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Weed control on rangeland -- Part II

This is the continuation of last week's article. The information was taken from an Oklahoma Extension Bulletin NREM 2882-5 "Weed Control on Rangelands." I will attempt to pickup where I left off. First, though, I probably need to review the main point of the last article.

Every year, thousands of acres of native prairie are sprayed with herbicide to control non-noxious weeds to benefit livestock production.

This practice is expensive and not often profitable when viewed in the light of potential marginal increase in income from livestock production.

Additionally, this practice can have serious effects on other land uses and landowner objectives such as management of wildlife habitat.

Herbicides also kill many plants that are valuable to livestock production and wildlife since they do not discriminate between desirable and undesirable plants.

To make sound land-management decisions, landowners need to understand the costs and benefits of spraying non-noxious weeds on their ground.

Understanding forb production

Plant growth fluctuates with the amount and distribution of precipitation; when rainfall is higher then forage production is higher. With this variation in precipitation, production and species composition of the forb community also fluctuates. In some years, there are large populations of annual forbs, while the next year there might be few present. For instance, Western ragweed will increase with a wetter fall followed by a wetter spring. Another example, dry years produce bare ground, which is required for common broomweed to germinate, so this forb flourishes in wet years following dry years. Bare ground also can result from over-utilization by livestock or other soil disturbances. In years with average or above-average precipitation, common broomweed is seldom abundant except in heavily grazed areas (e.g. watering points, feed grounds, etc.). This climatic variation makes weed control unnecessary because the plant community shifts without chemical intervention. Due to the fluctuation of precipitation, chemical non-noxious weed control would not yield any benefit by controlling annual forbs that are abundant one year and mostly disappear the next.

Does spraying for weeds pay?

The old saying "a pound of grass for a pound of weeds" always has brought visions of increased cattle production to ranchers, but is this saying based on objective fact or just folklore? Does spraying weeds translate into increased beef production or increased profits? Herbicide research by-and-large has not addressed cattle gain or cost-to-benefit ratio. Most herbicide research on grazing lands has been conducted on small, ungrazed plots in which plant response is measured. These are called efficacy studies.

In contrast to small-plot research, pasture-level research is more meaningful to a producer since it is the bottom line that counts. To date, research conducted on native plant communities has documented no increase in livestock production following herbicide application for the control of forbs. Thus, the assumption that an increase in grass forage on small plots following herbicide application can be scaled upward into increased livestock production should be viewed with skepticism.

A specific example from Oklahoma is research conducted during a five-year period by Oklahoma State University at the Marvin Klemme Range Research Station located near Bessie, Okla., to determine the effects of herbicide on livestock performance. This study found no improvement of livestock average daily gain or gain per acre with the application of herbicide to control non-noxious weeds. Thus, the cost of the herbicide was added to the cost of operation since there was no increase in cattle production. Producers easily could replicate this study on their properties to find out if herbicide application improves profitability.

If your time is limited and you feel your time is too valuable to spend digging and spraying musk and bull thistles and choose to spray the whole pasture, then the benefit to you would be more available time spent elsewhere. As far as improved livestock gains there probably will be none, and therefore, the cost-benefit ratio of spraying entire pastures is negligible.

The information from this fact sheet should not be taken to mean herbicide application always is an improper tool for managing non-noxious weeds. A weed is an undesirable plant, and Kansas has some serious introduced weeds, noxious weeds, and tree and brush problems. So herbicides are sometimes the best management tool. Land managers are encouraged to learn to identify and understand the plants they manage to determine if controlling those plants with herbicides will accomplish management objectives.

* Next week's column will address how cattle select a diverse diet of grasses, sedges, forbs, legumes and woody plants, if given a choice.

Stacy Campbell is agriculture

Extension agent in Ellis County.