The big topic today was heat — heat and drought. John discussed the evidence he’s seen in the field of the weather’s effect on a wide range of insects, including on ones that we’re seeing in apple trees for the first time ever. Download the recording and read the full transcript below. Also, be sure to check out the many articles referenced below.
Some other logistical notes:
-Â Â Â Â Â Â Â Â Â Our last call will be on Tuesday, August 7. That means we have three more weeks to go.
-         We never posted last week’s webinar. We will be re-recording it and posting that recording soon. We’ll send out an email when it becomes available.
-          Next week’s call: Craig Schultz suggested that we try to find an expert to talk to us about the effect of this heat/drought on 1) fruit bud formation, 2) fruit ripening, and 3) the effectiveness of Retain. We are trying to get some experts from Washington and California to join us on next week’s call. NOTE: We may have to schedule that call later in the day to accommodate the time difference.
Recording
Download the recording of the July 17 call here.
Related Links
Supplemental Links
- What do we know about injury, monitoring, and management of stink bugs in apples? (by Short and Hogmire): Download PDF
- Information about national weather patterns:
Articles Discussed in Call
- Michigan Drought Update, July 12: http://msue.anr.msu.edu/news/michigan_drought_update_for_july_12_2012
- Regional Report on Michigan Fruit, July 10:
- http://msue.anr.msu.edu/news/regional_reports_on_michigan_fruit_july_10_2012
- Ups and Downs of Japanese Beetle Populations: http://msue.anr.msu.edu/news/the_ups_and_downs_of_japanese_beetle_populations/
- Managing Japanese Beetle In Fruit: http://msue.anr.msu.edu/news/managing_japanese_beetles_in_fruit_crops/
- Why are we seeing so few Japanese beetles this summer?: http://msue.anr.msu.edu/news/why_are_we_seeing_so_few_japanese_beetles_this_summer/
- Black hunter thrips: http://www.virginiafruit.ento.vt.edu/Leptothrips.html
- Minute pirate bugs: http://www.entomology.wisc.edu/mbcn/kyf101.html
- Green lacewings: http://www.fcps.edu/islandcreekes/ecology/green_lacewing.htm
- Assassin bugs: http://bugguide.net/node/view/166/bgpage
- White-marked tussock moth: http://bugguide.net/node/view/521
- Stink bugs in apples: http://www.ipm.ucdavis.edu/PMG/r4300311.html
- General UC-Davis search on stink bugs: http://lyons.ipm.ucdavis.edu/cgi-bin/htsearch?config=&restrict=&exclude=&method=and&format=builtin-long&sort=score&words=stink+bug
Transcript Topics
On insects and the effects of heat and drought on insects
Weird insects we’re seeing on apples which we normally don’t see on apples
Questions: Efficacy of pesticides against stink bugs
Call Transcript, 7.17.2012
A note on the weather
John: A meterologist from MSU published some interesting things on the FruitCat newsletter on July 12. He indicated that within 8-14 days, there should be a change in the precipitation probability in our region, that this drought pattern might change.
However, I just looked at the 8-14 day forecast from NOAA published yesterday, and it doesn’t indicate any change. We’re still in a below-normal precipitation and above-normal temperature period.
Know that it looks like we won’t get a break from this weather in the next few weeks.
Another aside on weather and water use: in Michigan’s recent FruitCat regional report, one extension person discussed water use. They said that where soil water is available, trees are using about 1.25†of water every 5 days. However, the evapotranspiration rate is 1†of water every 5 days. So, basically, out of that 1.25†of water that is being consumed (if it is available) every 5 days, 1†of it is going to transpire and cool the trees, and only .25†is used for the running of the plant.
On insects and the effects of heat and drought on insects
John: I want to talk about how the heat and drought have been affecting major and minor insects, and how it will likely affect them to the beginning of harvest. Some of what I have to say is speculation, some is from observation, and some is simple biology.
