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Entomolgy Update with Monique Rivera
This is my first week for a while not doing an interview, but today I’m going to talk about a couple points of clarification. So first, treatment timing for woolly apple aphids. And then second, we’ll talk more about leafrollers. So when it comes to timing for woolly apple aphid sprays, I just want to give you the bad news that if you’ve been waiting to spray an infestation and the infestation is growing, you’re probably not going to solve the problem with the softer insecticides.
So what’s happening under the wool right now is population turnover. So even if you can get access to the top layer of insects underneath that wool, it doesn’t really matter, because underneath them are basically babies, so small nymphal larvae underneath them. And so this is why it’s important to target these with those systemic insecticides like Movento, or at least translaminar ones. However, I can really tell you this, that these aren’t going to work, because this is a big part of what I did last week. We were running a trial to compare some of the different insecticides for woolly apple aphid. And being the scientist that I am, I was like, let’s wait for these colonies to show up so we know that they’re there. So we are going to apply this treatment and we are going to try to correct that. But when we actually remove the colonies from the tree after treatment, what we found is that after three days, we were basically no longer seeing mortality.
Essentially what I’m saying here, is that if you’ve waited too long and you see a bunch of wool, Diazinon is what is going to work. A grower that I’m collaborating with is putting on the Diazinon to spray out the trial this week, and I’m going to go back and collect some colonies and look at that efficacy for comparison.
So I do think this is going to be a challenging pest to work with. And as much as I don’t love recommending prophylactic spraying, if you have a block where you have a history of woolies, put that Movento on before June 15, before you see the woolies in the block forming on the trees. And the key here is getting the treatment into the plant before you have that significant wool blow up, because the blow up of the wool is essentially caused by the insect actively feeding. So when they’re feeding, that’s when they’re putting out that white substance that we also refer to as honeydew or wool in this case.
And so that’s another reason why I think the next front here is really chemigation. But let’s see if I can convince my collaborators to install this or get it up and running at Agritech. I doubt this will happen quickly, either for the growers or for us, because it’s going to take us at Agritech a couple of years to get the plants established and then making sure that if I were to work with a collaborator, that the chemigation is installed properly so that we can actually compare treatments. This could be challenging.
So for now, I’m hoping to update the recommendations this year to make sure that I am very clear in the guidelines that those softer insecticides are to be used in blocks where you know you’re going to have them, you have a history of them, and to do it early.
So to move on to our next section here of talking about leafrollers, I wanted to first direct your attention to the leaf curling midge webinar that Mike Basedow recently hosted. I’ve heard that a small bit of apple leaf curling midge is around western New York, but I hear more on average about this pest from those in the North Country. I also want to clarify that just because we’re not seeing oblique banded leafroller in New York, that does not mean that it can’t pop back up and rear its ugly head in western New York.
For leaf curling midge, this used to be thought of as a pest that affected younger trees or a nursery issue. But these can explode apparently in high density plantings and the impact lies in the reduction in the photosynthetic abilities and winter hardiness to the tree. So that’s how these pests can potentially impact trees. There also can be a stunting of growth to young trees. So according to Kristy Grigg-McGuffin from the webinar, which will be linked in the show notes, this is a significant pest in Ontario, Canada. That’s not so far away from us. Webinar link
Also, as an entomologist, it was a bit mind blowing to hear that these are actually gall forming midges and the leaf curling is not due to the feeding of the insect. So basically, what it sounds like is that when they do feed in their salivary processing with the plant, they are releasing some sort of chemical that’s causing the leaf to curl up.
So typically the newly hatched larvae are feeding and exposing the plant to that chemical, which is causing the leaf to curl. But then after they have gone through their different larval stages, they drop down from the leaf and finish pupating in the soil. So anytime there’s something pupating in the soil, this is an opportunity for the insect to die by predation, infection, or infestation of the larvae or the pupae. So this might be something to look into. But I haven’t seen good success with entomopathogenic nematodes used for larvae and pupae that are so small. But it could be promising.
In my lab, we’re starting to think about combining entomopathogenic nematodes and entomopathogenic fungi to see if we can get an increased efficacy.
