Pigweed (Amaranthus spp.) interference in transplanted tomato (Lycopersicon esculentum)

Abstract

Interference of redroot pigweed (Amaranthus retroflexus L.) and prostrate pigweed (Amaranthus blitoides L.) in transplanted tomato (Lycopersicon esculentum Mill ‘GS12’) was studied in two field experiments in 1990 and 1991. Final yield was unaffected when the naturally occurring Amaranthus spp (mostly A. blitoides) were allowed to interfere with tomato plants for 28 days after transplanting in 1990. Significant yield reduction occurred when the weeds (mostly A. retroflexus) infested for only the first 14 days after transplanting in 1991. Further delay in weed removal treatments drastically reduced growth and yield of tomato plants and lowered fruit quality. Tomato plants kept weed- free for longer than 14 days after transplanting in 1990 or just for the same period in 1991 significantly increased tomato yields compared with tomato plants weed infested for the whole season. Yield was not significantly changed for various weed-free periods longer than 28 days after transplanting in 1990 and 14 days in 1991. The critical period of weed interference based on average yield in the two years was between 28 and 35 days after transplanting. Weeds emerging earlier or later than this period had no significant effects on the final yield provided the weeds were absent at this time.