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Targeted grazing to control cheatgrass in mixed-grass rangeland

Above image: Yearling cattle graze the study pasture near Cheyenne, Wyoming in 2019. Photo by Julie Kray.

Logos of collaborating institutions including the US Department of Agriculture and University of Nebraska Panhandle Research and Extension Center.

Cheatgrass has invaded millions of acres of North American rangeland, replacing more reliable perennial forage species, increasing fire frequency, and reducing native species diversity.

Above: Map of non-federal US rangeland where cheatgrass was present in 2015. Source: 2018 NRI Rangeland Resource Assessment, USDA-NRCS.

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 very high stocking density for a brief 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 working to identify the optimal timing for targeted cheatgrass grazing in two mixed-grass sites near Cheyenne, Wyoming, and Scottsbluff, Nebraska. Observations from both sites over several years will define the optimal times for targeted grazing as periods when cattle consume large amounts of cheatgrass, and select for cheatgrass over other plants.

Map of study site locations in the western United States. Source: Google Earth imagery.

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 are 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 is covered by cheatgrass, and the other half by native vegetation.

Map of the Wyoming study pasture. Cheatgrass patches mapped at the start of the study in 2016 are shown in green. Red areas in the background landscape image are mature cheatgrass. Source: Google Earth imagery.

Yearlings are outfitted with GPS collars to track time spent in cheatgrass versus native mixed-grass patches of vegetation.

GPS collars worn by cattle record location and grazing activity. Photo by Julie Kray.

Background photo: Cattle graze in cheatgrass patches in early May. Photo by Julie Kray.

Twice weekly fecal sampling helps us determine what the yearlings are grazing, and specifically, when they select cheatgrass versus cool-season perennial grasses.

Plant DNA in each fecal sample tells us what proportion of the diet is made up by cheatgrass, perennial grasses, or other native plant species. Photo by Julie Kray.

Every two weeks, we measure how much forage is available to cattle, and the proportion of available forage made up by cheatgrass, perennial grasses (western wheatgrass and needle-and-thread), and forbs.

Researchers clip and weigh plants in plots throughout the pasture to measure changes in forage available to cattle. Photo by Rachel Wolf.
Flowering cheatgrass in a small plot clipped to measure forage available to cattle. Photo by Rachel Wolf.

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 measure nutrition in plant leaves (forage quality) and plant growth stage (height and flower development) every week.

Nutritional quality of plant leaves is measured weekly on cheatgrass (above), western wheatgrass, and needle-and-thread grass. Photo by Julie Kray.

The study is planned for five years (2017-2021) to determine how results are affected by year-to-year changes in weather.

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.

EARLY RESULTS:

What have we learned from the first few years?

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 early June. Warmer, drier conditions in 2018 sped up growth and flowering, and cattle grazed it only in early May.

Below, grazing location data from GPS collars show where cattle grazed during two different time periods in 2018 at the Wyoming site.

How did grazing affect the cheatgrass?

Spring grazing reduced cheatgrass seed production inside our Wyoming study pasture in the first two years.

Cheatgrass seed mass inside the spring grazed study pasture, versus outside the fence in summer grazed pasture at the Wyoming site in 2017 and 2018. Fence line comparisons show that spring grazing can lead to 30-75% lower cheatgrass seed production.

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.

Our study is planned to continue through 2021. We will update this page periodically with new results.

To learn more, contact:

  • Dana Blumenthal, USDA-ARS: Dana.Blumenthal@usda.gov
  • Mitch Stephenson, University of Nebraska-PREC: mstephenson@unl.edu
Logos of collaborating institutions including the US Department of Agriculture and University of Nebraska Panhandle Research and Extension Center.

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