IPM Conference Call: May 22, 2012

Call Transcript, May 22, 2012

Grower Question: When I tried to use Sevin for thinning, it plugged the nozzles of the sprayers. Why did this happen?

Grower 1: What kind of rates are we talking about?

John: One quart per 100 gallons.

Grower 2: Anything else in the tank mix?

John: No.

Grower 3: Were they using powder or XLR? I’ve had trouble with the Sevin powder in years past.

John: The thinning recommendations usually stipulate XLR (the liquid formulation). The only thing I thought of, whether the sprayer having too fine a screen, is that the Sevin might be too old and prone to caking up.

Grower 2: We ran across a situation with Captan and Rimon EC. We saw a reaction between the two. In fine print on one of the obscure labels, it said that Captan can at times clog your spray if it’s mixed with an EC. It can gel. Now, I think Sevin XLR comes in an EC (emulsifiable). That’s why I ask about a tank mix.

John: I would look at the age of the material and the formulation. You might also look at the screen. Outside of that, I don’t know. Any other ideas?

Grower 1: What kind of sprayer is it?

Grower: It’s a Jacto airblast sprayer, high pressure. I had nothing else in the tank. The first application was with Sevin. I thought maybe my Sevin was old, so I threw that away and go the Carbaryl. The second time I tried it was with the Carbaryl 50 WP, and got exactly the same reaction. Both times, it was like cement. I had to pry my nozzles off, and though I was going to wreck them all.

John: Was the formulation that you started out with XLR? That formulation comes in liquid form, and comes with its own surfactants and things.

Grower: No. Perhaps that would have helped.

John: I’m not sure. Sevin has been around for 50 or 60 years, and I’ve never heard of it having a problem mixing with plain water. Is your water particularly acidic or basic?

Grower: It’s well water.

John: A lot of the carbamates will experience alkaline hydrolysis, but that wouldn’t cause the Sevin to cake up.

So, I guess the short answer here is to try to find a jug of the XLR formulation, if you’re still interested in trying to thin. But another thing to note: whatever you purchased, if it has on the label that it can be used for thinning, I would sure ask your supplier to explain what went wrong. They won’t be liable for your troubles, but they should have an explanation.

John: I’ve seen other people have blockages with materials like Delegate. That material has a very large particle size. The screens in airblast sprayers aren’t very fine, but in the grower’s big stationary sprayer with a high pressure gun, it plugged immediately. So, with Delegate, make sure not to acidify your water, because it will break down the particle size, which will reduce the length of time that it’s active on the tree. Plus, for people with unconventional sprayers, this clogging is a pretty messy situation to get into.

 

Plum curculio update

John: A couple things have happened with PC in the last week. First: if you waited until a couple of weeks after petal fall to put a perimeter spray on, you were too late. Last week, they were already inside the orchard already. That’s a cautionary tale for down the road. The situation depends on the weather that we’ve had, and we’ve had a lot of nights that are conducive to PC oviposition and movement.

In the Cornell Scaffolds from yesterday [FOLLOW], they talk about PC and the degree-day model. If I’m remembering right, the degree-day model stipulates that at 308 degree-days from Macintosh petal fall, base-50, is when we assume that the PC migration into orchards has been completed. In Southern Wisconsin, SE Minnesota, and Northern Illinois, we’re there, or really close to it, depending on when you set Macintosh petal fall.

What does this mean? The migration has finished. If you put a material on – whether it’s a perimeter, an alternate-middle, or a complete cover – you shouldn’t be expecting to see additional migration from the perimeter. A lot of people put two perimeter sprays on 14 days apart if they didn’t put a broad-spectrum material on the orchard as a cover. At this stage, then, the situation  for those people should start to get safer.

Growers who are further north are not at that point yet, and so must continue to be vigilant.

I want to make clear: that 308 degree-day point does not indicate when oviposition is done. The weevils that are inside your orchard will continue to lay eggs after the 308. I was in an orchard two days ago that had some sweet cherries. The other trees in that area had been protected, but the sweet cherries had not. The cherries had a large amount of PC oviposition that was 24 hours old or less. That’s the result of the warm temperatures we had over the weekend and having no protection.

However, I think that most people who put perimeters on have seen that the perimeter has done an adequate to excellent job.

Peter: When would PC oviposition end, if we’re finding some in orchard interiors?

John: I can’t remember. I’m not sure if the model covers the end of oviposition. It tries to model the behavior of the insect from overwintering sites through migrating into an orchard. In the next couple weeks, it will be very important that you be able to differentiate between old PC damage and new PC damage. In one case, I saw that PC got through the perimeter application of Avaunt. There was damage on 6 or 7 trees, but the damage was old. That tells me that the PC got through, but eventually succumbed to the perimeter spray. If the PC hadn’t died, you’d still be seeing fresh PC oviposition scars.

