Abstract
Spray application tests of copper fungicides were conducted to improve melanose and greasy spot control while minimizing the amount of copper (Cu) applied, particularly on grapefruit. Initial Cu deposition and weathering of Cu fungicides on fruitlets were determined in relation to spray volume, Cu concentration, fruit growth and weather conditions. Reducing spray volume to 1168 l/ha (125 gal/ac) increased deposition with no sacrifice of coverage. Generally, 1168 l/ha was more effective than 235 l/ha (25 gal/ ac) since 235 l/ha resulted in less coverage of fruit if the leaf canopy was dense. After application, Cu concentration decreased primarily as a function of fruit surface expansion. Weathering accounted for an average loss of 19% over the period of 10 to 16 days and 43% for periods of 19 to 22 days. Intervals between sprays may be adjusted to as frequently as 2 weeks shortly after bloom, when fruit surface area is small and percent surface expansion is greatest, to 4 week intervals later in the spring when percentage increase in surface area is less. Spray burn from Cu-oil sprays occurred in the early summer with the combination of 4.5 kg/ ha metallic Cu with oil at 46.5 l/ha in 235 l/ha water. A protocol of using less oil with higher Cu (9.3 l/ha oil with 4.5 kg/ha Cu) or higher oil with lower Cu (46.9 l/ha oil with 2.25 kg/ha Cu) in summer reduced spray burn and gave satisfactory melanose and greasy spot control.
