Last week, we focused on the drought. This week, we turned to the rain. John discussed John Wise’s most recent publication on the rainfastness of insecticides, gave us updates/heads-ups on several pests and diseases in anticipation of rain, and touched on how a grower might respond to a heavy rain event or hail event — among other things. See below for the recording and full transcript.
Recording
Download the recording of the July 24 call here.
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John Wise – The Rainfast Characteristics of Insecticides, June 2012
Call Transcript
Table of Contents
Post-rain expectations for several insect pests
On disease issues after wind damage or hail damage
An important update on rainfastness of insecticides
Question about rainfastness and sticker-spreaders
The physiological effects of drought
Fruit bud formation in drought conditions
More on sooty blotch and flyspeck
On the state of fruit ripeness and maturity
A grower experience controlling JB with pollinators around
On differentiating CM worms vs. LAW/OFM worms
Post-rain expectations for several insect pests
John: Before we get started, I wanted to ask you growers: has anyone noticed an uptick in apple maggot, oblique-banded leaf roller, or Japanese beetle populations over the last few days?
Peter: John, we had a grower up in the Sheboygan area that had a nice, healthy catch of apple maggot over the last 3-4 days.
John: Did they get rain last week, too?
Peter: Nope.
John: Okay. Well, I hope that most people are getting some rain today. It looks like we’ve got about an inch so far in SW Wisconsin, and it’s continuing to rain likely. It’s the second inch we’ve had in a week’s time.
If there were going to be a flush of apple maggots, you would think that it would happen fairly soon after these rain events. The degree-days have certainly been met.
Oblique-banded is also coming up.
The other insects that are on the docket that we should be watching for include:
-         The second generation of white apple leaf hopper. Again, this will usually be a localized problem, not orchard-wide. You should start seeing the nymphs. They won’t be out on the terminals like the potato leaf hopper nymphs. Instead, they’ll be running around inside the canopy.
-         Second generation San Jose scale cralwers. These should be out, or be getting close to being out. If you’ve had any concerns with San Jose scale, either last summer, last fall, or from first generation this year, then you want to refresh your San Jose scale tapes and start monitoring them on a 5-7 day basis, watching for crawlers.
An update on diseases
John: I wanted to start by talking about diseases: 1) diseases that we haven’t spoken much about recently; and 2) diseases that are a concern if we get hit with some violent weather, whether it might be heavy winds that cause breakage or hail.
Apple scab
John: With the heat that we’ve had, we haven’t been concerned about scab spreading. We’ve assumed that things have shut down fairly well in the heat.
But with the rains that we’ve gotten (assuming that you’ve gotten rains similar to what we’ve gotten), if you don’t have some protection on the trees (like Captan, for a conventional orchard), then I think that there will be enough conidia on those lesions to cause some localized spread. For example, if you haven’t put Captan on for a month and have gotten these rains, then you should expect to see some new, localized infections. By localized I mean within a few inches or a foot, at the most, of the old lesions. You might see things like sheet scab occurring on leaves, where one lesion is leading to reinfection through conidia streaming down the leaves in the rain. If that happens, then 3 weeks to a month from now, you might see a whole lot of new, fresh lesions putting out conidia. And even if it stays hot and those new lesions don’t start putting out many conidia, they will still be ready to be problematic in the fall, and increase the amount of innoculum that you have to deal with next year.
I think there could be some spread to fruit if the fruit is within a few inches of old lesions, but I don’t think there is enough conidia out there to cause spread throughout a whole tree, much less from tree to tree.
Powdery mildew
John: I wanted to mention Powdery mildew, as well, simply because we’re still seeing it out there. It’s not a concern if your terminals have set; in that case, it’s simply sitting there.
If you’ve put something on that is supposed to control the mildew, like sulfur or one of the sterile inhibitors, the symptoms won’t go away. You’ll still see the same damage on the terminals that are already damaged. They won’t change appearance, but hopefully you will have stopped the spread of the mildew.
