PC - Mother of all stone fruit insect pests

This was discussed as a sub topic recently on the following thread, but folks like @SpudDaddy, @thecityman, @speedster1, have had so much trouble this year, it deserves it’s own thread, imo

So, PC has always been a hard one for me to control, but this year, very hard. I have been spraying weekly because the pressure has been so high. But I’ve still had significant damage on smooth fruits, cherries, plums, and apples.

The plums were hit very hard, The apples were hit hard. The cherries had significant hits.

There were a couple things I did different this year which may have contributed to the increased damage.

I didn’t use a neonic like Actara or Belay as long as I had in the past, which I think significantly contributed to the damage. Instead I was using more pyrethroids, which aren’t as effective as some of the neonics on PC. The fruit was very clean until I switched to pyrethroids like Warrior II, and Baythroid, which are supposed to be as strong on PC as any other pyrethroid, but not as strong as the neonics.

Second, we got behind on the mowing and I had some huge weed patches where I had grown sweet corn last year. I suspect the PC were migrating out of that, or using it for cover.

Lastly, I have a theory that maybe stickers contributed to the PC damage.

I don’t know if I’ve mentioned it before, but I’ve long suspected stickers may inhibit some of the action of some insecticides at times.

Stickers obviously are designed to prevent wash-off by rain. Most of the good ones seem to do this by compounds which “stick” to the surface sprayed. They are latex based (think paint) or in the case of NUFILM 17, use pinene which is also the active ingredient in Wilt Pruf, a product which seals the foliage with sort of natural sealer.

Spreader/stickers improve spray deposition, prevent wash off, and in the case of Nufilm 17, also inhibit UV breakdown.

All these are positives, but I’m starting to think they inhibit the action of contact insecticides like pyrethroids. I theorize some of these stickers are like sealers, effectively sealing in the contact insecticide. Good contact insecticides are supposed to be lethal enough that even the insect walking around on the foliage supposedly absorbs the compound through their cuticle and dies.

However, if the insecticide is “sealed in” a substance which mimics paint, it seems to me the insect might not come in contact with enough of the compound to be lethal, especially after several days where the insecticide compound has had a chance to degrade. Of course if the insect ingests the compound through eating foliage, then it should receive a lethal dose, but the contact action may be handicapped with a sticker.

I doubt this has ever been checked by researchers. It would be a somewhat difficult test to set up. Spray some foliage with an insecticide, and some with an insecticide and sticker. Then let insect pests walk on the foliage for a while and see if both groups have equal insect lethality.

Instead researchers, just check the amount of pesticide which remains on the foliage or fruit after a rain event. This may have nothing to do with the amount of what I’ll call “lethal effective residue”.

I think if rain looks imminent before the next spray, stickers definitely have an advantage from the benefit of keeping some insecticide residue on the trees. But if the forecast looks clear of rain, it might behoove us to avoid a sticker.

I sprayed trees tonight and decided not to use a sticker because we have been in a dry weather pattern here.


Alan mentioned to me once that pyrethroids break down easily when heated and suggested obtaining product in the winter to avoid the possibility of it being overheated in transit. So the question of is the product good comes up? I use pyrethroids and have good results. What I noticed was more hits but a lot less takes. The fruit was attacked but failed to become infected. Hopefully you find the same thing this year. .

I am starting to subscribe to your theory… I have sprayed esfenvalerate with NuFilm a couple of weeks ago and just two days after spraying I saw a PC walking on a nectarine fruit, a couple of days later I saw another two or three walking on my apricots, so I started wondering if the spray actually has to hit the bug to kill it… Next time, I’ll try with out the NuFilm.

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Interesting theory, but with all the commercial acreage relying on these materials in the humid regions it seems unlikely the problem would not have been observed until now- there are just too many concerned eyes on too many acres of fruit being protected by the same types of materials. I would take your theory to the Cornell gurus who are involved with the commercial fruit industry in NYS- we have plenty of PC. You could also talk to one of the advisers working for CPS in our area- I get a lot of useful info from them. In KS you just may not have enough of an industry to get reliable guidance.

What was your high temp during PC season? Perhaps some Assail in your mix would be helpful- I actually mix it with my pyrethroid to provide kick-back because cost of materials is not an obstacle for me and I cover all fruit species with 2 insecticide sprays only- all species at the same time. The only species to ever have significant PC damage is Euro Plums, which never leads to crop failure, just a 25% reduction in crop or so when it happens- the main problem with this is that it inspires me to leave too much crop on trees at sites where it’s happened before. I also have to warn my customers away from the early ripening fruit.

Lots of growers use Indar in their programs- I do on first cover. A sticker is required with this material. I use Tactic with every insecticide spray.


I’m not sure if the stickers inhibit the action of some insecticides but the Apple/Peach specialist from NSCU indicated its a waste of money adding stickers and spreaders unless the label calls for it. This guy gets a lot of feedback from large apple and peach growers in my state.

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Curc pressure is very high this year @Olpea so it’s possible you could just be dealing with more PC this year. I do however think your suspicions are right.

