| Cooperative Extension College of Agriculture & Home Economics Washington State University Pullman Washington |
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Killing unwanted trees or preventing stumps from sprouting is a problem for many property owners. Various herbicides and application methods can kill unwanted stumps or trees. First, you must identify which tree is causing the problem. Once you are sure of the culprit, you can use the charts in this bulletin to match the tree to the appropriate herbicide and application. Successfully controlling unwanted trees or brush also means considering the consequences of the herbicide and application method you select. Herbicides that control undesirable woody plants vary in environmental stability, leachability, flashback potential, selectivity, and handling requirements. Control methods can damage surrounding vegetation and neighboring trees, contaminate groundwater, and prevent desirable vegetation from becoming established for several years. Herbicide drift onto adjacent desirable plants has been a problem when using handheld equipment, especially when treating brush growing along fence rows. Apply only when there is little or no hazard from spray drift. Very small quantities of spray, which may not be visible, may seriously injure susceptible plants. Do not spray when wind is blowing toward susceptible crops or ornamental plants near enough to be injured. When treating trees and brush use a low pressure coarse spray and treat all sides of the plant. Drift often occurs when trying to spray the entire plant from only one side. Read and follow herbicide label directions carefully. This bulletin suggests ways to avoid problems, but does not supersede product label instructions or cover first aid, or storage and disposal requirements. The herbicide label lists hazards that may make it unsuitable for use in certain situations. Read and follow requirements on the herbicide label closely. | |||
| Important Considerations | |||
| Consider the following factors carefully before choosing a control method. Each factor can affect the success of your project. | |||
| Suberization | |||
| Plants use this natural healing process to prevent insects or diseases from infesting tissues after cuts or wounds occur. The plants develop a layer of protective "corky" cells over the damaged tissue. Suberization can reduce herbicide effectiveness by preventing absorption. When you use frilling, cupping or cut stump methods of treatment, apply the herbicide immediately to achieve maximum absorption. Delaying application of water-soluble herbicide for as little time as one hour can reduce absorption and subsequent control of the undesirable woody plant. | |||
| Root Grafts | |||
| Sometimes the roots of different plants share vascular tissue through grafting. Root grafting occurs primarily within the same species, but may occur between plants within the same genus. This phenomenon can be of great importance. A herbicide can move (translocate) from a treated tree to an untreated desirable tree, killing or injuring it. Damage to desirable trees as a result of root grafting will occur from use of the following herbicides: amitrole, 2,4-D, dicamba, glyphosate, imazapyr, metsulfuron, picloram, and triclopyr. | |||
| Flashback | |||
| This term describes the passive loss of a herbicide from the roots of treated trees. Once the herbicide is released from one tree, it is available for uptake by another. The serious consequence of this is that a treated tree may release herbicide back into the environment, injuring other nearby trees and vegetation. This occurs with picloram, dicamba, and occasionally with 2,4-D. | |||
| Formulations | |||
The herbicide formulation may affect its performance characteristics. Match the formulation and application method. For example, water-soluble amine formulations of 2,4-D and triclopyr are preferred for cut surface applications. Use oil-soluble ester formulations for best control on basal applications. Other herbicide formulations include wettable powder, dry flowable, water dispersable granules, or flowables. These soil-applied formulations require moisture to move them into the soil and activate them. If you plan to use oil as the carrier or part of the carrier in the spray mix, use either diesel fuel or stove oil. Add an emulsifier when mixing fuel oil with water. | |||
| Stains and Dyes | |||
| Adding stains or dyes to the herbicide solution substantially increases applicator accuracy. Applicators use the dyes to monitor treated trees, so they are less likely to miss or respray targeted trees. Use of stains also will indicate personal exposure. The inexpensive, water-soluble stains wash off later. | |||