Really, though, what stops all spread of powdery mildew is the cessation of tissue growth in the tree. Once the terminals have stopped growing, the chance of reinfection drops off. That’s where we are on most varieties. Again, though, just be aware that you’ll see the same symptoms all the way through to leaf drop.
Sooty blotch and flyspeck
John: Most people have been thinking about this because of the high humidity (even in the days without rain). We should see symptoms of sooty blotch starting to appear. That should increase over the next couple weeks if a fungicide hasn’t been applied.
And really, this is independent of fruit load. So, even if you have a very light fruit crop, you can sill get them all infected with sooty blotch, if you haven’t put something on to control it. We’ve certainly had good conditions out there for sooty blotch. We’ve certainly had the humidity we’ve needed to cause some nice infections.
Bitter rot
John: This is one of the pathogens that I’m really worried about. We talk about fruit rots every late summer. But bitter rot, in particular — as opposed to black rot or white rot on fruit – is of concern. Bitter rot has concentric rings when it is fully developed, in its late infection stages. This is just like black rot or white rot. The distinction for bitter rot is this: if it has started to sporulate, the rings will have orangeish-colored dots as opposed to black dots. Again, bitter rot will have a ring or two of little orangeish-red or yellowish-orange dots.
Another distinction: the botryosphaeria rots (black rot and white rot) don’t spread from one fruit to another. But the bitter rot certainly does. Bitter rot can cause multiple infections on one apple from an initial infection, and then it can spread to all the apples in a cluster or in a tree.
People who have a light fruit crop might have a tendency not to thin those apples very heavily, because they’re so light. Those trees might have fruit that is clustered tightly together. If you can’t get a protectant (like Captan) in there to stop the spread of bitter rot, you can certainly see rapid infections of an entire cluster of fruit. I certainly saw it happen with a number of varieties last year, including Honeycrisp and Gala.
I don’t think there’s any difference between cultivars in terms of susceptibility. I think it’s pretty indiscriminate on all the cultivars, as far as I know. The key, then, is what kind of coverage you can get if you do put a protectant on. Further, when you have a lot of vegetative shoot growth along with un-thinned fruit, then, with the humidity that we’ve had, we should expect to see some fruit rot. I haven’t seen any yet, but I expect it.
So, if you have the possibility of putting out a protectant, then I’d recommend that you increase the coverage by slowing down or increasing the volume of water. If you’re organic, then you might have few options other than to search out the clusters and remove the fruit that might be the loci of infection, and to open up the canopy for air movement. They are limited kinds of things, but if you have a small crop and those are all your options, then you should stay on top of it, because we certainly have the conditions for bad fruit rot this year.
On disease issues after wind damage or hail damage
John: Diseases that we’d be concerned about after a wind storm or hail storm include fire blight, black rot, and white rot. We’ve seen in the past that hail that opens up wounds on first-year growth in areas with innoculum can trigger an extensive infection spread from even a single canker. But if you apply streptomycin within 24 hours of a hail event or a heavy wind event, you can reduce the amount of new infections that you’ll end up with.
The counter to that is this: this year, we’ve set our terminals, and when the shoot growth has stopped, the concern for fire blight spread reduces. Of course, the innoculum in the cankers could still be there, but the chance of an infected hail wound to go systemic in the tree is low. I think for most people, fire blight was not a major problem this year, and they should probably not think of it as a huge concern as we go forward.
So, I’d rather not see streptomycin applied within 24 hours of a hail event, unless you have a lot of young trees that may still be somewhat susceptible to systemic infection, or you have a lot of cankers in the orchard. If you have to apply it, I would do a localized spot spray instead of an orchard-wide spray.
For black rot/white rot spread, I think the situation would be somewhat similar, simply because the trees are less likely to allow that infection to go systemic once the shoot growth has terminated and the tree has stabilized.
