Translocation of Metalaxyl in Soybean Plants and Control of Stem Rot Caused byPhytophthora megaspermaf. sp.glycinea

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Abstract
Metalaxyl, applied to seeds, leaves, cotyledons and soil, was translocated mainly in an upward direction in soybean plants. Treatment of seeds with metalaxyl resulted in partial control (40% survival) at 30 mg/100 g of seeds and complete control (100% survival) at 200 mg/100 g of seeds of stem rot when wounded hypocotyls of 7-day-old plants were inoculated with P. megasperma f. sp. glycinea. The percentage distribution of metalaxyl (measured by gas chromatography) in 7-day-old plants after seed dressing (200 mg/100 g of seeds) was 79.2% in the cotyledons, 20.3% in leaves and stems, and less than 0.12% in roots. When 14C-metalaxyl (48.7 .times. 104 dpm per seed) was applied to seeds, 91.5% of the extractable radioactivity (metalaxyl and derivatives) in 7-day-old plants was detected in the cotyledons, 5.8% in leaves and stems, and 2.57% in roots. The extract of cotyledons from 7-day-old plants treated at 200 mg/100 g of seeds and assayed by TLC, contained 40% 14C metalaxyl, while 60% of the radioactivity remained at the origin of the chromatogram. When 14C-metalaxyl was applied to a leaf or to a cotyledon, 99% of the recovered radioactivity remained in the treated leaf or cotyledon. After 14C-metalaxyl was applied to soil by drenching, 80.5% of the radioactivity taken up by the plant in 7 days accumulated in the cotyledons, 15.1% in the other aerial portions, and 4.4% in the roots.