With Larry Gut, Codling moth expert from MSU
Download the June 7 recording here:
Get the MP3 version.
Paraphrased Play-by-Play:
-         02:30 – John: Could you cover the basic stuff your lab at Washington State has found out about how temperature and wind can affect Codling moth behavior.
- Larry: We have a project right now to work on just that.
- There is no mating taking place in the evening when it’s below 60 degrees. CM starts flying around 5 or 6pm. He thinks you can ignore most of this activity because they’re not mating. If you can delay that mating for 3 or 4 days with the weather, then the eggs that are laid are mostly not viable, so you end up shutting down the populations.
- This year, it’s not cold enough to have that effect.
- CM won’t fly when there is even a slight wind (3mph will knock them out)
- We are trying to incorporate those figures into a predictive model so that people can quantify how the conditions affect the population based on those factors. We will do this after 2 years of data collection.
- May 30 or 31 is a really good biofix date for people in Michigan, at least.
- When growers treat at 100 degree-days (if you’re targeting hatching eggs or covering eggs being laid). If you get insecticide on at around this time, you’re going to have a big effect.
- Either that, or wait till 200 or 250 degree-days: this year, people will probably be able to greatly reduce CM numbers.
-         09:10 – John: Will the model be able to reflect individual nights? If we had, for example, one cool night when there was no flight and the trap counts reflected that, do you anticipate that your model would be able to take that one night into account when calculating the female’s egg count/viability?
- Yes, that’s the idea.
-         11:30—John: What kind of research do you see coming down the line on CM? What else are you working on?
- Nothing much else, just this predictive model. And there aren’t a lot of new controls out there, either.
-         12:10 – John: One question that often comes into play with leaf roller control in the summer is about egg viability among oblique banded in the heat. Is there any evidence out there that the heat reduces the viability of CM eggs?
- I don’t know. In the degree-day model for CM, if the temperature gets too high, the CM doesn’t develop as fast, but it doesn’t completely shut down like leaf rollers.
-         13:45 – John: Our CM numbers the last two years have been down, for any number of reasons. This year, it looks they’ve grown again. Do you have a sense whether it’s more difficult to control CM hatching if they’re all hatching in a short window? Like with scab, the more compact the ascospore release, the harder it is to control.
- Larry: I think it will make it better for control. The most difficult part of the control is the residual. As time goes by in that 2-week window when you’re trying to keep residual on there to control hatching, your residual is diminishing. If you get the compound out there and have coverage during a concentrated hatch, you’re going to get good control. You should really try hard to target this current cohort.
- On the model: The model gets messed up by temperatures when it tries to predict adult flight. BUT it’s extremely accurate at predicting when a current group of adult will lay eggs and when those eggs will hatch. It can provide very accurate timing for your sprays and let you get really good control.
-         17:20—John: If your orchard has used mating disruption, but they’re still getting some catch in things like L2-baited traps, how do you gauge the level of the problem? For example, if they were to catch 5 or 6 in one of these L2 traps over the course of a week versus if they were to catch 5 per night over the course of that same week, how would you interpret it? How would you gauge the threshold?
- Larry: No one has figured out a hard and fast threshold. But in our experience, you don’t want to be catching any moths AT ALL in L2 lures if you’re looking to eliminate insecticides. Even 5 or 6 in an L2 trap is over threshold in my mind. If you get up over 3, 4, or 5 moths in a trap, you probably should be substituting your mating disruption program.
-         19:17—Peter: What about in a non-mating disruption block with consistent but low trap counts?
- Larry: My conservative threshold for CM: if you catch ones or twos and after three weeks your catch is up to 6 or 7 moths, I think that’s cause for treatment at the proper timing of the insecticides (not immediately, of course).
-         19:58 – John: But these moths don’t live terribly long, and egg viability diminishes after a week or so. I’ve never understood why I should add the three males that I caught in week 1 to the three males that I caught in week 3 and say that we’re over the five-count threshold, when those moths are almost different cohorts.
- Larry: Most of the controls are based on a couple week’s residual for the material. If you catch three, and then catch three more, you’re putting on a product that you hope will take care of the larvae from the first week’s cohort and continue on for the following weeks.
- Larry: I’m a less conservative person, so I would probably take those low cumulative counts a cue to delay my treatment.  Instead of 250 degree days, I might wait until 350, because the first few eggs that are hatching from the first cohort are not going to be very numerous.
-         22:10 – John: One issue that comes up in orchards with larger blocks is differential catches. The question that comes up is: do we need to treat the entire orchard when we see great differences between traps across the blocks? My experience is that if it’s a 30-acre block and there is only one corner of it over threshold, if only that corner gets treated then in a week or two the numbers will jump in the other areas. On the other hand, if the traps are separated by several hundred yards, then we’ve had success treating differentially. What is your experience? Does it make more sense to assume that the counts are going to vary and go ahead and treat the entire orchard at one time?
- Larry: We have a huge ongoing project on “trapping space,†that is, the space for which the trap is giving you information.
- Larry: With each trap, you’re sampling probably 2-3 acres. If you have a trap up every 2.5 acres or so, each trap is giving you a pretty good indication of what is happening in that region.
- Larry: If you have one trap in 10 acres, you will get a good picture of what is happening in the inner 2.5 acre area, but you’ll have no idea what’s happening on the remaining 7.5 acres.
- Larry: If you’re trapping at one every 2.5 hours, you absolutely can make decisions not to treat certain blocks. We have a grower with 120 acres, and because of his tight trapping layout, he only had to treat 2 sections of his orchards (5 acres) for CM over the entire year.
