Plum Curculio


Anyone know if PC are active during rain? Think I found an answer at Penn State website:

Periods of cool, rainy weather with maximum temperatures below 70°F are not suitable for curculio activity.

This coming Wednesday looks ominous: 72 degrees during day and 61 low at night.


Is it possible for the weather just not to be suitable for PC this year? Has that ever happened?


I don’t think so. Beetles are pretty tough bugs. As I recall, the female can lay over 100 eggs. She is programed to reproduce. Hot weather shuts PC down, but I’ve never seen it get hot enough fast enough to skip egg laying. Just as it starts to warm up, PC are quickly out attacking fruits.


I don’t mean that there would be no pressure, but maybe a lot less than normal. I was wondering what would happen if it stayed unseasonable cold.


I got to thinking the other day while reading the freeze tonight thread that PC may suffer a setback due to so many people having their fruit destroyed before even getting to the size in which PC would be striking it.

Does anyone know if Plum Curculio has a back-up plan when there just isn’t any fruit available due to freeze damage? Are there back-up egg-laying sites for these critters?



Gotchya. I don’t know how much less it would be in unfavorable weather conditions. I do know that despite probably near 100% control from PC, every year I get some scars on cherries. Because of the chemistries I use, there are no live grubs inside the cherries.

I don’t know if every year there are new PC which fly in from the woods which are close to the orchard, or if just enough PC get through my spray program to reproduce. I know I’ve never had a customer complain they found a worm in their fruit…at least not yet.


Hoping PC stay inactive this week of cold rainy weather but there is one day of favorable temps for them over 70 day high and over 60 nightly low. Hoping they need more than one day of favorable weather to cause problems. Spraying Surround now will just wash off


I have no warmer weather til this coming weekend in the current forecast, so my plan is to wait until this coming weekend for my first post-dormant spray. I don’t think one day just barely in the PC range would make much difference. It is a sliding scale, with every degree warmer they move a little faster. Just like how Surround does the opposite - every bit more Surround slows them down a bit more. One really warm night can be really bad though, I have seen some massive attacks that happened in only one day.

Having a complete freeze-out of fruit I am sure will set them back, but they must have some alternate hosts as they always seem to come back fast.


@scottsmith I had read years ago that the first 90 degree night is the start of ‘Curcurlio Fest’. So in the Midwest I had always sprayed my plums with Imadon at petal fall in the evening, with one second spray ten days to two weeks later, and that would get me thru the season with no damage. Then Black knot attacked all my plum trees over a three year period and I lost em all. You can see the zillions of PC’s in your trees during the first 90 degree nights by going out with a flashlight at midnight and lighting up the canopy while standing under it and shaking the tree.


Sorry if this has been coveted at length but im still trying to understand how much of a problen PC are in my apples. Id say 5-10% of fruit have at least one bite or egg laying scar and thats after thinning and bagging. I bagged a few bitten ones and a few appear to have been biiten after bagging. But ive never seen one drop due to PC larvae. In fact ive never seen a single larva after checking dozens of thinned bitten fruits. I left some bitten ones on last year and they made a nice fruit that had one or more bite mark scars. It was really not a problem for eating, just.minor cosmetic issue. Is this the norm for apples or are most cases more like peaches where the PC larvae nuke a large portion of the crop seemingly overnight? Or do the apples get extremely deformed and i just got lucky last year with minor cosmetic issues?


Well i saw my first pc larvae in apple (i know most of you are yawning at that haha). It was in sundowner. Still none in goldrush. GR does serm a lot more dense even at marble size. maybe that helps crush the bad guys.


Yes the PC gets crushed by apples and pears as they grow. The only exception I have seen to this is some crabapples can mature a PC, also occasionally flukes happen where one will grow to maturity in an apple… it is extremely uncommon though. If you don’t have too many bites the fruit is completely edible, the only issue is the ugly looks.

I am now eating the few Yates I have left over from last year (perfect now, by the way) and I am noticing a fair number have curc bites in them. I thought I had thinned out all the bitten fruits but I still missed quite a few.

I finally did my first curc spray last night. It is nowhere near the warm temps for the curc party, but there is at least some activity if the temps are around 70 at dusk. I found a few spots on my plum trees with infestations. Still, 99+% of the fruit is untouched… I felt like I was living in California looking at all the perfect fruit without any sprays :grin:


It’s warm enough this weekend, but no fruitlets yet.


I’m not sure. I had a ton of PC scars on my apples last year and almost every single one of them dropped. The dropping could have been unrelated, I guess.

I resprayed after the big rainstorm Thursday. I hope the smaller burst of rain that night didn’t wash too much of the Triazide off. I did notice my single apricot had some damage, but it was golfball sized, and I haven’t found much damage elsewhere. Mainly on the cherries, and actual plums remain completely untouched as far as I can tell.


Good to know. I do see more bites each year which doesnt make sense if they are not maturing on the tree. But im not going to worry too much about it unless the apples start getting riddled with many bites. Im bagging which helps im sure but they start biting fruits when they are tiny.

Still waiting on my yates to fruit. I think its going to be a good one here. Ripen in cooler weather and last still spring. Sounds good to me.


We are having our first nights in or near 70 in NJ. My wife thinks I am crazy everytime I inspect the fruitlets for bites



Time to spray just in case PCs sneak up on you.


I am spraying my plum no matter what the temperature is.
Last year I didn’t sprayed the plum on its own stages of petal fall, shuck split,…but on peach schedule. My Plum is quite a few days ahead of peach. Peach was fine, but every single one of my two tree full plums dropped at dried date size. They all had bite mark. I was so looking forward to a great plum harvest.

I am taking no chances this year.


@scottfsmith, can you describe whether a full surround coverage with multiple sprays is still beneficial on a tree with no fruit!


Only for Japanese beetles in June… oh and maybe a bit on peach shoot tips if you have OFM. I don’t spray it myself on non bearing trees unless it happens to be in the spray tank with something the non bearing trees need.