I've had aphids showing up on my apple and plum trees since August this year, and the leaves are curling up. I read that you need to use something special in the fall so the pests don't survive the winter. What exactly should I use and when should I spray - before the leaves fall or after?
Have the leaves already dried up and fallen, or are they still green on the tree?
Because you need a two-stage approach here, and the guys are basically right, but they're mixing up the timing a bit. If the leaves are still on the tree (and by October they usually drop or almost drop), then yeah, it makes sense to treat with an insecticide like Aktara or Fufanon - there's live aphids there, and they're still active. That'll kill the current generation. But after leaf fall, when the tree is completely bare, you use oil emulsions - they work on the eggs that overwinter under the bark and in cracks. The oils clog the spiracles of pupae and egg masses, and that's actually effective for prevention in spring.
The key thing is don't mix up the timing. Treating with oil while the leaves are still green is a waste, because live insects won't suffer from oil - they'll be waiting for you under the leaf. But if you treat with oil after leaf fall and then it suddenly gets warm again and some aphids wake up on bare branches (it happens), the insecticide won't help anymore - there are no leaves, no feeding point.
If your leaves are still green - grab the insecticide now, don't wait. If half of them have already fallen - hurry up with the chemicals, then you'll wait for complete leaf fall and apply the oil. Two different products, two different stages - that's how you'll make it work.
In fall, it's best to use oil emulsions or mineral oils - they clog the pests' breathing pores and their eggs, which overwinter on the bark. You should spray after the leaves drop, when the tree is already pretty much bare, otherwise the oil can burn the foliage. Preparations based on paraffin oil work well; they're sold as winter oils or late-fall insecticides. If you want, you can treat the tree before the leaves completely fall using gentler options like potassium soap or neem - they're less harsh on the foliage.
Oils work, but there's a catch - on apple and plum trees with this early aphid infestation, I'd treat them with an insecticide like Aktara or Fufanon back in late August or September while the leaves are still on the tree and the pest is active. Oil emulsions are more for preventing the overwintering eggs, and you apply those once the branches are bare, in late October or November depending on the weather. So it's better not to wait for the leaves to fall - start fighting them earlier while the aphids are still feeding.
The key thing is to not miss the window and treat twice: first against living aphids, then against eggs 🎯
I had something similar at my dacha - by August you could already see curled leaves, which means aphids are actively breeding. I sprayed with insecticide (Aktara, Iskra, or even cheap Karbofos work) specifically in late August-September while the leaves are still on the tree and the pest is clearly visible. This kills the current generation of aphids, otherwise they'll keep damaging the tree until the frost comes.
After the leaves drop, once all the foliage is gone, you need a second treatment - this is where oil emulsions (mineral or dormant oils) really help. They clog the breathing holes of the eggs that overwinter on the bark and branches. Usually that's November-December, depending on your region - the main thing is that it's at least 5-10 degrees Celsius, otherwise the oil won't spread properly. By the way, oils are safer for beneficial insects if they're still active 👍
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