Field dodder is a parasitic plant that attaches to the stems and leaves of broadleaf plants, including weeds, field crops, vegetables, and ornamentals, throughout most agricultural regions of the world. Effective field dodder control is extremely difficult to achieve, due to the nature of attachment and close association between host and parasite, which requires a highly effective and selective herbicide to destroy the parasite without crop damage. Previous studies have demonstrated the tolerance of certain tomato varieties to dodder parasitism. The aim of the present study was to evaluate the ability of sulfonylurea herbicides to control field dodder under greenhouse and field conditions. Two greenhouse studies and three field studies were conducted to evaluate the efficiency and crop selectivity of the sulfonylurea herbicides sulfosulfuron, rimsulfuron, halosulfuron, and flazasulfuron in controlling field dodder parasitizing tomato plants. Sulfosulfuron at 50 or 100 g ai ha−1 was effective and safe for tomato in field dodder control, while the other herbicides exhibited little or no dodder control.

Limited information exists on the tolerance of processing tomato to postemergence (POST) application of thifensulfuron-methyl. The tolerance of 13 processing tomato varieties, ‘CC337’, ‘H9144’, ‘H9314’, ‘H9478’, ‘H9492’, ‘H9553’, ‘H9909’, ‘N1069’, ‘N1082’, ‘N1480E’, ‘N1480L’, ‘N1522’, and ‘PETO696’, to POST applications of thifensulfuron-methyl at the maximum use rate (6 g ai/ha) and twice the maximum use rate (12 g/ha) for soybean was evaluated at two Ontario locations in 2001 and 2002. At 7 days after treatment (DAT), thifensulfuron applied POST caused 0.2 to 1% visible injury to CC337, H9144, N1082, N1522, and PETO696 at the high rate. H9553, H9909, N1069, and N1480E were the most sensitive to POST thifensulfuron-methyl, with visible injury ranging from 1 to 6% at the high rate. There was no visible injury to H9314, H9478, H9492, or N1480L at either application rate of thifensulfuron-methyl. By 28 DAT, no visible injury was noted to any variety, except for H9909, N1069, and N1480L, which showed minimal (<2%) visible injury. There were no adverse effects on shoot dry weight and marketable yield for any variety at either rate. Although thifensulfuron-methyl applied POST caused minimal and transient injury to the varieties tested, more tolerance trials with other fresh and processing tomato varieties are required to confirm these initial results.