As opposed to the case with fire blight, with black rot or white rot concerns, we have limited ability to control after the infection. The better solution would be go have a good protectant on prior to any storm. Outside of that, there is one set of fungicides called the phosphorous acid fungicides – for example, Aliette and Agrifos. One of the distributers has a generic version called Linebacker. There are about 10-12 different generic versions out there. Some of them are OMRI approved, some of them aren’t. They’re all basically the same type of fungicide, which is very short-lived and very systemic. Within a couple of days of application, it will run through the whole tree, from leaves to roots, and then will be gone. It can also clean out things like phytopthera problems in the roots (although lepidoptera should be minimal this year). There has been some evidence that shows it can reduce the amount of black rot spread. It doesn’t affect the amount of black rot canker that eventually forms or the amount of black rot fruit infections, if I recall correctly, but it may reduce the amount of infected limbs.
On the other hand, that group of fungicides is expensive, across the board. I think it’s around $50-70/acre for an application. It would not need to be put on within 24 hours of the storm, but still fairly soon afterward. Considering the cost of it and the stage of growth our trees are at right now, I think that there’s a minimal concern. My main concern would be with trees that are less than three years old. You don’t want to get a systemic fungus involved in any way in those trees, if you can help it.
I can’t say whether the phosphorous acid will be highly effective against black rot after a storm or not, but even if it saved 2-3 small trees per acre, it would probably pay for itself. So, if I’m going to recommend it, I’ll recommend it only on a limited basis.
An important update on rainfastness of insecticides
John: I’m going to be referring to the John Wise article that Alex sent to you last night [FOLLOW].
On page 3 of that 5-page article, it lists the main pesticides that we would use in a conventional system for the control of codling moth. The columns indicate the amount of rainfall that they tested them under (1/2â€, 1â€, 2â€). They further divide those rainfall amounts into: rainfall occurred 24 hours after the insecticide was applied, or 7 days after the material was applied.
On that chart, the X’s show where there is not enough insecticide residue to control codling moth satisfactorily after the specified amount of rainfall at the specified time.
Looking at this chart can be fairly daunting. For example, consider Assail, something that many people use. (Note that John Wise is using full rates of these materials in his research. For example, he’s putting out 8oz of Assail before putting the branches into the rain simulator). Well, with Assail, ½†rain fallen 7 days after application is enough to cause a failure in codling moth control. And, of course, everything beyond that point fails, too. Further, if you put Assail on and then get 1†of rain within 24 hours, according to John’s research, there won’t be enough Assail left to control codling moth.
My main point is this: John’s results look pretty disappointing from the grower’s perspective. It implies that when we spend a lot of money applying these materials, they’re at a high risk of being washed off.
I want to mention a couple of things that come into play. John doesn’t really talk about these things in this article.
Number One: He’s talking about controlling first instars of newly-hatched codling moth larvae. Very tiny little things that take a bit and enter the fruit. Those first instars get a very small amount of insecticide exposure. When he says that you’ll have to re-cover, it may be true that you’ll need to do that if your codling moth numbers are high. But there are other things that you have applied that Assail for that are not so problematic, like Japanese beetle, apple maggot. Apple maggot is a little strange because they don’t eat as adults, but they get a lot of exposure, walking around. Japanese beetle eat a lot of foliage. Even if there’s not a lot enough Assail residue after a 1†rain that falls 24 hours after application to control first instar hatching codling moth, there probably still is enough residue there to control other things. It depends on the insect. It also depends on your overall pest numbers, obviously.
Ordinarily, if we put out one of these materials at a reasonable rate – say, somewhere toward the high end – we assume we’re going to get 14 days of control if nothing untoward happens. What I’ve usually had people do in the past is ignore the first 7 days of codling moth numbers and pay attention only to the second 7 days of CM numbers. Implicit in that is that the number of CM that fly in the first 7 days after you’ve put a material out there (a larvacide like one of the ones listed on John WIse’s chart), in the first 7 days, any eggs that are going to hatch from those codling moth will probably encounter enough residue to suffer complete mortality. So, I say, don’t worry about the first 7 days of codling moth numbers after you apply a larvacide.