Codling moth
John: It seems to me that the heat is not affecting the adult flight to a great degree. Blocks and orchard that have high populations are getting substantial numbers in the traps. Overall, from what I’ve seen, there are fewer CM adults this year than in a normal second generation. But there are certainly orchards and parts of orchards that have experienced very high numbers over the last 10-14 days. I think that the flight has been more clumped and less spread out. In any case, the numbers are accumulating in these orchards.
One big question I’ve had is whether this heat is affecting the CM egg survival. Obviously, once the egg hatches and the larva, within in 30 minutes, climbs into an apple, it is then protected from the weather conditions. We’re seeing pretty dramatic mortality in leaf roller young (we’ll talk about them in a minute). But I have no idea whether we can expect the same kind of thing with CM eggs. The bottom line, I think, is that if you have CM numbers over threshold in your traps, you should not rely on speculation that the heat might kill the eggs. Even though we might be getting a bit of an assist, we have no way of knowing.
The bottom line: keep on treating CM like you always do.
Apple maggot
John: We’re not seeing large numbers of AM adults flying. We’ve just seen small flights here and there. Again, the contention here is that the dryness is behind the low numbers.
The old figure that people went by was that AM needed .25-.50†of rain for the adults to climb out of the soil. However, we’ve seen a number of summers when we didn’t have that rain and still had significant AM emergence.
This year, I have yet to see any large numbers of AM in any one location, or any kind of sustained flight. So, I guess that’s good.
What about AM adults? If adults are already out there and laying eggs, I’d guess that the survival of those young would be pretty high, because the eggs are being laid in the fruit.
Leaf rollers
John: Regarding both Red-banded and Oblique-bandeds: over a number of years, we’ve seen that high temperatures and low humidity can adversely affect LR survival.
In past hot & dry summers, we’ve seen a substantial adult flight followed by a low hatch from that flight. I’ve witnessed that in a number of years with OBLR.
This year, things with the RBLR look different. The RBLR are just winding down their adult flight. We’ve seen a fairly significant hatch from that flight in the last couple of weeks. I saw lots of RBLR in terminals, or evidence of RBLR having hatched out in terminals.
However, on return visits to those orchards, where I initially saw RBLR hatch, I could find no live worms. It looks like they’ve hatched out, done a little bit of feeding, and died.
So, RBLR have seen substantial mortality, presumably from heat. I don’t think it was due to biological control. I was seeing nearly 100% mortality. Biocontrol agents are not usually able to achieve such levels.
One caveat: in past years, we’ve seen that when we have hot temperatures during the first LR flight (around 2-3 weeks after petal fall), OBLR initially feed on the terminals but then exit those areas and enter inside the canopy to look for fruit to feed on. Presumably they were driven into the canopy by the high temperatures on the exterior of the tree.
I haven’t seen the RBLR doing that – feeding on fruit – but I suppose it is a possibility.
This is the last flight and the last generation of RBLR. The larvae that survive through this period are going to overwinter as pupae in the groundcover and emerge next spring as adults. (That’s why we see the RBLR fly with the Spotted-tentiform leafminer, around early April, around bud break). If I’m right that RBLR larval survival has been low, then we should see low RBLR numbers next spring.
On the scale of things we’re faced with, this little piece of good news is probably more of a curiosity than anything.
Secondary insects
John: Other than the CM, AM, and leafrollers, I’ve seen the heat affect various other insects (pests and beneficials). I’m just going to run through the list:
Dogwood borer, spider mites, aphids, stink bugs, tarnished plant bug, Japanese beetle, and predators and parasites. This is obviously not an exhaustive list.
After I talk about these, I’ll discuss some of the insects the are appearing in trees that we normally don’t ever see in apple trees – again, ostensibly, because of the heat.
Aphids
John: By aphids I mean both green apple aphids and wooly apple aphids.
I’ve been seeing an interesting phenomenon with both species. I’ve seen colonies of both species that have just disappeared. This is not so unusual for green apple aphid. But wooly apply aphid is usually everywhere, on shoot growth and pruning cuts. In the last month, we had seen those colonies start to grow and expand out the shoots.
