Green Horizons

In most parts of the Mid-West, this is the time of year that the heat is on and the good Lord’s irrigation is shut-off. This combination can spell trouble for trees, especially those newly- planted. Yet, there are ways to help ensure that trees live through droughty periods. This same management will also help maximize the growth potential of a given tree on given site. Maximized growth means trees will be taller, have fuller crowns, and better diameters. The management I am referring to the control of competition from nearby vegetation.

There are many methods for controlling competition from "weeds" And let me be up front, I use the term weed broadly to also include most grasses. Grasses, especially those like tall fescue that form sods are, in many cases, the most competitive of weed types. What is not included in my definition of weeds is all legumes. Some legumes can in fact be beneficial to tree growth in that they "fix" nitrogen from the air as well as incorporate it into the soil where it becomes available to the trees while competing minimally with trees for water. The methods for controlling competition are many. Whatever method you choose, its application can be facilitated by proper spacing (as defined by the equipment used) of the managed trees.

Chemical weed control applied around individual trees.

Included in the list of weed control options are cultivation (often termed mechanical), mulches (including weed barrier fabrics) and the use of chemicals. Mowing is not good weed control! Although mowing controls competition above the ground for light, weeds are still in competition for the available water and nutrients on a site. Moreover, with both cultivation and mowing you run the risk of hitting a tree and creating a wound that is likely to reduce the tree’s value if harvested for timber. While economics might not be the overriding concern of all landowners, a healthy tree that maximizes it’s growth potential on a site will better meet any and all objectives, whether conservation, aesthetic or timber production. So, regardless of your reason for managing trees, why not strive to produce the best. That said, let’s take a brief look at the individual methods of weed control.

Mechanical
Cultivation can be effective in controlling vegetation. Equipment such as a disc, rototiller and hoe can be used individually or in combination. Cultivation should begin in the spring and should be done as necessary to control weeds as they reach about 6 inches in height. You will probably need to cultivate anywhere from 3-6 times a growing season. To avoid damage to seedlings and trees, you should keep disc, rototiller and other mechanical methods of control at least 6-9 inches from your trees and till no deeper than 4 inches to avoid damage to root systems. While this is preferable to no weed control, to really be effective will require supplemental hand cultivation (or herbicide, or mulching) adjacent to individual trees or seedlings.

Mulching
Mulch can effectively reduce or eliminate weed competition close to the tree, conserve moisture and, in some cases, increase organic matter in the soil. In addition to the more traditional mulches like sawdust, wood chips, bark, shredded newspaper or aged silage, weed barrier fabrics can provide excellent weed control. Prior to applying a mulch treatment, soil should be weedfree. This again underlines the point that planning prior to planting goes a long way towards making easier the application of your selected weed control method. Mulches should be 4 inches deep and extend out from the seedling in a 2 to 4-foot diameter circle. When seedlings are small, the area of weed control can also be small, but as the seedling begins to grow, it will benefit from more extensive areas of weed control.

As previously stated, weed barrier fabric is an alternative to the more traditional mulches. There are a number of different types of material used in making these fabrics. You should choose one that is permeable to air and water, yet not to sunlight. Typically, you will need to eliminate the existing vegetation and install the weed barrier prior to planting. The weed fabric, normally sold in rolls, is used to cover predesignated planting rows. An exception to this is a weed mat that is typically 4 feet square and has a cut from one side into the center to allow placement around existing trees.

Finally, there has been research on the use of certain plants, in particular legumes, for use as "living mulches". Because living mulches provide ground cover, they can be extremely beneficial where erosion concerns exist. The ground cover they provide can also serve to limit the loss of soil moisture when compared to alternative control methods that may leave soil exposed to direct solar radiation. Legumes such as common hairy vetch, common white clover, red clover, and birdsfoot trefoil, have been shown to result in tree growth comparable to that observed where little or no vegetation exists. It is desirable that a living mulch have dense foliage, exhibit prostrate growing habits and be of a cool-season variety. Other points to consider are, that the plant is good at suppressing the growth of undesirable weeds, it is shade tolerant, contributes nitrogen to the soil, is easy to establish, persists relatively well and competes minimally with the trees.

Chemical
When applied according to label instructions and under the appropriate conditions (weather, time of year, etc.), herbicides can be a safe and effective means of controlling competition from weeds. Application can be made with handheld sprayers, backpack sprayers, or tractor mounted boom sprayers. Granular formulations can be applied using mechanical or handoperated spreaders. Whatever the form, when applying herbicide keep your equipment calibrated properly and follow label directions. Label directions will include information on application rate and methods, vegetation controlled and whether the chemical is compatible with the trees you have planted.

Primarily, there are two types of herbicides that exist -- preemergent, applied to the soil before weeds emerge, and post- emergent, applied directly to foliage of growing weeds. When applied to the soil, pre-emergent herbicides stop seed germination or development. Foliar applied herbicides applied after weeds have emerged work in a number of different ways. There are also herbicides that have both soil and foliar active compounds that will eliminate weeds. In many cases a combination of pre- and post- emergent herbicides are necessary for effective, lasting control of weedy competition. Always read and follow label directions to be sure of each chemicals compatibility for mixing. And, when in doubt, contact the manufacturers representative for recommendations.

Considerations in deciding which herbicide is appropriate will include:

1. tree species
2. weeds to be controlled
3. soil types and site conditions
4. method of hebicide application
5. the age of your trees

Conclusion
Proper management of competition from weeds will prove to be significant in helping achieve your goals for establishing and growing trees. Understanding the benefits of weed control leads to the next step, deciding which method is right for you and the trees you manage. Hopefully, this article will help get you started in making the decision to control competition from weeds. Remember, before you spend money on other cultural treatments, invest first in weed control!

For additional information on cover crops please refer to
http://www.attra.org/attra-pub/PDF/covercrop.pdf

To assist in determining the proper selection of herbicide(s) to meet your needs the following web sites contain valuable cross reference information and should be consulted.
(1) http://www.oznet.ksu.edu/library/forst2/mf656.pdf
(2) http://forest.wisc.edu/extension/publications/76.pdf

If you would like additional information on weed control or design of a tree planting please contact:
Dusty Walter, UMCA Technical
Training Specialist at
(573) 884-7991