| Dripline | |||
| Refers to the area directly underneath the spread of the tree limbs or canopy. Herbicide labels frequently caution against making applications within the dripline to avoid damaging desirable trees. Tree roots often extend well beyond the dripline. More appropriate is the rule-of-thumb that tree roots extend a distance equal to the height of a tree growing east of the Cascades, and equal to half of the height for a tree growing west of the Cascades. If the tree has been topped, increase the height estimate to more accurately gauge the drip line of the tree. | |||
| Heavily Pruned Trees | |||
| Some trees sprout prolifically, particularly after severe pruning. It is impossible to control the sprouts chemically without injuring the tree. Contact herbicides, such as paraquat (Gramoxone) and MSMA may be used to burn off these suckers. However, these non-selective herbicides will injure any plant incidentally sprayed. CAUTION: do not use paraquat around homes, school, or recreational areas. | |||
| Methods of Application | |||
| Several methods exist for control of woody vegetation. Some treatments apply herbicide to a localized area on the tree. Directed applications can reduce impacts on adjacent nontarget vegetation from drift or overspray. Other methods require thorough herbicide coverage on foliage or soil. Review the herbicide labels for registered application methods and choose the best system for your needs. For the methods listed below, it is important to calibrate your application equipment and follow all of the herbicide label guidelines. | |||
| Cut Surface Treatments (frill, or cup treatments). | |||
| Bark on larger trees (diameters larger than 5 inches) is often too thick for most water soluble sprays to penetrate. In this situation, it is necessary to provide a direct pathway for herbicide entry into the plant's vascular tissue. Do this by making a series of downward cuts through the bark, leaving the chip connected to the tree (frilling cuts overlay, and spaced-cut injection does not overlap). Make cuts around the entire circumference of the tree trunk with an axe or hatchet. Immediately apply the selected herbicide into the cuts. Avoid application during heavy upward sap flow in the spring, when sap flowing out of the wound will prevent good absorption. Apply herbicides registered for this use pattern undiluted or in dilution ratios of one-half to one-quarter strength. The amine formulations of picolinic acid (triclopyr and picloram) or phenoxy (2,4-D, dichlorprop, etc.) herbicides are generally more effective than the esters. | |||
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| Injection | |||
| This is similar to cut surface treatments. Use specialized equipment to inject a specific amount of herbicide into the tree when the cut is made. Treatments are effective when injections are made every 2 to 6 inches around the tree. For best results, treat trees 1.5 inches or more diameter at chest height. | |||
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| Stump Treatment | |||
| This involves cutting a tree down and treating the freshly cut surface with herbicide. Cut the top of the stump level to allow uniform herbicide coverage. Thoroughly wet the cambium layer next to the bark so the conducting tissue will carry the herbicide to the roots. On larger trees treat only the outer 2 to 3 inches of the stump (the internal heartwood of the tree is already dead). On trees 3 inches or less in diameter, treat the entire cut surface. Apply treatments immediately after cutting to achieve maximum effectiveness. If application is delayed after cutting, recut the stump and apply the herbicide to the live tissue. Delaying herbicide application to freshly cut trees can result in prolific sprouting from the tree collar and roots. Moisture stress may affect control during the summer and early fall. Applications during the spring upward sap flow are not as successful as late spring and early summer treatments. Undiluted water-soluble herbicide formulations are more effective than the esters. | |||
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| Basal Bark Treatments | |||
| Apply the herbicide to the lower 12 to 18 inches of the tree trunk from early spring to mid-fall. Some species can be treated during winter. Use herbicide spray mixed with oil, until the bark is saturated. The low volatile ester formulations are the only oil soluble products registered for this use. This method is effective on trees of all sizes. | |||
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| Foliage Treatment | |||
