VT Weed Control

Publication SPES-58P

Control of Common Grassy Weeds
in Pastures and Hayfields
Lucas Rector, Graduate Student, School of Plant and Environmental Sciences, Virginia Tech
Kara Pittman, Research Associate, School of Plant and Environmental Sciences, Virginia Tech
Michael Flessner, Extension Weed Science Specialist, School of Plant and Environmental Sciences, Virginia Tech

Introduction
Weeds decrease pasture and hayfield forage yield
and aesthetics. Grassy weeds can be especially
troublesome due to the limited herbicide options to
selectively manage them. This publication discusses
weed management tactics and herbicide application
techniques to control grassy weeds. Additionally,
management of Johnsongrass, Japanese stiltgrass,
broomsedge, and foxtail species is discussed in more
detail.
While this publication focuses on weed management,
maintaining optimal soil fertility and practicing proper
grazing and haying management are vitally important.
Herbicides alone cannot provide a substitute for
proper management, and relying solely on herbicides
as a weed control program will not be successful. A
healthy, vigorous stand of desirable grasses is the best
weed management tool. Stopping grazing or cutting
hay at 4 inches in height and resting between grazing
or cutting events can reduce weed densities and allow
for quicker regrowth, adding up to a third more forage
to be produced in a season (Sollenberger et al. 2012).
Optimizing soil fertility begins with taking routine soil
tests and following the recommendations provided.
Maintaining optimum soil pH increases nutrient
availability. Optimum soil pH is 6.2 to 6.5 for most
cool-season grass (Teutsch and Smith 2009) and 6.5
to 7.0 for legume forages (Redmon and McFarland
2013).
The first step in weed control is correct identification.
Virginia Cooperative Extension maintains the Weed
Identification Guide website (https://weedid.cals.
vt.edu/), which provides pictures and descriptions
of common weeds, as well as the ability for users
to identify weeds by selecting plant characteristics.

The Virginia Weed Identification Clinic also provides
weed identification services free of charge via your
local Extension agent (https://ppws.vt.edu/extension/
weedid-clinic.html).

Herbicide Application Methods
Herbicide application timing and method depends
on the species being targeted and the life cycle of
the species. Different approaches need to be taken to
control annual compared to perennial grassy weeds.

Annual Weedy Grasses
Annual weedy grasses can be controlled with
pre-emergence or postemergence herbicides.
Pendimethalin is a pre-emergence herbicide that
can control many annual weedy grasses when it is
applied before germination. Prowl H20 and Satellite
HydroCap are two pendimethalin products with
supplemental labels for this use in Virginia. Summer
annual grasses, such as crabgrass (Digitaria spp.),
annual foxtails (Setaria spp.; discussed below), field
sandbur (Cenchrus incertus), jointhead arthraxon
(Arthraxon hispidus), and others, can be controlled
by pendimethalin. While application timing varies
by region and weed species, it is recommended prior
to germination, which is typically in early April.
Pendimethalin will also prevent the establishment of
desirable grasses and legumes from seed, so do not
apply it to newly seeded or establishing fields.
Certain annual grasses can be selectively controlled
postemergence. Generally, the best application
timing is when annual grasses are young and actively
growing. Quinclorac herbicides (Facet L and Quinstar)
can control crabgrasses, annual foxtails, and other

www.ext.vt.edu
Produced by Virginia Cooperative Extension, Virginia Tech, 2018
Virginia Cooperative Extension programs and employment are open to all, regardless of age, color, disability, gender, gender identity, gender expression, national origin, political affiliation, race, religion, sexual orientation, genetic information,
veteran status, or any other basis protected by law. An equal opportunity/affirmative action employer. Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the
U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg.
VT/1018/SPES-58P

annual grasses. Application timing is critical for
success. Grasses are most effectively controlled when
they are less than 2 inches in size at application.
Including proper adjuvants according to the product
label is also important.

herbicides because there are fewer food reserves stored
underground after regrowth. However, depending
on species, herbicide application might need to be
delayed to allow for regrowth to ensure there is
adequate leaf area for optimum herbicide uptake.
More information on spot spraying and weed wipers
can be found in the Forages chapter of the 2018
Pest Management Guide: Field Crops, available at
http://pubs.ext.vt.edu/content/dam/pubs_ext_vt_
edu/456/456-016/ENTO-239-2.pdf.

