The sweetpotato whitefly, Bemisia tabaci (Gennadius) since 1976 has been consistently one of the major pests in Israeli cotton fields (Melamed-Madjar et al. 1979, Horowitz et al. 1984)(1). Growers in the Bet She'an Valley since 1980 have had a cotton pest management program that during the last three weeks of the growing season has often required applications of insecticides at 4-day intervals in an effort to control the whitefly and prevent honeydew and sooty mold from contaminating the lint. Even with this intensive insecticide program, the size of the whitefly populations has not been lowered below the initial level prior to treatment. Growers have experienced reductions in cotton duality due to whitefly damage because there has been no adequate chemical control.

In a previous experiment we found a mid-August application of Bacillus thuringiensis in 1986 in Israel reduced cotton aphid, Aphis gossypii Glover, populations. It was suggested that this may have occurred because of the cottonseed oil used in the formulation (G.D. Butler, Jr., and M. Broza, unpublished data). Three advantages of oils for pest control are: (1) they pose little human health hazard, (2) insects and mites apparently are less likely to develop resistance to oils, and (3) oils are usually cheaper than competitive pest control products (Chapman 1967).(2) Greenhouse experiments in Phoenix, Arizona during the spring of 1987 demonstrated that a cottonseed oil spray to the undersides of the leaves not only gave excellent control of the cotton aphid but also of the whitefly (G. D. Butler, Jr., unpublished data). We therefore conducted field tests in Israel during the summer of 1987 to evaluate cottonseed oil for whitefly control with two commercial ground sprayers selected for their capability to provide coverage of spray on the undersides of leaves.

Crude cottonseed oil, (5 to 7%) aqueous sprays applied with high clearance air-blast sprayers that provided under-leaf coverage, effectively suppressed sweetpotato whitefly numbers throughout the season on cotton. Results were superior to control provided by insecticides. Applications of oil alone applied at 120 1/ha at 3- to 8-day intervals with an inflatable sleeve boom sprayer reduced whitefly populations when treatments were initiated in early August before the whiteflies had become too abundant. There were 24 whitefly pupae/leaf in insecticide-treated cotton and one whitefly pupa/leaf in the oil-treated cotton in mid-September. Results were equally satisfactory when tractor speeds were 8.5 or 3.5 km/hr, delivering 50 or 120 1/ha (5.3 or 12.8 gal/A), respectively. Cottonseed oil treatments applied with a mist blower sprayer after a mid-season aldicarb application, gave good adult whitefly control when applied at 4- to 7-day intervals (14.0 whitefly pupae/leaf in insecticide-treated cotton and 0.3 pupae/leaf in the oil-treated cotton in midSeptember). Oil applications with mist blower equipment were not as effective (35.0 pupae/leaf) without a mid-season aldicarb treatment.

A sampling method for adult whiteflies consisting of hitting the tops of 10 plants over a box with an oilcoated black bottom was developed and found to efficiently and quickly evaluate the need for or the effectiveness of control measures.