How fast does BT work or can you win Gypsy Moth battle?

Here we go again… Gypsy moth is back. I see a lot of very small ones on my young apple trees. I am going to apply BT, but I don’t want them to continue eating my tiny trees, so if they are not going to die today, I would also hand pick them. Spinosad is effective as well, but trees are in bloom, don’t want to affect pollinators.

I would be curious to the answer of this question as well. I have problems with Spider Mites, And Moths as well and just bought some BT…Maybe someone can answer. Thnx

I don’t think BT works for spider mites, in my understanding it is for caterpillars only. And it is not contact insecticide, they have to eat it. But what I don’t know is how fast it will work.

You are correct. Have my bugs confused. Here is a fact sheet on BT

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Lepidoptera larvae stop feeding within 12 hours and die within 24 hours. BT is ineffective after 3 days exposed to full sun. Re-apply every 3 days for continuous control.


I don’t think BT working against GM. I sprayed yesterday, more than 24 hours late there are plenty of caterpillars on each apple tree. So I started to hand pick them… My trees are small, so I literally look at each leaf. I finished one tree, moved to another. Then looked at the first one - 5 caterpillars on the top again. And I realized, they been blown by the wind… So if a caterpillar get to the tree and eats BT infected leaf, it can continue to feed for 12 hours until it looses its appetite. But for that time many more fresh ones will arrive, and they can eat the leaves non-stop, until they grow big enough not to be blown by wind… I literally need to had pick them non-stop… Battle lost?

I am wondering it myself. I usually have lot of leaf rollers every spring. I’ve squished them with my fingers. As my trees are getting bigger, it is harder to reach some branches. Headr that BT is good against them and winter moths and tent caterpillers, etc. best, BT does not hurt be. So I went out and buy BT for the first time. Sprayed on 5/7.

As soon as I finished spraying, I found those tiny black tent caterpillars on the side of my sprayer!!! Next day , they were munching leaves on every tree. And if I have to spray every 3 days like a poster above said, I am not sure if BT is for me. I have not seen many leaf rollers. Maybe, BT worked against them.

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