Coverage of Onion Foliage as a Requirement for Control of Onion Thrips on Onions, 1984

Four ground and 1 aerial application were evaluated for coverage of onion plants. Potted onion plants, with 6 leaves each, were used as indicators of the coverage by the various pieces of application equipment. These plants were placed within the rows of commerieal fields and replaced onion plants which were removed. Five potted onion plants per field were placed in a diagonal pattern encompassing 5 adjacent double-rows approximately 50 ft in length. Placing the onion plants along this diagonal helped to reduce any variation along the spray boom, as well as any variation which might have occurred as the boom traveled through the sprayed area. The area within the field which contained the potted plants was marked with flags for the benefit of the applicator and the application was observed to be certain that it was made over the test area. Fluorescent dye, at the rate of 300 g/acre, was added to the water of each piece of application equipment. All applications were made on 9 Aug, and the plants were returned to the laboratory the same day. All leaves were then examined under an ultraviolet light and rated for fluorescent dye deposition (coverage) according to a scale of 1 (sparse) to 10 (nearly solid). Separate ratings were made for the top half and bottom half of each leaf as well as the base of the plant, i.e. where the foliage leaves join the bulb. The entire leaf rating which is also listed is simply the average of the bottom and top halves.