Weed Control in Pastures-Getting Started Early

By Rakesh Chandran, Extension Weed Specialist WVU Extension Service – Agricultural and Natural Resources

Chemical weed control may be executed only when other measures are not feasible. Typically, good management practices will keep a pasture or hayfield to remain competitive with weeds. Low levels of weeds need not necessarily warrant a herbicide application. However, if weed infestation levels are high it may be prudent to manage them and before resolving to improve management practices that discourage them in the future.

Application Timing

Annual and biennial weeds typically become noticeable when they are in bloom; however, they have successfully competed with the crop by then. Based on the biology and life-cycle of weeds present in a pasture or hayfield it may be necessary to manage weeds early on in the year in some instances, or later on, in others. Timing of executing a control method is critical for successful weed management.

Applying herbicides to annual weeds when they are young and actively growing is most effective. If a pasture has a history of broadleaf weeds in spring, it may be worthwhile applying a broad-spectrum broadleaf herbicide with some residual activity at first green-up (as early as March). Weeds may not be readily visible to the naked eye then, but several of them have germinated already! Contrarily, perennial weeds tend to germinate later on and transport sugars towards storage organs from the pre-bloom to post-bloom stage. Application of a systemic herbicide during this time is more effective to control such weeds. Systemic herbicides are usually not effective applied under drought conditions.

January – March

autumn_olive Obnoxious brushes such as autumn olive not only deprive the pasture of valuable resources but also reduce its effective grazing area. Application of an oil-based herbicide containing the active ingredient triclopyr (such as Crossbow or Remedy), mixed with a high-grade mineral oil or No.2 diesel oil as a carrier, during the dormant period (winter months) to the base of autumn olive can effectively control it. If using Crossbow, mix one part of the herbicide to 25 parts of the carrier, or if using Remedy, mix 1 part of herbicide to 5 parts of the carrier. The mixture should be sprayed carefully on the stem from the ground level to a height of about 15-18 inches while avoiding runoff or dripping on nearby grasses. The application can be made at any time as long there is no snow on the ground.

April – May

In general, this is a good period to implement control measures for most winter annuals, biennials, and earlygerminating summer annuals, or to weaken certain persistent perennial weeds. Low rates of common herbicides such as 2,4-D and dicamba may be effective to control young and actively growing weeds. Stronger herbicides with residual activity such as Milestone, Grazon P+D, Forefront, or Surmount may provide an additional benefit of controlling weeds that germinate later on. Complete kill may not be necessary always. In some instances, the weeds may remain suppressed, essentially non-competitive to desirable forage. Late-spring is also a good time to control brushes such as multiflora rose and Japanese barberry during the pre-bloom period. Herbicides such as Cimarron Plus, Grazon P+D, Forefront, Surmount and Crossbow are effective to control these weeds.

Potential Weed Problems in 2013

broomsedge As a result of the relatively dry summer in 2012, warm-season perennial grasses such as broomsedge and Johnsongrass may have established foothold in some pastures. Both these grasses establish in pastures that have lost its competitive ability due to poor management practices. Low pH, poor fertility, and improper grazing practices may predispose pastures to such opportunists. Both broomsedge and Johnsongrass are palatable to livestock, especially when they are young, although the former is not as competitive as the latter. Broomsedge can be managed when they are young by allowing a higher grazing pressure in spring. Once they are mature, they are not as palatable and a high grazing pressure in summer may reduce the competitive ability of the pasture, further aggravating the problem. Check the soil pH and rectify if necessary. Areas of the pasture with dense stands of broomsedge may have to be renovated following the application of a non-selective herbicide such as glyphosate. Johnsongrass may also be controlled by glyphosate by directed spot application of the same or using a weed wiper. The weed wiper selectively controls tall weeds while providing minimal injury to desirable grasses and legumes. Johnsongrass can be toxic to livestock if they consume it soon after a killing frost.