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

Abstract

. Effect of imazethapyr and imazamox soil residues on several vegetable crops grown in Ontario. Can. J. Plant Sci. 78: 647-651. 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.

Determination of imazethapyr residues in soil and grains after its application to soybeans

“…30) In another study conducted in soils with a high pH (alkaline, cracking clay, pH 8.6) no residue was found in the top 10 cm of soil; however, 0.6-1.6 ng/g of imazethapyr was reported at 20-40 cm soil depths after four months of imazethapyr application. 21) O'Sullivan et al 21) demonstrated the marked effect of rainfall on imazethapyr persistence and concluded that the herbicide was lost from the profile either by leaching to below 40 cm or by microbial breakdown due to the wetter years' being more conducive to microbial activity in the topsoil. The bioassay results showed a marked effect of rainfall on residue persistence.…”

“…A low concentration of imazethapyr in soil is also compensated for high microbial activity, which increases the rate of degradation. 6,8,30,[32][33][34][35][36] O'Sullivan et al 21) reported imazethapyr residues mainly in the top 0-10 cm soil fraction; however, some quantity of imazethapyr residue was found at 10-20 and 20-40 cm depths, also. Besides the organic matter, clay can also play an important role in the degradation of pesticides.…”

“…6,8,21,[26][27][28][29][30][31][32] Dissipation of imazethapyr is faster in soils with a high pH and low adsorption since the amount available in the soil solution for microbial transformation is greater. A low concentration of imazethapyr in soil is also compensated for high microbial activity, which increases the rate of degradation.…”

“…14,19) Reports have shown that residues of ALS inhibitors or their metabolites can persist into the following growing seasons. 20) Phytotoxicity to sensitive crops grown in rotation such as canola and lentils, mustard, or sugar beets 18,[21][22][23][24][25] is reported as a result of prolonged persistence in the soil.…”

Response of four spring-seeded cover crops to residues of selected herbicides

“…Injury of sensitive crops to herbicide residues that are grown 1 yr after herbicide application can result in yield reductions due to herbicide persistence (Curran et al 1996;Helling 2005). For example, several vegetable crop species are sensitive to residual commercial herbicides like imazethapyr (O'Sullivan et al 1998), mesotrione (Felix et al 2007), and saflufenacil (Robinson and McNaughton 2012). A related concern for which growers lack sufficient understanding is the effect of residues from herbicides applied in the previous year on cover crop growth and effectiveness.…”