RESPONSES OF SPRING BARLEY (HORDEUM-VULGARE L) AND SPRING WHEAT (TRITICUM-AESTIVUM L) TO FOLIAR OR ROOT ENTRY OF CHLORSULFURON

The objective of this study was to determine whether chlorsulfuron app lied post-emergence enters more by roots or by foliage of spring barle y (Hordeum vulgare L.) and spring wheat (Triticum aestivum L.). Such d ifferences could explain observed variation in tolerance between culti vars and interactions with environmental factors. Two experiments were conducted in the glasshouse, where chlorsulfuron was applied to eithe r foliage, soil or combined foliage and soil. In the first experiment, application of chlorsulfuron to foliage had less effect on dry matter (DM) than the combined treatment in two cultivars each of barley and wheat. Root DM was more sensitive to chlorsulfuron than shoot DM in bo th species. Shoot DM of wheat cv. Vulcan tended to be more sensitive t o chlorsulfuron than cv. Olympic or both barley cultivars. In the seco nd experiment, application of chlorsulfuron to foliage of two barley c ultivars reduced shoot DM by 30-40%, compared with about 70% after soi l or combined applications. Root DM was more sensitive than shoot DM, with reductions of 80% after soil or combined applications, and about 50% after foliar application. Root entry of chlorsulfuron in barley th us leads to greater crop injury from the herbicide than foliar entry, and this may explain why rain soon after application leads to more inj ury from the herbicide. If no rain follows application, uptake of chlo rsulfuron primarily by foliage may still reduce barley root growth in some circumstances, which will impair the ability of plants to take up nutrients and water, and the consequences for grain yield will be mos t severe in drought conditions. Differences in root or foliar entry di d not explain cultivar differences in tolerance to chlorsulfuron measu red previously in the field.