The damage they cause David Adams , a UGA Extension Service entomologist, said the thrips weaken the plants. When it hurts the farmer, it hurts the consumer, too, Riley said. But with Riley's research data, farmers can be sure their thrips control dollars will pay off in the long run. He's working to learn what thrips species damage onions and when it's most effective to apply insecticides. Adams said that the insects cause varying levels of damage at different times in the season.
Effective control is vital then.
Later in the season, he said, a few thrips may not cause as much damage. So control efforts should be aimed at thrips during the spring. The damage thrips cause is hard to see. The insects are no bigger than the period at the end of this sentence. It's hard to spot them.