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.