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 commercial products were applied to 0.3-0.4m tall cotton plants, Gossypium hirsutum L., for control of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring (= Bemisia tabaci Gennadius, strain B), in greenhouse tests. Plants from an uninfested greenhouse were splayed and placed in a greenhouse containing whitefly infested cotton plants. Applications 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 control of whiteflies in both greenhouse and small field plots for several days. However, the concentrate also contained unknown amounts of soybean 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. Combinations of 1 and 2% each of garlic oil and soybean oil gave some protection but were not significantly better than 2% soybean oil alone. One of two commercial garlic water products tested did not reduce the numbers of resting whiteflies or eggs and nymphs on leaves. The other garlic water product caused reductions in adults, eggs and nymphs in some weeks of the 4-wk test period. Three commercial products containing garlic oil as well as a complex of materials for plant growth were more effective than the garlic water products, but none exceeded the control attained by 2-4% soybean oil in its commercial formulation. In aggregate, the results indicate that garlic oil alone or in complex formulations does not merit cost above that of soybean oil when control of the silverleaf whitefly on cotton is the sole objective.