Seasonal Abundance and Control of the Rhododendron Gall Midge, Clinodiplosis rhododendri (Felt), in Container Grown Rhododendron catawbiense Michaux

Abstract

The seasonal abundance and control of the rhododendron gall midge, Clinodiplosis rhododendri (Felt), were investigated on container grown Rhododendron catawbiense Michaux. Most of the midge population studied completed 3 generations, and at least some completed 4–5 generations during the growing season (May–October 1989). Adults that developed from overwintered larvae began emerging on May 14, 1989. Three of the peaks in adult emergence coincided with bud break during the three growth flushes observed in the nursery. Only 20% of the buds were infested during the first growth flush, while 95% were infested during the second and third growth flushes. The low level of infestation during the early growth period provides an opportunity to detect an infestation before extensive damage occurs. Five insecticides were tested as soil drenches to control overwintering larvae. All five were equally effective and reduced the number of emerging adults by 95–100%. Further tests with Dursban 2E (chlorpyrifos) showed that soil surface applications were also effective, and that the timing of irrigation did not affect control. Soil drenches with two additional materials, Safer's insecticidal soap and Pratt horticultural oil, were not effective.