by Hank Stelzer
Extension Forester
Weed control is crucial during the early years of a new forest planting. With limited amounts of moisture and nutrients around each planting spot, it is either your seedlings or the weeds.
Some people think that mowing or weed-eating is a good way to control weeds. At best, this practice will improve the amount of sunlight the seedling receives. However, it will not increase the availability of moisture and nutrients for seedling growth. Additionally, a few grasses, such as tall fescue, produce a chemical that inhibits tree growth. During the mowing process you also run the risk of damaging the tender bark of a seedling. These wounds can provide an easy entry point for disease and insects. It can also lead to internal defects, such as heart rot, that can structurally weaken the tree and eliminate the possibility of producing high quality lumber at harvest time.
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A backpack sprayer is a commonly used and effective method for applying herbicides in forest plantings. |
Weed barriers are another way to control weeds, but they can be costly and labor-intensive to install. Also, in a few cases it has been noted that the mat material does not degrade, and over time may become ingrown into the tree.
A living mulch is vegetation, usually a legume, established at a high enough density to suppress the growth of undesirable weeds. A few examples of living mulches include crown or hairy vetch and sweet, red or kura clovers. While legumes can take up atmospheric nitrogen and return it to the soil, they also compete for available water and nutrients. So, this organic form of weed control may not be suitable for new plantings.
Chemical weed control means herbicides. The mere mention of the word should not strike fear in your heart. When the right herbicide is selected and properly applied, chemical weed control is the most effective and economical way to insure the survival and growth of your new forest. Wherever you plant, good weed control begins with site preparation and can be most effective when started the fall prior to a spring planting. Mow vegetation in mid- August and allow the weeds to grow back until they are 6" to 8" tall. Then treat your planting spots with a foliar-applied broad spectrum herbicide such as Roundup™. Today several chemical companies make this glyphosate-based herbicide. Your best bet is to buy an undiluted product containing at least 41% glyphosate and follow the label instructions for mixing and application rates.
Pre-emergent herbicides applied before tree planting kill germinating weed seeds, but do not harm seedling roots unless improperly applied. If you are forced into preparing your site this spring it is not a big problem. You can combine (or “tank mix”) the contact herbicide along with this pre-plant treatment. Again, it is essential that you fully read the labels of both herbicides prior to their use in a tank mix. Pay particular attention if there is a period of time either before or after planting when the chemical may not be applied.
Weed pressure will increase through the growing season. Most chemical treatments begin to lose their effectiveness 60 days after application and are usually totally ineffective 90 days out. Depending upon the environment, site quality and moisture conditions, additional chemical treatments may be necessary. If you applied your herbicide in mid-April, count on a second application in mid- to late-June; maybe even again in early August if summer rains prolong the growing season.
| Weed Control: Internet Resources and Contacts The following web sites provide information on commonly used forestry herbicides and application methods: http://forest.wisc.edu/extension/publications/76.pdf; and www.oznet.ksu.edu/library/forst2/mf656.pdf An excellent website for obtaining herbicide labels is www.cdms.net. For specific weed control questions, contact Hank Stelzer, MU forestry extension specialist, at (573) 882-4444; or email at stelzerh@missouri.edu. |