Pathology Update with Kerik Cox
Last week I got a couple of questions about Marssonina blotch, Marssonina leaf blotch specifically. Now I’m going to talk a little bit about that disease I mentioned. I’m just going to do another little brief sort of description and talk a little bit about what the disease is like, what its life cycle is like. And then next week we’re going to crack down into the management. I’ve mentioned some things to do to manage it already briefly in some of the other episodes that just happened a few weeks ago.
So what is Marssonina leaf blotch? Sadly, it has a new name. It is now called apple blotch. Same disease now by the sexual state of the pathogen diplocarpon. Previously it was named after the asexual reproductive state. Now it’s named after the sexual stage. This is what mycologists like to do. You need a new paper, change the name, do some more phylogenetics and confuse the growers for the next five years. Don’t worry, I will be here talking about both diseases anytime I give an extension talk. So Marssonina leaf blotch is now known as apple blotch and it’s caused by diplocarpon, making it a lot harder to call it Marssonina leaf blotch.
Anyway, so what is this disease going to do? What it’s going to do is it’s going to defoliate your tree early. And usually some of the defoliation that we’ll start to notice will happen mid to late August. And that’s a little earlier than you want. The leaves falling off the tree, they’ll start to lose leaves probably around the end of July at a very slow rate. It’ll happen from the insides of the tree. This is what you’ll begin to see. It’ll first look like, “oh no, do I have a little bit of captan injury?” It’ll be sort of a reddish maroon color. And this would be the value of being able to do a live twitch stream for this sort of thing. I just show you the pictures of what this looks like. It’ll start out kind of a maroon and the leaf area around it looked like someone sort of just misted captan on under slow drying conditions and it kind of burnt. It looks sort of maroon and off color. Then what will happen is the chlorophyll in these sections will die and it’ll look really splotchy with yellow mixed with the darker maroon colors. At this time, various spores are being produced inside it. And right before the leaf will fall off, you’ll see that in a cluster, all the other leaves are normal except for the ones that are affected, and they might look quite clean and healthy.
But that’s just the beginning of a big problem. And if you could get down in there, it’s going to look splotchy. If you think about it in terms of animals, think about this disease looking like a dalmatian versus a giraffe, which has very defined margins to its spot. And this is sort of a diffuse, dalmatian, spotty kind of dog thing. And if you get down in the darkened areas in the very center, it’ll be like a center of brown area highlighted in an island of green. And in a field of yellow chlorosis, you’ll be able to see these little tiny, black, specks, little fruiting bodies. Also what will end up happening is these will lead to little lenticel infections, which could look like captan injury, could look like botrysphaeria. Infections of lenticels could even look like a little tiny splotch of herbicide, depending on what the problem is. But this is all the diplocarpon and apple Blotch type symptoms.
How this is going to happen? It’s going to be just like apple scab. The leaves are going to defoliate, and they’re going to fall to the ground. They’re going to overwinter, and they’re going to mature just like apple scab. They’re going to make their sexual structure. In this case, it kind of looks like an apothecia, if you will, like a little cup with ascospores in it. Oh, my goodness. We’re still talking about ascospores. That’s right. These are going to eject when the rains come. Usually it’s going to be sort of late. Bloom, petal fall timing, it really likes that. 66 to 77 degrees Fahrenheit. They’ll be starting to happen there and then that’s when the infections of the leaves will begin to mature. They might happen early on, just like with apple scab, but they’re going to begin to mature and they’re going to have this sort of dalmatian splotchy pattern and they’re going to fall onto the ground and they’re going to start the whole cycle over again.
Now, you might be asking, well, how does this look different from glomerella leaf spot? Glomerella leaf spot is a more southern disease. It’s going to be more like your giraffe in terms of its spots. They’re going to be large. They’re going to be almost kind of angular and a little bit more concentric. It won’t be an irregular, brownish, magenta looking mass with little black dots in it, surrounded by a green island, surrounded by a yellow island. It’ll be more delineated, more sharply defined looking spot.
And when we get to the winter meetings next year, I’ll show you some picture of these. So next week’s episode, I’m going to actually talk about what to do about management. It’s going to begin with sanitation, and it’s going to begin with when to start your fungicide programs, which fungicides seem to be the best according to those places in the south. Welcome to the world of what it must be like to be a North Carolina apple grower in the 90’s. We’re starting to see things we’ve never seen before, and we may have to keep our fungicide programs going longer and into the summer with some of our single site fungicides. All right, that’s all I’ve got for this week. I’ll talk to you later.
