When brush or woody plants become invasive and begin to ruin forage quality, an economical control program is warranted. There are many options for controlling brush and the selection of a method or a combination of methods should depend on the factors listed in the sidebar. Brush control methods are grouped as mechanical, chemical, cultural and biological.
Choices of mechanical brush control methods are either entire plant removal or the cutting of the aboveground portions. Shredders, roller choppers, hydraulic shears, and various types of saws are used to remove aerial parts of plants. Entire plants are removed with grubbers, disks, and root plows.
Brush shredders are actually flail mowers built strong enough to cut woody stems 3 inches or less in diameter. Flail mowers cut plant material with knives mounted vertically on a cylindrical drum that rotates. An advantage of using a shredder is that it mulches brush, leaving a good environment for grass and forb seed germination. A disadvantage is that it requires a high amount of maintenance.
“Roller choppers are cylinders hung on a frame with blades welded on them in a longitudinal pattern,” said Robert Thomas, Marden Manufacturing Company. “The drums are pulled as single units, side by side in duplex or triplex, or one behind the other in tandem. Roller chopping provides moderate brush control through the crushing and cutting action of the drum and blades,” he explained.
Saws are effective tools for removing plant top growth and the type used is dependent on amount and density of brush. Chainsaws are used for thinning and removing individual trees. Saws mounted on tractors or skid steers are usually more economical when there is an acre or more of woody plants to remove. Saws are especially useful for cutting large stems and trees. A disadvantage of using saws is that the limbs and stems are left lying on the ground and may need stacking.
“Grubbing is the severing of tree roots below ground by a sharp, U-shaped blade mounted on a tractor,” said the late Harold Wiedemann, former agricultural engineer with the Texas Agricultural Experiment Station in Vernon, Texas. “Tractors used for grubbing include farm-type, crawlers, or skid steers, depending on the size of trees.”
Many contractors use trackhoes (excavators) to grub brush. The machine is called a trackhoe because it moves on tracks and resembles a backhoe. Small to moderately sized woody plants are dug with one stroke of the bucket, which allows them to excavate a lot of brush per hour at an economical cost. A disadvantage of grubbers is that they leave holes in the ground where trees are extracted.
Disks used for brush control are the heavy-duty offset style. Blade diameters range from 30 to 36 inches and units are 8 to 12 feet in width.
“Rootplows are heavy-duty V-shaped, horizontal blades, 10- to 16-feet-wide that are pulled by a large crawler tractor,” said Wiedemann. “The blade severs roots at a depth of 12 to 14 inches, preventing regrowth of nearly all brush species. Three to five fins, 20 to 30 inches long, mounted at a 28-degree angle on the cutting blade, help loosen the soil surface and destroy many of the shallow-rooted species that might otherwise survive.”
Several herbicide application options are available and selection of the method depends on the factors listed in the sidebar. Broadcast applications are appropriate for controlling susceptible brush species on large acreage and where unwanted plant populations are dense. Aerial broadcast sprays are applied with either helicopter or fixed-wing aircraft.
Broadcast ground applications are done with sprayers mounted on tractors, trucks, or all-terrain vehicles (ATVs). Trailer-type sprayers are mounted on wheels and are towed. The two primary spray delivery systems on ground broadcast sprayers are nozzles mounted on a boom or boomless nozzles.
On a small amount of acreage, it is often more economical to treat unwanted plants individually. Individual plant treatment (IPT) is the only way some plants like cedar or juniper are controlled with chemicals. Certain methods of IPT are an excellent way to control plant regrowth following broadcast sprays or mechanical treatments.
Different application equipment such as small pump-up garden, backpack, and cattle sprayers are all suitable for IPT. Sprayers mounted on 4-wheel-drive ATVs are also commonly used. Garden sprayers are best for treating a few scattered plants, while backpack sprayers are usually more efficient for treating higher densities of plants on larger areas. ATV sprayers work well on large acreages or when plants are far apart.
The leaf spray method is thoroughly wetting all leaves of each plant to the point of runoff. This application method is effective when plants are actively growing and works best on plants less than 3 feet tall. For leaf sprays, the herbicide is usually mixed in water.
Stem sprays were known in the past as low-volume basal applications and are suitable for low-density, large tree-type plants. A mixture of herbicide and diesel fuel is sprayed lightly but evenly on the plant’s stem or trunk up to 12 inches from the ground. Stem sprays are effective at any time during the year, although best results occur when plants are treated during the growing season.
Cut-stump sprays are effective in preventing woody vegetation from resprouting after its top growth has been removed by mechanical means such as with pruning shears, ax, chainsaw, or hydraulic shears. Stumps are effectively treated any time of the year, but the best results occur from applications during the growing season.
Whenever using chemical brush control, always follow label directions and university application recommendations for best results.
Cultural and biological
Cultural control methods include grazing management and prescribed fire. Proper grazing management promotes a healthy stand of forage that can help prevent growth of unwanted plants. Properly timed controlled fires eliminate some brush seedlings and remove accumulations of dead materials to provide a healthy environment for forage production.
Biological control refers to any technique that involves use of the plant’s natural enemies to control its spread. Examples of biological control agents include arthropods (insects and mites), plant pathogens (fungi, bacteria, viruses, and nematodes) and ruminants (goats, sheep, cattle, and white-tail deer).
Shinnery oak, blackjack oak, and post oak sprouts are controlled by goats. They eat enough juniper to provide control as long as their browsing is followed by prescribed fire. Several people in the Western states have taught cattle to eat sagebrush, which is a plant they don’t normally consume. As a result of this training, the cattle become a sagebrush control alternative.
Saltcedar is being controlled in Texas by a beetle introduced into the United States from northern China, Uzbekistan, Crete, and Tunisia. Beetle larvae and adults feed on the small, scale-like leaves of saltcedar causing them to turn brown and die. Larger larvae and adults may also feed on the bark of small twigs, causing the ends to die. A large infestation of larvae can quickly defoliate saltcedar trees. Although the trees can grow new leaves, they are not expected to be able to withstand repeated feeding by several generations of beetle larvae.
Selected brush control methods should fit the management plan and provide a good return on the investment. Often a combination of brush control options provides the best mix of effective and economic results.
Factors to consider when selecting a brush control method:
- Fits the overall land management plan
- Thinning trees or removing all trees from an area
- Brush density and size
- Size of the area
- Soil type
- Brush species
- Distance from bodies of water and areas where people gather
- Estimated return on investment
This article appeared in the March 2018 issue of Hay & Forage Grower on pages 26 and 27.
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