Comparative Fungitoxicity of Captafol and Metalaxyl toPhytophthora capsici

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Abstract
In vitro fungitoxicity of the nonsystemic fungicide cis-N-[(1,1,2,2- 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 5 isolates of P. 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 (< 2.5 .mu.g active ingredient [a.i.]/ml medium) in inhibiting oospore germination. At fungicide concentrations from 2.5-10 .mu.g/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 [Capsicum annuum] 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 2-leaf plants was sufficient to effectively protect pepper plants against foliar infection for at least 7 days after drenching.