CHEMICAL COVERAGE ON SOYBEAN AND COTTON PLANTS SPRAYED WITH LITHIUM-SULFATE USING AN AIRPLANE, CHEMIGATION, OR A MULTIFUNCTION IRRIGATION PESTICIDE APPLICATION SYSTEM

Comparisons of spray coverage on soybeans, Glycine max (L.) Merrill, and cotton, Gossypium hirsutum L., were made using several application technologies. Lithium sulfate monohydrate was applied by three methods: (1) chemical application with the multifunction irrigation system (MFIS) so spray nozzles moved vertically within the canopy while spraying, (2) traditional chemigation with irrigation nozzles located above the canopy and spraying large volumes of water, and (3) spray application using an airplane. Methods 1 and 2 were compared using high- and low-volume nozzles. The most lithium was recovered on soybean and cotton plants sprayed with MFIS using the low-volume nozzle moving downward every 50 s. Lithium concentrations on the plant were low when applications were made with the chemigation nozzles. The distribution of chemical within the plant canopy varied among treatments, and the best vertical coverage on soybeans was obtained using chemigation with high-volume nozzles. Obtaining spray penetration into the inner portion of soybean plants was difficult. MFIS using the high-volume nozzle oriented and moving upward every 25 s was the only application that provided even coverage on the outer and inner portions of soybean plants. Distribution of lithium on cotton plants was more uniform than on soybeans. More lithium was deposited on cotton plants using the MFIS with low-volume nozzles than with any other method. In contrast, the most uniform coverage on cotton was obtained with chemigation using high-volume nozzles. Distribution of spray applied by airplane on both crops was uneven, and more than two-thirds of the chemical was recovered on the fully exposed leaves on the top half of the plant and on the outer leaves of the canopy.