Instead, pay attention to what happens in the second 7 days. That’s what will tell you how quickly you need to go back in and spray something else. It will tell you whether you need to re-apply a larvacide at day 14, or whether you can hold off.
You can apply that sort of model to this rainfastness issue, as well, like this. Suppose you had > 1†of rain 7 days after you applied a larvacide. According to John Wise’s chart, you should re-cover. The timing for that re-spray has a lot to do with the numbers from right before it rained.
So, if it rains on the 7th day after you put something out, and it rains enough that you fall into the re-spray zone of John Wise’s chart, then you probably need to look at the CM numbers that came in during those first seven days. If you’re one of the lucky ones who is able to check your CM traps more than once a week, you’ll be able to discern approximately where in that 7 days you encountered high numbers.
If you had relatively high flight of CM in the 2-3 days prior to the rain event that washed off the protective residue, then you need to reapply ASAP. The eggs are there, the pressure was there. And the residue has basically disappeared, and that’s that. You’ll have to make a decision fairly promptly. Luckily, for most of us, CM numbers have not been consistently high this year.
Note, though, that we also need to be paying attention to our lesser apple worm and oriental fruit moth trap counts. They will also pose the same problems in terms of being able to be controlled. Like CM, their first instars just nibble a little bit and enter into the fruit.
On the other hand, John Wise indicates that some of the reduced-risk materials that we use are much more rainfast. Those include the Spinosan, the Diomedes like Altacor and Belt, and the neonicatinoids for the most part. So, Delegate and Altacor and Belt would have the ability to stick around through some rain. The neonics are the main ones that we would alternate with.
Nonetheless, John Wise indicates that with 2†of rain 7 days after application of Altacor or Delegate, you will need to reapply.
If it were me, I would be checking those CM, LAW, OFW traps. If I hadn’t checked them before the rain, I would check them right away after the rain and see what kind of pressure I had in the last few days. I’d make sure, too, to pay attention to exactly how much rain I had and in what interval after pesticide application that rain fell.
Historically, in situations like these, we have not re-applied pesticides. Michigan growers say they do it routinely. The difference may depend on whether you have a serious in-house population capable of blowing up given an opening. In our area, even with some high numbers in our traps in some locations, we have yet (in most orchards) to see failures of control since we’ve stopped using organophosphates on a routine basis. It may be that we don’t have in-house populations in serious numbers that can flare up quickly; instead, we have ones that will flare up over a longer period of time.
This last point raises the issue of resistance management. Consider the following situation: you put an insecticide on and then get the proper amount and timing of rain to cause failure (according to John Wise) of that product in controlling CM, and then you don’t re-cover. Even in that case, not all the CM will live. Not all the CM that hatch out in the next few days will live and enter the fruit without getting exposed to any of the material. Instead, what will happen is that a lot of them will be exposed to sub-lethal doses of it. Sub-lethal doses tend to foster resistance – principally metabolic resistance – over time. If we follow this kind of spray technique year after year, we could expect to see some resistance developing sooner rather than later.
Again, if you’re using an additional control like virus or mating disruption, then you have an automatic insurance policy in there.
I think that’s enough to confuse everybody on the issue of rainfastness. John has a nice discussion in that article about the difference between how toxic something is versus how rainfastness is. He has talked often about how easily Guthion residues or Imidan residues are removed after a rain, but that they’re so toxic that even with just a small percentage of the residue, they are still capable of killing an adequate number of CM. It’s an eye-opener to show us how toxic these things really were that we were using so freely for so many years.
Question about rainfastness and sticker-spreaders
Grower: Your rainfastness discussion has really gotten me concerned. You didn’t mention anything about the possibility of using spreaders or stickers to improve rainfastness.
John: Good point. John has said in the past that those are useful for improving distribution. He’s always a little nebulous when he speaks about how well those products help keep the residue on the trees.