 

Grower Question: John, I sent you a photo of an egg mass that had hatched out. What was it?

John: It was a lepidoptera species, but I don’t know exactly what it was. But you haven’t applied any insecticide to your orchard except a perimeter spray, so you’re likely to get occasional lepidoptera species that pop in from the woods and lay eggs. Those species might include Eastern tent caterpillar, Forest tent caterpillar, Spring cankerworm, or one of a couple scores of tortricid species that generally are not problems.

The question remains: if you didn’t have biocontrol going on, what would happen to those uncommon pests? Would they become common?

 

Grower Question: I caught 11 OBLR in my traps this week. Does that mean that the larvae are hatching and we can let those go in the terminals? What does it mean if I’m already having flight?

John: It’s a site-specific question. In some orchards I go to, I see their OBLR come out at various times from green tip, on. If some individuals came out of their hibernacula around tight cluster or pink and started feeding, by now they would be almost fully grown. And in your situation, it sounds like they’ve already pupated and emerged as adults. On the other hand, we’re still seeing some of this overwintered population as small larvae. That variability of emergence happens with all species. You’ll get a range of maturity.

What does this mean? That set of adults was your first summer generation of OBLR. You need to start watching the terminals for new hatches. I will usually wait a week to 10 days from your first OBLR flight to begin checking terminals.

Again, with this insect, we’ve seen orchards that have had 100% predation and parasitism that have eliminated the overwintering situation.

Your situation is a concern if you have young trees, or if you have trees that are fruited – and especially if they are lightly fruited, simply because with light fruit, you can’t stand 2% damage like you can when you have a full crop.

I’d hate to see people putting a spray out for OBLR without waiting to check the terminals for new hatches. Next week I’ll show pictures of the sort of damage we’re looking for. Knowing what to look for will make scouting very fast. You can walk through the orchard at a good clip and spot the slight discolorations in the emerging leaves in the shoots. It’s obvious when it’s there, and when it’s not there.

Codling moth update

John: For the orchards who had a biofix on May 3 or 4: right about now, you will be approaching 250 degree-days, which is the traditional timing for a larvacide, whether it’s Bt for organic use, or Delegate or other materials for conventional CM control. You don’t want to apply an ovicide; it’s too late for that.

To reiterate Larry Gut’s message over the last several years: when your CM numbers don’t start out strong, it’s probably not wise to come in at 250 degree-days with an insecticide. Rather, you might want to wait until maybe 350 degree-days. It all depends on what your trap catches have been. My general rule of thumb is this: if I’ve caught 20 or less in the time between biofix and 250 degree-days, then I don’t consider it a big flight, and I’m willing to push the envelope to 350. Delaying the spray in that situation has a very small risk with such a low population. If, on the other hand, I got 20 on the first night, and I had two nights that were conducive for mating and egg-laying, then I wouldn’t want to wait past 250 to apply a larvacide.

Grower: I have hardly trapped any CM this season, so far. I’m not using mating disruption. I’ve used the virus in the past, for second generation. I’ve also used Rimon, and either Assail, Calypso, or Delegate as a larvacide. But this year, it’s been difficult to set a biofix because I haven’t been over threshold at all. On a daily basis I might capture 2 or 3 in the entire 40-acre orchard, across 12 traps.

John: Is there any variance in the location of the catches, or is it pretty much random?

Grower: I have a couple of hotspots. Whenever they’re flying, I’ve always trapped some in those areas. I’ve set somewhat of a mental biofix this past week, when I trapped CM on two successive days. Other than that, I’ve only trapped about every other day or so. We’ve had good temperatures for them to be flying, but I’m just not seeing that many.

John: Yep. Overall, I’d say that my counts are down from the average, but there are orchards that have numbers up there in the scary range.

One thing I’d say to an orchard in your situation: In an orchard that is getting unusually low numbers, I would recommend that we still do something. Why? When we ended up with organophosphate-resistant populations, I assumed that if I didn’t find successful worms at first or second generation, then we didn’t have CM in the orchard. Obviously, I learned that that’s probably not true. Instead, the CM is at an incidence that is low enough that I can’t pick it up. If it’s at 1%, we’d all see it sooner or later. If there are worms only in 0.1% of the fruit, then most of us may not see it at all. So, it’s safe to assume that there is a population there.

The question, then, is: what happens if you let the population go? My feeling is that the population growth from first to second generation is so substantial that you should not forget about CM if you still have a fruit crop this year. If it were my orchard, and I caught 1 per week in a block for 5 successive weeks, I might not ever spray. But that’s usually not what happens. You will usually pick up 2 or 3 or 4 in a week some place.

We shouldn’t forget about the CM because the bigger the endemic population you have, the higher your risk of encouraging resistance development, no matter what your alternating materials are.

