Inadvertent thinning with imidan

Used imidan at my usual 1 tbsp per gallon. If I was off it wasn’t by much. Came out two days later and about 80 percent of the apple crop had dropped off. The king bloom fruit survived. Many fruitlets in early stage were completely removed. Others had two apples remaining. Some trees completely stripped. I didn’t use a sticker.

Has this happened to anyone else? I’m predicting a small amount of really big apples.

Boy this was shocker! Still speechless. Very disappointed since I was hoping for a big harvest after judicious thinning.


Update to post. A bit more apples left than I thought but only on trees that had fruit marble size or larger.

Was hoping someone could comment. @PomGranny and I think that it has the most to do with the fact that most apples were in a really early immature stage.

I won’t make that mistake again. Wooly aphids gone.


Sorry to hear this. I used Sevin (new formula “zeta-cypermethrin” from big box store) few weeks ago, but not Imidan. No ill effect from Sevin on apples that I could tell based on label dosage.


Chemical thinning is used by orchardists to reduce crop load. As I grumble thinning fruit, I’ve always wonder how well chemical thinning works. You’ve got the answer.
Apple Chemical Thinning | WSU Production Guide.


We sometimes thin Apples with Sevin XLR and sometimes a PGR like NAA but this is the first time I have heard of Imidan thinning Apples. It is not mentioned as a thinning agent in any spray guide I can find.

We don’t use Imidan much anymore because of the restrictions but it would be great if we could thin and kill insects at the same time without flaring the mites using Imidan.

Was your Imidan still in it’s 1 pound water soluble bag.

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My first spray post bloom has always been Captan and Imidan with sticker. I never had any thinning effect. My Imidan is gone and I can no longer get it (unless I get private sprayer certification). Just got an order for pesticides from Keystone, $720, OUCH!


No diluted powder. Bag was open.i guess I won’t be using it much anymore.

Imidan is pretty inexpensive and it and kills a lot of bad insects. Also has a reputation for killing fewer good insects than many other insecticides. Somebody described it as a "soft’ Organophosphate. Not sure about that description since many OP chemicals are no longer labeled for fruit or vegetables.

We used Imidan on Apples for a good while but never had a problem with thinning. It’s the most effective chemical we ever used against PC on Apples and Peaches.


@Rosdonald I am still thinning! And the peaches seem to be thinning themselves, too.
I’ll be interested to hear if anyone has any other ideas of why your trees dropped so much fruit?

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