Benefits of increasing grazing height on weed suppression in grass based grazing systems

2009 Annual Report for GNC09-114

Project Type: Graduate Student
Funds awarded in 2009: $9,199.00
Projected End Date: 12/31/2010
Grant Recipient: University of Wisconsin
Region: North Central
State: Wisconsin
Graduate Student:
Faculty Advisor:
Dr. Mark Renz
University of Wisconsin

Benefits of increasing grazing height on weed suppression in grass based grazing systems


Few studies provide information on how to maximize the prevention of emergence of weed species in grazing systems in Wisconsin without the use of herbicides. This research will assess whether increasing grazing heights in the fall will suppress weed emergence the following year. It will also account for changes in forage yield in the year following the treatment. I currently have funding to determine the mechanisms responsible for suppression of weed emergence and estimating how different grazing treatments affect yield of forage species. However, forage quality can be more important than quantity, most notably in the dairy sector.

I would like to compare our forage quantity data with a forage quality analysis using a near infrared reflectance spectrometry (NIRS). It is crucial that recommendations include possible changes in forage quality as this can have a significant effect on animal weight gain as well as milk production.

In Addition, to ensure that the practices we recommend are in line with typical farm practices I would like to hold two focus groups including farmers, agency staff, and extension. The first meeting took place in September 2009. In conjunction with the producers, agency staff and extension agents I used the data from year one to restructure the treatments to further examine which treatments had the most suppressive effects while providing acceptable forage quantity and quality into year two. In August 2010 I was featured at a pasture walk to discuss the results form 2009. Additionally, I am currently conducting a survey that was filled out at pasture walks as well as online to compare the 2009-2010 weed suppression results with current on farm weed management techniques. I feel it is extremely critical that producers are involved in the dissemination of the results as it encourages farmer implementation. The results of this project have been presented at field days, pasture walks, and conferences.

Objectives/Performance Targets

The main objective of this study is to develop an understanding of how producers can balance suppression of weed seedling emergence with potential reductions in forage yield and quality by altering grazing heights.

The 2009-2010 grazing season data was discussed at a focus group and treatments were altered to mimic what management practices were most practical for farms while including weed suppression, forage quantity and forage quality. I also presented this material to grazing networks and sustainable agriculture organizations. Two journal articles will be submitted to peer review journals this fall. This information will include a discussion of the mechanisms we determined to suppress weed seedling emergence and how it can be applied to a range of grazing production systems (e.g. beef production, sheep production, dairy).

Long-term objectives include a better understanding of how to use cultural practices to not only prevent weed emergence, but balance this prevention with forage quantity and quality. This research also has the potential to be useful in other areas where weed seedling suppression is desired, such as restorations in natural areas, or weed management for programs such as CRP.


A focus group meeting was held in September 2009 to discuss treatments and results. The focus group decided on five new treatments that were implemented in 2009-2010. The 2009 data was presented at the Annual Weed Science Society of America Conference in February 2010 in Denver, CO. The data was also presented at the Wisconsin Grazing Conference in February in Wisconsin Rapids, WI. In August 2010 a pasture walk in Trempealeau County, WI highlighted the results. The results of a survey that is being conducted will be submitted to a peer-reviewed journal in fall 2010.

Impacts and Contributions/Outcomes

Our data demonstrates retaining 6-8 inches of residual height in the fall through the following grazing season can decrease burdock establishment 74-89% compared to typical residual heights (2 inches and 4 inches). Increased light interception, particularly in the early spring (April), appears to be one mechanism for the suppression of burdock. Although increasing grazing height to 6-8 inches has the potential to reduce forage quantity, this was only observed in the fall and at the 1st spring grazing event. Forage quality may also be reduced with grazing in the late summer, but this can vary considerably depending on forage species composition and other site specific variables.

Our focus group meeting in September 2009 used these results to restructure treatments for the 2010 grazing season. In addition, the survey results from pasture walk will be used to help direct future weed research in managed pastures.


Mark Renz
Extension Weed Scientist
1575 Linden Dr
Madison, WI 53706
Office Phone: 6082637437
Marie Schmidt
Graduate Researcher
University of Wisconsin - Madison
909 E Dayton St
Madison, WI 53703
Office Phone: 4144673597