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The problem as I see it is if you’re wrong, it could be worse if you spray without it. I think the amount of the pest has increased this year and many will not be killed until they try to lay eggs and bite into the flesh. The eggs are probably killed. Not sure, just trying to figure out why I get so many hits and never a worm.
Changing strategy now will not tell us anything. As if good or worse you can’t conclude anything as you did it both ways. I’m still in the school of thought that it is better to use a sticker. I don’t know what makes this year special? If you had good results with stickers in the past, not sure why one would suspect it’s the problem now? This has been my experience, and it ain’t broke so I’m not fixing it.
I got more hits, but infection rate is the key, not how many hits. We all will know more in a month. How bad it really is.


I’ll go along with you on the neonics. 2nd year using them and I see no PC hits on my fruit.

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Why do you switch from neonics? Concerns about bees?

This probably is the reason.

My thinking is they must smell the poison and stay out. As the quickest killer still going to take an hour to two weeks to kill the insect. Why i believe I have a lot of hits but no infections. I don’t use neonics.


This year was different for me I think for a couple reasons. This year I relied more on a pyrethroid vs. a neonic Actara/Belay. If you look at efficacy trials, Actara/Belay are top tier compounds for curc. It’s my opinion that universities aren’t recommending them as much because they are so hard on bees (I’ve read some experts basically say as much).

I was relying on a different class of insecticides for later curc emergence (pyrethroids). Although weaker for curc, they should have done the job, but didn’t, so I’m looking for a reason why. I want to emphasize I’ve been spraying weekly at the max rate with commercial high quality stuff, with an airblast (good coverage, etc.).

The Warrior 2 I bought this spring from a supplier with a storage facility which doesn’t freeze. I’m not sure if it’s air conditioned. I picked it up in person along with some other chemicals. I think it was this year’s inventory, as the guy sells a lot of chemicals and the pallet of Warrior still had the shrink wrap on it. I’m also fairly certain the Baythroid hasn’t been subjected to extreme temps because I bought it last year from a supplier who has very little on site storage and so in the spring when they move a lot pesticide, they order pesticide after the customer orders. But of course I have no way of knowing for sure what temps the pesticides were subjected to, prior to my purchase.

One good thing is that I’ve cut open a lot of fruit and not seeing any larva (like you mentioned) except that on some of the plums the area around some of the curc bites is turning blue, so I suspect there is a curc in there. I’ve cut open quite a few of them and can’t find the curcs, but I suspect they are just so small I can’t see them. The cherries and apples look like there is no evidence of live curcs. I was able to thin off most of the curc bites off the apples, simply because there was a heavy fruit set on most of them.


I’ve thought of that quite a bit and has been one reason I haven’t voiced my opinion on this suspicion in the past (at least I can’t remember that I did). One thing which may be different is the level of curc pressure in some of these minor states.

This is a very anecdotal observation, but at least this season we have people on this forum using Imidan (in one case weekly) and still tons of curc bites. As you know Imidan is supposed to be highly effective for curc but it appears to be failing for folks which are warmer than the Northeast. I suspect even MI has less insect pressure than places further south. When we mowed about 3 acres of weeds close to the orchard the other day, the insects just poured out. As you know, many of these places with higher insect pressure don’t grow enough fruit to justify university research. I’m wondering if the dynamics are different enough further south, that with the disadvantage of higher heat and heavier pressure, compounds which should be effective, aren’t (even with higher heat, a good pyrethroid should be effective at weekly sprays - Warrior II even has the microencapsulation to protect against UV radiation).

Of course lots of fruit is grown in the south, but few smooth stone fruit are grown (my peaches are pretty much untouched by curc). There may be extra pressure on the smooth skinned fruits as a sort of trap crop in my orchard, even though it’s not my intention. I guess I’m wondering if some of these “fruit powerhouse” universities don’t experience some of the same challenges we do further south with smooth skinned fruit. So, some of the normal spray practices which work in orchards there in the north, may be more challenged further south where smooth fruits aren’t grown much.

Maybe my theory is all wet, but I don’t see any harm in withholding a spreader sticker if there is no rain. The spreader could be a benefit for better coverage, but I have a cheap spreader (without the sticker) I use for herbicides, so I can still use that during dry spells.


I am concerned about the bees (I have a neighbor who recently installed two hives right next to the orchard. I’ve used neonics before and had a friend catch two wild swarms at the orchard the last two years. But still the neonics which are best on curc are extremely hard on bees. I’m careful, but it’s always on my mind when I spray. Another reason for using less of the neonics is that they are quite a bit more expensive than pyrethroids. The Warrior 2 I use is $2.50/acre. Neonics are considerably more expensive. Actara is $20/acre. Assail is about double that. So it’s a combination of concern for bees and cost that I’d rather minimize use of neonics.