When he does his research, he puts shoots with fruit in the rain simulator and then pulls them out and takes residue samples. When he does this, he samples the residues at many different layers. He takes the surface residue, the surface wash, to see what is right there on the surface. Then, he samples at the cuticle and the waxy layer. Then, the epidermis, and then inside the epidermis. So, whether it’s a fruit or a leaf, he’s sampling residues over a series of layers progressing deeper and deeper into the plant.
What has he found? With the neonics, there is a stark difference between a material like Assail and a material like Calypso in terms of where the residue resides over time. The strange thing is that Assail more quickly enters the deeper layers of the fruit and the leaves than Calypso. When you look at Calypso, you find that after sitting on the tree for 7 days, it is no deeper than the epidermis or the cuticle. It is not down deep in the tissue of the fruit or the leaf like Assail is.
So, you’d think that Assail would be more resistant to wash-off than Calypso is. However, that’s not the case. Take a look at John’s report.
This is counterintuitive. It may have to do with the level of the materials toxicity. Another hypothesis of mine: if the Assail spreads throughout the tissue layers so deeply, so quickly, it becomes diluted. So, you’ll have some on the surface, some in the wax, some in the epidermis, and some deeper. Visualize it streaming through a larger mass of tissue. Maybe it gets a little diluted compared to Calypso. When that CM worm takes those little bites, we need to deliver a lethal dose within a few bites. Maybe Assail fails to do this.
In your situation, if you’ve applied Assail and then gotten enough rain to eliminate its effectiveness against CM according to John Wise’s paper, in an orchard like yours, I think you can push the envelope by paying attention to your CM traps. If you continue to have hotspots, you might reapply the material in a tank or two just in those hotspots rather than as a full cover.
The physiological effects of drought
John: As Alex indicated in his email to you, we were unable to get some of the people from Washington to participate. And not because they were not willing to, but after looking at our questions, they sort of felt like they didn’t have answers for us. That sort of response is not unheard of. If a professor doesn’t have research experience with questions you have, they often will not go out on a limb and take a stab at things, like I do. That’s good, in one sense.
I wanted to mention a lot of things about drought.
First, pay attention to your trees. I know a lot of people have been watering. Some people have watered everything, some people have watered the young trees, some people have watered trees with more fruit. The bottom line is to keep an eye on it.
I was in an orchard the other day that had 15-to-20-year-old trees – Paula Reds, Gingergolds – that were just dying. They just collapsed. The issue had had some issues with black rot, which usually causes a slow death. But these trees were collapsing. Those are symptoms of acute failure probably due to black rot or white rot. As Dave Rosenberger said in one of our first conference calls this year, when black rot and white rot are in a tree, they can be sequestered and walled off by the tree’s internal defenses, as long as the tree is healthy. If it’s healthy, it will continue to put out compounds that build a barrier between the site of the infection and the rest of the tree. But one of the first things that a tree gives up is the production of these secondary, defensive compounds. What you’ll see when the defenses fail is a delayed effect over 1-2 months that ends in the tree collapsing. If this orchard had watered those trees consistently, I think that this wouldn’t have happened. Even though the trees already had black rot, if the grower could have saved the trees if they had been watering.
That’s a worst-case scenario with an old block of trees that has been severely drought stressed.
On the other hand, when you look on the web for information on drought effects and water management for tree fruit, the information available is pretty spectacularly slim. There’s very little information on mid-summer drought effects.
They normally say the following: the critical time for soil moisture is about from full bloom to a month after petal fall, during the period of time when you have fruit-set. Then, the last 30 days or so before harvest are another critical time. During that time, soil moisture is obviously a big issue, because the fruit won’t size without soil moisture. All of the final fruit sizing is due to water swelling. The number of cells in the fruit don’t change at that point.
Those are things that are mentioned over and over again. Two critical times: full bloom to a month after bloom, and then a month or so before harvest.
