Volume 2, Issue 9 (October 2005)
Development and Testing of a Recommendation System to Schedule Copper Sprays for Citrus Disease Control
Copper (Cu) fungicides are contact action products commonly used for control of citrus fungal diseases. Cu residues are subject to weathering (rain and wind) and dilution from fruit expansion during early growth. Growers often over-spray, which leads to inadequate disease control, or under-spray, which leads to environmental concerns and Cu phytotoxicity to fruit. Fruit surface Cu residue data were collected, developed into an expert recommendation system, and tested for accuracy in predicting fruit surface residues to determine need to re-spray. Trees were sprayed with different amounts of copper fungicides using different water volumes per tree. Cu on fruit surfaces was analyzed over time. These data were used to build a Cu spray scheduling recommendation system (CuSSRS) that predicts initial residue after spraying, depending on spray volume rate and Cu content and then predicts dilution and loss of the Cu residue as fruit grow and rainfall weathering occurs. The model indicates a warning and a danger level of low residual Cu based on necessary levels of Cu for disease control, thus providing the grower with advanced notice of the need to re-spray. The system was grower tested for six years. Verification data on actual versus predicted residues were collected over a three-year period. Success in preventing fungal disease fruit blemishes was determined also. These tests indicated the CuSSRS works reasonably well and in some years can reduce the number of copper fungicide sprays needed.