Learning that "gummosis" is a
prunus response to any injury has value, and now zeroing in on the actual cause means you will get on top of this, Peter. The fact that this borer is the larvae of a moth shifts a few of the thoughts with which we approach beetle grubs of the borer persuasion.
Bt has value if the borer larvae consume the moth-specific protein toxin. I doubt much will happen on that score, given the inner cambium feeding but a surface application ... but it doesn't hurt to try.
Neem oil impacts the molting cycle so you will eventually stop many larvae in their development and thus life cycle. The fats in neem are readily absorbed by bark tissues so the azadiractins (active insect constituents) will be in the cambium to act both by ingestion and on contact. Neem trunk sprays may deter the female moth from laying eggs but that timing has to be preemptive. Your situation is more like finding RHAB egg slits at the soil line, only LPTB works branch crotches. Spreading "neem butter" directly from the jug (literally with a butter knife) to damaged areas is an experimental idea which I'm finding very useful in my own borer battles.
The clay slurry works principally to confuse the crawling female beetle as she works her way down from the canopy to the soil line. This may not have much value with moths who fly into place. A clay coating (especially with a tad of latex paint as part of the slurry) also helps make grub damage more obvious.
The other thing to consider with moth borers is spinosad. Very expensive, yes, but it too works on contact as well as by ingestion. Just be sure to rotate approaches as we don't want any pest building up resistance to this spray.
Last fall I worked with a grower in Idaho with bad peach tree borer infestation. Same idea but this moth cousin concentrates its larval activity at the soil line. I suggested a neem soil drench. Here's what she reported back though it goes beyond what I understand about neem action:
I went ahead and used 70% Neem Oil since we had this on hand. We poured this full strength on the trunks of trees and saturated around base until it puddled. I checked our plum tree that is completely girdled with eggs again about 20 to 30 minutes after applying the NEEM oil and we found 12 ugly borers laying on the soil all around base of tree. So it is having some effect at least. I also saw some pop out from bottom of trunk right after pouring--amazing to watch.Lost Nation OrchardZone 4b in New Hampshire
Edited 1 time(s). Last edit at 09/09/2015 06:58AM by Michael Phillips.