Perennial Weedy Grasses

Control of Selected Troublesome
Grassy Weeds
Johnsongrass, Japanese stiltgrass, broomsedge, green
foxtail, yellow foxtail, giant foxtail, and knotroot
foxtail are common grassy weeds found throughout
Virginia. They each require unique control methods.

Johnsongrass
Figure 1: Weed wiper applicator. (Photo by Lucas Rector.)

There are no selective herbicides that can control
established perennial grasses in cool-season grass
forages. Spot spraying and wiper applications are
ways to achieve selectivity with a nonselective
herbicide. Spot spraying is accomplished by only
spraying areas infested with weeds using a hand-held
sprayer. Glyphosate (Roundup and other products)
is recommended for spot spraying and wiper
applications. Glyphosate will kill all vegetation,
including desirable grass and clover species that it
contacts.

Figure 2: Johnsongrass. (Photos courtesy of Shawn Askew,
associate professor, School of Plant and Environmental
Sciences, Virginia Tech, unless otherwise noted.)

Wipers applicators (also known as rope wick
applicators) are devices that physically wipe herbicide
directly onto weeds (fig. 1). To achieve selectivity,
there must be a height difference between weedy and
desirable species. The wiper is set at a height above
the desirable species and below the weed species so
that herbicide is wiped onto the weedy species as it
moves through the field and avoids desirable species.
Grazing can sometimes be used to create the required
height difference. Wiping in two opposite directions
with sufficient drying time between applications is
generally more effective than a single pass. Mowing
or clipping perennial weeds increases effectiveness of

Johnsongrass (Sorghum halepense) is a perennial
grass that can spread by rhizomes and seed (fig. 2).
When under stress, Johnsongrass produces prussic
acid that can poison livestock, especially ruminants.
Frost, drought, and high levels of nitrogen fertilization
with low levels of phosphorus and potassium increase
stress, which increases prussic acid production
in Johnsongrass (Comerford 2012). Controlling
Johnsongrass in hayfields can be difficult; it can take
multiple years due to its extensive root structure and
ability to sprout from rhizomes.

www.ext.vt.edu

2

Johnsongrass can be controlled by frequent low
cutting, but monthly cutting is not economical. Hay
cutting is not sufficient to control Johnsongrass.
Grazing can control Johnsongrass in two to three
seasons, but grazing should be avoided directly after
the plant has been under stress. Spot spraying or using
a wiper to apply glyphosate provides good control of
Johnsongrass, but multiple applications over multiple
years could be required. There are currently no
selective herbicides for Johnsongrass control in coolseason grass forages. Rotating to row crops such as
corn, which allows for effective control with selective
herbicides, could be an option in heavily infested
fields (Flessner and Cahoon 2018)

species. Stiltgrass should be aggressively controlled
when it first invades a field in order to prevent
establishment (Neal and Judge 2013).
Spot spraying glyphosate is highly effective at
controlling stiltgrass, but it does not provide longlasting control, and it will also kill desirable grasses.
Herbicides containing aminopyralid, such as
Chaparral, Milestone, and GrazonNext HL, are fairly
effective at controlling stiltgrass (table 1). Stiltgrass
is best controlled when plants reach 3 to 5 inches in
height, which usually occurs in late May to June.

Broomsedge

Japanese Stiltgrass

Figure 3: Japanese stiltgrass.

Japanese stiltgrass (Microstegium vimineum) is a
summer annual that thrives in moist, shaded areas
(fig. 3). Most livestock and wildlife will not graze the
grass, so it is often left to outcompete desired grass

Figure 4: Dormant broomsedge.

Broomsedge (Andropogon virginicus) is a warmseason perennial grass that often goes unnoticed until

Table 1. Relative effectiveness of herbicides for Japanese stiltgrass control in pastures and hayfields.

