AbstractFour greenhouse experiments were conducted in 1981-82 to determine the effect of different irrigation regimes on the phytotoxicity of prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] in four soils. The fresh weight of pigeon pea plants treated with prometryn at rates of 2.24 and 3.36 kg/ha was greatly reduced in San Anton soil (Mollisol) as the irrigation regime increased to a maximum. This finding confirms our assumption that excessive irrigation has contributed to the aggravated prometryn injury to pigeon pea plants. However, no significant fresh weight reduction was noted in Corozal (Ultisol), Coto (Oxisol) and Fraternidad (Vertisol) clays under increased irrigation regimes. Precaution should be taken not to overirrigate the soils having a texture similar to that of San Antón. To avoid crop injury precaution should also be taken not to use prometryn for weed control in pigeon peas during the prolonged rainy months of September to November.
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