Timing of codling moth spray in Portland

Asked June 12, 2020, 5:09 PM EDT

I have two Asian pears (one in the backyard, one in the front yard). We have a very heavy codling moth infestation (our traps have captured ~10 moths per trap already). There is an abandoned apple tree in a neighbor's yard about 40 feet away, so I suspect that's the original source of the infestation. We decided to use a spinosad-containing spray to control the moths, but are unsure about the timing. Is there an online resource we can check to find out when to do the sprays?

Multnomah County Oregon

3 Responses

Yes there are many sources of codling moth across the urban landscape, moths can fly quite far too, so it may not be completely your neighbor's trees. There is not an online source for management timing, though there may be one in the near future. You are a bit behind the curve as far as timing, roughly 50% of codling moth eggs have already hatched. The apples are already getting attacks by codling moth larvae. At this stage you will see small depressions and little bits of frass on the surface of the fruit indicating that the larvae have started to attack. The first spray is ideally timed for the onset of egg hatch, and this timing can be determined very effectively by combined use of traps and the degree-day model. Briefly, you use the traps to determine when the first moths were consistently captured. That gives you the "biofix" date. You then use the biofix date to set or calibrate the degree-day model. The model also required temperature data and from this you can predict the optimal timing for your sprays. In the online version of the model linked below, you can simply pick a public weather station for the temperature data.

The model can really help predict the second generation of codling moth as well. For now it looks like second generation eggs will start hatching in the last week of July or early August.

If this seems overwhelming, you could also apply your treatments after you find the first sting, or evidence of codling moth feeding on fruit. Your traps give you a good indication of when to start looking for evidence of feeding.

Thank you. This is great information. I may have gotten slightly lucky as I have not seen any depressions or frass. Unfortunately, I didn't record the biofix date, so I can't plug that into the model.

I sprayed about 13 days ago and followed up with another spray 5 days ago. Unfortunately, it started pouring rain for several days right after my second spray (presumably washing off the pesticide). Should I plan on respraying once the rain lets up for the week (i.e., sometime tomorrow)?

Great! Because you sprayed 13 days ago you are in good shape and the fact that you are not seeing entries of larvae into fruit also suggests that your treatment worked. Insecticides are remarkably rainfast, but yes when there is a break in the weather it would be a good idea to reapply.