| Foliar spraying is a common method of applying herbicides to brush up to 15 feet tall. Make applications from early summer to late September, depending on choice of herbicide. Treatments are least effective during very hot weather and when trees are under severe water stress. Use 2,4-D, triclopyr, dicamba, and picloram in early summer, glyphosate in August and September, and imazapyr from June through September for best results. Fosamine and amitrole are additional choices. Except in very sensitive species, spraying plants with rapidly elongating stems will often result in excessive sprouting. Saturation of the tree is not necessary. | |||
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| Soil Treatment | |||
| Herbicides applied evenly to the soil surface move into the root zone of the targeted plants with rainfall or overhead moisture. Common soil applied herbicide choices include: bromacil, hexazinone, and tebuthiuron. Hexazinone and tebuthiuron may be applied in narrow bands. Banding (also called lacing or streaking), applies concentrated solution to the soil in a line or band spaced every 2 to 4 feet. Use this type of application to kill large numbers of trees. | |||
| Chemicals listed below are commercial packages and in some cases are restricted to licensed applicators. Materials described are not designed for homeowner use. | |||
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| Amitrole (Amitrol-T) | |||
| Apply as a foliar spray to susceptible woody plants from the full leaf stage until the onset of dormancy. Amitrole is most effective when all plant parts (leaves, stems, and suckers) are wet. Use only on noncropland and hardwood nurseries. Do not allow spray or drift to contaminate edible crops or water intended for irrigation, drinking, or domestic purposes. Do not allow livestock to graze or feed on treated areas. | |||
| Bromacil (Hyvar) | |||
| Broadcast apply bromacil in the spring to control undesirable woody plants on noncropland. This herbicide may stay in the soil for several years. Avoid areas with standing water, irrigation ditches, rights-of-way or immediately adjacent areas with desirable trees, shrubs, or marketable timber. Do not use water from treated drainage ditches for irrigation or livestock. Do not contaminate water, food, or feed by improper application, storage, or disposal. | |||
| 2,4-D (several trade names) | |||
| Apply the ester formulations as a water-based foliar spray during periods of active growth or as an oil-based basal spray. Apply undiluted. The amine formulations are effective on many species as a stump, cut surface, or injection treatment. Apply undiluted. Use in pastures, rangeland, forest and noncrop areas. Thorough coverage is necessary; hard to control species may require retreatment. Do not allow spray to drift onto nontarget plants. Check additional label precautions regarding individual formulations. | |||
| Dichlorprop (2,4-DP, Weedone 2,4-DP) | |||
| Use for control of mixed brush on highways, railroads, forests (limited uses), and utility rights-of-way. Apply as a foliage spray from full leaf stage until the start of dormancy. Thorough coverage is necessary, and hard to control species may require retreatment. Do not allow spray to drift onto cropland or nontarget plants. | |||
| Dicamba (Banvel) | |||
| Use as a cut surface, basal, stump, or foliage treatment to control woody plants on pasture, rangeland, forest (limited uses), and noncropland. Do not treat areas where downward movement into the soil, or surface washing can bring dicamba into contact with roots of desirable plants. Conifers are particularly sensitive. Avoid applying when environmental conditions may favor drift to sensitive crops. Do not contaminate irrigation ditches or water used for domestic purposes. Dicamba can flashback to adjacent trees. | |||
| Fosamine (Krenite) | |||
| Use to control brush in noncropland areas. Apply fosamine as a foliage treatment from full leaf in the spring to first fall coloration. Treatment does not immediately affect treated woody plants; they remain green for the remainder of the growing season. Treated susceptible plants fail to grow the next spring. A spray directed to only part of susceptible brush species will provide control of the portions sprayed, resulting in a trimming effect. | |||
| Glyphosate (Roundup) | |||
| Apply glyphosate to actively growing trees with fully elongated and developed foliage, in late summer or early fall for best results. Treat early-maturing species such as poison oak by July. Repeat applications may be necessary. Wait 7 or more days after application before removing or tilling brush. For good control, do not treat plants under severe water stress; do not treat mowed or tilled brush until after a full season of regrowth. Vegetation damaged by mechanical or previous chemical treatments may be resistant to glyphosate. Do not allow drift to nontarget plants. Spray foliage thoroughly, but not to the point of runoff. Rainfall occurring within 6 hours of the application may reduce effectiveness. | |||
