Turf Talk
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By Jeffrey Derr, Ph.D., Professor of Weed Science, Virginia Tech
erennial grassy weeds — including bermudagrass (commonly referred to as wiregrass), dallisgrass, quackgrass and johnsongrass — commonly infest lawns, athletic fields, roadsides and other turf areas, as well as landscape beds. These four weed species are referred to as creeping perennials since they spread vegetatively through rhizomes or stolons, as well as spreading by seed. If left uncontrolled, clumps of these weeds will continue to get larger. There also are clump-type perennial grassy weeds, such as orchardgrass and tall fescue. First, I’ll start with the easy part of this question — controlling perennial grasses in broadleaf ornamentals. Hopefully, I can fill up the space allocated to this article with my answer to this one, so I will not have to answer the harder question: How do I control perennial grasses in turf?
Control in conifers, broadleaf ornamentals and non-grass monocots
This group of plants, which includes trees, shrubs, herbaceous perennials, annual bedding plants and groundcovers, generally has very good toler-
ance to the selective postemergence grass herbicide group. Chemicals in this class include the systemic herbicides clethodim (Envoy Plus), fenoxaprop (Acclaim Extra), fluazifop (Fusilade II, Ornamec Over-The-Top and others) and sethoxydim (Segment). Among this group, fenoxaprop overall is less effective on perennial grasses than the other three herbicides. For perennial grass control, fenoxaprop has a better fit in turfgrass situations than in ornamentals. I often hear, “I sprayed a systemic herbicide, and it looked good for a month, but the weedy grass came back.” Although these products are systemic (and thus move downward into roots and rhizomes), multiple applications will generally be needed for long-term control. For a wellestablished creeping perennial, one application will not provide complete kill of underground plant parts, and uncontrolled buds on rhizomes will send up new shoots. Repeat applications will be needed to completely control underground plant parts. Some of these products, such as Fusilade II, require the addition of an adjuvant, either a crop oil concentrate or nonionic surfactant.
22 | VIRGINIA TURFGRASS JOURNAL January/February 2012 www.vaturf.org
If you’re making applications during hot, humid weather, avoid the use of crop oils, as these could lead to a contact burn on newly developed leaves or flower petals. I generally do not add anything to Segment, since an adjuvant has been built into the formulation, although some people add a surfactant or crop oil. Check the herbicide labels for any landscape cultivars to avoid. For example, certain cultivars of juniper and mondo grass (Ophiopogon) can be injured by overtop applications of fluazifop. Non-grass monocots would include such ornamentals as daylily, liriope, iris, lily and hosta. In these ornamentals, clethodim, fluazifop and sethoxydim can be used to selectively control bermudagrass, johnsongrass or quackgrass. If you want to control tall fescue, though, sethoxydim would be a better choice than fluazifop. In established woody ornamentals, another option for controlling quackgrass, tall fescue and orchardgrass would be a winter application of dichlobenil (Barrier, Casoron). The nonselectives glyphosate (Roundup PROMAX, others) and glufosinate (Finale) could also be