Thrips on Cabbage
The onion thrips, Thrips tabaci Lindeman, is a cosmopolitan insect and one of the most important and destructive pests of cabbage in Pennsylvania. If not adequately controlled, serious economic damage from immature and adult stages often results. Estimates of crop damage and losses to the cabbage industry have averaged 3 to 5 percent during the past decade.
Onion thrips are small, less than 2 mm in length, and because of their minute size usually go unnoticed by growers. Adults are pale yellowish to brownish, with four long, narrow wings fringed with long hairs. Immature thrips are similar in shape to the adults, but smaller in size, wingless, and lighter in color.
Onion thrips overwinter as adults in alfalfa, clover, and wheat fields. In late spring, as the daily mean temperature rises above 60o, thrips migrate to one of their many hosts. They lay eggs singly and indiscriminately in incisions made in plant tissue by a saw-like tube. More eggs are laid during the hot summer months than in cooler days. Eggs hatch and young larvae develop into adults in about two weeks. Adults live for three weeks, during which females may lay over 100 eggs. A warm, sunny, dry summer encourages reproduction and survival.
Thrips build up on alfalfa, small grains, and weeds. As alfalfa is cut for hay, and small grains are maturing and cut for threshing, movements of thrips to and from large acreages are intensified. When cabbage is nearby, thrips can infest it.
Cabbage are blistered, scarred, and bronzed by thrips feeding on leaves; with thrips present, heads are unmarketable. Thrips feed on leaves by puncturing and rasping the outer leaf tissue and sucking the sap as it exudes from the cells. Where many thrips have fed, the discolored areas coalesce to form large brownish, blister-like areas.
Nonpersistent systemic insecticides are effective against thrips. Nonpersistent contact insecticides are usually unsatisfactory for controlling thrips unless used on a regular schedule during head formation. Applications of insecticidal sprays during head formation is important for control.
Penn State College of Agricultural Sciences research, extension, and resident education programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
Visit Penn State Extension on the web: http://extension.psu.edu
Where trade names appear, no discrimination is intended, and no endorsement by Penn State Cooperative Extension is implied.
This publication is available in alternative media on request.
The Pennsylvania State University is committed to the policy that all persons shall have equal access to programs, facilities, admission, and employment without regard to personal characteristics not related to ability, performance, or qualifications as determined by University policy or by state or federal authorities. It is the policy of the University to maintain an academic and work environment free of discrimination, including harassment. The Pennsylvania State University prohibits discrimination and harassment against any person because of age, ancestry, color, disability or handicap, national origin, race, religious creed, sex, sexual orientation, gender identity, or veteran status. Discrimination or harassment against faculty, staff, or students will not be tolerated at The Pennsylvania State University. Direct all inquiries regarding the nondiscrimination policy to the Affirmative Action Director, The Pennsylvania State University, 328 Boucke Building, University Park, PA 16802-5901; Tel 814-865-4700/V, 814-863-1150/ TTY.
© The Pennsylvania State University 2013