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  4. »Controlling Weeds and Grass

Kansas Forest Service

Kansas Forest Service
2610 Claflin Road
Manhattan, KS 66502
785.532.3300

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Controlling Weeds and Grass

Control of competing weeds is essential during early years of seedling establishment. The minimum establishment period is three years on good sites, but will be longer on poorer sites and with slower growing trees.

In general weeds should be kept less than 6 inches in height. Several methods of controlling weeds are available, including weed barrier fabric, mechanical cultivation, and herbicides

Weed Barrier Fabric
Weed barrier fabric is the preferable weed control method for many people. It's use usually results in better survival and growth, while greatly reducing irrigation and weed control labor. The weed barrier fabric offered through the Kansas Conservation Tree Planting Program is guaranteed for 5 years against ultra-violet degradation.

However, routine inspection of the material is required due to the fact the material breaks down with sunlight.  Once the seedlings are are established, shade is created and the material is less apt to break down. Therefore, the material is often times viable longer than 5 years. So it is important to check the seedlings to insure they are not growing into the fabric. If this happens, the seedlings will become girdled and die. If there is evidence that the plants are growing into the fabric, it is imperative to increase the size of the “slit” to allow the plant to continue growing. It is also important to try and keep the material free from dirt and debris on top of the fabric. This is important for two reasons. The first is again due to the fabric’s requirement of sunlight to break it down. The second is that if mulch, dirt, or tall grass is allowed to accumulate on top of the fabric, weed seed can germinate and send roots though the material. Weeds cannot grow from the bottom up through the fabric, but they can grow through the fabric from the top-down. 

Mechanical
Common mechanical cultivation tools include disc, roto-tiller, hoe, weed badger and others. Cultivate no deeper than 3 to 4 inches to avoid injuring tree root systems. Do not hit or "bark" the plants. Do not try to get closer than 9 inches to the plants. Clean up the job by hoeing around individual plants, or if that is not feasible, leave a narrow row of weeds down the row. This is not ideal but it will reduce the competition for nutrients, moisture and sunlight.

Mowing between rows is an alternative to cultivation on certain highly erosive sites, but does little to reduce the competition for moisture and nutrients. Mowing reduces fuel buildup, rodent cover, and makes the plantation more accessible for other management activities. Mowing, however, is primarily cosmetic and may encourage the growth of detrimental perennial grasses.

Herbicides
Post emergence or contact herbicides are applied directly to the foliage of actively growing weeds. It is important to read the labels and follow the directions of all herbicides. Some common contact herbicides include Roundup, Poast, Fusilade, and Stinger.

Roundup will kill most plant species if they are actively growing. This is a very useful herbicide, but you must keep it off of the tree or shrub's foliage.

Poast is a grass killer. It must be used in conjunction with an oil concentrate at the rate of 2 pints per acre. It has not been tested on all tree species, but is safe for over the top applications on most broadleaf trees and shrubs.

Fusilade kills most grass species if applied while the grass is in a rapid stage of growth. Fusilade can be applied over most trees and shrubs.

Stinger is a selective, post emergent broadleaf killer and can be applied over the top of most actively growing trees

Pre-emergence herbicides are applied to soil before weed seeds germinate. Labels must be followed very carefully. Equipment must be calibrated to ensure accurate application. Applying too much may kill the trees and shrubs and, of course, too little will fail to control the weeds. Some common pre-emergence herbicides are Casoron, Dacthal, Oust, Penulum, Surflan, Treflan, Goal and Princep (check the label to see which trees and shrubs can be treated and which weeds the herbicide controls.).