When a predator controls wooly apple aphids, the colonies stay about the same in appearance – they stay fluffy and white. But what I’m seeing are things like a shoot dusted with white – a shoot that was clearly infested with woolies from top to bottom – with nothing but a faint dusting left. The colonies are absolutely wiped out. I’ve never seen WAA colonies disappear before like they have in the last 10 days. I’m attributing it mostly to the heat.
I’ve seen this happen in my local counties, Richland and Crawford. I haven’t been to enough counties in the last week to know if it’s happening everywhere.
Peter: The woolies go through a winged or alate phase, correct?
John: All aphids do have a winged phase. Woolies, though, may not use that phase very much. Most of their colonies are underground and feeding on apple roots. That’s where the bulk of their population is. According to the descriptions that you find for the life history of WAA, the populations of WAA that you find on the aboveground portions of the trees (the “aerial†populations) will crawl down the trunk and into the ground in the fall to join colonies on the roots. With that sort of lifestyle, there would not be much of an inducement to form wings.
But most aphids certainly do have winged forms. Green apple aphids do, rosy apple aphids do.
Peter: Yesterday, I saw what looked like white pieces of cotton fluff flying around. I caught it and looked at it with my hand lens. It looked to me like a wooly apple aphid with a little bit of its cottony fluff still attached.
John: I can’t remember what those are, but they aren’t wooly apple aphids. They threw me for a loop the first couple years that I saw them. They have the outward appearance of woolies. But they’re not coming from a fruit crop, and they’re not wooly apple aphids. Don’t ask me how I’m so certain, because I could be wrong. But I finally did find out what they were, and it made sense. It was kind of disappointing when I did find out, because I thought I was seeing wooly apple aphids dispersing by air.
I’ll try to dig out information about that critter and let you know.
John: So, our aphid situation may have been dissipated because of the heat. Just watch it and see if your observations fit with what I’ve been seeing.
Stink bugs
John: Stink bugs are a different story. We haven’t talked much about them for a few weeks. One of the reasons is that stink bugs haven’t been visible on the trees for a while. Earlier this season, though, we did see a lot of a adults and lots of egg masses. We saw brown stink bugs and green stink bugs – and plenty of them – in tree fruit. They seemed to have gone away. Until a week ago, I was thinking that they had been knocked down by the heat and dryness, as well.
But since last weekend, out of the blue, I’m seeing green stink bug nymphs – not just in the trees, but all over: in fence rows, on parked cars. They’re all late instars, and some are adults. (The final instar/adult of green stink bug looks partially green, as opposed to the black, orange, and yellow coloring of earlier instars.) I also saw my first collections of stink bug egg masses in the trees yesterday.
This is what stink bugs are supposed to do. I’m just reporting that it looks like they could unfortunately be a big threat despite the weather. Ordinarily they leave the trees and go into alternate hosts in the summertime, then come back at some point to the tree fruit.
Based on the number of nymphs I was seeing in places yesterday and over the weekend, I’d guess that they’re going to cause real headaches if they all end up on apples.
There’s nothing to do about it right now. But it’s worth keeping an eye on. Aside from bitter pit, stink bugs might be the main threat to the few fruit that remain on the trees.
Peter: From what we learned about Brown marmorated stink bug, it sounds like (at least as far as BMSB goes) stink bugs are easiest to kill them by targeting the recently-emerged overwintering adults in the spring, and the nymphs right after they have hatched out. How well does that hold true for these native stink bugs? We have two growers for whom this has been an ongoing problem for several years. I don’t think we want to wait until we start seeing summer adults before we try to do something.
John: The only thing I can agree on is this: they’re at their most vulnerable when they come out of overwintering as adults. So, if you could locate the population at pink, and, God forbid, spray Danitol or something as a selective spot spray, that would clearly be the easiest time of the year to kill them.
But I’m not sure what is going on here. When you see them doing fruit damage in August, typically what you’re seeing is adult feeding. Yet, yesterday I found these freshly-laid egg masses.
