PRE- AND POSTHARVEST TREATMENTS TO CONTROL GREEN MOLD OF CITRUS FRUIT DURING ETHYLENE DEGREENING.

Authors: Smilanick, Joseph; Mansour, Monir; SORENSON, DAVID - FRUIT GROWERS SUPPLY

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2005
Publication Date: 1/1/2006
Citation: Smilanick, J.L., Mansour, M., Sorenson, D. 2006. Pre- and Postharvest Treatments to Control Green Mold of Citrus Fruit During Ethylene Degreening. Plant Disease. 90:89-96.

Interpretive Summary: Citrus fruit rot after harvest, particularly during wet years when treatment with ethylene gas is used to improve the peel color of the fruit. Two approaches to minimize rot losses, fungicide sprays to trees before harvest, and drenching bins of harvested fruit after harvest with fungicides, were investigated. We developed economical and effective measures by both approaches; the best fungicide (thiophanate methyl) for tree application was identified, and a new fruit bin-drenching regime, using the fungicide thiabendazole in combination with sodium bicarbonate, was described.

Technical Abstract: Two approaches, fungicide applications to trees before harvest and drenching fruit with fungicides promptly after harvest, were evaluated to minimize postharvest losses due to citrus green mold, caused by Penicillium digitatum, particularly among fruit subjected to ethylene gas after harvest, a practice termed “degreening” that eliminates green rind color. Grove applications of thiophanate methyl (TM) controlled green mold consistently. In five tests, the average green mold incidence among navel oranges was 16% where TM had been applied one week before harvest followed by inoculation of the fruit and degreening for 3 days in ethylene gas, while among similarly handled fruit not treated with TM the incidence was 89.5%. The effectiveness of aqueous treatments of thiabendazole (TBZ), applied to harvested fruit in bins before degreening, was greatly enhanced by mild heating (41°C) of the solution, adding sodium bicarbonate, and immersing fruit, rather than drenching them, with the solution. TBZ residues in lemons approximately doubled if treated at 41°C compared to 24°C. These measures improved TBZ performance; even an isolate of P. digitatum with a high level of TBZ resistance was significantly controlled. Neither TM applied before harvest nor TBZ and sodium bicarbonate applied after harvest influenced the rate of green color removal of oranges during ethylene degreening, although sodium bicarbonate slightly reduced the rate of color change of lemons. In semi-commercial tests with naturally inoculated fruit, TBZ and sodium bicarbonate treatment reduced green mold incidence from 11% among untreated oranges to 2%.