Green Horizons

In the last issue of GH, I talked about selecting which tree species you were going to plant this coming spring before it was too late to place an order. This same advice holds true in planning your weed control strategy for the coming growing season.

Without timely weed control you will be robbing your young trees of valuable sunlight, water and nutrients; all three are needed in abundance for a seedling to become established and be allowed to grow freely.

While mowing might look nice and satisfy some innate need to be on a tractor, it does little good for the seedling. True, available sunlight is increased. But, water and nutrient availability may actually be decreased because mowing stimulates weed growth. You also run the risk of injuring the seedling if you try to mow too close.

Chemical weed control is the most cost effective weed control method.

The choice of a herbicide depends upon: (1) the time of chemical application, (2) the tree species planted, (3) the kind of weeds to be controlled, and (4) the site.

Herbicides are either pre-emergent, applied before weed seeds germinate, or post-emergent, applied after weed seed germination. Pre-emergent herbicides are soil-applied and control weeds by inhibiting seed germination and seedling development. Post-emergent herbicides are generally applied to the foliage of established weeds to be absorbed and translocated. Often pre- and post-emergent herbicides are mixed to control both existing vegetation and newly germinating seeds.

Select an herbicide with specific label directions for use on the kinds of trees in the planting. An herbicide recommended for one species may not be safe for another. The age of the seedlings and how long they have been planted also should be considered.

Most herbicides used in tree plantings are effective against a particular group of weed species; grasses vs. broadleaves, annuals vs. perennials. One size does not fit all. Your best strategy is to select the herbicide that will control your most pressing problem.

The herbicides below are grouped according to time of application and age of the planting. The common names are listed alphabetically within each group. After the common name, the active ingredient, or chemical name is listed in ( ). The application rate is the range per treated acre listed on the label. Increase the rate as the weed pressure increases, but NEVER EXCEED THE MAXIMUM RATE. The remaining information gives the relative effectiveness of the herbicide and any special application notes.

For complete and up-to-date herbicide labels, as well as Material Safety Data Sheets (MSDS), visit www.cdms.net.

Common Sense Rules for Herbicides Herbicides are safe for the environment if one follows some common sense rules. READ THE LABEL and follow instructions for precautions and application rates. Spray herbicides with low pressure (10-20 p.s.i. max) on calm days only. Use lower rates of herbicide on coarse, sandy soil. When mixing two different chemicals, be sure to determine their compatibility by checking the labels or consulting your local MU Extension specialist. Wettable powder formulations require constant agitation for uniform application. Application equipment should be in proper working condition, calibrated, and free of contamination. Most pre-emergence herbicides require sufficient moisture to activate them. Dry soil conditions will require shallow cultivation if significant rainfall is not received within two weeks of application. Do not spray the foliage of desirable trees with postemergence herbicides. Clean equipment immediately after use. COLLECT RINSE WATER and apply to treated area. DO NOT DUMP IN STORM DRAIN OR ANY WATERWAY.

Pre- and Post-Emergent Treatments for New and Established Plantings Pre-emergent Treatments in New Plantings Dacthal F (DCPA): 7-8 qt/ac. Controls annual grasses and certain broadleaf weeds. Apply prior to bud break. May need to re-apply for season-long control. Goal T/O (oxyfluorfen): 2-8 pt/ac. Controls certain annual grasses and broadleaf weeds. Apply prior to bud break. May need to re-apply for season-long control. Pendulum (pendimethalin): 3.3-6.6 lbs/ac. Controls most annual grass and certain broadleaf weeds. Apply before weeds emerge and after the soil settles around the roots. Surflan AS (oryzalin): 2-4 qt/ac. Controls many grass and broadleaf weeds. Apply after the soil has settled around the roots, but before weeds emerge. Pre-emergent Treatments in Established (1- to 3-yr-old) Plantings Dacthal F: same rate as in new plantings Goal T/O: 5-10 pt/ac otherwise same as for new plantings Oust: 0.5-1.0 oz/ac. Controls many grasses and broadleaf weeds. Apply in fall or spring before weeds emerge or shortly thereafter. May be ineffective on soils with pH above 6.9. Use lower rate on sandy soils. Pendulum: same rate as in new plantings Princep L (simazine): 2-4 qt/ac. Controls wide variety of annual grasses and broadleaf weeds. Apply in late fall or early spring before weeds emerge. Do not use until one year after planting. Use lower rate on sandy soils. Post-emergent Treatments in Established Plants Fusilade II (fluazifop-P-butyl): 16-24 oz/ac. Controls annual and perennial grasses. Goal T/O: 5-10 pt/ac Poast (sethoxydim): 1.5-2.5 pt/ac. Controls many annual and perennial grasses. Add an oil concentrate at 2 pts/ac. Do not use in conifer plantings. Roundup (glyphosate): 1-2% solution. Spray to wet foliage. Kills on contact any grass or broadleaf weed. Transline (clopyralid): 0.25-0.33 pt/ac. Controls many broadleaf weeds. Can be applied over the top of actively growing trees. Excellent rescue treatment in thistle-infested fields. Vantage (sethoxydim): 2.2-3.75 pt/ac. Controls many annual and perennial grasses. It will slow or stop grass growth within 2 days. Burnback may take 3 weeks.