6. Woody Plant Control in Northern Prairies

Encroachment of woody vegetation threatens the biology and ecology of prairie grasslands. Historically, wildfire and large herds of bison maintained open prairies. The loss of these natural forces, human-caused disturbance, and the introduction of non-native plants combine to impact native prairie vegetation and its associated wildlife. Removing invasive woody species improves the function of prairie systems and opens the landscape to provide more suitable habitat for birds and other wildlife that need large blocks of grassland for survival.

Managing invasive plants such as Siberian elm (Ulmus pumila), buckthorn (Rhamnus cathartica), honeysuckle (Lonicera spp.), locust (Robinia spp.), and other woody species is often difficult. Herbicide treatments applied alone or in combination with fire and mechanical methods, such as cutting and shredding, can provide cost effective management of woody vegetation. Use of herbicides minimizes site disturbance compared to mechanical methods, and can be applied on a variety of sites often throughout the year.

Woody plants and understory vegetation vary in their susceptibility to different herbicides and application methods. Land managers need to consider factors such as the biology, density, size and distribution of the target plants across the landscape. Combining two herbicides in a tank mix may improve woody plant control especially when treating a mixed stand of different species.  It is also important to consider goals for desirable understory vegetation on the site. For example, if the goal is to maintain desirable grasses, then apply selective herbicides such as Vastlan™, Garlon® 4 Ultra, Pathfinder® II, Milestone®, and Opensight® to control woody species and allow grasses to thrive.  Non-selective herbicides such as those containing glyphosate or imazapyr can cause injury to desirable understory vegetation. Read herbicide labels carefully and refer to “Recommendations, Methods and Equipment” below for species-specific recommendations.

Recommendations, Methods and Equipment

Controlling woody plants while they are small is the best management strategy. Woody growth less than six feet in height can be controlled efficiently and effectively with a foliar herbicide application. Trees and other woody plants scattered across the site can be treated by spraying either the foliage or the lower portions of the bark (referred to as “low volume basal applications” or LVB). Low Volume Basal applications with Garlon 4 Ultra or Pathfinder II will provide good control of trees too tall to treat with a foliar application.

Trees over six inches in diameter are difficult to control with a LVB application. The best management strategy for larger trees is to cut the tree down and treat the stump with a herbicide mixture. Follow-up monitoring and control will be necessary to treat re-growth that may occur from the cut stump or roots. Recommendations for larger trees that sucker from roots (such as cottonwood [Populus deltoides]) include cutting down the tree, treating the stump, and then monitoring the area for any new sprouts and seedlings. After one growing season, follow-up treatments can be made with foliar herbicide applications.

Foliar Applications

High Volume Foliar

The most efficacious and cost effective method to control woody plants is the use of a dilute herbicide/water mixture applied with a hand gun to fully emerged leaves and stems, referred to as a HIGH VOLUME FOLIAR application. It is important to thoroughly cover all leaves and stems, including the tops of the woody plants. Control will be greatest with complete coverage of the target plant with the herbicide mixture. Application with ground-based equipment is restricted by height of the target plant. Aerial application may be an option for taller trees (discuss with your Dow AgroSciences Representative http://www.dowagro.com/vm/contact/specialists.htm). Aerial treatments are suited to sites where there is less concern for damage to desirable plants (herbaceous and woody) growing in close proximity to the target plants. Aerial applications are generally less targeted to specific plants than backpack, LVB, or cut-surface treatments. See Table 6.1 for herbicide recommendations when using high volume foliar application.

Basal Applications

LOW VOLUMBE BASAL (LVB) treatments are well suited for controlling individual woody plants near desirable vegetation or sensitive areas, in low density brush situations, and for trees less than six inches in diameter that are too tall to foliar spray. Apply the herbicide solution (Table 6.2) entirely around the circumference of the stem in a band 12 to 15 inches wide, until the stem is thoroughly wet, but not to the point of runoff or puddling (Figure 6.1).

BASAL CUT STUMP treatments involve cutting six inches above the ground level followed by an herbicide application (Figure 6.2, left). Apply the herbicide solution (see Table 6.2 for a tank-mix guide) to sides of the stump, including the root collar area, and outer portion of the cut surface (cambium) until thoroughly wet but not to the point of runoff. Avoid cutting followed by herbicide application during heavy sap flow since this can interfere with penetration of oil-based basal mixes and decrease control. Heavy sap flow can also carry the herbicide mixture off the stump resulting in poor control. While it is customary to treat soon after cutting, applications may be made any time after cutting (for example, cut in winter and treat the following spring).

