Thrip Control in Onions

Detect Thrips

• Thrips can be difficult to see because of their size and tendency to hide between leaf blades and onion bulbs. Onion thrips are about 0.05 inches long; a hand-held magnifying glass can help in detection. Thrip damage creates a distinctive pattern on onions and may be the first sign of trouble.

Cultural Control

• For small onion plantings, checking transplants carefully for thrips before planting is paramount. Avoid planting onions near grain or alfalfa fields, since these plants are often hosts for thrips. Interplanting onions with carrots can also help to keep thrips from onions by attracting them to the carrots, where they cannot cause significant damage. Sprinkler irrigation has also been shown to deter thrips, who prefer a dry environment.

Organic and Biological Controls

• Thrips can be controlled using spinosad applications, which are considered acceptable for organic crops. They are also a favorite prey of many predatory insects, including predatory mites, pirate bugs and lacewings. Other non-chemical controls include diazinon, kaolin clay (when used as a barrier), insecticidal soap and horticultural oil. Small stands of onions can be sprayed with a water hose to wash thrips from the plants.

Insecticides

• When cultural controls fail and insecticides are an option, they are used widely to control onion thrips. Like with many insects, however, thrips have been developing a resistance to insecticides, so use them as a last resort. Frequently rotate insecticide classes and spray as infrequently as possible. Several insecticides are successful against thrips, including pyrethrins, carabamate and pyriproxyfen.