I recently underwent a battle in the greenhouse against thrips. Let me tell you, these little guys are destructive and tough to get rid off, but it can be done organically! The difficulty comes in that they lay their eggs in the soil so breaking the cycle is the tricky part.
Thrips are tiny little buggers that literally suck the life out of plants when they feed. My leaves exhibited mottling in the their coloring before finally wilting and dying. The tell tale sign that thrips have been there is little black specks all over a leaf. And for lack of better tact, it’s bug poo. An infestation can happen quickly, so it is important to act fast.
I started off trying insecticidal soap, but that had no effect of the thrips. I set out sticky traps and while they did catch some, there was not much effect on the population. The spiders also had a veritable buffet, but again, no effect on the population.
Where I struck success was I saw in an issue of Garden Gate magazine the mention of Spinosad. What appealed to me is that it is an organic product and would leave my spiders be. It has very little effect on beneficials! (The exception is bees, so use caution outside and only spray when bees are not active.) It is most effective on insects that suck on leaves.
Let me tell you, I ran out to the garden center and picked up a bottle. I went to town in the greenhouse and the next day, a severe drop in the thrip population. AND all my greenhouse spiders were still active.
I am very pleased with this product. Although I prefer not to spray anything in the greenhouse, drastic measure had to be taken otherwise I would have lost more plants. With this product not affecting the beneficials and doing what it was intended (getting rid of thrips), it gets an A+ in my book.