I thought the problem with neonics was supposed to be the way it attracts insects, including beneficials

I don’t know anything about all of these theories, but I’ve had NO pc this
year, at all. I sprayed twice with plain Malathion, and I pick up ALL fallen
fruit on a daily basis and keep the grass cut. If you don’t try to disrupt the
breeding cycle of whatever insect you’re fighting, you’ll never have clean fruit. :

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You mention Warrior has UV protection. My sticker does this too, so this might be a concern. I read where many pyrethroids are sensitive to UV. I see you are using some Warrior so not a concern there.
I also read that with pyrethroids insects will pick it up if walking over dry residue. but is a lot more effective on chewing insects. This may support your theory as the walking part may not be working? You know though you use so little, so who knows?. Not fair to compare to Wilt Stop which you’re spraying a 17% solution. It is also a different formulation because the color is different than pinene stickers.
Maybe I will just increase dose to make up for any loss to sticker. For me without UV protection, it is not worth using pyrethroid for backyards. For the record I use Lambda-cyhalothrin I don’t know how well it holds up in UV light? I also use Malathion at times. Only 3 times a year at most.

I use it about 3 times but the last spray is usually for Japanese beetles, what I’m trying to target with that 3rd spray. So my results are good too but tells me nothing, what is working better? Malathion or Lambda-cyhalothrin?

I also pick up all fallen fruit. Which is usually very few, most fallen fruit in my yard is when it’s ripe it falls on some stone fruit. Flavor King and Queen both fall off usually when I’m harvesting, obviously ripe! Moving branches they easily fall when ripe. Unlike Dapple Dandy that holds on forever. Those fallen fruit still lasted 5 weeks too! Plums are awesome!

Aren’t insects increasingly resistant to pyrethroids as temperature goes up?

Just some comments on the various posts, all of which I appreciate and learn by. Olpea’s suggestion that stickers may reduce the effectiveness when used with phosmet such as Imidan is something that I will have to experiment with. I do not have the knowledge to guess if it is right or wrong, I can only try and see if I get better results. Alan in another thread recommended permethrin as a control for PC. I did some research and found a university steady showing the effectiveness of Permthrin and Imidan with and without rain over time. Without rain Imidan was rated to last long than Permethrin, Permethrin did better if it rained.

Based off the university study I will use Permethrin if rain is forecast short term, Imidan if rain is not forecast. I will experiment not using a sticker. I will use Imidan as a curative. As a side note it appears that Imidan worked well as a curative - most of the PC damage did not go very far past the skin - no larva or holes in the center of the peaches. Most peaches formed pits.

I have always hesitated to use Permethrin because it kills a lot of beneficial insects, but I am not sure that it matters on peaches. On apples I feel that it does have a negative effect.

The discussions around the other commercial insecticides do not have a lot of relevance for people using smaller tanks, the insecticide mix ratios to small amounts of water seem to small to properly measure the insecticide. Anyone can correct me on this if I am wrong. I still like reading about the different insecticides and there use, they just do not seem practical for the small grower.

For reference this year I am using a 4 gallon back pack sprayer, I have a 16 gallon sprayer new in box but i will likely save that for next year.

I saw where someone posted about keeping your trees and property clean. That is not possible in my area - 5 to 10 acre lots next to 40 to 400 acre lots/farms. Nobody tries to clean/remove downed/dead trees unless they block a road or are a threat to a building.

I cannot comment on PC pressure being worse this year because I only learned what PC was last year. But in a prior post I commented commercial orchards manage to get good peaches in springs with lots of rain (and we had lots of rain in Virginia) therefore I must be doing something wrong to get the PC damage that I got this year.

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I thought I had the PC in the peaches and apples under control but it looks like I have new generation to deal with.

Here is some info for NC that may be relevant to other locations:

PC activity is correlated with weather conditions after bloom: infestation tends to occur the first day after petal fall when high temperatures exceed 70° F. After bloom, check fruit twice weekly for feeding and egg-laying scars. Typically, an insecticide at petal fall and first cover (if adult emergence is protracted) is used for control. However, second generation adults emerge and can damage apples from late June through July, depending on location. Additional insecticides should be applied if any new damage is observed.


Oh, I’d point out that when you read the literature on PC, there is discussion about a “multivoltine southern strain” and “univoltine northern strain.” Down south PC has two generations per year. Up north they only have one. Not sure where the line is. Probably approximately the Mason-Dixon line.

Years ago when I first started using Imidan 70 I used it at a rate of 2.5 tsp/gallon and had great results against PC. I spray weekly in spring during curculio season. The past 7 years I have used Imidan 70 at rate of 1 TB/gallon as just easier to measure. At first I had no trouble with PC. Last year I had PC damage. It really rained a lot last spring so hard to keep the insecticide on with all the rain.

This year I am noticing a lot of PC damage on my apples. I have to wonder if PC populations are just increasing so much or if Imidan at the rate I am applying is not as effective as it once was against curculio?

I also have some Assail that I use primarily on sweet cherries and Haralson apples since Imidan really scars the fruit on those varieties. I don’t recall any PC damage last year on those crops with Assail. Anyone else having good PC control with Assail? Just wondering as perhaps I should use that during the PC season on the rest of my apples instead of Imidan?

I’ve read that

I’ve read that apples usually crush them unless they are aborted.

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