Management of dandelion to supplement control of western flower thrips (Thysanoptera: Thripidae) in apple orchards

Abstract

We evaluated whether management of the broadleaf weed dandelion, Taraxacum officinale F.H. Wigg. aggr., affected damage to apples by westem flower thrips (Frankliniella occidentalis (Pergande)). Four commercial apple orchard blocks in central Washington having high densities of dandelion were monitored over a 3-yr period. Herbicides were applied to the drive rows in one-half of each orchard for each year of the study. A 92% reduction in dandelion densities in the low-weed plots was achieved by the third year of the experiment. The number of thrips per dandelion plant did not change as dandelions became less numerous. This resulted in an overall reduction in western flower thrips per unit area on dandelions throughout the course of the trial. However, the number of westem flower thrips in the apple flowers and shoots were not affected by the treatment. Estimated westem flower thrips population density per ha on apple and dandelion indicated that dandelions harboured a much smaller pool of westem flower thrips in comparison to apple. No significant reduction in fruit injury was detected in any year. Thus, reduction or elimination of dandelion from the orchard floor appears to be of limited value in managing westem flower thrips in apple orchards.