Lime-Sulfur Bath Curbs Citrus Mold, Rot

California researchers say giving oranges and lemons a warm bath in a lime-sulfur solution might offer packinghouses an effective and environmentally friendly way to quell green mold and sour rot. These fungi are among the worst threats to stored citrus.

Chemically, lime-sulfur is calcium sulfide, widely used as a soil conditioner. This fact may help enable packinghouses to gain approval to dispose of fruit "bathwater" on soil or in sewer systems.

In preliminary lab tests, researchers dipped oranges and lemons in a 3-percent solution of lime-sulfur in water heated to about 105 degrees F. The tactic reduced up to 99 percent of green mold (Penicillium digitatum) and up to 65 percent of sour rot (Geotrichum citri- aurantii). Joseph L. Smilanick with the Agricultural Research Service in Fresno, Calif., led the study.

Today in Parlier, Calif., Smilanick plans to describe the technique to visitors at a scheduled groundbreaking ceremony for a new, 78,000-square-foot ARS research center. Within about two years, ARS labs now in Fresno will move to the Parlier complex, called the ARS San Joaquin Valley Agricultural Sciences Center.

Currently, scientists are scrutinizing the dipped fruits to ensure they retain their taste and texture. ARS is doing this jointly with Sunkist Growers, Exeter, Calif.; Best Sulfur Products, Fresno; and the University of California's Citrus Research and Extension Center, Lindcove, Calif.

Larger tests are under way, using a commercial-size packing-line at the Lindcove center. Scientists expect to try the dip with grapefruits and mandarin oranges, as well. They will also conduct lab tests to determine whether calcium and sulfate residues are easily removed by rinsing the fruit. A grant from the California State Department of Pesticide Regulation helps fund the research.

Use of lime-sulfur as a fungicide dates to the 1800's, but the ARS-led team is apparently the first to extensively test potential packinghouse application of the compound to safeguard citrus.

Scientific contact: Joseph L. Smilanick, ARS Horticultural Crops Research Laboratory, 2021 So. Peach Ave., Fresno, CA 93727, phone (209) 453-3084, fax (209) 453-3088, Jsmilanick@aol.com.