Effect of imazethapyr and imazamox soil residues on several vegetable crops grown in Ontario

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Abstract
Use of imidazolinone herbicides has often resulted in carryover effects on sensitive rotational crops. The effect of soil residues of imazethapyr and imazamox on several vegetable crops grown in rotation with soybean (Glycine max [L.] Merr.) was investigated over a 5-yr period in southern Ontario. Imazethapyr at 0, 100 and 200 g a.i. ha–1 was applied preemergence to soybean from 1991 to 1993. Imazethapyr at 0 and 100 g a.i. ha−1 and imazamox at 35 g a.i. ha−1 was applied postemergence to soybean in 1994 and 1995. Cabbage (Brassica oleracea L.), potato (Solanum tuberosum L.), tomato (Lycopersicon esculentum L.), sweet corn (Zea mays L.) and cucumber (Cucumis sativus L.) were planted each spring, 1 and 2 yr following preemergence imazethapyr application and 1 yr following postemergence imazethapyr and imazamox application. Potato and sweet corn showed visual injury symptoms 1 yr after preemergence imazethapyr application in 2 of 3 yr while cabbage, tomato and cucumber showed visual injury symptoms all 3 yr. Minor visual injury symptoms did not reduce yields. Cabbage was the most sensitive to imazethapyr soil residues. Cabbage yields were reduced in 2 of 3 yr, due to carryover residues from 100 and 200 g ha−1 of imazethapyr applied the previous year. Tomato and potato also showed yield reductions in 2 of 3 yr due to imazethapyr soil residues. The degree of injury and yield reduction was influenced by soil pH and soil moisture. There were no yield reductions for any crop 2 yr after imazethapyr application. Imazamox soil residues were less injurious than imazethapyr soil residues to vegetable crops grown in rotation and resulted in only minor visual injury symptoms and no yield reductions on tomato, potato or cabbage. Key words: Crop tolerance, yield, rotation, herbicide carryover

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