Influence of Date and Method of Metribuzin Application for Quackgrass Control in Alfalfa1

Abstract

AbstractIn Wisconsin, alfalfa (Medicago sativa L.) occupies about 1.2 of the 1.6 million hectares of forage grown. However, quackgrass (Agropyron repens L.) causes deleterious effects on alfalfa productivity. In order to evaluate alfalfa tolerance to, and quackgrass control by, metribuzin [4‐amino‐6‐rert‐butyl‐3‐(methylthio)‐as‐triazin‐5 (4H)‐one] applied postemergence, established stands of ‘Vernal’ alfalfa at two field locations were treated at four growth stages during 1978‐1979 and 1979‐1980. Metribuzin was applied to Piano silt loam (finesilty, mixed, mesic Typic Argiudoll) in early fall and late spring (growing alfalfa) and in late fall and early spring (dormant alfalfa) at the rate of 1.12 kg/ha, using either water or dry fertilizer as the carrier. Weed control, crop tolerance, and influence of metribuzin on botanical composition and dry matter yield were evaluated. Alfalfa tolerance and quackgrass suppression depended upon the growth stage at the time of application. In both experiments, alfalfa tolerance, and. full season alfalfa and herbage dry matter yields were greater when dormant alfalfa was treated than when growing alfalfa was treated. In general, spring dormant applications were superior in controlling weeds and resulted in greater alfalfa yields than fall dormant applications. For both studies, spring treatments improved botanical composition of the forage harvested in the first cutting, as compared to fall treatments. Although differences in yields were found between methods of application, they were not constant throughout the dates. These data indicate that season or method of application were not as determinant as the growth stage at the time of treatment in providing consistent herbicidal response from metribuzin.