The story I just related about the collapsing Gingergolds and Paula Reds clearly has not been commonly considered. Yes, those trees had black rot. But I think that any trees that are 10-15+ years old probably have a considerable amount of black rot inside. As long as the grower can keep those trees relatively healthy, they will probably keep the trees alive and productive for a long time.
Fruit bud formation in drought conditions
I haven’t found much information at all on fruit bud formation in drought conditions. The fruit buds that are forming now have been forming, and will continue to form, over the course of the entire year, for next year. It’s not a done deal at any single point. There isn’t a lot of information about the effects of drought stress on that process. But I do have some articles to read through to see if I can find something on that topic.
More on sooty blotch and flyspeck
Grower: Could you elaborate on sooty blotch and flyspeck?
John: At the recent field day at Oakwood, Patty McManus talked a little bit about sooty blotch / flyspeck. Historically, we’ve used leaf wetness hours. But we know from the research that she collaborated on with a number of universities, that relative humidity is actually a better predictor for the upper Midwest than leaf wetness hours. They’re interchangeable in terms of the number of hours. The only thing I can’t remember is whether the relative humidity cutoff is 90% or 95%.
So, if you have the ability to chart relative humidity, you should be able to use that. But I guarantee you that if you haven’t put something on to control sooty blotch/flyspeck in an orchard located where yours is that you will have exceeded the model hours for relative humidity.
It’s not going to matter how light the fruit is. The innoculum is coming in from elsewhere. It’s be too bad to see it form on the Honeycrisp when you just have a light crop.
Grower: I’ve not seen it yet, so I don’t think it’s too late to put something on.
John: No, it’s not. Once the symptoms are there, you can’t get rid of them. The infections have already occurred, but it’s like scab: there’s a lag between the time of infection and the time of symptom appearance. So, as long as you can catch it with one of the materials that we normally use – like Topsin, one of the strobilurins, or one of the newer sterile inhibitors like Indar – then you should be good.
On the state of fruit ripeness and maturity
John: Richard, where do you think we are in terms of fruit ripeness and maturity, this year? Are we still way ahead?
Richard Polansky: Yeah, I picked Pristines already. I’m going to start tasting Zestars in a couple of days. There’s some really nice color on a few Zestars. They’ve been irrigated all season, so they have size. From shoulder-height down, there’s no fruit. But above shoulder height, there’s some nice fruit. And they look wonderful, probably the best thing in the whole orchard.
John: How did the Pristine do?
Richard: They tasted good. The fruit quality was surprisingly good. It’s a really heat tolerant tree. The Dudley’s, though, are really mealy. They didn’t take the heat very well. I’d be interested to see how the Zestars are.
John: So your Pristines have already been harvested?
Richard: Yep.
John: That’s got to be close to two weeks early, isn’t it, RIchard?
Alright, well that’s Richard, and he’s basically down on the state line with Illinois. So those of you with Pristines can maybe gauge your maturity by his experience.
A grower experience controlling JB with pollinators around
John: Did you find an answer to how to control Japanese beetle in raspberries without killing all the pollinators?
Grower: Yeah, we’re using Altacor.
John: Really? I didn’t know Altacor worked on JB.
Grower: Yeah. I’d heard that they’d been using Altacor successfully right over the bees in cranberries.
John: Right, I’ve heard that, too.
On differentiating CM worms vs. LAW/OFM worms
Peter: You mentioned something briefly about lesser apple worm. Doesn’t lesser apple worm still go through the core of the fruit, while it just avoids the seeds? Whereas we find CM in the seeds? Could you clarify that difference.
John: I think that if you see a CM-like worm in the core, you should assume that it’s a CM, whether it’s in the seeds or not. I have pictures of OFM that show them actually tunneling around in the flesh of the apple. Some university descriptions will claim that OFM will go to the core but not into the core, and that LAW stay closer to the outside walls. Obviously, al this can be based on pretty subjective determinatons.
If you see a worm tunneling around in the flesh of an apple and with frass in the hole that looks like CM, but it hasn’t gone into the core, then it’s pretty safe to assume that it’s LAW or OFM.
