For Release April 16, 2002

The Theory of Brush Control in Pastures

by Chuck Otte, Geary County Extension Agent

If you take most any grassland ecosystem and remove fire from it for an extended period of time, it will become a forest, or at the very least a scrubby brush land. The tall grass pastures of the Flint Hills are no exception. It starts with woody shrubs, quickly moves to cedar trees and over a longer period of time it will become a hardwood forest.

Periodic burning, not every year necessarily but once every two to four years, will greatly reduce the risk of this conversion occurring. Once a serious brush invasion has occurred, fire alone will probably not be effective in removing it. It may stop it from spreading any further, but it may not eliminate it.

How does fire control brush and trees? First of all letís separate the woody plants into two groups; the sprouting and the non sprouting species. A non sprouting species is one that, when cut off at ground level, or all the foliage is removed, does not put up new shoots from ground level or below. Cedar trees are about our only non sprouting species. Cedar trees are very flammable. Send fire past a small cedar tree and you will quickly remove all of itís growth buds and foliage and it is dead.

A sprouting species has the ability to generate new growth, stems and buds from whatever living, above or below ground, plant parts are left. Think of an elm tree in a fence row or a mulberry tree in your flower bed. If the shrub or tree becomes large enough, grass will cease to grow around itís base and then a fire is not capable of generating enough heat to damage the growing points 10 feet or more above the ground.

In the spring, a sprouting species starts to develop new leaves and buds. For a while, it is working completely off of stored food reserves within the plant. After a while, the leaves become big enough that they produce enough food to live on, plus replace the stored reserves within the plant. This switch from stored to produced food occurs about the time the plant reaches full leaf stage. If the plant is cut down ,or defoliated, at this point, it has to use more reserves to produce more growth thus making it weaker. Repeated timely cutting, can weaken a plant to the point that it dies.

Some brushy species, like buckbrush and dogwood, leaf out early enough that we can do serious damage, over time, to these stands with fire. However, the burn has to be in late April to be effective. Burning prior to April 20th is too early to provide control. Sumac leafs out enough later that it is hard to get much control with fire.

The other options for controlling brush are mechanical removal or herbicides. For reasons that we donít fully understand, using a herbicide the same year that we burn results in much poorer control. So if this year you donít burn many (any) of your pastures, it would be a good year to consider spot herbicide treatments. Or, go in monthly with a large rotary mower and keep mowing those sumac and dogwood patches off.

Our pastures are constantly at risk to being invaded by woody plants. Take the time to understand why this happens and how it happens and it will make your job of keeping grasslands growing grass a lot easier!


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