Here's a Fact Sheet from Cornell

http://nysipm.cornell.edu/factsheets/treefruit/pests/pc/pc.asp

Here is a link that might be useful: plum curculio

Early early early early spraying. That is the secret...for me. Even on fruits that are tiny...there is a very short window there that you have to get that first spray on. After that regular sprays for as long as they egg laying activity is happening. The later sprays can be very tough ....if you cut them off too early..bam..the fruit are big by that time (bigger) so a curculio can just go to town on them.

This year was probably the worst i've seen them in my yard.

Early and late. I discovered last year that I was getting a lot of curc damage long after I'd assumed they were out of business. Almost-ripe plums with larvae and rot.

Christy, I'm only surprised you didn't have an issue before because in our region PC tends to be omnipresent. How to manage it will vary somewhat from site to site and a great deal from species to species.

Itilton suggests spraying late but that very often isn't necessary, even for European plums, which I assume are the plums he's talking about. In southeastern NY Japanese plums have never been hit late for me and E. plums at most sites, most years are fine with two insecticide sprays a season. You may lose a portion to PC, but not enough to bother with more applications.

I manage about 100 home and very small commercial orchards in a range of a couple hundred miles that runs from Z5-Z7 and most of these sites get away with this basic program.

Alan Haigh- The Home Orchard and Nursery Co.

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Low Spray Schedule for Home Orchards in the Northeast

Here's my spray schedule for the scores of orchards I manage around SE NY adapted for home owners managing a few fruit trees. It has functioned well for me for over 2 decades, although J. Beetles and brown rot of stone fruit increases the number of sprays and necessary pesticides some years some sites. Stink bugs are also an increasing problem requiring more subsequent sprays when they appear. Time of spray is based on apple bloom as that is the predominant fruit here but I generally get away with spraying all trees at the time I spray apples.

Please note that pesticide labels must be read before their use and my recommendations do not override the rules on the label. The label is the law. This document only communicates what has worked for me and your results may vary depending on local pest pressure, which may require a different spray schedule.

Spray needs to be applied thoroughly throughout the trees and with a back pack or any human powered sprayer this is accomplished much easier when there is not more than a slight breeze.

Dormant oil (this is optional if there were no mites or scale issues the previous season, which is usually the case in home orchards). Do oil spray from when emerging green shoots on apple trees are 1/2" to just before the flower clusters begin to show a lot of pink. Mix Immunox (myclobutinol) at highest legal rate (listed on label for controlling scab and cedar apple rust on apple trees) with 1 to 2% oil( 1 to 2 quarts per 25 gallons of water). If it's closer to pink use 1%. Never spray oil on open or almost open flowers.

Don't spray again until petal fall when petals have mostly gone from latest flowering varieties and bees have lost interest. Then spray Triazide (Spectracide Once and Done) + Immunox mixed together at highest legal rates. Repeat once in 10 to 14 days.

Where I manage orchards, the space between earliest flowering Japanese plums and latest flowering apples is only 2 weeks or so which usually allows me to wait until the latest flowering trees are ready to begin spraying anything. Plum curculio seems to time its appearance conveniently to the rhythm of the last flowering apple varieties. This may not be true where you are.

If plums or peaches need oil they may need application before apples. I’ve only had mites on European plums here and never need oil for other stone fruit.

All this is based on plum curculio being your primary insect problem which is the case most areas east of the Mis. River. These sprays will also absolutely control scab, CAR and Mildew as well as most of the crop fatal insects. Apple fly maggot is an exception as it tends to emerge a couple of weeks after last spray looses effectiveness, but I haven't had much of a problem with this pest in the orchards I manage. This pest can be controlled with a lot of fake apples smeared with tangle trap.

If you don't want to use synthetic chemicals try 4 applications of Surround about a week apart starting at petal fall. You may need to start on earlier flowering varieties as soon as they drop petals because Surround is a repellent and can’t kill eggs after they’ve been inserted into the fruit. When temperatures permit it is good to mix horticultural oil with 2 or those applications as Surround makes a nice home for mites and scale.

Stone fruit may require the addition of an application or 2 of Indar (Monterey Fungus Fighter is closest available chemical for home growers) starting 4 weeks before first peaches ripen. Apricots must be sprayed sooner if they are scab susceptible with same compound. On some sites that single spray will also prevent serious rot on later ripening varieties on seasons not particularly wet. If it is wet spray the later varieties again two weeks later.

Because I manage so many orchards so far apart I have to resort to a spray schedule that is based on expectations rather than actual monitoring. You may be able to reduce insecticide sprays with monitoring but PC can enter an orchard overnight and if your insecticide lacks kick-back (as is the case with Triazide), do a lot of damage in a couple of days..

Other problems may occur later in the season and you will in time learn to monitor and react to the pitfalls.
Good luck, Alan Haigh- The Home Orchard and Nursery Co.