Chemical weed control in transplanted tomatoes

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Virginia Polytechnic Institute

Weed control in transplanted tomatoes with diphenamid, trifluralin, and paraquat was evaluated under field conditions on a predominantly Grosclose silt loan soil on the Virginia Polytechnic Institute Horticulture farm near Blacksburg, Virginia. The herbicides were used singularly and in certain combination at various rates and times of application. Diphenamid applied on previously cultivated soil at two weeks after transplanting tomato plants gave superior weed control with no apparent injury to tomato plants. However, the eame herbicide gave poor post emergence weed control and yield of tomatoes when applied after small weeds were present. Growth of tomato plants·was. suppressed by competition from weeds; however, ripening of tomatoes was accelerated as compared to untreated cultivated plants. Trifluralin applied pre planting also gave good weed control, but when applied post transplanting weed control was poor po•eibly due to incorporation technique. The higher rate of this herbicide seaweed a decrease in growth and yield of the crop. A mixture of diphenamid plus paraquat was effective on small weeds, but this treatment has less possibilities in commercial production as the spray cannot be directed to avoid contact injury to tomato plants.