Herbicide Recommendation for Basal Applications

Garlon 4 Ultra herbicide plus basal bark oil is recommended for LVB and basal cut stump treatments. Basal bark oils are available from your herbicide supplier. To prepare the herbicide/oil mixture, make a solution of 25% Garlon 4 Ultra with 75% basal oil (Table 6.2). These mixtures can be applied all year; however, do not treat when stems are wet from rain, dew or condensation. Pathfinder® II is a ready-to-use formulation if you do not wish to mix your own herbicide solution; however, it becomes too thick to spray out at temperatures below 30⁰F.

Cut Stump Applications

Cut stump treatments involve cutting the tree close to the ground and applying herbicide only to the exposed cambium (Figure 6.2, right). Cut stump treatments may be made any time of the year as long as the herbicide does not freeze when applied, and the tree is not frozen. Avoid cutting followed by herbicide application during heavy sap flow since this can interfere with translocation. Heavy sap flow can also carry the herbicide mixture off the stump resulting in poor control. Cut stump applications should be made by thoroughly spraying the outer two inches of the cut stump of the tree. Apply herbicide in a continuous ring between the bark and the wood of the stump. If the bark is torn away from the stump, be sure to treat down the side to form a continuous ring around the bark since the coverage and uptake is essential for root kill. Cut tree surfaces should be treated immediately (within 30 minutes) with undiluted Vastlan™.

Control of scattered individual trees or other woody vegetation is best suited to low volume basal or high volume foliar treatment. 

Control of scattered individual trees or other woody vegetation is best suited to low volume basal or high volume foliar treatment. 

Clusters of woody brush, including species that “sucker” from roots such as cottonwood, are best controlled with high volume foliar treatments. 

Clusters of woody brush, including species that “sucker” from roots such as cottonwood, are best controlled with high volume foliar treatments. 

Buckthorn and Black Locust Control

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To control buckthorn with a high volume foliar application, mix a 2.5% solution of Garlon® 4 Ultra (2.5 gallons Garlon 4 Ultra in 100 gallons of water) + 1 quart surfactant (0.25% v/v) and spray to thoroughly wet all leaves and stems. When treating buckthorn with a low volume basal application, mix 25% Garlon 4 Ultra with basal oil (Table 6.2) and apply to the lower 12 to15 inches of the stem, all the way around the bark.

Black locust is more difficult to control than most woody plants. It spreads vigorously by sending up new sprouts from its stump and entire root system, especially after cutting. Foliar applications with Milestone® at 7 fluid ounces per acre (fl oz/ac) offers outstanding control on sprouts, provided coverage is complete. Low volume basal treatments can be used effectively if applied several months prior to cutting. Apply a 25% Garlon 4 Ultra + 2% Milestone LVB mixture (Table 6.2) to thoroughly coat bark completely around the entire stem, 12 to 15 inches above the ground level; allow at least two months of growing season conditions to elapse before cutting down black locust. Cut surface and basal cut stump treatments are not effective.

Photos, bugwood.org: Buckthorn by John Randall, The Nature Conservancy; Black locust by Richard Old, XID Services, Inc.

Tips for Successful Low Volume Basal and Basal Cut Stump Applications

  • Use a sprayer that has a shut off at the spray tip (Figure 6.3) to avoid wasting material.
  • Sprayer seals, hoses and pumps should be resistant to oil-based carriers.
  • Use an adjustable cone spray tip, such as Spraying Systems ConeJet 5500-X3 or Y3 up to X8 is ideal.
  • Apply herbicide spray to plant stems similar to applying spray paint.
  • Treat all the way around the plant stem in a band from the soil surface (root collar area) to 12 to 15 inches in height (Figure 6.1).
  • Do not treat plant stems that are saturated with water/precipitation.
vp Updated 8/2015

vp Updated 8/2015

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Always read and follow label directions.
Milestone has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. However, label precautions do apply to forage treated with Milestone and to manure from animals that have consumed treated forage within the last three days. Consult the label for full details. Some states require an individual be licensed if involved in the recommendation, handling or application of any pesticide. Consult your local Extension office for information regarding licensing requirements. Milestone is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.
Opensight specialty herbicides: When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product label for details.
State restrictions on the sale and use of Garlon 4 Ultra, Opensight, Accord XRT II and Transline apply. Consult the label before purchase or use for full details.