Onion

Onion: Thrips, Thrips tabaci Lendeman, Thysanoptera: Thripidae

Photo 129

Photo 130

Biology:  Very little commercial onion is now produced in Arkansas.  In the limited onion production area of southwestern Missouri, thrips have been a common problem.  Thrips are minute insects found on onion by pulling leaves apart.  Adults are tan in color and less than 2 mm in length (Photo 129).  Two pairs of wings are present and long hairs occur on the edges of the wings.  Immature thrips are smaller and lighter in color. Adults and immature stages “rasp” the leaf surface with their mouthparts and feed on the exuding plant sap.  On onion, their feeding causes the leaves to yellow and distort (Photo 130).  Size and quality of the bulb can be reduced.  After mating, females insert eggs into the plant tissue.  Larvae emerge and feed by scraping the plant surface and ingesting plant sap.  Maturity is reached in less than one week and pupation occurs in soil.  Adults emerge in about four days and the cycle is repeated.  Multiple generations occur annually in Arkansas.

Management:    Low numbers of thrips may be tolerated with a minimal effect on yield.  If thrips numbers increase beyond acceptable levels, use of insecticides may be warranted.  Thrips feed predominately on unfolded onion foliage.  Thus, getting insecticides into contact with thrips is very difficult. If traditional contact insecticides are used, efforts must be taken to apply the insecticide to the whorl of the plant.  Use of a surfactant should assist the spread of the insecticide to the bottom surface.  Systemic insecticides will likely provide more effective control. Sanitation including destruction of crops immediately following the last harvest may have some effectiveness in reducing damage in subsequent plantings.