📌 Quick Summary (TL;DR): Treating Onion Thrips Without Chemicals
- ⚠️ The Greenhouse Risk: Onion thrips won’t immediately devour your greenhouse tomatoes or peppers, but they are notorious vectors for viral plant diseases. It’s risky to introduce them into a closed greenhouse environment.
- 🧅 Sets vs. Multipliers: Tiny store-bought onion sets are usually clean. Large bulbs and multiplier onions (shallots) are highly susceptible to overwintering thrips.
- 🛁 Chemical-Free Soaks: If growing onions specifically for the green tops (scallions), you cannot use systemic pesticides. Peel them down to the clean white scales and soak them in a heavy hot salt brine or cheap vodka!
Ninu (Nina) wrote:
Could the thrips jump ship and infest my tomatoes, peppers, and eggplants?
Nina, if you are planting store-bought onion sets (the tiny bulbs), they usually don’t carry thrips. However, large bulb onions and multiplier onions (shallots) are notorious for them. You absolutely must peel them down to the clean white scales and treat them with either hot water or pure alcohol.
Thrips aren’t a huge direct threat to tomatoes and eggplants, but they can act as vectors for viral plant diseases.
An onion infected with thrips is very easy to spot. As soon as the green tops sprout, they look off: the leaves grow flat and have yellow or grayish longitudinal streaks instead of being perfectly round and green.
Aleksan9ra (Ludmila) wrote:
An onion infected with thrips is very easy to spot…
Ludmila! Thank you so much! You never skip our questions, even the total newbie ones!
I’m looking at my shallots right now, and I can literally see these little bugs crawling all over them. 😡 They aren’t keeping well in storage this year either, lots of them are already sprouting early. My variety is ‘Aristocrat’.
Aristocrat?! I know there is a multiplier onion called ‘Aristokratichesky’.Yeah, a lot of growers are complaining about thrips on their onions this year. If you are planting them to grow actual bulbs, you have to treat them with a chemical pesticide before planting, otherwise the tops will yellow way too early and you’ll end up with tiny, stunted onions.
BUT, if you are growing them specifically for the green tops, you cannot use chemicals, not even mild ones! Your only option is to peel them and soak them in a hot, super-heavy brine (about 1 lb of salt per 1 quart of water / 500g per 1L). Rinse them thoroughly afterwards.
Alternatively, you can soak them in a 50/50 mix of pure grain alcohol and water, or just use straight, cheap vodka.
Honestly though, there is still no 100% guarantee. The live adult thrips will die, but the eggs might survive.
First, a quick note on those “crazy Russian gardening tips”! While soaking onions in straight vodka is a classic Eastern European homesteading hack, you don’t need to raid the liquor cabinet. Standard isopropyl (rubbing) alcohol diluted 50/50 with water will give you the exact same pest-killing effect at a fraction of the price!Secondly, Ludmila is completely right about the eggs surviving surface treatments. Female onion thrips (*Thrips tabaci*) use a sharp ovipositor to cut into the plant tissue and lay their eggs inside the scales of the onion.Because the eggs are protected inside the plant material, surface soaks (like alcohol or brine) often fail to kill them. If you are growing onions for greens in a greenhouse alongside valuable crops like tomatoes, the safest route is to discard heavily infested bulbs entirely to prevent a potential viral outbreak (like Tomato Spotted Wilt Virus).