State of the State with Anna Wallis
As always, this information has been aggregated from the regional specialists around the state, NEWA, and my own observations. Fruit is continuing to size and color nicely throughout the state. Moving into July, we should have seen the effect of thinners by this point and natural June drop. Now is a good time to be taking tissue samples for leaf tissue analysis for nutrient management. We’ve continued to get lots of rain over the past couple of weeks. This past weekend, an inch or two were recorded at most NEWA locations across the state, although some places only recorded about a quarter of an inch, with high winds reported in many places in northeastern New York. So it seems we’ve received very heavy rain events, but very specific to location. Last week we also had very heavy rain, an inch or two in many locations. Over three was recorded in Geneva. Unfortunately, some of those storms also included reports of hail in western New York.
A reminder that a good place to search for severe weather updates, including hail and heavy wind reports are on the NOAA Storm Prediction Center, which I’ve linked again in the show notes. According to the Northeast Regional Climate Center, for the month of June, most of the Northeast continues to be very dry with locally heavy rain. In New York, most production regions received less than the average precipitation, but close to average temperatures were near average or a touch cooler, which is a little bit hard to believe right now given the heat wave that’s happening across the country. You can see more information about that on the Northeast Regional Climate Center website, which is also linked in the Show Notes. For the month of July, however, the outlook is predicted to be warmer and wetter than average, and that’s also information that we’ll link in the Show Notes. It’s available on the NOAA Climate Prediction Center website.
https://www.spc.noaa.gov/exper/archive/event.php?date=20230626
https://www.cpc.ncep.noaa.gov/products/predictions/30day/
We’re continuing to track Degree Day base 43 as an indicator of insect and pest activity. Both Degree Day base 43 and 50 have been used in the past and are summarized in the table in the Show Notes. You can also find this information about accumulations related to phenology and arthropod pest activity in the Cornell Tree Fruit Guidelines, table 7.1.4. As we always remind you, degree days since January 1 isn’t the best predictor of all apple pests, so we encourage you to use the models in NEWA that correspond to each pest.
A few things that are active now include:
Apple maggot, which typically becomes active at the beginning of July. If you haven’t already, now is the best time to be hanging red sticky sphere traps for monitoring. Typically overwintering pupa emerge in the latter half or the end of June. They move from wet, really dense hedgerows into the orchard, so place your traps near these locations or where you’ve seen damage in the past. Put three at each site, and then if an average of five flies are captured per trap, that’s the action threshold for making a management spray.
Codling moth in western New York began its second generation on June 26, so cover sprays are probably going on at the end of this week.
Oblique banded leafroller first generation is now active in northeastern New York and western New York for blocks with a history of this pest and application. Targeting larvae should be timed at about 350 degree days base 43 after the first sustained trap catch and then again in about two weeks.
OFM is beginning second generation flight in most of the state.
Mites are present now in many orchards. Use the sampling procedure in the Cornell guidelines. Figure 7.1.4. Sample 20 leaves, and now the threshold will be five mites per leaf. It increases a little bit in July compared to June.
Rosy and green apple aphids continue to be active throughout the state.
Woolly apple aphid has continued to be reported in many locations throughout the state, starting typically on pruning cuts and inside the canopy, or lower in the canopy, and then moving to young tender shoots.
San Jose scale is now active in most of the state. It has been for the past couple of weeks in the Hudson Valley and now in western New York. You can be monitoring for these again by placing black or double sided sticky tape around branches just above active infestations, so you can know when those crawlers are beginning to be active.
As Monique discussed, apple leaf curling midge has continued to pop up in some locations across the state. It’s an emerging problem in some regions, so we encourage you to watch that webinar.
In terms of diseases, we continue to see fire blight infections in places that had outbreaks last year, so keep an eye out, and also keep an eye out for scab infections where it may have slipped through. We’re seeing continued lesions in unmanaged or other troubled spots. We’re entering the infection periods for summer rots, so pay attention to those as well. Mildew has again been less problematic this week with all of the wet weather that we’ve had.
And finally, here’s the rundown of degree day base 43 accumulations from NEWA weather stations throughout the state.
As of the end of the day on July 5, accumulations were:
