You can treat thrips any time of year. But any insecticide is best applied early in the growing season. Then applied again additionally through the year. Neem oil is more a preventer than killer and must be applied weekly until the population goes down, then apply every few weeks.
You could also use a systemic insecticide which will kill any insect. So it's best applied very late in the evening so it doesn't kill the bees. Bayer tree and shrub is one which comes in pellets that soak into the soil when watering, and also sold as a liquid which is poured at the base of plants and trees. But the instructions are vague for daylily application, and the product isn't recommended by bayer to use for daylilys. it's a 12 month systemic.
Bayer Advanced which I think is applied every 3 months. That's what I used, sprayed it all over when it was almost dark out. I don't think i applied it very well, as I still see thrips but it's an improvement. But it wont kill whatever thrips are already inside the buds. So it must be applied every 3 months to kill the cycle of the thrips. Soil must be sprayed also. I think also Bayer Rose and flower care kills thrips too.
