Brush Management in Wisconsin

Jerry Doll

Woody plants often interfere with the productivity and utility of both agricultural and non-crop lands. In pastures, brush reduces forage production, limits the animal's ability to graze, and may cause physical or chemical injury to livestock. Along roadsides and in other right-of-way sites, unmanaged brush reduces visibility, interferes with the utility of electric power lines, causes clogging and sedimentation problems in drainage areas, and may create a fire hazard. Poisonous woody plants, such as poison ivy and poison oak, present serious health problems to humans.

In many areas, woody plants serve useful purposes. They may reduce or prevent soil erosion, provide or contribute to habitat for wildlife, fish and beneficial insects, and trees and woody plants often give beauty to roadsides and other areas. Where these considerations outweigh the disadvantages, woody plants should be left undisturbed.

Management Methods

Cultural Control. In general, the principles of suppressing vegetative weeds like Canada thistle in pastures by maintaining a highly competitive mix of desired species also apply to woody species. However, once established, cultural practices alone are not sufficient to achieve brush control. Nevertheless, efforts to maintain a dense, vigorously growing mix of desired forbs and grasses usually prevent brush species from germinating and becoming established. And once brush has been controlled mechanically or chemically, a sound cultural management program of rotational grazing, plant nutrient application, etc. will help the desired species remain the dominant vegetation in the site.

Mechanical control measures vary in effectiveness from species to species. Oaks, maples, black cherry, mulberry, honey locust, and box elder will usually resprout from the stump. Ash, hickory, sycamore, alder, willow, and elm resprout readily when cut as young saplings or small trees but lose much of this potential as they age. As a general rule, sprouting is most vigorous in young deciduous trees before they reach the seed bearing age. Conifers will not resprout after cutting.

The season when trees are cut influences resprouting vigor. Food reserves stored in the roots are highest during the dormant season from November to early May and lowest just after the leaves are fully expanded in the late spring. The greatest degree of sprouting occurs when trees are cut while dormant and the least if they are cut after full leaf expansion. Cutting in the late summer may not give sprouts time to harden before winter comes.

Stump height also affects resprouting vigor. Trees with a stump diameter of less than five inches should be cut at ground level. This will remove many of the food reserves available to the sprouts. It is often difficult to cut large trees at ground level.

Chemical brush control is often very effective and economical. Herbicides often require less labor per acre to control brush than mechanical means. Frequently, mechanical and chemical means can be integrated into successful control programs by treating the cut stumps to prevent resprouting or by cutting brush over 8 feet tall and spraying the regrowth several weeks or months later.

Follow these steps to achieve the desired results with herbicides for brush control:

1. Identify the species to be controlled. Woody plants vary in susceptibility to herbicides, and accurate identification of the species to be killed is essential. Many brush species are easily recognized. If there are some that you cannot identify, collect a sample of the plant and send it to your local County Extension office, Department of Natural Resources forester, or another plant expert in your vicinity. Leaf shape and bark characteristics are usually sufficient to identify brush species.
2. Select the herbicide and the appropriate rate and carrier. The site to be treated will influence the selection of the herbicide to be used. As Table 1 shows, relatively few products are registered for brush control in pastures. The alternatives in Wisconsin pastures are 2,4-D, Banvel, or the combination of these products (Weedmaster), Spike, Roundup, Crossbow, and Garlon. None are approved for application to brush in water and most prohibit treating sites where runoff into water may occur.
3. Select the preferred method of treatment. Several alternatives exist, and the appropriate one for each situation must be determined (see Table 3). The possible methods of application and their characteristics are as follows:

A.  Foliage-stem sprays. The spray solution is applied to just wet the leaves or leaves and stems. Water is used as the carrier for many products while a mixture of water and diesel fuel or kerosene are used for others. Treatment is usually made from the time the leaves are fully expanded until they begin to turn color in the fall. Some products, like Krenite, should only be applied in late summer or early fall. Plants should not be under moisture or heat stress when treated. The risk of particle drift to nearby sensitive vegetation is greater for foliage-stem sprays than for other application methods.

B.   Basal sprays are directed to the lower 12 to 18 inches of stems and trunks that are less than 4 to 6 inches in diameter. The root collar area around the base of the plant is usually treated as well, and this normally prevents resprouting. Basal treatments are usually effective on canes and small stems as well as on trees up to 6 inches in diameter. Diesel fuel or kerosene are the usual carriers used to apply herbicides in basal treatments. Only oil soluble or ester herbicide formulations can be used with diesel fuel or kerosene. Application can be made any time of the year except when snow is present.

