Western flower thrips is a polyphagous species with and extremely wide host plant range that includes more than 200 different plant species from more than 50 families. In southern Africa it has been recorded from a variety of vegetables, deciduous and subtropical fruit, grapevine, cut flowers such as roses and chrysanthemums, as well as from a variety of indigenous flowers and weeds. On berries, it has been recorded mainly in blueberry and strawberry plantations.
Feeding by western flower thrips on the leaves of blueberry (illustrated) causes severe scarring of the leaves post-harvest and after summer pruning. Besides affecting photosynthesis, new growth is stunted, negatively affecting production of new wood for the following season. Russeting of the blueberry fruit may also occur. On strawberry flowers, feeding on petals causes them to shrivel, and more seriously, when they feed on developing fruit, berries become misshapen. Bronzing of the fruit also occurs. However, other thrips such as Thrips tabaci, may also be involved in some areas.
Economic damage to blueberry plants by western flower thrips tends to be sporadic, but mostly occurs from December to March. Stunted growth caused by this pest can have a significant effect on the size of the following season’s crop. Areas most affected include Worcestor, Villiersdorp and Porterville in the Western Cape. On strawberry, western flower thrips can cause severe economic damage.
Thrips can be monitored with the aid of blue sticky traps. A number of species can occur, not all of which cause economic damage, and because identification of thrips is difficult, traps should be sent to an expert for identification before control decisions are made. Control with contact insecticides can be considered; however, western flower thrips is known to very rapidly develop resistance to pesticides, further limiting control options. Weeds and other flowering plants in or near by blueberry plantations that also attract thrips should not be disturbed or mowed while berries are flowering, as this may result in masses of thrips migrating into the berry plantations.