Grazon P+D1 3–4 pt
(VA, WV)

Metsulfuron 60DF
0.1–0.3 oz

Milestone 5–7 oz (PA, VA, WV)

Overdrive 4–6 oz

Pature-Gard HL1 1–1.5 qt

Remedy Ultra 2–4 pt

N

N

7

-

N

7

-

-

N

10

Surmount1 1.5–3 pt (VA, WV)

GrazonNext HL1 1.5–2.6 pt
(PA, VA, WV)

8

Stinger 0.66–1.33 pt

Crossbow1 2–4 qt

N

Roundup/glyphosate 1–2 qt
(spot treatment)

dicamba1 1 pt

N

Chaparral1 2–3 oz
(PA, VA, WV)

N

Aim 1–2 oz

Stiltgrass,
Japanese

2,4-D + dicamba1
1 qt + 1 pt

Species

2,4-D1 3–3 pt

Control ratings: 10 = 95-100%; 9 = 85-95%; 8 = 75-85%; 7 = 65-75%; 6 = 55-65%; N = less than 55%; - = not applicable.

N

N

Source: (Table reprinted from Flessner and Cahoon [2018, 5-264]).

www.ext.vt.edu

3

it turns reddish brown and forms broomlike leaves
(figs. 4 and 5). Poor nutritional quality and palatability
make broomsedge an undesirable forage. Its presence
is an indicator of low fertility and phosphorus
deficiencies in soil (Brakie 2009). As soils become
more acidic, phosphorus becomes less available, so
maintaining a soil pH above 6.0 can increase available
phosphorus. Broomsedge requires less phosphorus
than other grass species, so it is able to outcompete
desired grass species in unfertile soils.
Figure 7: Green foxtail.

Figure 5: Actively growing broomsedge.

At optimum nutrient levels and pH, tall fescue and
other grass forages increase in density and will
outcompete broomsedge. It can take multiple years to
completely control broomsedge (Peters and Lowance
1974). For established broomsedge, spot spraying or
using a wiper to apply glyphosate when broomsedge is
actively growing provides good control.

Figure 8: Giant foxtail.

Foxtails

Figure 9: Knotroot foxtail. (Reprinted by permission from
McCullough [2016].)

Figure 6: Yellow foxtail.

Yellow foxtail (Setaria pumila; fig. 6), green foxtail
(Setaria viridis; fig. 7), and giant foxtail (Setaria
faberi; fig. 8) are all summer annuals, while knotroot
foxtail (Setaria parviflora; fig. 9) is a warm-season

www.ext.vt.edu

4

emergence early in the season and followed by a
postemergence application of quinclorac, or quinclorac
alone applied later in the season after the first hay
cutting, provides the greatest control of annual foxtails
(Flessner, Johnson, and Randhawa 2017).

perennial. The hairlike barbs on foxtail seedheads
can cause mouth ulcers in horses and other livestock.
These ulcers lead to reduced weight gain and a decline
in animal health.
The easiest way to identify knotroot foxtail from
annual foxtails is to pull up the plant and examine
the roots. Knotroot foxtail has rhizomes and knotlooking roots, while annual foxtails have fibrous roots
(McCullough 2016). Established knotroot foxtail also
produces a seedhead much earlier in the year (June)
than annual foxtails (August to September).

Established knotroot foxtail is not controlled by
pendimethalin or quinclorac because it emerges from
a rhizome. Spot spraying with glyphosate is effective
at controlling knotroot foxtail when it is actively
growing. It is recommended that applications be made
prior to seed production (Flessner and Cahoon 2018).
Fields heavily infested with knotroot foxtail might
require renovation or rotation out of forage.

Improving the competiveness of desired pasture
species can suppress foxtail species. Annual foxtails
germinate in spring when soil temperatures reach 60 F.
High rates of nitrogen fertilization should be avoided
during foxtail germination to reduce seedling survival.
Excessive nitrogen can also promote seedhead
production and seed spread, so it should be avoided in
fields with heavy foxtail pressure (McCullough 2016).
At the same time, fields with dense stands of desirable
forages require nitrogen applications to compete with
foxtail species and prevent them from establishing.

For more information, please consult the Pest
Management Guide: Field Crops (http://pubs.ext.
vt.edu/content/dam/pubs_ext_vt_edu/456/456-016/
ENTO-239-2.pdf) or the Mid-Atlantic Field Crop
Weed Management Guide (https://extension.psu.edu/
mid-atlantic-field-crop-weed-management-guide).
Commercial products are named and/or shown in
this publication for informational purposes only.
Virginia Cooperative Extension does not endorse these
products and does not intend discrimination against
other products that could also be suitable.

