Cover Story
Taking Grass Weeds out of Non-mowed Fine Fescues with ACCaseinhibiting Herbicides By Peter Landschoot, Ph.D., Professor of Turfgrass Science
O
ne of the toughest tasks for a turfgrass manager is to control grass weeds without injuring desirable grasses. One group of postemergence herbicides, the acetyl-CoA carboxylase-inhibiting herbicides (or ACCase-inhibiting herbicides), is particularly important for selective suppression or control of stubborn weeds like quackgrass, wirestem muhly, tall fescue, bentgrass, and annual grasses in non-mowed fine fescue stands (Figure 1). Achieving successful weed control with ACCaseinhibiting herbicides requires some experience and careful examination of herbicide labels for rates, timing of applications, and use of surfactants.
General characteristics of ACCase-inhibiting herbicides The ACCase-inhibiting herbicides are foliar absorbed and move through phloem to the growing points of target weeds. Hence, they are classified as systemic herbicides. Generally, herbicides in this group act slowly on susceptible grass weeds, taking two to three weeks to express complete suppression or control following
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Pennsylvania Turfgrass • Winter 2022
applications. The mode of action of ACCase-inhibiting herbicides involves inhibition of the acetyl-CoA carboxylase enzyme (abbreviated ACCase) in plants. ACCase is an essential enzyme catalyst in fatty acid and cell membrane synthesis. The ACCase inhibitors are important for controlling weed grasses in broadleaf crops such as soybeans, in ornamental beds, and in stands containing some wildflower species because of the high degree of tolerance of broadleaf plants to these herbicides. Fine fescue species are known to have a high degree of tolerance to most ACCase-inhibiting herbicides, perhaps because of a less sensitive ACCase enzyme or the ability to quickly degrade the herbicide (Al-Khatib, 2019). Sedges are also tolerant of ACCase-inhibitors, thus none of these herbicides are labeled for control of nutsedge or false green kyllinga.
The PROPs, FOPs, and DIMS The ACCase-inhibiting herbicides include two major subgroups, the aryloxyphenoxypropionates and the cyclohexanediones. To simplify terminology, aryloxyphenoxypropionates are often referred
