Four foxtail species may be found in the region: yellow (Setaria pumila), knot-root (Setaria parviflora), green (Setaria virids) and giant (Setaria faberi). In the southeastern region, the two most common species are yellow and knot-root foxtail, and they are spreading into managed and unmanaged grazing and hayfield stands. Although it may provide early-season grazing opportunities in perennial grass stands, by mid-to-late summer, their seedheads are everywhere, cattle won’t graze it, and hay growers avoid baling it. Research suggests that planning ahead for timely weed control associated with proper management practices could allow for both early summer grazing and successful weed suppression.
Foxtail Management
One of the most difficult challenges in forage weed management is removing certain grassy weeds from desirable grass forages. In addition, it is important to know how to identify the species occurring in the area early in the season to provide proper control. The main difference between yellow and knotroot foxtail is found in their roots. Knotroot foxtail has a knotty rhizome (underground stem) that allows it to overwinter and regrow each spring, which also makes it more difficult to control. In contrast, yellow foxtail is a true annual species and only survives by seed production.
When plants are young, livestock will actively graze foxtail, and previous research conducted by the Auburn University team determined that both yellow and knot-root foxtail in the vegetative stage consistently maintained at least 10% crude protein and at least 70% total digestible nutrients (TDN) on a dry matter basis. However, in mid-to-late summer, foxtail seedheads develop, and they are unpalatable mainly due to their bristles (or awns), which can cause ulcers in the mouths of horses and interfere with livestock grazing. Also, foxtail plants are prolific seed producers, and little is known about how long seed may remain viable in the soil.
An integrated pest management (IPM) approach is the best way to suppress foxtail species and slow their spread. This process begins by implementing improved management practices that support a thick, healthy forage stand that can compete against encroaching weeds. Utilizing rotational grazing management, properly cleaning equipment after use and before moving to a new field and maintaining proper soil fertility are the first steps toward this goal. Mowing will not eliminate foxtail, but clipping the tops of plants will delay seed maturity. Also, remember that cutting hay and moving bales containing mature seedheads will easily spread foxtail between fields.
In terms of chemical control, there are pre- and post-emergence options. The pre-emergence (“before plant emergence”) herbicides are designed to inhibit root and shoot growth. For these to work effectively, applications should be made before weed seed germination and incorporated into the soil by rainfall. Since yellow foxtail germinates between 60 – 75°F, seedlings could emerge between mid-March and mid-April, depending on your location. Post-emergence (‘after emergence’) application ideally should be made while weeds are small and actively growing. Although these herbicides have proven activity, there’s no guarantee the desirable forage won’t be slightly damaged, especially during mid- to late-summer when plants are stressed from drought and heat. If proper product and rate recommendations are followed, desirable grasses may turn yellowish or brownish and crispy for a few days but should recover with adequate soil moisture. For herbicide selection, there are specificities for warm- (bahiagrass and bermudagrass) versus cool-season (tall fescue) perennial grass stand recommendations and those can also vary by state. For example, Rezilon (indaziflam) is labeled for use in established bahiagrass and bermudagrass as pre-emergent. Facet L (quinclorac) is labeled on many established cool- and warm-season grasses, including tall fescue and bermudagrass. With each post-emergence option, it is important to treat foxtail when it is small and actively growing and when adequate soil moisture is available. Research has shown that rainfall within a week following these herbicide applications usually helps foxtail control. For proper product recommendations and rates, please reach out to your local Extension agent or Specialist. Thus, when using any pesticides, it is important to read and follow all product label recommendations carefully. The reference to single products is not an endorsement of that product but is rather intended to be an example of an active ingredient that can be used. More detailed forage-labeled herbicide recommendations may be found in your land-grant University’s IPM Guides.
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Authors: Dr. Liliane Silva, Extension Specialist, Clemson University
Dr. David Russell, Extension Specialist, Auburn University
