IMPROVED CONTROL OF GREEN MOLD OF CITRUS WITH IMAZALIL IN WARM WATER COMPARED WITH ITS USE IN WAX

The effectiveness of imazalil for the control of citrus green mold (ca used by Penicillium digitatum) improved significantly when fruit were treated with heated aqueous solutions of the fungicide as compared wit h the current commercial practice of spraying wax containing imazalil on fruit. When applied at less than 500 mu g.ml(-1) in solutions heate d to 37.8 degrees C, control of postharvest green mold of citrus was s ignificantly superior to applications of 4,200 mu g.ml(-1) imazalil in wax sprayed on fruit at ambient temperatures. The improvement in imaz alil efficacy was obtained with a decrease in fungicide residues on th e fruit. Residues of about 3.5 mu g.g(-1) imazalil deposited by the ap plication of imazalil in wax reduced the incidence of green mold on le mons from 94.4% among untreated controls to 15.1%, whereas an equal re sidue deposited by passing fruit through heated aqueous imazalil reduc ed green mold incidence to 1.3%. Similar differences were found in tes ts with oranges. Residues of 2 and 3.5 mu g.g(-1) imazalil were needed to control the sporulation of P. digitatum on oranges and lemons. res pectively. The mode of application of imazalil did not influence contr ol of sporulation. The influence of:immersion time, imazalil concentra tion, and solution temperature on imazalil residues on oranges and lem ons was determined in tests using commercial packing equipment, and a model that describes residue deposition was developed. Residues after a 30- or 60-s treatment in heated aqueous imazalil were sufficient to control sporulation, but residues after 15-s treatments were too low a nd required an additional application of 1,070 mu g.ml(-1) imazalil in wax to deposit an amount of imazalil sufficient to control sporulatio n. An imazalil-resistant isolate of P. digitatum was significantly con trolled by heated aqueous imazalil. The incidence of green mold of nav el oranges was reduced from 98.8 to 17.4% by treatment in 410 mu g.ml( -1) imazalil at 40.6 degrees C for 90 s. However, control of the resis tant isolate required imazalil residues on the fruit of 7.9 mu g.g(-1) , which is within the U.S. tolerance of 10 mu g.g(-1) but above the 5 mu g.g(-1) tolerance of some countries that import citrus fruit from t he United States.