TESTS OF GARLIC OIL FOR CONTROL OF THE SILVERLEAF WHITEFLY, BEMISLA-ARGENTIFOLII BELLOWS AND PERRING (HOMOPTERA, ALEYRODIDAE) IN COTTON

Extract from chopped garlic, garlic oil, and garlic-containing commerc ial products were applied to 0.3-0.4m tall cotton plants, Gossypium hi rsutum L., for control of the silverleaf whitefly, Bemisia argentifoli i Bellows and Perring (= Bemisia tabaci Gennadius, strain B), in green house tests. Plants from an uninfested greenhouse were splayed and pla ced in a greenhouse containing whitefly infested cotton plants. Applic ations were made weekly using a hand sprayer and maximum labeled rates for commercial products. The effects of applications were determined from counts of resting adult whiteflies on leaves and eggs and nymphs on 3.88 cm(2) leaf disks taken from fifth mainstem node leaves. A 10% solution of concentrate made from commercial chopped garlic provided c ontrol of whiteflies in both greenhouse and small field plots for seve ral days. However, the concentrate also contained unknown amounts of s oybean oil, an effective whitefly control agent. Commercial garlic oil at 2% concentration caused some leaf damage but evaporated within 48 h and gave little or no control of whiteflies. One percent garlic oil with an anti-evaporant did not provide additional protection. Combinat ions of 1 and 2% each of garlic oil and soybean oil gave some protecti on but were not significantly better than 2% soybean oil alone. One of two commercial garlic water products tested did not reduce the number s of resting whiteflies or eggs and nymphs on leaves. The other garlic water product caused reductions in adults, eggs and nymphs in some we eks of the 4-wk test period. Three commercial products containing garl ic oil as well as a complex of materials for plant growth were more ef fective than the garlic water products, but none exceeded the control attained by 2-4% soybean oil in its commercial formulation. In aggrega te, the results indicate that garlic oil alone or in complex formulati ons does not merit cost above that of soybean oil when control of the silverleaf whitefly on cotton is the sole objective.