Suggested neem oil rates for spray application range between 0.5% and 2.0%. We generally assume a foliar rate of no more than 0.5% biological fats (neem, karanja, etc.) to be safe as regards phytotoxic damage to leaves . . . but as observed in other posts in this forum, certain cultivars (oh, those tender pears!) seem especially sensitive and thus a 0.25% spray rate might be a better rate. Ditto when spraying perhaps any plant when temps are in the 80s and the sun is shining brightly. Applied to non-foliage (the trunk zone) is where the borer game begins. Translate that 1% or 2% concentration into costly gallon jugs of neem oil. Adding one full gallon into a hundred-gallon spray tank costs like $75 to make a 1% concentration borer trunk spray. Some spray splashes off-target but on the other hand we actually up the net concentration by saturating the soil zone right at the base of the trunk to make this strategy effective. Mesh trunk guards (for voles) help to contain the spray where you want it to go. It helps to sit on the sprayer when there's many trunks to treat, plus bigger trees are easier to protect since RHAB particularly goes for younger bark given the choice.
Part of my current strategy is to brush pure neem oil on younger trunks by the third week of June but only do a 4 to 8 inch wide band right at the soil line and not much further up. I like to pull soil back to expose as much as an inch of buried trunk zone, then apply, even puddling up ever so slightly, before pushing back the soil (or peastone or bark mulch). This 100% concentration is cost-effective directly applied but takes the labor of going from tree to tree thus why I'm only going to do this in the tender years. That could mean as many as ten years, especially where an apple orchard borders the woods where borer continues to thrive in alternate hosts and/or you are personally involved in some sort of karmic debt from a past life. Ha! I have applied pure neem to trees on Antonovka, MM.111, Bud.118, and Geneva rootstocks. The marvel of this is that it need only be done once a year whereas I have done borer trunk sprays as many as three times a summer. I still intend one trunk spray in mid July to larger trees but now see brushing neem on younger trees as replacing the need for a late June trunk spay. We are timing this to repel the female during the egg-laying period which runs from late June through August in northern zones. I will also note that I have only done the preemptive brush-on approach two years running at this point but that my initial use of pure neem to treat borer wound cavities goes back several seasons (along with a comfrey leaf wrap around the damage zone). The point being what does a trunk look like after ten years of such treatment? None of us know so keep that in mind.
Now let's bring in the nursery nuance. This is where Seth's observation of damage to adventitious roots (arising from burr knot zones) on MM.111 becomes relevant. Nursery stock may be planted deeper in the orchard so losing these potential roots that are above ground in the nursery would not be good. So sure, cut the neem oil concentration with canola or even water. Just be aware that renewing a lesser application rate like 10-20% may turn out to be necessary later in summer. Once a tree is planted in its orchard location, the soil line has determined which adventitious roots have legitimate rooting potential and so I wouldn't worry about hardening off burr knot zones above. But I also have not seen what Seth has seen so feedback on this should continue.
And just to be clear, we are giving all this focus to one damn beetle species RHAB because it kills young trees. Those of you dealing with Prunus borers are dealing with the progeny of moths, and that's where nematodes and spinosad have relevance in shifting an active infestation.
Lost Nation OrchardZone 4b in New Hampshire
Edited 3 time(s). Last edit at 07/09/2020 08:39PM by Michael Phillips.