Cheatgrass has invaded millions of acres of North American rangeland, replacing more reliable perennial forage species, increasing fire frequency, and reducing native species diversity.
Herbicides can be used to manage cheatgrass (Bromus tectorum), but they are costly.
To address a problem at this scale, land managers need additional control methods that are both economical and effective.
Background photo: Targeted grazing study team surveying a cheatgrass-invaded section of a pasture near Scottsbluff, Nebraska. Photo by Julie Kray.
One approach that shows promise but has not been widely tested on cheatgrass in the Central Plains is targeted grazing: grazing designed to achieve specific vegetation management goals via specified timing, duration, and intensity of use. In our case, this would mean grazing at a high stocking density for a limited period, timed carefully to maximize removal of cheatgrass and minimize negative effects on cool-season perennial grasses.
When done well, targeted grazing could increase cattle weight gains while suppressing cheatgrass—potentially a “win-win” outcome. But in order for this strategy to succeed, we need to know exactly when to begin and end the targeted grazing.
Background photo: Cattle graze cheatgrass at the Nebraska study site. Photo by Julie Kray.
What is the best time to apply targeted grazing to control cheatgrass?
Scientists at the USDA-ARS Rangeland Resources and Systems Research Unit and the University of Nebraska are studying the optimal timing for targeted cheatgrass grazing in two mixed-grass sites near Cheyenne, Wyoming, and Scottsbluff, Nebraska. We used four years of observations from both sites to identify when cattle consume large amounts of cheatgrass, and select for cheatgrass over other plants.
Find out more about our study and what we are learning below.
Background photo: Scientists observe cattle behavior at the Wyoming study pasture in mid-April. Photo by Julie Kray.
HOW THE STUDY WORKS:
Our 10 acre study pastures were grazed by 3-4 yearling cattle from mid-April through late June or early July, to match the period when cheatgrass is actively growing. Half of each study pasture was covered by cheatgrass, and the other half by native vegetation.
Yearlings were outfitted with GPS collars to track time spent in cheatgrass versus native mixed-grass patches of vegetation.
Background photo: Cattle graze in cheatgrass patches in early May. Photo by Julie Kray.
Twice weekly fecal sampling helped us determine what the yearlings were grazing, and specifically, when they selected cheatgrass versus cool-season perennial grasses.
Every two weeks, we measured how much forage was available to cattle, and the proportion of available forage made up by cheatgrass, perennial grasses (western wheatgrass and needle-and-thread), and forbs.
Background photo: Researchers clip plants in small plots throughout the study pasture to measure changes in forage available to cattle. Photo by Rachel Wolf.
To learn what might influence when cattle select or avoid eating cheatgrass, we measured nutrition in plant leaves (forage quality) and plant growth stage (height and flower development) every week.
The study took place over four years (2017-2020) to determine how year-to-year changes in weather affected the timing of cheatgrass grazing.
Background photo: A re-grazed patch of cheatgrass remains in a vegetative stage, while surrounding cheatgrass plants are flowering in Wyoming in 2018. Photo by Julie Kray.
RESULTS:
What have we learned?
Cattle relied on cheatgrass for large portions of their diet at certain times, but the timing varied a lot between years.
Scroll down to watch timelapse videos that show how cheatgrass consumption changed during the spring in 2017 and 2018 as cheatgrass grew and flowered at the Wyoming study site.
Timelapse of 2017--Wyoming study site
Timelapse of 2018--Wyoming study site
These results highlight how year-to-year weather differences shift the timing of a targeted grazing window. Cooler, wetter conditions in 2017 delayed cheatgrass growth and flowering, and cattle selectively grazed it from late May to mid-June. Warmer, drier conditions in 2018 sped up growth and flowering, and cattle grazed it only in May.
Below, grazing location data from GPS collars show where cattle grazed during two different time periods in 2018 at the Wyoming site.
When did cattle eat the most cheatgrass?
We learned that cattle consumption of cheatgrass depends on growth stage rather than time of year. Cattle consume the most cheatgrass starting when plants are 9 centimeters (3.5 inches) tall and continuing until seeds mature (become firm to the touch). On average, this grazing window lasts 38 days, but its timing varies among years and places.
How did grazing affect the cheatgrass?
Spring grazing reduced cheatgrass seed production 30-77%.
Background photo: Mature red cheatgrass marks the fence line contrast between spring grazed study pasture to the left and summer grazed pasture to the right. Photo by Julie Kray.
How much weight did cattle gain during spring targeted grazing?
Average daily gains were 2.1-3.5 lbs/day (1.0-1.6 kg/day) at the Wyoming site.
Background photo: Yearlings grazing at the Wyoming site in June 2019. Photo by Julie Kray.
The above study ended in 2020, and a publication describing the results is coming soon. A second study focused on effectiveness of targeted grazing for cheatgrass control is currently in progress.
To learn more, contact:
- Dana Blumenthal, USDA-ARS: Dana.Blumenthal@usda.gov
- Julie Kray, USDA-ARS: Julie.Kray@usda.gov
- Mitch Stephenson, University of Nebraska-PREC: mstephenson@unl.edu
The content of this publication does not necessarily reflect the views or policies of the USDA, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.
Webpage created by Julie Kray, USDA-ARS
Photo credits: Julie Kray, Rachel Wolf