On the other hand, what you might do is either use a material that is unconventional, or use a very low rate of something, to at least gain some benefit from the material.

Note: In the old days, my threshold was 10 per week. Then, about 10-12 years ago, I switched and went to 5 per week. But you know what the recommendations are from the universities: a cumulative 5 per week. I still don’t understand that recommendation, biologically. Most females don’t live more than 10 days, so if you catch a moth in a block over five successive weeks, the CM that was alive at the beginning is not alive after those 5 weeks.

John: This raises another question: Would orchards with a very light crop be prone to CM infestation? If an M7 tree only has a dozen apples, will the CM female find the fruit and eliminate the few fruit that are there? Or will they search out rows or cultivars or other orchards that have a better fruit load?

I don’t have a good answer for that. I can relate it to the PC situation, somewhat. If I had a very light crop on a tree (like 3 apples on a Bud-9), I would not expect PC to mess with that fruit. However, from what I’ve seen this season, the PC will still search out the fruit, even if there are better-set varieties close by. That implies that you have to worry about PC in a light-cropped variety or block.

But that doesn’t say anything about CM. I don’t know where the break point is, and I don’t know of any research that has been done on CM movement with light crops. Research has been done that shows that when there is no fruit, the females will fly away and find better opportunities for their oviposition. They will fly much, much further than usual if they have to find fruit. What I don’t know is the threshold below which the CM will be forced to leave.

Grower: Well, I’ve gone ahead and followed my usual protocol for CM. I usually do a ovicide and a larvacide. We’ve used the virus for about 4 or 5 years in a row, now, and it’s handled the second generation very well. But I haven’t even trapped a single OBLR yet, and the Red-bandeds have been very low, when it used to be nothing to pick up 30 or 40 in a single trap.

John: Keep in mind that the winter had major effects on thing. With CM, I would have expected that they would have overwintered better than normal, because it was so mild on the trees. On the other hand, they had a cold period after that, and I thought they would be negatively impacted when it got down to 25 degrees all those nights. What I do know for sure is that the situation is different from place to place, and it’s hard to generalize.

Regarding Red-banded leaf roller: RBLR is at its low point between flights.

Regarding OBLR: OBLR is just beginning, so it doesn’t surprise me that you haven’t picked up OBLR, particularly if you controlled them with some methodology late last summer (again, I’ve found that people that controlled for 2^nd-gen OBLR have seen very little activity this spring).

Keep in mind that I’ve never seen a correlation between OBLR numbers in your trap and the actual OBLR hatch. Even a catch of 5 can sometimes yield significant larval hatch 10-14 days later. So you still need to scout for it.

 

Apple scab update

John: If you look for Apple scab right now and can’t find any, then I would suggest pulling back from a fungicide program, particularly if you have a light crop. (If you’re up north, it may be a week early to make this call.)

For most people, the bigger question is this: if you have scab in a few varieties, what is happening with it? I would caution you, and say that if you have found scab some place in your orchard, look to see where on the shoot the infections are. If the new growth on the tree (the newest 5 or 6 leaves) is clean of scab, then you’ve been doing something right, and the risk is lower. Old lesions on old leaves are less dangerous, less able to produce a lot of conidia, and are therefore less of a concern.

I’m not telling you that everyone should stop spraying; I’m saying that if your new growth is clean and you have a light crop, I would stop spraying.

 

Question: With the CM sprays, what opportunities do growers have in their pesticide selection to also manage those OBLR or RBLR that are hatching out? How can OBLR/RBLR overlap with CM control?

John: It’s pretty straightforward, unless you’re using ovicides. If you’re using larvacides, then know that the neonicatinoids you might use for CM are virtually useless against leaf rollers, but almost everything else is effective against leaf rollers. Those materials include Proclaim, or the diamides like Altacor and Belt, the spinatorum (Deletage or Entrust). All of those control leaf rollers as well as CM. Again, Avaunt is certainly an option for leaf roller control.

 

Update on secondary insects: stink bugs and San Jose scale

John: I’ve found numerous stink bug adults (brown and green, both) and numerous egg masses in orchards. They have laid a lot of eggs in a lot of orchards.

If you’ve ever had problems with San Jose scale, you should probably tape some branches. There are already crawlers settling  on trees and on fruit along the Wisconsin-Illinois state line. Again, this is a site-specific thing. So somebody like Sara at Galesville, if she already has OBLR flying, that probably means that her degree-day accumulations are a little higher than a lot of people. That would mean that if she had scale in the past several years, her crawlers would probably be a step ahead of other orchards, as well.

The scale may not be a problem this year for you. Oil may have wiped them out, or beneficials may have knocked them out. But the only way to tell is to put some double-sided tape on some scaffold branches.