatively on the tame side this year aside from some known problem areas. So fingers crossed on the fire blight, but keep scouting and making sure that you don’t see any strikes in your orchard as we move into this hot weather. Apple scab lesions have continued popping up in some unexpected places, so be looking out for spores that could be contributing to secondary infections. Powdery mildew continues to be fairly severe in a lot of places given the really hot, humid weather. We’re seeing primary and secondary infections more prevalent in this continued warm, humid weather.
Sooty blotch and fly speck and other rot diseases are at high risk with the rain and wetness during the past few weeks. We haven’t seen a lot of infections at this point in time, or at least not a lot of reports of them. Other diseases and disorders that we expect to see more of around this time of year include the yellow leaf blotch and spots including marssonina, glomerella, and necrotic leaf blotch. So we’re starting to look for those at this time.
Looking now at cherries and berries, for spotted winged drosophila, we are continuing to have trap captures across the state. For this insect we usually see low trap captures and then quick escalation into high populations, and so in many locations we are seeing that at this time. To follow trap capture information in your region or your area, you can subscribe to the new Berry Pest monitoring network which reports site specific locations on spotted wing drosophila trap captures as well as some other berry pests that we’ve been monitoring this season. There’s information on that new blog in the show notes. We’ve also had a high report of disease incidence in cherries this year, including both blossom blast and brown rot, among other things, mostly related to the very hot, humid conditions which has led to really good conditions for disease to proliferate this season and cause infections.
To help teach some of these orchard scouting protocols and monitoring techniques, we’ve had two virtual orchard scout trainings this season with Mike Basedow, Janet van Zoeren, and myself teaching monitoring and scouting protocols and identification. In case you missed it, both the first and second trainings are now available online on the New York State IPM YouTube website. Mike, Janet, and I reviewed some of the most economically significant diseases in insects, including mite sampling, disease identification, internal leps (both codling moth and OFM), plum curculio, woolly apple aphid, apple maggot, apple leaf curling midge, stink bugs, and spotted winged drosophila. If you’d like to see those recordings, we’re including links to those videos in the show notes.
And now here are the current degree day accumulations in major fruit producing regions of the state throughout the season. We’ve been aligning this information with previous work done by Art Agnello related to McIntosh phenology and degree days base 43 Fahrenheit. Degree day accumulation through July 8 was: in Geneva, 2010; in Highland at the Hudson Valley Research lab, 2153; Clifton Park, 2003; Peru, 1775; Medina, an inland site ,1952; Appleton North, a lake site, 1803; Fairville, an inland site, 1897; Williamson, a lake site, 1916.
That’s all for this week, and good luck until next week.
Phenology & DDs for NY NEWA Stations from 1/1 – 7/8
Station || Stage || DD 43F || Weekly Rainfall (in)
Geneva || fruit sizing || 2010 || 0.06
Highland (HVRL) || fruit sizing || 2153 || 0.79
Clifton Park || fruit sizing || 2003 || 0.3
Peru (Forrence) || fruit sizing || 1775 || 0.36
Medina – Inland || fruit sizing || 1952 || 0.11
Appleton North – Lake || fruit sizing || 1803 || 0.01
Fairville (The Apple Shed) – Inland || fruit sizing || 1897 || 0.41
Williamson (DeMarree) – Lake || fruit sizing || 1916 || 0
*all DDs Baskerville-Emin, B.E
Upcoming Pest Events
Pest/Phenology Event || DD Base 43˚F || Approx. Date
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
Peachtree borer – peak catch || 1579 ± 465 || 7-Jul ± 19 days
Lesser appleworm – 2nd flight starting || 1768 ± 339 || 14-Jul ± 12 days
OFM – 2nd flight peak || 1450* ± 147* || 11-Jul ± 9 days
American plum borer – 2nd flight starting || 1850 ± 290 || 16-Jul ± 11 days
RBLR – 2nd flight peak || 1721 ± 232 || 13-Jul ± 7 days
San Jose scale – 2nd flight starting || 1804 ± 170 || 15-Jul ± 8 days
Codling moth – 2nd flight starting || 1887 ± 313 || 20-Jul ± 13 days
Dogwood borer – peak catch || 1611 ± 226 || 8-Jul ± 10 days
STLM – 2nd flight ending || 2167 ± 177 || 28 Jul ± 8 days
American plum borer – 2nd flight peak || 2290 ± 285 || 1-Aug ± 8 days
OFM – 2nd flight ending || 2044* ± 233* || 31-Jul ± 7 days
*Base temperature for OFM 45F
WSU Decision Aid System:
Virtual Orchard Scut Training #2
https://www.youtube.com/user/NYSIPM
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/
NOAA NWS Storm Prediction Center
https://www.spc.noaa.gov/
U.S. Drought Monitor
https://droughtmonitor.unl.edu/CurrentMap/StateDroughtMonitor.aspx?Northeast