Some products are available as undiluted material that are ready to be applied directly as basal sprays. Examples are Weedone CB, Banvel CST, Pathfinder and Pathway. While such products are convenient to use because no mixing is required, they may be more expensive than other alternatives. Basal treatments can be more labor intensive than foliar sprays but are useful in selectively removing undesirable species from stands of desirable trees.

C.   Cut-stump treatments are made to freshly cut stem or stump surfaces. As with basal sprays, diesel fuel or kerosene are the usual carriers. Application should generally be made within 2 to 3 hours after cutting because if the cut surface drys, control is reduced. Usually the cut stump, the remaining trunk and exposed roots are treated with the herbicide solution. Some products are applied only to the outer edge of the cut surface (the cambium area). Cut stumps applications are effective most of the year, but most products prohibit application when snow is on the ground and during periods of heavy sap flow in the spring.

Several ready-to-apply products for cut surface treatment are available. This eliminates the need to purchase, haul and mix a carrier with the herbicide. Cut surface treatments are recommended when trees are 4 inches or more in diameter and are usually more effective than basal bark sprays on plants larger than this size.

D.   Soil applications of sprays, granules, pellets, or concentrated liquids applied with exact delivery hand application devices control many brush species. After application, rainfall moves the herbicide into the root zone. The herbicide is taken up by the roots and translocated to the shoots, stems and leaves where it then kills the plant. Treatment is usually made to the base of the plant. Sometimes the product is distributed in a broadcast or random pattern under the drip line of target plants. Nearby trees may be injured or killed if their roots extend into the treated zone. Soil-applied herbicides usually remain active in the soil for several months or even years. Treatments can usually be made any time of the year when the ground is not frozen, but control will only occur after sufficient rain has fallen.

Product Descriptions

All products have limitations and precautions described on their labels: read and follow them closely. Because these herbicides are often different from those used in field and vegetable crops, a brief description of each one follows.

• Access is a premix product containing 1 lb/gal picloram and 2 lb/gal triclopyr. It can only be used in non-cropland sites and can only be applied as a basal bark treatment. Access has a groundwater advisory statement because of picloram's high solubility and long persistence in the soil. Both active ingredients have growth regulatory activity and primarily affect primarily broadleaf species.
  

• Accord contains 3 lb/gal glyphosate and is identical to Roundup except that it is labelled for use only in forestry and right-of-way sites. Over 50 woody brush and tree species are listed on the label. Glyphosate is a systemic, non-selective herbicide with no soil activity or residues. It kills plants by stopping protein synthesis, but not in the same way that sulfonylureas and imidazilinones do. Therefore, the development of weeds resistant to glyphosate should not be affected by the use of other herbicide groups.
  
• Arsenal contains 2 lb/gal of imazapyr, a member of the relatively new herbicide family, the imidazilinones. It kills plants by inhibiting the production of an essential amino acid and its mode of action is described as an ALS inhibitor. The mode of action is essentially identical to that of sulfonyl-urea herbicides and unless precautions are taken, the use of herbicides with the same mode of action may lead to the appearance of herbicide resistant weeds. Arsenal is systemic and treated plants stop growing soon after application but complete kill may not be evident for several weeks. It can provide complete vegetation control of a wide range of brush and grassy weeds.
  
• Arsenal is also available in granular formulations that contain 5% active ingredient for use in forestry sites only or 0.5% active which is for preemergence control of only herbaceous weeds in right-of-way areas. Imazapyr is also available as "Chopper", a 2 lb/gal formulation for application only to brush and trees via cut stump, basal bark, or infection treatments. Chopper RTU contains 0.255 lb/gal imazapyr and is applied undiluted as a basal bark or cut surface treatment to kill trees and brush.
  
• Banvel is available in several formulations, all of which contain dicamba as the active ingredient. Conventional Banvel contains 4 lb/gal dicamba amine and is usually applied as a foliar spray. A new formulation, Honor, is being introduced that miminizes the risk of dicamba vapor movement from the target site.
  
• Banvel CST is a ready-to-use formulation of dicamba for cut surface applications. It contains 1.0 lb/gal dicamba. Banvel 520 is an oil-soluble premix of 1.9 lb/gal 2,4-D ester and 1.0 lb/gal dicamba for basal and cut surface applications. Banvel 720 is a water soluble premix of 1.9 lb/gal 2,4-D amine and 1.0 lb/gal dicamba that can be applied to the foliage and stems of brush and trees. Dicamba has a growth regulator mode of action and is adsorbed through both the foliage and roots.
  
