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Disease Control and Pest Management

Comparative Fungitoxicity of Captafol and Metalaxyl to Phytophthora capsici. G. C. Papavizas, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research, Beltsville, MD 20705; J. H. Bowers, Science and Education Administration, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 71:123-128. Accepted for publication 20 June 1980. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1981. DOI: 10.1094/Phyto-71-123.

In vitro fungitoxicity of the nonsystemic fungicide cis-N-[(1, l, 2, 2-tetrachloroethyl)thio]-4-cyclohexene-1, 2-dicarboximide (captafol) and the systemic fungicide N-(2, 6-dimethylphenyl)-N-(methoxyacetyl) alanine methyl ester (CGA-48988, metalaxyl) to five isolates of Phytophthora capsici was studied in lima bean agar and broth. Captafol was more effective than metalaxyl in reducing growth in solid and liquid media, inhibiting zoospore release from sporangia, stopping zoospore motility, and inhibiting germination of sporangia and zoospores. Metalaxyl was more effective than captafol in inhibiting production of sporangia and oospores and equally as effective as captafol at low concentrations (less than 2.5 μg active ingredient [a.i.] per milliliter of medium) in inhibiting oospore germination. At fungicide concentrations from 2.5 to 10 μg/ml, metalaxyl inhibited oospore germination more than captafol. Approximately 40% of oospores of P. capsici germinated in distilled water after 16 days of incubation. Water extracts from tops (stems and leaves) and roots of pepper plants that had been drenched with metalaxyl 7, 11, 17, and 24 days before the assay completely inhibited germination of sporangia and reduced growth in liquid medium. Similar extracts from captafol-drenched plants were much less inhibitory. Water extracts from tops of pepper plants that had been drenched with metalaxyl 1, 7, and 21 days before extract preparation reduced or eliminated oospore production. Extracts from captafol-drenched plants did not. A single soil drench containing 3.0 mg a.i. of metalaxyl applied to two-leaf plants was sufficient to effectively protect pepper plants against foliar infection for at least 7 days after drenching.