Pasture & Range: February 2001

Western Ragweed

By definition, a weed is an unwanted plant or a plant out of place. To many livestock producers, a weed is any plant other than grass. Although grass is the maintenance portion of a cow's diet, it may or may not be the preferred portion, depending upon the species of weed or time of year. Therefore, let's be careful to not be too hasty to kill those pesky weeds until we know what we are eliminating and evaluate the cost benefits of doing so. For example, according to research at Oklahoma State University, we need a threshold level of 30 percent Western ragweed on native range before it is cost effective to chemically spray for removal. An even bigger question should be, If ragweed populations are 30 percent or higher, what is happening to cause this increased population, and is spraying really the answer to the problem?

So what are forbs? They are broad-leaved, nonwoody, herbaceous plants that differ from grasses in that the latter have narrow, linear leaves. Many forbs have significant food value for livestock as well as wildlife, and livestock even prefer them to grasses. Even Western ragweed will be used by livestock during certain times of the year.

Some examples of forbs that livestock highly prefer, at least seasonally, include the following:

Maximillian Sunflower	Compassplant	Engelmann Daisy	Ashy Sunflower
Click on plant images above for a larger view.

All four of these plants are rarely found in pastures where animals are grazing. They are typically found only along roadsides and well-managed pastures or in hay meadows. Protein content can be as high as 20 percent in May and June and 12 to 14 percent even in August.

Giant ragweed, redroot pigweed, and lambsquarters typically grow in waste places, disturbed sites, fields, and monocultures of pastures such as bermudagrass. Although livestock may not prefer these plants twelve months of the year, they will definitely graze them seasonally and often prefer them to bermudagrass.

Giant Ragweed	Redroot Pigweed	Lambsquarters
Click on plant images above for a larger view.

I thought it might also be worthwhile to show you some of our more inconspicuous legumes that are typically preferred by livestock but susceptible to weed spray.

Hairy Vetch	Tick Clover	Korean Lespedeza
Black Medic	Hop Clover	White Clover
Click on plant images above for a larger view.

Too often we pull the trigger without clearly focusing on the target or focus on the target but use a shotgun to hit a bull's-eye. In other words, we weed-spray to remove anything but grass, or we spray in an effort to eliminate a known target species without regard to other species that might be beneficial. Either approach could prove costly as well as undesirable!

Thought for the day: Most weeds are forbs, but most forbs are not weeds.

Interested in plant identification? Take a look at our Plant Image Gallery.