Control of postharvest decay of citrus fruit with calcium polysulfide

Incidence of green mold of citrus, caused by Penicillium digitatum, was reduced by 80% or more by the immersion of lemons or oranges for 1–4 min in warm (40.6–43.3°C) ‘liquid lime-sulfur’ (LLS) solution that contained 0.75% (wt vol) calcium polysulfide. The incidence of sour rot, caused by Geotrichum citri-aurantii, was reduced 35–70% by this treatment. LLS was similar in effectiveness to other treatments employed to control postharvest decay. Effectiveness was higher on lemons than oranges, and on green compared to yellow lemons. LLS did not stop sporulation, a benefit now obtained with some fungicides. The sulfide content of oranges, lemons, and grapefruit after LLS treatment was 31.9, 33.1, and 36.3 mg g, respectively. Rigorous cleaning of fruit with water applied at high pressure after LLS treatment slightly improved LLS efficacy; conversely, similar cleaning reduces the efficacy of sodium carbonate or borax–boric acid solutions now in use. The risk of injury to fruit by LLS was low. Fruit of one lemon and five navel orange cultivars were not visibly injured after LLS treatment for 3 min at 40.6°C followed by storage for 7 weeks at 10°C. After LLS treatment at 48.9°C, 5°C higher than needed for effective LLS use, only Lisbon lemons and Bonanza navel oranges were slightly injured. Sulfide concentration in LLS solution declined at a rate of about 7% every 24 h, this rate was similar between 25 and 65°C, and it was accompanied by the appearance of resistant deposits on the equipment. Additional losses would occur when some LLS solution is carried on fruit out of the tank. Although H2S in the air above LLS solution in pilot tests was less than 1 ml l and below the worker safety threshold of 10 ml l, LLS solution has an odor of H2S that can be a nuisance to workers. The disposal of used LLS solutions is more readily accomplished than other tank treatments whose disposal can be difficult because they contain synthetic fungicides, are caustic, or have a high salt concentration. Because LLS improves water penetration in soils and is commonly used for this purpose, in many locations it can be disposed of by application to agricultural soils. Published by Elsevier Science B.V.