119 Non-Chemical Insect and Disease Management in Cucurbit Production Systems C.G. Summers J.P. Mitchell Department of Entomology Department of Vegetable Crops University of California University of California Davis, CA 95616 Davis, CA 95616 USA USA J.J. Stapleton Statewide IPM Project University of California Parlier, CA 93648 USA Keywords: Aphis gossypii, Bemisia argentifolii, aphid-borne viruses, UV reflective mulch, cover crops, biological mulch, squash silverleaf Abstract We conducted experiments in 2000 and 2001 in California’s San Joaquin Valley to evaluate the effectiveness of wheat straw and UV reflective plastic mulches for the management of silverleaf whitefly, Bemisia argentifolii Bellows and Perring, and several aphid-borne virus diseases of zucchini squash. The effectiveness of these mulches was compared to a pre-plant application of imidacloprid (Admire ® ) insecti- cide and an unmulched, untreated control. Symptoms of both squash silverleaf, induced by nymphal whitefly feeding, and virus infection were significantly delayed and reduced by the baled wheat straw that was scattered over the beds and the UV reflective plastic. Wheat straw mulch obtained by planting winter (December) wheat, threshing the grain (June) and cutting the stubble (August) prior to squash planting discolored between harvest and squash planting and did not provide the high degree of reflectivity observed in straw that has been cut immediately after harvest, baled and then scattered prior to planting. Pre-plant Admire insecticide was not as effective in managing either whiteflies or the virus diseases as were the mulches. Yield of marketable fruit was significantly (P < 0.05) higher in 2000 from plants growing over the scattered wheat straw and the UV reflective plastic mulches than from those growing in the Admire treated or the control plots. In 2001 plants growing over the scattered wheat straw produced yields significantly (P < 0.05) greater than those from all other treatments. These data indicate that acceptable squash yields can be obtained without using chemical insecticides. INTRODUCTION Zucchini squash (Cucurbita pepo L.) is susceptible to several aphid-borne viruses, including cucumber mosaic (CMV), zucchini yellow mosaic (ZYMV) and watermelon mosaic (WMV). All are transmitted in a non-persistent manner by aphids. Plants may become infected with one or all of the viruses during their development. Plants infected by multiple viruses generally suffer more damage than those infected with only one virus. Insecticides offer little relief, as the viruses are acquired and transmitted within a short time, usually before the aphid vector obtains a lethal insecticide dose (Gibson and Rice, 1989). Some insecticides may actually enhance virus spread (Ferro et al., 1980). Silverleaf whitefly (Bemisia argentifolii Bellows & Perring) is also a serious pest of zucchini squash. Whitefly management using chemicals has not been effective (Denholm et al., 1996; Horowitz and Ishaaya, 1996) and there are few examples of effective biological control in vegetables (Heinz, 1996; Hoelmer, 1996). Silverleaf whitefly rapidly develops resistance to all classes of insecticides (Denholm et al., 1996; Prabhaker et al., 1998; Elbert and Nauen, 2000). Proc. XXVI IHC – Sustainability of Horticultural Systems Eds. L. Bertschinger and J.D. Anderson Acta Hort. 638, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA)