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Weed control on rangelands -- Part III

Published on -8/17/2014, 1:30 PM

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This is the last article in a series on weed control in rangelands. A brief summary of last week's article is research conducted by Oklahoma Cooperative Extension published in a fact sheet. Weed Control on Rangeland NREM-2882 on native plant communities has documented no increase in livestock average daily gain or gain per acre with a broadcast 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 broadcast herbicide application improves profitability.

Are weeds really that bad?

Given a choice, cattle ordinarily select a diverse diet of grasses, sedges, forbs, legumes and woody plants. Studies across the U.S. show the total amount of forbs consumed in cattle diets varies from 20 percent to 30 percent, depending upon availability. Many forbs have a higher nutritional value than grasses, even though forbs make up a small percentage of the total cattle diet. Therefore, herbicide application will reduce some of the most nutritionally valuable forage plants for livestock production forbs.

Let's compare the nutritional value of a common grass with a forb: Crude protein in big bluestem peaks at 10 percent in May and then declines to 9 percent by the end of summer. In contrast, Illinois bundleflower, a native legume easily killed by broadleaf herbicides, which also readily is eaten by livestock, has a crude protein (CP) of 35 percent in April and 13 percent at the end of summer. Western ragweed is one of the most commonly sprayed forbs in Oklahoma and Kansas, is consumed by cattle when young, and is one of the most important fall and winter foods of Northern Bobwhite quail. Western ragweed has a CP level more than 20 percent in May and approximately 15 percent in the fall. Research in Kansas and Oklahoma has shown Western ragweed does not compete with grass due to its deeper root system, so controlling it by applying herbicide does not yield more grass. Consider this trade-off: The cost of a pound of 20-percent protein cubes compared to the cost of spraying herbicide on plants that have more than 30 percent CP and readily are consumed by livestock. In fact, many broadleaf plants enhance quality of cattle and wildlife diets without the cost of supplements.

When to spray

Spot spraying or selectively targeting invasive plants can be effective in treating targeted species (true weeds or invasive) without harming other plants. Almost all approved herbicides have spot treatment recommendations on the product label. If a weed problem is so extensive spot spraying is not practical, then understanding the biology of the targeted plant species can provide important insight into managing the plant. Finally, the manger should consider if controlling the plant will meet management objectives including cost-benefit ration. Using an example of $10 per acre herbicide and application cost with cow/calf operation and are stocked at 10 acres per cow, the herbicide application will cost an added $100 per animal.

Alternative to spraying

More effective and economical alternatives to herbicide deserve consideration. For example, prescribed fire can accomplish many objectives of land owners, and an economic analysis of burning clearly shows break-even usually is exceeded. Some plant species targeted with broadcast applications of herbicide are woody plants that can be managed with prescribed fire. Burning improves livestock performance by increasing stocker cattle gain by 10 percent to 15 percent and increasing the body condition score of cows. It also increases forage quality and palatability, and benefits wildlife habitat.

Another alternative is patch burning (rotational fire with grazing), which has been shown to reduce or stop the increase of several invasive plant species.

Herbicide effects on wildlife

Killing most forbs with a broadcast herbicide application is detrimental to many wildlife species by decreasing habitat diversity and limiting food resources. If wildlife is a goal, landowners carefully should consider any herbicide application.

In summary, this information 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.

Stacy Campbell is agriculture

Extension agent in Ellis County.

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