| Hexazinone (Velpar) | |||
| To control undesirable vegetation in forests and noncropland primarily through soil uptake, make one foliar application in early spring, late fall, or winter. Fall applications generally give superior control in low rainfall areas. For best results, apply to brush seedlings or sprouts less than 18 inches tall. Use as a lace or streak application, but not on gravelly or rocky soils, on soils with greater than 85% sand, or on soils with less than 1% organic matter. Do not use in irrigation ditches or next to areas having desirable trees or shrubs. | |||
| Imazapyr (Arsenal) | |||
| Use to control brush in forest and noncropland areas, such as conifer plantations, rights-of-way, fence rows, and storage areas. Use as a foliage, frill, or stump treatment. Do not use on food or feed crops, contaminate irrigation water (as injury to crops may occur), or use on lawns, walks, driveways, tennis courts, or similar areas. This herbicide may persist in the soil for several years. | |||
| Metsulfuron (Escort) | |||
| Use as a foliar spray or soil treatment to control brush on noncropland. For best control, apply as soon as the brush is fully leafed out. Do not use on food or feed crops, or apply where roots of desirable trees may extend into the treated zone. Do not allow drift to contact nontarget plants. This herbicide may persist in the soil for several years. | |||
| MSMA | |||
| For forestry and noncropland use, apply as a cut surface or injection treatment. Do not feed clippings to livestock or graze treated areas for one growing season. | |||
| Picloram (Tordon) | |||
| Use as an all-season broadcast, stump, frill, or injection treatment to control woody plants in forest and noncropland areas such as fence rows or rights-of-way. Do not treat frozen soil. Do not contaminate cropland, water, or irrigation ditches. Avoid areas where downward movement into the soil or surface washing may cause picloram to reach the roots of desirable plants. This product can flashback, and may persist in the soil for several years. Do not use in western Washington where shallow water tables occur. | |||
| Tebuthiuron (Spike) | |||
| Use as an all-season broadcast, lacing, or spot treatment to control undesirable broadleaved or woody vegetation on noncrop areas only. Apply just before the wet season in dry regions. Do not apply to frozen or saturated oil, sidewalks, driveways, tennis courts, streets, lawns, patios, under asphalt or concrete pavement where future landscaping is planned, or to any area where desirable roots extend. Injury symptoms appear slowly and may depend on moisture and soil conditions. This herbicide may persist in the soil for several years. Do not use in western Washington where shallow water tables occur. | |||
| Triclopyr (Garlon 3A, Garlon 4, Crossbow). | |||
| Crossbow is a combination of triclopyr and 2,4-D. Use Garlon to control woody plants in forests and noncropland. Use Crossbow to control woody plants in noncropland, pasture, and rangeland. Best results are obtained during early summer. Do not permit spray or drift to contact desirable plants, as severe injury may occur. Do not apply to irrigation ditches or allow lactating animals to graze treated areas for 1 year following application. | |||
| Plant Susceptibility | |||
Plant susceptibility depends on a number of factors: time of year; stage of plant growth; type of application and spray carrier; soil moisture before, during, and after application; precipitation (rain or snow); and temperatures of soil and air before, at, and immediately after the application. The addition of oil and/or a surfactant will enhance control of some species. The susceptibility charts are complied from several sources. Use these charts only as a guide when planning control operations. Consult research reports, product labels, and knowledgeable personnel for additional information. | |||
| Herbicide | ||||||
| Amitrole | ||||||
| Bromacil | ||||||
| 2,4-D* | ||||||
| Dicamba | ||||||
| Dichlorprop (2,4-DP) | ||||||
| Fosamine | ||||||
| Glyphosate | ||||||
| Hexazinone | ||||||
| Imazapyr | ||||||
| Metsulfuron | ||||||
| Picloram* | ||||||
| Tebuthiuron | ||||||
| Triclopyr | ||||||
*All formulations of these herbicides are not suitable for all the uses undicated. Check manufacturer's label for uses and additional precautions. FOLLOW LABEL INSTRUCTIONS.