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Control of Phytophthora Root and Foot Rot of Citrus with Systemic Fungicides Metalaxyl and Phosethyl Aluminum. R. M. Davis, Assistant Professor, Texas A&I University Citrus Center, Weslaco 78596. Plant Dis. 66:218-220. Accepted for publication 8 June 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-218.

Soil drenches of metalaxyl (100 mg a.i./L) and foliar sprays of phosethyl aluminum (2,000 mg a.i./L) reduced root rot of potted sour orange seedlings inoculated with Phytophthora parasitica. Metalaxyl at a higher rate (200 mg a.i./L) was phytotoxic to potted citrus but not to field trees. Lesions caused by P. parasitica on the trunks of 2-yr-old trees were controlled with foliar sprays of phosethyl aluminum or treatments with metalaxyl as either a soil drench or trunk paint. Metalaxyl as a trunk paint was the only treatment that arrested development of lesions on 5-yr-old trees. In a bioassay using zoospores of P. parasitica, systemic fungicidal activity was detected in bark disks from the trunks of 2-yr-old trees for at least 12 wk following application of metalaxyl as a trunk paint. Activity of metalaxyl as a soil drench was detected for 6 wk and activity in phosethyl aluminum treatments for 8 wk. Activity in trunks of 5-yr-old trees treated with metalaxyl as a bark paint was detected for at least 21 wk. Little or no activity was found in 5-yr-old trees treated with phosethyl aluminum or soil drenches of metalaxyl.