So, does that mean that they’re going to have another generation? I don’t know.
This is another place where the importance of scouting comes in. If you’re out counting mites and run across have a dozen stink bug egg masses in your Honeycrisps, then that may be a spot where you’d want to target the emerging nymphs.
The nymphs that I saw yesterday that were large, half the size of a dime, will turn into adults in the next few days. I’m anticipating that those are the adults that will be doing damage to the fruit in August. But since I saw egg masses at the same time, I’m not sure what’s going on.
Once they start feeding, they’re pretty tough to kill. The best option may be to put Surround on selected cultivars, to throw a wrench in the stink bug feeding.
The other thing that I’ve emphasized too little is seeking out all their alternate hosts and trying to eliminate them from the orchard. The further away those alternate hosts are, the less likely you will be inundated by stink bugs. Some growers who have routine problems with stink bugs probably have some issues with some of those summer host plants.
Spider mites
John: This is mostly a no-brainer. Most of the damage being done by spider mites is being done by the European red mite.
There’s a caveat, though: there are Two-spotted spider mites out there. If you read the pest survey bulletins from DATCP, you’ll see that Krista has mentioned Two-spotteds in a number of crops. Two-spotteds also can be found in apple trees.
There are lots and lots of predators of mites out there right now, as well (which I’ll go through in a minute). Many of the predators are ones that I don’t usually see at this time of year.
A big caution: don’t be complacent about spider mites. The trees are very stressed right now. Even if you have irrigation and the trees have adequate water, the heat is still a stressor. If mites take away their chlorophyll in late July, it will do bad things to the trees for at least the next year.
If you don’t normally spray miticide, more power to you. In a lot of cases, the predators are doing a good job of keeping them under control. But considering how fast these things are multiplying in some places, they remain a major threat. You can’t be complacent, because the mite situation in a block can change dramatically in a 5-day period of time. Don’t assume that what looked good last week still looks good today.
Two-spotteds are relatively easy to differentiate from other mites. First, they’re rarely on the upper side of the leaves like European red mites; they’re normally on the undersides. Also, if there are two-spotteds on a tree, you should see a couple things. When you turn the leaf over and look at it from two feet away, you’ll notice some light-colored patches on the underside, usually along the midrib. The patches are not uniform. They look slightly whiter than the underside of the normal light green. If you look at it more closely, you’ll see what looks like fine spider webbing. When you see those indicators, you can be fairly certain that you have or used to have two-spotteds there. With a handlens, look along the midrib where they congregate.
One point of difficulty with identifying two-spotteds: their eggs resemble the eggs of many of the predator mites. European red mites have distinctively red eggs. Most of the predator mites have white or cream-colored eggs. As it turns out, two-spotteds also have clear or whitish-colored eggs. Look at the eggs with a handlens. If you see webbing, then those eggs are probably not predator mite eggs – they’re probably two-spotted eggs.
Dealing with mites comes down to a judgment call. I have some blocks with very high counts of European red mites but with such incredibly high counts of predators that we’re not spraying. In other cases, blocks like that are getting a miticide. The difference may be that the latter is in a block of larger McIntoshes with a crop on it. The longer those mites stay on the trees, and the more chlorophyll they remove, the more likely it is that they will lead to apple drop. Since McIntosh — and particularly the older-type McIntosh on bigger rootstocks – can have a catastrophic fruit drop at fruit ripening, I want to make sure not to stress them more than they’re already stressed.
With other varieties – Gala, for example – it’s a different story. If the predators are in such high numbers that victory looks almost assured, then why spend the money on miticide.
Tarnished plant bug
John: You know what tarnished plant bug damage looks like in the spring after petal fall: a single needle-like puncture wound, and the malformed fruit that develops around it.
Well, tarnished plant bug have multiple generations and multiple hosts, and there are a lot of them. They seem to be leaving their hosts now. Not a lot of them are in the trees, yet, but I anticipate that we’ll start seeing some late tarnished plant bug punctures. Also, a lot of the TPB hosts are not doing as well as the apple trees, so we’re going to see more of them on the tree fruit.
