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Disease Note.

First Report of Squash Silverleaf Disorder Associated with B-Biotype Sweetpotato Whitefly in New York. M. T. McGrath, University, Long Island Horticultural Research Laboratory, Riverhead, NY 11901-1098. D. Gilrein, Cornell University, Long Island Horticultural Research Laboratory, Riverhead, NY 11901-1098, and J. K. Brown, Department of Plant Sciences, University of Arizona, Tucson, AZ 85721. Plant Dis. 78:641. Accepted for publication 7 March 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0641B.

Symptoms of squash silverleaf (SSL) were observed in field plantings of greenhouse-grown transplants of yellow and zucchini squash (Cucurbita pepo L.) at the Long Island Horticultural Research Laboratory in Suffolk County, New York, during August 1993. This is the Inst reporl of SSL in the northeastern United States. Five whileflies were identified individually as the B-biotype of Bemesia tabaci (Gennadius) on the basis of general esterase profiles containing the diagnostic B-1 and B-2 bands (1). Feeding by nymphs of this whitefly biotype has been shown to induce SSL (2). Whileflies and silvered leaves were observed on a few seedlings prior to transplanting on 4 August, 16 days after plants were moved out of the greenhouse. By 25 August, adult and immature sweetpotato whileflies were noticeably abundant, and 45% of 1,526 plains exhibited SSL symptoms The upper surface of affected leaves was partially to completely silver, but on some leaves only veins were silver. To confirm that the field whitefly population could induce the observed SSL symptoms, 10 adults from squash plants were collected by aspiration, transferred to zucchini seedlings in the laboratory, and allowed to oviposit for 3 days. Adults were then removed, and immatures were allowed lo develop on the abaxial leaf surfaces of these seedlings. SSL symptoms developed on the newest leaves 10 lo 14 days after adults were removed. The B-biotype sweetpotato whileflies have been observed in greenhouses on Long Island for 6 yr but not in commercial fields prior lo 1993. In 1993, whileflies were found in commercial plantings of zucchini, potato, sweetpotato, gourd, and zinnia These zucchini plants showed SSL symptoms. SSL symptoms were not seen in a production field of summer squash where no whileflies were found. The B-biotype whitefly and associated disorders have become a major limitation to vegetable production in Florida, Arizona, California, and other southern stales. A similar impact may not be fell in northern stales where this whitefly is unable lo overwinter outside. The unusually hot, dry conditions during the 1993 growing season were very favorable for whitefly development and may have contributed to this late-season outbreak.

References: (1) H. S. Costa and J. K. Brown. Entomol. Exp. Appl. 61:211, 1991. (2) H. S. Costa el al. Phytopathology 83:763, 1993.