Pendimethalin (Prowl H2O and Satellite HydroCap)
and quinclorac (Facet L and Quinstar) can be used
to control annual foxtails. Quinclorac at 0.375 lb
active ingredient (ai) /A (Facet L at 32 fl oz/A) plus
methylated seed oil at 1% volume/volume (v/v) is
most effective when applied within 10 days after the
first hay cutting. Foxtails should be allowed to regrow
after hay cutting or grazing to provide adequate leaf
area for uptake of herbicide. Quinclorac has some
short residual soil activity that will control foxtails
that could emerge once sunlight reaches the soil after
hay cutting. Quinclorac has the potential to injure
orchardgrass under stress. Avoid applying quinclorac
during high temperatures or drought stress.

References
Brakie, M. 2009. Broomsedge Bluestem Andropogon
Virginicus L. USDA NRCS Plant Fact Sheet.
https://plants.usda.gov/factsheet/pdf/fs_anvi2.pdf.
Comerford, J. 2012. “Prevention of Prussic Acid
Poisoning for Cattle.” Farming, September, 37.
http://link.galegroup.com/apps/doc/A305837223/
ITOF?u=viva_vpi&sid=ITOF&xid=fba052c7.
Flessner, M., and C. W. Cahoon, eds. 2018. “Forages,
CRP, and Farmstead Weed Management.” In Pest
Management Guide: Field Crops. Virginia
Cooperative Extension Publication 456-016,
pp. 5.235-294. Blacksburg, VA: VCE.

Pendimethalin (Prowl H2O or Satellite HydroCap)
at 3-4 qt/A is most effective when applied as a preemergence application. It should be applied in March
or April, depending on location, before annual foxtails
emerge. Pendimethalin generally provides about four
to six weeks of weed control per quart applied if it is
effectively incorporated into the soil. Thick residue or
forage canopy can inhibit pendimethalin contact with
the ground and prevent it from becoming active in the
soil. Using higher spray volumes and selecting nozzles
that produce courser droplets can help pendimethalin
reach the soil surface. Pendimethalin applied pre-

Flessner, M. L., Q. R. Johnson, and R. S. Randhawa.
2017. “Management of Foxtail Species (Setaria spp)
in Hayfields With Quinclorac and Pendimethalin.”
Poster Abstract in Proceedings of the 2017 Southern
Weed Science Society 70th Annual Meeting, 249.
Raleigh, NC: SWSS.

www.ext.vt.edu

5

McCullough, P. 2016. Foxtail Identification and
Control in Georgia Pastures and Hayfields.
University of Georgia Extension Bulletin 1464.
https://secure.caes.uga.edu/extension/publications/
files/pdf/B%201464_1.PDF.
Neal, J., and C. A. Judge. 2013. Japanese
Stiltgrass Identification and Management.
North Carolina State Extension. Horticulture
Information Leaflets. https://content.ces.ncsu.edu/
japanese-stiltgrass-identification-and-management.
Peters, E. J., and S. A. Lowance. 1974. “Fertility and
Management Treatments to Control Broomsedge in
Pastures.” Weed Science 22:201-5.
Redmon, L. A., and M. L. McFarland. 2013. Soil
pH and Forage Production. Texas A&M AgriLife
Extension Publication SCS-2013-11. http://
publications.tamu.edu/FORAGE/Soil%20pH%20
and%20Forage%20Production.pdf.
Sollenberger, L. E., C. T. Agouridis, E. S. Vanzant,
A. J. Franzluebbers, and L. B. Owens. 2012.
“Prescribed Grazing on Pasturelands.” In
Conservation Outcomes from Pastureland and
Hayland Practices: Assessment, Recommendations,
and Knowledge Gaps, edited by C. J. Nelson,
111-204 Lawrence, KS: Allen Press.
Teutsch, C. D., and S. R. Smith. 2009. Maintaining
Healthy Horse Pastures. Virginia Cooperative
Extension Publication 418-105. https://pubs.ext.
vt.edu/content/dam/pubs_ext_vt_edu/418/418105/418-105_pdf.pdf.

www.ext.vt.edu

6