Residual Phytotoxicity of Chlorsulfuron in Two Soils

Abstract

Chlorsulfuron {2‐chloro‐N‐[(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl) amino carbonyl] benzenesulfonamide} selectively controls broad‐leaf weeds in winter wheat (Triticum aestivum L.), but also is extremely persistent in soil, resulting in residual injury to succeeding crops that are susceptible to chlorsulfuron. To determine the factors affecting chlorsulfuron degradation, the effect of environmental variables and method of application on chlorsulfuron persistence was measured in a loam and sandy loam soil using a corn (Zea mays L.) root bioassay. Increasing soil temperature from 20 to 40°C decreased chlorsulfuron persistence, with significant differences in chlorsulfuron concentration occurring 31 d after application to the sandy loam soil. Soil water level affected chlorsulfuron persistence only in the loam soil, where increasing the soil water level decreased persistence. Adding wheat residue to the soils increased chlorsulfuron persistence in the sandy loam, but not in the loam soil. One possible explanation for this reduced degradation in the sandy loam was a shift in pH toward basicity, as the addition of 0.050 kg kg−1 wheat residue raised the pH from 6.1 to 7.2. In the loam soil, the wheat residue did not affect soil I~H. Chlorsulfuron persistence was affected by texture, with longer activity occurring in the loam soil in all studies. Incorporating chlorsulfuron caused a greater loss of chlorsulfuron activity in the sandy loam, indicating that incorporation may influence chlorsulfuron persistence.

Persistence of Sulfosulfuron Under Wheat Cropping System

“…Soil pH has a dramatic effect on solubility and hydrolytic breakdown of sulfonylureas herbicides. These herbicides are rapidly degraded in low pH soils by acid hydrolysis and persist for longer period in soils having high pH and clay content (Anderson and Barrett 1985). Therefore, incidences of sulfonylurea injury to following crops are higher in high pH soils.…”

A review of the activity, fate and mode of action of sulfonylurea herbicides

“…The presence of growing wheat plants in metsulfuron-methyl treated soil did not affect the duration of activity. 49 Increased soil moisture and temperature decreased chlorsulfuron persistence. 43,44,50,51 Anderson and Barrett ,@ however, observed that soil moisture affected chlorsulfuron degradation in a loam but not in a sandy loam soil.…”

“…Greater persistence of chlorsulfuron was observed in soil with high than with low organic matter although pH may also have been different.46v47 Chlorsulfuron performance is unlikely to be affected by changes in soil organic matter or ash resulting from conventional cultivations but large local concentrations of straw ash on the soil surface might give rise to variable performance in minimum tillage systems.48 Metsulfuron-methyl, however, retained on surface straw residues, was washed off by simulated rain and resulted in increased duration of activity. 49 Chlorsulfuron disappearance was rapid in the first 15 days after treatment after which there was a slower rate in all four soils examined in the 1aborato1-y.~~ Calculated half-lives on soil with pHs 6.2,7.1,7-7 and 8.1 were 33,60, 82 and 99 days respectively, if data for the period 0-15 days were included or 89,105,136 and 143 days respectively if these data were excluded. Drying of soil samples followed by rewetting may have stimulated the microbial population.…”

In vitro selection for improved chlorsulfuron tolerance in barley (Hordeum vulgare L.)

“…Chlorsulfuron breakdown is slow under alkaline soil pH (Groves, 1985) and low soil moisture regimes (Anderson & Barrett, 1985), both of which occur in the North American prairies. This slow chlorsulfuron breakdown restricts the subsequent crops that can be grown in rotation as many are sensitive to this residual herbicide.…”