This is not a big deal; I just wanted to let you know.
Japanese beetle
John: If you read the regional report in the FruitCat newsletter from last week (see Link 1, Link 2, and Link 3, and Link 4), you’ll see that one of the guys talked about JB being down because of the heat, the dryness, etc. But he says that they’ll just be delayed, and that they’ll come out if we get some rain – and presumably come out in big numbers.
However, I’m thinking that these low numbers are a reflection of larvae starving to death in the ground. I think they’re not able to complete their larval stages because the grass roots shut down so quickly this spring with the lack of moisture.
It’s pretty easy to see other examples of insects that have starved to death or dessicated this year. I don’t see any reason why JB shouldn’t fall into the same category.
I hope that we get some rain to see if the JB come out. If JB emergence is what it takes to get rain, I’m happy to be wrong.
Overall, I think we’ll continue to see a slow emergence of beetles. Most people who sprayed once in a targeted way on some crop or cultivar haven’t seen a lot of JB return to those spots.
Dogwood borer
John: Dogwood borers are doing well. Flights are substantial. If you have susceptible rootstocks (like M-9), I think dogwood borer could do more damage this year – in a dry year—than they could in a normal year. The tree may not be able to produce some of the compounds that inhibit dogwood borer penetration. The borer larvae may penetrate further into the trunk seeking water and food.
This is something that could bite us in a year or two, and it may be occurring over the next 6 weeks. Whether or not you have a dogwood borer trap out there, you should spend an hour looking at your susceptible rootstocks some evening when it’s cool enough to get down on your hands and knees. Look for frass or sawdust around that graft union. If you can’t find any sawdust anywhere, then the chance of you having a substantial population of dogwood borer coming back in and attacking it is minimal.
Potato leaf hopper
John: Places like Cornell and New York are talking about potato leaf hopper problems. Most of us around here don’t seem to have them much anymore. We had them earlier in the season, but they haven’t rebounded to a great extent. I found a few nymphs yesterday, but nothing to write home about.
Predators and parasites
John: I mentioned that there are three species of predator mites out there. But there are also other predators, some of which predate on mites.
Black hunter thrips: These we usually see in the spring around petal fall. Adults are black with a white arrow shape on its wings. I don’t typically see a lot of those this time of year. In the last week, I’ve seen a lot of dead ones in places where there is plenty of mite prey around: a lot of dead adults and considerable numbers of nymphs (which don’t have the white pattern on the back and are sort of dark purplish-colored). I think some of them are just dying of old age. But there are also young ones, which is a good sign that means we’re getting reproduction.
Minute pirate bugs: These are one of the better generalist predators that we have in orchards. They’re reproducing. I’m not seeing very many adults right now, but I am seeing nymphs. They’re kind of hard to describe, so I’ll just stick to letting you know that they’re out there.
Green lacewing larvae: There are way, way more green lacewing larvae. Every year we see thousands and thousands of the little white eggs on stalks – the green lacewing eggs. There have been years where you might see 500 of those in the first few weeks after petal fall but never see a single larva hatch out. These days, not so. We’re seeing larvae running around everywhere. They may have been feeding on aphids before, when there were plenty of rosies. I don’t know what they’re feeding on now, but I hope that they’ll use some of the mites. That’s the most likely food source for them. If there are any leaf rollers, they could likely feed on those as well.
Assassin bugs: I’ve seen two species of assassin bugs out there. I don’t know how much good they are, but I’m seeing more of them.
Small wasps: This is something I’m not seeing a lot of this year. I saw two of them in one orchard yesterday. That’s not a lot. I imagine that they might be suffering some mortality just because of their size. But, again, that’s pure speculation on my part. They could be parasites of codling moth eggs, or leaf roller larvae, or parasites of aphids, or they could be parasites of some of the predators, for that matter.
