ONION THRIPS

Onion plant showing severe thrips damage. Insert, adult thrips ( about 40 times natural size).

ONION THRIPS

The onion thrips occurs wherever onions grow. It attacks many cultivated crops and weeds. Its damage varies with seasons, localities, and the variety of onions.

In the South the onion thrips feeds on onions and other host plants throughout the winter. In the North they pass the winter in both the adult and larval stages on onion plants left in the fields and in the crowns of alfalfa and clover. They over-winter in discarded onions and sometimes in stored onions. The female lays her small whitish eggs in the more tender tissues of the leaves of the host plants. The eggs hatch in 4 to 10 days. The tiny white larvae emerge from the eggs and immediately begin to feed upon the growing tender points of the center leaves, where they are well protected. The larvae pass through two stages while feeding upon the plants and complete their growth in about 5 days. Then they enter the soil,where they pupate. The pupal stage lasts about 4 days if conditions are favorable. Thus a generation is completed in about 2 weeks. Generations overlap considerably. All stages may be in fields at the same time during the summer. Thrips often build up large populations on alfalfa, other cultivated crops, or weeds, and migrate to onion fields when the hosts mature or are harvested.

Control: Apply a dust containing 10 percent of DDT or a spray containing 2 pounds of 50 percent DDT wettable powder per 100 gallons of water. Use 20 to 25 pounds of dust, or 150 gallons of spray, per acre for each application. Repeat applications every 7 to 10 days. The spray should be applied as a fine mist so as to cover all parts of the plants thoroughly. Do not apply DDT to onions if the tops are to be eaten. If the onion tops are to be eaten, use a spray containing 1 quart of 40 percent nicotine sulfate per 100 gallons of water.