- Larry: BUT in a pheromone block, that’s not true. In a pheromone block your catch is probably representing about a 10th of an acre because it’s competing with all the pheromone dispensers. In this situation, it becomes very hard to make good decisions about section spraying.
-         27:03 – John: These days I’ve become wary of being too liberal with timing sprays against CM. I’ve had experiences where I’ve been too loose and consequently seen CM numbers increase to damaging levels over the course of several years. I’m loathe to stretch things out and risk introducing resistance or allowing an explosion down the road.
- Larry: I think it would be good for resistance management to base your spray locations on your catches.
- John: I agree that when it’s not a solid block, that seems to have worked in the past.
-         29:16 – John: Can CMDA lures replace L2 lures in a no-pheromone block and have the same effect?
- Larry: That has NOT been my experience. I would stick to the L2 in a no-pheromone block.
-         30:05 – John: I assume that in an organic orchard that has pheromone disruption, if that is not working 100%, then is their best secondary option to use virus?
- Larry: Yes. The virus, no matter what you do, is effective for 4 days, maybe even a week. You don’t need the highest label rates. If you’re an organic grower, the best thing you can do is go with low rates, frequent applications.
-         30:05 – John: Does virus get washed off?
- Larry: I don’t know. But you could assume that 3 or 4 days is the activity length in the sunlight. In general, people use weekly intervals.
- Dennis @ Royal Oak Farm: I’ve used virus every season for a number of seasons. I find that whenever we spray that virus, I have to clean off my leaf wetness monitor because the virus activates it.
-         32:45 – John: What is the effectiveness and utility of Surround against CM larvae, in both organic and conventional orchard?
- Larry: In our experience, the hardest part of using Surround is getting enough coverage. You have to have a good residual out there, and then that residual disappears with the rain. I’ve never gotten efficacy greater than about 50 or 60%.
- John: In combination with a virus, the control should be additive, right?
- Larry: Probably, because the surround is probably having more of an effect on what the adults are doing than what the larvae are doing.
-         33:58 – John: Is it correct that here is very little utility in using Bt products on CM larvae?
- Larry: Yes, that’s correct. But it’s also correct that Bt is very effective against leaf rollers if you have problems with them.
-         33:32 – John: In conventional orchards without pheromone disruption, most people are using larvacides: neonicatinoids, Delegate, and Altacor. How we make our choices for what to use is based on what other insects we have. So, if thrips are a concern in anybody’s orchard, then Delegate would be one material of choice, particularly if the orchard had low pressure from Plum curculio. If scale were a concern, we might use something like Assail. I know that products like Belay or Clutch are not quite as strong against CM as Calypso or Assail, but it seems like Belay is a great PC and apple maggot material. How do you rate Belay as a material against first-generation CM compared to other compounds?
- Larry: For first generation, we’d rank it “Good.†It would be below the best materials, that is, below the level of Delegate or Altacor.
- John: But Belay has better PC efficacy than those two materials?
- Larry: Right, Delegate and Altacor have almost none.
-         39:00 – John: Growers who have PC problems and some CM numbers have the choice of Assail and Belay. Do you see any reason to go with one over the other, not considering price?
- Larry: No, I’m not going to pick products for growers. I think about it differently, though. If you have already some PC, you are going to have a problem. At petal fall it was really hot. PC would have been there doing it’s thing and you should have already been controlling for it. It’s not likely that PC will all of a sudden show up at 250 degree-days if you haven’t seen any PC yet. If you do have a PC problem in your orchard already, though, you want to pick a product that will take care of both of them.
-         41:50 – John: How does rate relate to level of control? Is it just a question of longevity, or also of efficacy?
- Larry: You need higher rates for PC to get control.
- John: But for CM, if someone uses a middle-rate of any of these materials, can they expect 14 days of control if they don’t get rain on it?
- Larry: Our experience suggests NO. With these new chemistries, companies have been a lot tighter on the rate. As soon as you start lowering the rate, you’re going to get a shorter residual.
-         44:08 – John: Are you saying that growers should not calculate a proportional rate based on the size of their orchard?
- Larry: No, they can do that.
-         44:55 – Peter Werts: How do neonicitanoids for first-generation CM tie in with apple maggot later in the season?
- Larry: I’m a big fan of saving my Assail and Calypso for the summer, because they’re better apple maggot materials. They are the ones that have stood out against apple maggot and CM.
- Peter: Is there a window between first and second generation CM where I could use Assail and still be able to use Assail later in the season?
- Larry: You don’t want to use it now against first and then against second. That’s not a good resistance strategy.
-         46:33 – John: On the other hand, if you’ve controlled first generation CM very well, the second generation will be lower in intensity and also spottier. So there’s the potential of spraying the Assail or Calypso on apple maggot in blocks that are not catching any CM, but there is no assurance. But if you have apple maggot pressure and don’t have a lot of tools to control it with, and you also have CM, could you tank mix Assail with Altacor to knock out the resistance potential for Assail?
- Larry: I don’t know, but I don’t think it’s a good strategy. It would better just not to use it at all.
- But really, the combination for that first spray that we’re concerned about is the leaf roller – CM combination. Growers that choose Altacor tend to do much better at controlling leaf rollers.
-         52:25 – Last notes on other pests and diseases
- San Jose scale crawlers are beginning.
- Black and white rot pressure is fairly high, so if you have a lot if it in your orchard, you don’t want to reduce your protection levels for the next few weeks.
- Scab should be pretty much done. If you’re clean of scab now, you’ll probably be clean of it for the season.
- Apple maggot: They’ve emerged as early as June 15 in some places. It seems too early to do it, but you should think about getting apple maggot traps out in the next 10 days or so. If you can’t do the entire orchard, do at least the known hot spots.
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