ROW COVERS EFFECT ON SWEET-POTATO WHITEFLY (HOMOPTERA, ALEYRODIDAE) DENSITIES, INCIDENCE OF SILVERLEAF, AND CROP YIELD IN ZUCCHINI

The use of polyethylene row covers is an effective method to reduce wh itefly, Bemisia tabaci Gennadius, and aphid, Aphis gossypii Clover, de nsities and the incidence of squash silverleaf in zucchini. Mean densi ties of whiteflies and aphids were significantly lower in row-cover tr eated plots than in untreated plots. Under conditions of low silverlea f incidence (<25% of plants with symptoms), row-cover treatments reduc ed the incidence of silverleaf, although no significant increase in yi eld per plant was found, and no relationship between silverleaf incide nce and yield was found. Under high levels of silverleaf (>50% of plan ts with symptoms), there was a significantly higher total marketable y ield per plant in row-cover treated plots than in pesticide-treated or untreated plots. In addition, increased yields were correlated with l ower ratings of silverleaf severity and lower proportions of plants wi th silverleaf.