I read online recently that dormant oil is not effective until just before bud break because insects are not respiring until that time. I thought that dormant oil could be applied in February in 6b for example because trees are still dormant. What is the current recommendation?
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I thought that heavy dormant-season oils were effective because they are present when eggs start to hatch and respire in the spring. I’ll try to get a heavy spray on as soon as it warms up enough (I missed the spray I try to get to in the fall) and then again just before bud break.
A local grower claims to get control of codling moth with an oil spray at bud break and then another in the middle of June (that would probably be middle of May further south).
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My understanding is they are respiring but much more slowly … hibernating. In either case spraying as close as possible to bud break is ideal as the closer you are the more active they will be.
I sure wish a couple oil sprays would control CM for me… no such luck here in bug-land.
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I don’t depend on oil for codling moth myself either. Spinosad and Sprectracide have been doing the trick so far.
This may — or may not — be a consensus opinion, but here’s what I think:
When used as dormant spray, horticultural oil smothers insects coming out of hibernation. Its action is mechanical rather than toxic, so it needs to be applied while pests’ respiration is increasing — above about 40° F. The latest that such benefits are obtained is about 1/4-inch green, which can be a tolerably narrow window.
Concerning horticultural oil for control of codling moth:
I believe that apples universally reach full bloom at about 175 DD °F and that codling moths’ first flight (biofix) is about that time. Egg hatch begins around 425 DD °F (biofix + 250 DD °F), which is the traditional timing for first codling moth treatment. What the above article recommends is an early treatment at 375 DD °F to kill eggs before hatching. The author(s) suggest horticultural oil.
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I remember a past discussion about dormant oils being lighter and more refined than they used to be. I think I have purchased a dormant oil and an “all seasons oil” in the past. Is that distinction important?.
I do know that I have had injury to new leaf growth on some trees, esp pears, when using neem oil.
Any comment about the statement below that says that dormant oil can speed up spring bud development? It’s important to me that I try and avoid that in my area.
Dormant or Delayed Dormant Application
There are two methods for dormant horticultural oil application. One is to apply it before the buds break or show any color. However, this can speed up spring bud development, making buds more susceptible to frost and cold temperature damage. The second method is the delayed dormant application. This occurs when buds are open at the tip showing 1/16-inch to ½-inch of green leaf tissue.
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