My onion leaves have silvery white streaks and blotches and the bulbs are not sizing. I think it is thrips. How do I manage them?
6 Answers
Those silvery white streaks and blotches on onion leaves are classic thrips damage, and heavy thrips reduce photosynthesis so the bulbs stay small, and they also help spread disease. Manage them with an integrated approach because thrips build resistance fast. Use blue sticky traps to monitor, keep the field and bunds weed free, avoid excess nitrogen, and maintain good moisture since stressed crops suffer more. Because onion leaves are upright and waxy, always add a sticker or wetting agent so the spray reaches the thrips hiding in the leaf axils, otherwise sprays run off and fail. Rotate recommended insecticides for thrips strictly per label and KVK advice and never repeat the same chemical group, as continuous use of one molecule is what breeds resistance. Direct the spray into the central whorl where thrips shelter. Confirm the products and schedule with your KVK.
Adding a sticker to the spray made a big difference for me. Without it the spray just rolled off the onion leaves and the thrips survived.
Directing the spray into the central whorl where the thrips hide was the trick. I used to spray the outside of the leaves only and miss them, since they shelter down in the leaf axils. Aiming into the heart of the plant with a sticker finally reached them.
Rotating the chemical groups is what kept it under control here. A few of us kept hammering the same product and it stopped working. Keeping the bunds weed free and not overdoing nitrogen reduced the pressure too, so I did not have to spray as often.
Blue sticky traps let me catch the thrips build up early so I act before the bulbs are set back. Once I see the numbers rising I move, because if you wait till the leaves are silvery all over the bulb is already smaller. Watching with the traps beats spraying blind.
Keeping the field and bunds free of weeds reduced my thrips pressure a lot, since the weeds were sheltering them between sprays. Along with not overdoing nitrogen, the cleaner field meant fewer thrips moving in and I did not have to spray as hard.