Green Horizons

I don’t know how many calls I received this spring on how to control weeds in new forest plantings. But, they all pretty much went something like this. "I just finished planting my seedlings in an old field. What herbicide can I use to kill the weeds?"

By applying a 3 to 5-foot chemical barrier this fall, the seedlings you plant next spring will get off to a good start.

Weed management in new tree plantings begins with proper site preparation the fall before planting. The objective is to provide new seedlings with a 3- to 5-foot vegetation-free area. This weed-free zone can either be a strip or circle.

If planting in perennial sod (like fescue), the most effective way to kill existing vegetation is with a contact herbicide. Fall applications will provide more consistent control than spring applications. An added benefit is that your planting rows, or spots, will already be "marked" come planting time.

Control can be improved by mowing the area in late August or early September to eliminate existing foliage and treating the tender (and more susceptible) re-growth when at least 10" of new foliage is present.

Glyphosate (e.g., Roundup, Touchdown, many others) is the most effective contact herbicide for perennial sods. The recommended rate is dependent upon the type of vegetation (fescue, brome, bluegrass, etc) and the particular formulation of the herbicide you apply. For tall fescue, the recommended Roundup rate is 2 quarts per treated acre.

Remember that a treated acre is always smaller than an actual acre. This is because you are not treating a solid area; only the area around your trees. For example, planting trees on a 10’x10’ spacing will give you 435 trees per acre. If you plan to prepare a 4’-diameter circle around each tree, then your treated area is 1/8 acre [3.14(2 ft) 2 = 12.56 sq ft; 12.56 sq ft per tree (435 trees per acre) = 5,464 sq ft].

Make sure you read the herbicide label at least twice: before you purchase the product and again before you apply the herbicide. An excellent online source for product labels can be found at www.cdms.net. On the website’s main page, click on "Labels & MSDS"located on the left side. On that page you will find a search window. Just type in either the chemical name of the active ingredient (if you know it) or the product name to locate the product label.

I also recommend adding a second herbicide containing sulfometuron (e.g., Oust XP) alongside glyphosate to take care of any late-season grasses and broadleaf weeds. Sulfometuron has both pre- and post-emergent activity. As with glyphosate, make sure you carefully read the label as rates do vary depending upon where you live and what species you intend to plant. Here in the Midwest, the Oust XP label will allow fall application rates of 3 to 5 oz of product per treated acre on sites where northern red oak, white oak, ash (green or white), sweetgum or yellow-poplar are to be planted. These rates will also provide some pre-emergent control the following spring.

Sometimes weed control in new plantings cannot be started until the spring of the planting year. If it is begun early enough, before weeds have begun substantial growth, an application of a soil-applied herbicide at least two weeks before planting might get you out of your jam. For optimum tree growth, you may wish to respray dormant seedlings for the first 3 years following establishment.

But, spring weather conditions are usually dicey at best and the risk of damaging actively growing roots of freshly planted seedlings is high if you do not correctly apply the herbicide. So, your safest and surest bet is to prepare next year’s planting sites this fall.