Thrips are a common greenhouse pests that attack a wide variety of plants. A mild infestation can scar leaves and fruit. A more virulent one can destroy entire crops. But, however tempting it may be, blanketing your greenhouse plants in insecticide is not the answer. Not only can they be harmful to you and your plants, but thrips are notorious for developing resistance to chemical pesticides. A much more safe and effective way to rid your greenhouse of thrips is to strengthen your plants, physically remove the pests and then introduce a predator insect to permanently solve the problem.
Water your plants frequently. The first line of defense against thrips is healthy, well-watered plants. Vigorous plants are less attractive to most parasites than dry, sickly ones. Blast each plant with a firm spray of water from the hose to dislodge a mild infestation of thrips.
Remove any injured, diseased or infested leaves, blooms or branches. Once you have clipped them off with pruning shears, drop them in a bucket of water mixed with mild detergent to kill the thrips. Simply by removing affected plants, you can significantly reduce the thrip population in your greenhouse.
Hang blue or yellow sticky traps. Adult thrips are attracted to the colors blue and yellow. And when they venture to close, they'll find themselves stuck and unable to lay any more eggs.
Hang the sticky traps so that the top of the trap hangs two feet above the top of the affected plants and the bottoms reach within an inch of the uppermost leaves.
Buy and release predatory insects. There are many insects that prey on thrips. However, lady beetles are the most effective as they feast on thrips in the larval and adult stages. Plus, they eat other greenhouse pests such as scale insects, aphids, mealy bugs and mites.