Summer Weed Control Options in Smooth Bromegrass Hayfields and Pastures

Questions are arising regarding weed management in smooth bromegrass pastures and hay meadows. The smooth bromegrass stands in many of these fields were damaged by fall armyworm infestations in the recent past. These thin stands, coupled with good growing conditions for summer annual weeds, have resulted in weed infestations that need to be addressed if the bromegrass is to recover or be reseeded this fall (Figure 1). Herbicides labeled for use in smooth bromegrass are described in Table 1.

Figure 1. Broadleaf weed horsenettle encroaching into a fall armyworm-damaged smooth brome hayfield in Jackson County. Photo by Tina Sullivan, K-State Extension.

Actively growing summer annual weeds that have not yet produced seed can be controlled now by timely herbicide applications. Examples of these species include common ragweed or common sunflower. Herbicides that include 2,4-D, dicamba, aminopyralid (Milestone, others), or metsulfuron (Escort, others) could be considered for these applications.

If annual grassy weeds, such as weedy bromes, foxtail species, or large crabgrass, have already set seed, waiting until next spring may actually be the most cost-effective strategy, as a herbicide application now will do little to control these unwanted species. Herbicides such as quinclorac (Facet, others) can be used to control foxtails or crabgrass if applied when seedlings are about 2 inches tall. An application of pendimethalin (Prowl H2O, others) can also be effective if applied prior to germination. Weedy bromes are more challenging. There is some evidence that aminopyralid (Milestone, others) will suppress seed production when applied to downy brome between the seedling and boot growth stages.

Perennial weeds may be controlled with late-summer applications, but in some cases, the best time for application may have passed. For example, hemp dogbane is best controlled by applications of fluroxypyr (Vista, others) before the bud stage.

Factors to Consider

There are a couple of points to keep in mind, regardless of the target weed species and herbicide application timing.

• First, know the future plans for the area. If the area might be reseeded in the future, it is important to understand the planting interval between herbicide application and seeding.
• Second, ensure good herbicide contact with the target weed or, in the case of residual herbicides, the soil. Haying the area before making herbicide applications can help by removing forage biomass to increase herbicide deposition on the target.

Table 1. Herbicides labeled for post-emergence weed control in smooth bromegrass. Consult the label for the appropriate rate and adjuvant selection.

Herbicide	Active ingredient	Weeds controlled	Growth stage restriction	Plant-back interval	Smooth brome suppression
2,4-D	2,4-D	Broadleaf	After 6-leaf stage	30 days	Unlikely
Amber	Triasulfuron	Broadleaf	60 days after emergence	4 months	Unlikey
Chaparral	Metsulfuron + aminopyralid	Broadleaf	None	1 year	Likely
Cimarron Plus	Metsulfuron + chlorsulfuron	Broadleaf	6 months after seeding	2 months	Likely
Clarity, others	Dicamba	Broadleaf	None	45 days per 16 fl oz/A	May be injured with > 16 fl oz/A
Crossbow	2,4-D + triclopyr	Broadleaf	None	3 weeks	Possible
DuraCor	Aminopyralid + florpyrauxifen	Broadleaf	None	45 days	Likely
Escort, others	Metsulfuron	Broadleaf	6 months after seeding	2 to 4 months	Likely
Facet, others	Quinclorac	Grass/broadleaf	None	10 months	Unlikely
Grazon P+D	Picloram + 2,4-D	Broadleaf	None	60 days	Likely
GrazonNext HL	Aminopyralid + 2,4-D	Broadleaf	No	Grasses may be reseeded in the fall after a spring or early summer application	Likely
Milestone	Aminopyralid	Broadleaf	No	1 year	Likely
PastureGard HL	Triclopyr + fluroxypyr	Broadleaf	After tillering	3 weeks	Possible
Plateau, others	Imazapic	Grass/broadleaf	No	26-36 months	Likely
Range Star	2,4-D + dicamba	Broadleaf	> 6 leaves	3 weeks per quart	Possible
Rave	Triasulfuron + dicamba	Broadleaf	60 days after emergence	4 months	Possible
Remedy Ultra, others	Triclopyr	Broadleaf	No	3 weeks	Possible
Tordon 22K	Picloram	Broadleaf	After tillering	Grasses may be reseeded in the fall after a spring or early summer application	Likely at rates > 1 qt/A
Yukon	Dicamba + halosulfuron	Broadleaf	No	2 months	Possible

Always consult current herbicide labels and the 2026 Chemical Weed Control for Field Crops, Pastures, Rangeland, and Noncropland guide before making application decisions (https://www.bookstore.ksre.ksu.edu/pubs/CHEMWEEDGUIDE.pdf ).

The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements. Users should read and follow all label directions.

 

Sarah Ganske, Weed Management Specialist
slancaster@ksu.edu

Molly Reichenborn, Range Management Specialist
mreichenborn@ksu.edu

Tina Sullivan, Northeast Area Agronomist
tsullivan@ksu.edu