Spraying pasture weeds

Farm Forum

I recently received the question, is now a good time to spray pasture weeds? A little questioning revealed that musk thistle was the main weed species the producer was after. This is important, as the window of proper herbicide application in the early part of the season could range from early spring to mid-June, depending on the species. It turns out that musk thistles should be controlled in the rosette stage, either in late fall or spring, generally mid to late May, but definitely before the plant bolts or shoots a seed stalk.

An excellent resource for controlling weeds in pasture and rangeland is the SDSU Extension publication, “2013 Weed Control – Pasture and Range”, which can be obtained at SDSU Regional Extension Centers or online at: The publication offers valuable information on each of the herbicide products in the document, which are essentially, all of the herbicides that are labeled for use on pastures and rangelands. Separate sections are devoted to new grass seedings, pasture renovation, special weed problems and when to treat them, a table with weed response ratings for the various herbicide products, a summary of grazing and haying restrictions, and a table listing the amount of herbicide to either one gallon or 10 gallons of water for spot treatment of noxious weeds.

The publication also contains a section on pasture and range IPM (Integrated Pest Management). Progressive range managers recognize that healthy grasslands contain a diversity of plant species and selective weed control is much better than routine herbicide applications.

Multiple research trials have shown that weed control in pastures can produce positive results in production and economic returns, but there are definitely other ways to manage weeds than herbicides. Grazing management, mowing or clipping, hand chopping, digging, burning, and biological control are all alternate methods of controlling weeds in pastures to herbicides. Quite often, these mechanical, cultural and/or biological control methods preserve the desirable plants, primarily forbs (desirable broadleaf plants), that will likely be susceptible to herbicides. Certainly there are noxious or particularly aggressive weeds that might best be controlled with herbicides, but application can often be limited to spot treatments. Anything you can do to preserve native plants and particularly forbs, will provide diversity and provide habitat for the pollinating insects that have suffered alarming declines in recent years.

Weed control factsheets are also available for all the major crops grown in South Dakota and several special situations. Ask for them at your Regional Extension Center or online at Type “weed control” in the search box and possibly add “corn”, “soybean”, “wheat”, “lawn” or whatever crop or site you are looking for weed control information on. These factsheets have been incorporated into the “Crop Protection Guides” for corn, soybeans, wheat, and oilseeds and alfalfa for 2014, which are not available online. They are available in print form from the Regional Extension Centers or you can order them online at the iGrow Store: These factsheets/Crop Protection Guides contain many of the same features as the Pasture and Range Weed Control factsheet.