• Crossbow is a premix that contains 2 lb/gal 2,4-D ester and 1 lb/gal triclopyr ester. Because both ingredients are esters, take all due precautions to prevent vapor drift. Crossbow can be applied in many sites and by several methods for selective control of many brush and herbaceous broadleaf species.
  
• Escort is a sulfonylurea containing 60% metsulfuron which kills plants by inhibiting the production of certain amino acids, thereby stopping protein synthesis. It is an ALS inhibitor, similar in mode of action to the imidazilinones. Application rates are in ounces or fraction of ounces per acre so calibrate sprayers and measure the product very accurately. Escort is generally more effective on broadleaf species but can suppress grass, especially at moderate and high rates. It is applied as a foliar spray during the growing season and kills plants slowly. Do not use sprayers that have applied Escort to apply pesticides to crops.
  
• Garlon products contain triclopyr as the active ingredient. Garlon 3A contains 3 lb/gal of the amine and Garlon 4 has 4 lb/gal of the ester formulation. Triclopyr has growth regulatory properties towards broadleaf species but has little effect on grasses. It is often applied in combination with other 2,4-D or other herbicides.
  
• Hyvar is a non-selective, persistent herbicide available in several formulations that contain bromacil as the active ingredient. It kills most species and could be used where total vegetation control is desired or to kill individual brush/tree species via a spot application to the soil. Hyvar can be mixed with other herbicides to broaden the spectrum or increase the speed of vegetation control.
  
• Krenite contains 4 lb/gal fosamine and is a selective contact herbicide that has almost no soil activity, kills many brush species and is safe to grass. It only affects treated vegetation so thorough coverage of the brush to be killed is essential. Krenite has little visible effect on plants the year of application so "brownout" is not evident. The following season plants do not leaf out and subsequently die.
  
• Pathfinder is a ready-to-use product that contains 1 lb/gal of triclopyr ester, the same active ingredient in Garlon 4.
  
• Pathway is a ready-to-use product that contains 3% picloram and 11.2% 2,4-D, both as amine formulations. It is identical to Tordon RTU and is primarily used as a cut stump or injection treatment.
  
• Roundup can be used for brush control in pastures and right of way sites. Comments regarding mode of action, etc. are the same as for Accord. All vegetation below and immediately around treated brush is usually killed. No more than 10% of an acre can be treated per season.
  
• Spike contains tebuthiuron as its active ingredient, a very persistent, non-selective herbicide in the substituted urea family. It controls nearly all brush and herbaceous species, persists in the soil for several years, and kill plants by stopping photosynthesis. It is sold in several formulations, but only the 20P formulation is clearly labelled for use in pastures. The pelleted formulations are easy to apply but take care not to over apply and to limit the area treated on sloping sites.
  
• Tordon contains picloram as its active ingredient and is available in several formulations and brand names that can be applied in several methods to control a wide range of brush species. It is a systemic, selective and persistent herbicide that moves readily is soil and therefore the labels of all products containing picloram have a ground water advisory statement. Many formulations of picloram-containing herbicides are restricted use products due to the risk of contaminating ground and surface waters, as well as to the risk of injuring sensitive vegetation outside the target site.
  
• Velpar contains hexazinone as its active ingredient. The liquid formulation has 2 lb/gal hexazinone while the granular product "Pronone" has 10% active ingredient. It is a non-selective herbicide that is absorbed by either plant foliage or roots and kill plants by stopping photosynthesis. It is subject to leaching or horizontal movement from the application site but is less persistent the Spike or Hyvar.
  
• Weedmaster is a premix of 2.8 lb/gal 2,4-D amine and 1 lb/gal dicamba (Banvel). It can be applied as a foliar spray to control several brush species, but it is used primarily on herbaceous vegetation.
  
• Weedone 170 contains 1.85 lb/gal of the ester formulations of both 2,4-D and 2,4-DP. It can be mixed with water for foliar applications or with oil for basal and cut surface treatments.
  
• Weedone CB contains 0.67 lb/gal of the ester formulations of 2,4-D and 2,4-DP and is applied without mixing as a basal or cut surface treatment.

The following tables summarize basic information on these products:

Table 1 lists the approved sites of application.

Table 2 describes the spectrum of species affected by herbicides and gives their approximate length of persistence in the soil. Selectivity and persistence are affected by several environmental conditions and the information in this table assumes normal weather and typical soil conditions. The currently approved application methods for brush control products are listed in

Table 3 Product uses change occasionally so be sure to consult recent product labels and supplemental information for up-to-date registrations before making any herbicide application.

October 1992