RATE OF METRIBUZIN BREAKDOWN AND RESIDUE EFFECTS ON ROTATION CROPS

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Abstract
Field studies on Prince Edward Island loam to fine sandy loam soils from 1977–1980 evaluated the rate of breakdown of metribuzin (4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one) and soil residue effects on crops grown in rotation with potatoes (Solanum tuberosum L.). Yields of winter rye (Secale cereale L.) seeded in September and red clover (Trifolium pratense L.) seeded in spring were not reduced with metribuzin applied at rates of 0.5, 1.0, and 1.5 kg/ha to the preceding potato crop. Yields of barley (Hordeum vulgare L.) and timothy (Phleum pratense L.) seeded the next spring after metribuzin were significantly reduced in the first experiment at applied rates of 1.0 and 0.5 kg/ha, respectively, but not in the other two experiments. Barley and timothy yields apparently were reduced in the second but not the third experiment at an applied rate of 1.5 kg/ha. The rate of breakdown of metribuzin was rapid in all three experiments but slower in 1977 than in the other 2 yr. The half-life of metribuzin averaged over rates applied was 39 days in 1977, 32 days in 1978, and 30 days in 1979 in P.E.I. soils. From these data, it is doubtful that metribuzin will persist in sufficient amounts in P.E.I. soils to adversely affect crops of winter rye or red clover grown in rotation but may result in some yield reduction of barley at the high rate of application of 1.0 kg/ha and reduction in timothy yield at applied rate of 0.5 kg/ha in those years when rate of breakdown was slow.Key words: Metribuzin, residue, red clover, timothy, winter rye, barley

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