Injury to Vegetable Crops from Herbicides Applied in Previous Years1

Some herbicides applied to corn or soybean can carry over and injure vegetable crops grown the following year. Injury and yield effects on vegetable crops from carryover of nicosulfuron and flumetsulam 1 yr after application to corn and from carryover of imazethapyr and imazamox 1 yr after application to soybean were evaluated. Experiments were conducted at Oakes, ND, on sandy loam soils with pH 7.7 in 1994 and pH 7.3 in 1996. Nicosulfuron and flumetsulam were applied to corn, and imazethapyr was applied to soybean at a standard herbicide rate (1××) (35, 56, and 70 g ai/ha, respectively) or 2×× rates in 1994 and at 1××, 2××, or 4×× rates in 1996. Imazamox was also applied to soybean at 1×× (35 g ai/ha), 2××, or 4×× rates in 1996. Cabbage, carrot, potato, onion, acorn squash, and tomato were planted in 1995, 1997, and 1998. In 1995, residual imazethapyr delayed tomato maturity but did not reduce tomato yield. Other vegetable crops were not injured by herbicide residues. In 1997, flumetsulam carryover injured plants and reduced yields of cabbage and squash; nicosulfuron carryover injured cabbage and onion plants and reduced onion yield; and imazethapyr carryover injured cabbage, onion, and tomato plants and reduced tomato yield. Most crop injury occurred only at the 2×× or 4×× herbicide rates. Potato and carrot were not injured by herbicide carryover. Herbicides applied to corn or soybean in 1996 did not carry over to injure any vegetable planted in 1998. The low rate of injury to vegetable crops in this study was mostly due to adequate soil moisture and warm summer soil temperatures, which enhanced microbial degradation of these herbicides and hastened their dissipation. Low clay and moderately low soil organic matter, and slightly alkaline soil pH, also promoted dissipation of some herbicides.Nomenclature: Flumetsulam; imazamox; imazethapyr; nicosulfuron; cabbage, Brassica oleracea L. var. capitata (L.); carrot, Daucus carota L.; corn, Zea mays L.; onion, Allium cepa L.; potato, Solanum tuberosum L.; soybean, Glycine max (L.) Merr.; squash, Cucurbita maxima L.; tomato, Lycopersicon esculentum Mill.Additional index words: Crop rotation, herbicide carryover, herbicide dissipation in soils, herbicide residues.Abbreviations: OM, soil organic matter; ××, standard herbicide rate.