EPIDEMIOLOGIC STUDIES ON THE STUNT DISEASE OF HIGHBUSH BLUEBERRY

Population levels of Scaphytopius spp., possible sharpnosed leafhopper vectors of blueberry stunt disease (BBSD), were monitored during 1989, 1990 and 1991, using yellow sticky traps and a D-Vac power aspirator. Scaphytopius magdalensis (Prov.), S. frontalis (Van D.) and S. acutus (Say) had two population peaks, one after the petal fall stage and a larger second peak in late Summer to early Autumn. Healthy cv. Bluecrop highbush blueberry (Vaccinium corymbosum L.) plants were placed under stunt-diseased bushes in the field for 2-wk periods during 1989 and 1990. These plants and some of the leafhoppers trapped during 1990 and 1991 were tested for mycoplasma-like organism (MLO) infection with a DNA probe that detected BBSD-associated MLO. The percentage of plants and the number of Scaphytopius spp. that were MLO-positive tended to follow the same bimodal distribution found in the population studies. BBSD transmission tests were performed with Scaphytopius spp. collected from the field. Stunt-related MLO transmission was achieved with S. magdalensis, S. acutus and S. frontalis.