Annual and perennial grasses can be selectively controlled in most broadleaf crops and landscapes using postemergence herbicides that control only grasses -- chemicals often referred to as “postemergence graminicides.” There are four graminicides labeled for use in horticultural crops -- fenoxaprop, fluazifop-p, sethoxydim and clethodim. Each graminicide is systemic (translocated) and has short-term soil residual (about 2 weeks). Although each herbicide kills grasses in the same way (acting upon the same site of action), they differ in their effectiveness on some grass weeds, safety on crops, and labeled uses.
The four postemergence graminicides labeled for use in landscape plantings are:
Fenoxaprop-ethyl – Acclaim Extra
Fluazifop-p – Fusilade II, Ornamec, Grass-B-Gon
Sethoxydim – Segment, Sethoxydim, Take-Away, Poast
Clethodim – Envoy, Arrow, others
Fenoxaprop-ethyl is labeled for postemergence control of summer annual grasses in cool-season turfgrasses and landscape beds. It is most commonly used to control crabgrass in fescue or bluegrass turf. It is not as effective as the other three graminicides on perennial grasses; therefore it is less commonly used in landscapes or nurseries. While safe on most broadleaf crops and ornamentals, it has been shown to injure certain cultivars of prostrate junipers and some azaleas.
Fluazifop-p is labeled for annual and perennial grass control in ornamentals, a few vegetable crops and some fruit crops. Fluazifop-p controls perennial grasses including bermudagrass and johnsongrass, but is weak on fescues. Under certain conditions fluazifop-p can be applied to tall fescue to control other weedy grasses, but high rates can kill tall fescue. Like fenoxaprop, fluazifop-p can be safely applied over the top of most broadleaf plants but has injured certain cultivars of prostrate junipers and azaleas.
Sethoxydim controls both annual and perennial grasses. Sethoxydim is sold under several different trade names, each with specific crops and uses. Some are labeled for use in vegetable and fruit crops or some warm-season turfgrasses. Search for a formulation specifically labeled for use in ornamental plantings. In my research, sethoxydim has provided slightly better control of crabgrass compared to fluazifop-p or clethodim, but is generally considered to be weaker on perennial grasses.
Clethodim is the only postemergence graminicide that controls annual bluegrass. It is generally considered to be one of the better graminicides for perennial grass control, including bermudagrass and fescues, but is somewhat less effective on large crabgrass compared to sethoxydim.
Getting the Most Out of Graminicide Treatments
Use the right product at the right time. Actively growing, young grasses are better controlled than established plants. The graminicides are more effective when applied to young, actively growing weeds, and less effective when applied to large, mature weeds. For example: Acclaim is most effective when applied to young plants, 1 to 3 tillers in size. At larger growth stages higher doses and repeated applications are required. Fusilade II and Envoy are more effective on bermudagrass in early summer (with 6 to 8 inches of new growth) than in late summer when plants are flowering.
Although these herbicides are selective and generally safe on most broadleaf plants, some injury to broadleaf plants and junipers has been reported (see Table 1). Fusilade is labeled for use on more herbaceous ornamentals than the other three herbicides, but it will injure Bar Harbor juniper and a few azalea varieties. Sethoxydim is not labeled on as many ornamental species, but it has not been reported to have variable injury between varieties of a species. Clethodim (Envoy) is labeled for a wide range of woody and herbaceous ornamentals but the addition of some surfactants to the spray has caused increased injury to tender herbaceous plants. Read the label carefully to determine which herbicide is labeled for your ornamental plants. And, test the safety of herbicides and surfactants before wide-scale use.
As stated above, the herbicides differ in their effectiveness on several weeds. Envoy is the only postemergence graminicide that controls annual bluegrass and is the best for fescue control. Crabgrass is controlled by all four graminicides but sethoxydim tends to provide the best overall control. See the table below for a comparison of POST-graminicides on some common grass weeds.
|Bar Harbor Jun.||No||No||OT||OT|
|OT= Over the Top; Dir = Directed applications only; * = on certain varieties; ? = unknown safety; No = not safe (based on label or research)|
For more detailed information about herbicides registered for use on ornamental plantings see the Southeastern US Pest Control Guide for Nursery Crops and Landscape Plantings.
|Control rankings: E = excellent, G = good, F = fair, P= poor|
For more detailed information about postemergence herbicide efficacy see the Southeastern US Pest Control Guide for Nursery Crops and Landscape Plantings.
Publication date: Sept. 21, 2018
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