Research Accomplishment Reports 2009

Integrated Weed Management Strategies to Increase Pasture Productivity

J.D. Green, W. Witt, K. Burdine, G. Schwab
Department of Plant and Soil Sciences

 

Non-Technical Summary

Problematic weeds such as tall ironweed, musk thistle, spiny amaranth, buttercup, common cocklebur, and horsenettle have been increasing in pastures during the past several years as grazing has intensified within Kentucky, Tennessee, and the surrounding region where cool-season grasses are the predominant type of forages grown. These weeds are becoming more prominent in pastures because they are unpalatable to animals or have spines or thorns. Livestock producers are seeking ways to increase pasture productivity by minimizing the impact of these weeds on grazed lands. One of the primary methods used to combat weeds in pastures has been mowing, but due to increasing energy cost producers are beginning to question the economic viability of this option. Other weed control methods which are available including integration of weed management practices need to be considered.

The objective of this project is to evaluate mowing (mechanical control), herbicide (chemical control), and added fertility (culture practice) as independent factors and as integrated weed management methods that best reduce populations of unpalatable weed species which compete with the productivity of desirable forage species in grazed pastures. Field research trials will be used to determine pasture productivity relative to these weed management strategies combined with an economic analysis that would assess the cost/benefits of each of these different weed management practices. During the final stages of this project field days will be held, meeting presentations and publications will be used to educate livestock producers, county extension agents, and other interested individuals on best management practices for weed control in pastures.

2009 Project Description

ACTIVITIES: Field studies were initiated in July 2008 at three different sites in Anderson, Madison, and Monroe counties near Lawrenceburg, Richmond, and Tompkinsville, Kentucky, respectively. These on-farm field sites are located on grazed pastures in cooperation with county Extension agents and local livestock producers. Eight different treatments are being studied at each site to evaluate three primary weed management strategies (mowing, herbicide, and added fertility). Treatments range from no strategy (untreated control); mowing alone, herbicide alone, or added fertility; combinations of mowing plus herbicide, mowing plus fertility, herbicide plus fertility; and a combination of all inputs which consist of mowing plus herbicide plus added fertility.

The weed species composition and the density of the primary weeds present (which includes tall ironweed as a common plant species at each site) were determined at the time field studies were first initiated. Mechanical control treatments were mowed in mid-July 2008 and herbicide applications made in mid to late-August. Added fertility was applied in early September 2008 to designated treatments based on soil test results. Cattle have been allowed access to the field plot areas depending on the local livestock producers grazing practices except for a period of time in the early spring in which half the individual plot areas were isolated from grazing.

Available forage and weed biomass yields were determined in May 2009 by sub-sampling grazed and ungrazed areas within each plot. The amount of forage produced was botanically separated into desirable forage grasses, clovers, tall ironweed, and other weeds present. The economic cost/benefits of each of these treatments are being evaluated based on the cost of weed management inputs and forage yield data.

EVENTS: Two field days were held in August 2009 (Madison) and September 2009 (Monroe) to highlight the results obtained after the first year of these studies.

2009 Impact

Field days were held at two of the field study sites (Madison and Monroe) in which 360 individuals attended. Observed differences in weed populations, weed biomass, and forage yields for each of the weed management treatments were discussed with participants along with the economic assessments for the inputs and forage yields obtained at these two locations. The target audience for these field days was primarily livestock and forage producers.