Annual broadleaved weed control in transplanted tomato with clomazone in Canada

Field experiments were conducted from 2001 to 2003 at two locations in Ontario, Canada, to obtain weed control and crop tolerance data for clomazone use in transplanted tomato. The study focused on three problematic weeds: Abutilon theophrasti, Chenopodium album, and Solanum ptycanthum. Clomazone was tested at doses ranging from 120 to 840 g ha−1. The pre-transplant application of clomazone at a rate of 720 g ha−1 caused transient crop injury, with no impact on yield. Tomato yield increased as clomazone dose increased but there was no further increase in tomato yield above 600 g ha−1 at Harrow and 480 g ha−1 at Ridgetown. Although clomazone did not provide full-season biologically effective (>80%) control of these species, at least 50% mortality of weed populations for the entire season was possible for all species. To maintain full-season biologically effective control, clomazone would need to be applied at doses higher than those used in these tests. The data show that clomazone used alone is not a viable option for full-season control of A. theophrasti, C. album, and S. ptycanthum in transplanted tomato. Clomazone followed by herbicides already registered for use on transplanted tomato may be a more viable option for the control of these problem weed species while maintaining crop safety.