Chemical Coverage on Corn and Sorghum Plants Sprayed with Lithium Sulfate Using an Airplane, Chemigation, or a Multifunction Irrigation-Pesticide Application System

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Abstract
A new method for irrigating and applying pesticides using moving truss irrigation systems has been developed (multifunction irrigation system [MFIS]). This system is uniquely designed to apply chemicals through pesticide spray nozzles that are independent of the irrigation nozzles. Also, spray nozzles can be moved vertically within the crop canopy while spraying. The experimental pesticide application system provided a means to evaluate spray deposition on corn, Zea mays (L.), and sorghum, Sorghum bicolor (L.) Moench, using a lithium sulfate monohydrate marker. The amount of lithium deposited at several locations on plants was measured for both crops. Applications with three spray methods were compared: (1) nozzles that moved vertically within the canopy while spraying (moving every 50-s either up or down while spraying or every 25-s which provided a double overlap of spray in any one direction), (2) traditional chemigation nozzles located above the crop canopy and spraying continuously, and (3) spray application using an airplane. All applications with MFIS were compared using high- and low-volume spray nozzles. In general, the most uniform coverage was obtained on both crops with the MFIS nozzle spraying at 50-s intervals. Low amounts of lithium were often measured on plants sprayed with chemigation or high-volume nozzles on MFIS spraying at 25-s intervals. The large volume of water applied with these two application methods (up to seven times more water) might have washed some of the water soluble lithium off of the plants. Aerial spraying provided the most uneven coverage of the application methods evaluated on both crops. Most of the chemical applied by airplane was recovered on the top leaf and distal leaf locations.

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