Lady beetles: We’re seeing lady beetle egg masses again, but not too many. We had so many of them this year across the region feeding on rosy apple aphid colonies, to the point that they were eating themselves out of a food source. I have a number of pictures of young in the terminals that had starved to death. There we just too many of them for the food source that they had.
My big message? If you have to spray something really toxic because you have stink bugs, apple maggot, codling moth, or whatever, you should stick to targeted spot sprays. Do anything you can do to preserve islands to help these guys continue to play a role in subsequent years.
Diseases
Sooty blotch
John: This is the one disease I’ll mention today. If you haven’t put anything on for sooty blotch, I think it’s likely that you’ll be able to find some sooty blotch starting on yellow-skinned cultivars. You’ll just see the early signs of it.
Weird insects we’re seeing on apples which we normally don’t see on apples
John: These things aren’t actually that weird. Most of them actually aren’t that exciting to look at. But what they do is throw a wrench in your scouting, because you don’t recognize them and you don’t know what they’re doing.
Typical of a year in which a lot of forbs and a lot of grasses have bit the dust early, we’re getting all kinds of uncommon insects in the trees. Most of them are in the beetle family. A number of them are in the true bug family.
Most of what I’ve seen are small beetles of 3 or 4 different species. They’re mostly on the leaves (on the undersides), and occasionally on the fruit. They’re about 2mm long, either drab brown or drab grey. They’re not weevils. I have no idea what they’re doing on the trees.
They’re small, but they’re quite visible to the naked eye.
I imagine that they’re scavengers and just feeding on detritus and whatever they can get a hold of. I haven’t seen any leaf feeding.
Another one is the white-marked tussock moth. Colonies could be showing up. These insects can do a lot of damage. The best that I can do to assist you on this one is to direct you to Google to look at some pictures. In their later stages, they’re so spectacularly colored that they’re easy to differentiate. Luckily, they’re pretty rare.
Anyway, keep an eye out for things like this. If you see something strange out there, let us know. Some of these things certainly could do some economic damage.
Questions: Efficacy of pesticides against stink bugs
Grower: The efficacy chart in the spray guide doesn’t say anything about stink bugs. Can we fairly assume that materials that are effective against plant bugs will have good efficacy against stink bugs? In other words, Assail should have good efficacy against these stink bugs, right?
John: Yes, relatively so. And Alias will probably be a little less effective.
Peter: I like to default back to some of Tracy Leskey’s work on the Brown marmorated stink bug. That bug is the most difficult to kill of all stink bugs. Her laboratory tests of pesticides showed great variability in control of stink bugs in all chemical classes within each individual chemical class. That means that not all pyrethroids acted the same, not all neonicatinoids acted the same, not all organophosphates acted the same. Her test showed that Actara was the best neonic with the highest efficacy. Using Surround in combination improved the efficacy of Actara.
John: The pre-harvest interval for Actara is pretty long, though, isn’t it?
Peter: It’s a 35-day pre-harvest interval, so it should still be available to us for this season.
John: You’re right. If Brown marmorated is controlled significantly better by Actara than it is by Assail, then brown and green stink bugs will most likely show the same response. But Actara is more expensive, has a smaller group of pests that it controls, and, because of its longer pre-harvest interval, isn’t as commonly used in orchards.
If I had to choose something, I would choose to use a combination of Assail and Surround.
Quite honestly, if you have a crop, then there’s sunburn showing up on things. You also might have CM hatching out, or tarnished plant bug, or apple maggot, or mites – all of which Surround has efficacy against. So, I think I would put Surround out no matter what, to work against any number of things that could be going on in the orchard.
Peter: I want to chime in on another thing. If you do a web search on stink bugs, you won’t find much about stink bugs in apples. But they are a much more significant pest of stone fruits. If you’re looking to read more about their biology and behavior, try looking up stink bug & stone fruit. You’ll get a lot more information. Just remember that the recommended pesticides for stone fruit may or may not be appropriate for apples.
John: That’s a good point, Peter. UC Davis has quite a bit of information on stink bugs. (Link1, Link2)
