Woody weeds are trees and shrubs with woody tissue. They are perennial and typically classified as eudicots or gymnosperms (conifers). Examples of woody weeds include tree-of-heaven, bush honeysuckle, and poison ivy.
These weeds can be particularly difficult to manage, especially if they grow large.
Keeping ahead of weeds and controlling them when they are small is essential for good weed management. This requires persistence throughout the entire growing season to remove weeds as they emerge.
Pulling & Digging | Mowing & Cutting | Herbicides | More Information
Pulling & Digging
Some woody weeds can be controlled by pulling and digging. This method is best for small, newly emerged trees and shrubs and is easier after a soaking rain or deep watering. Utilize a trowel, spade, or weeding tool to dig and pull the plant from the ground. Pliers can be used to grab firmly onto the base of the stem and pull it from the ground. Young woody plants have bark that can easily slip when pulled, so use a tool with good gripping strength. Spring-loaded needle-nose pliers are a good option.
Pulling and digging are the best management options that do not involve using chemicals.
Mowing & Cutting
Mowing or cutting off woody weeds can temporarily improve the garden's appearance, but stumps left behind often resprout. Often, the plant that regrows is bushier with more stems and even more challenging to manage. With enough persistence and regular cutting or mowing, it is possible to exhaust the root system and kill the plant, especially when plants are smaller and less established. However, most gardeners do not have the time or consistency/persistence needed to make cutting and mowing a successful management technique, especially for large, established weeds. For this reason, cutting is typically ineffective as a control method for these weeds.
Herbicides
Herbicides are the most effective, practical, and efficient way to manage woody weeds. Not all woody species will respond in the same way to the same herbicide or application method. Often, more than one application is needed to eradicate the weed completely. Both selective and non-selective herbicides work on many woody weeds. You can use a broadleaf selective herbicide such as triclopyr, dicamba, 2,4-D, or products that combine these active ingredients. Non-selective herbicides such as glyphosate and imazapyr are also effective against woody weeds. Some herbicides, such as imazapyr, have a higher potential for off-target damage as they are highly mobile and/or long-lasting in the soil. Picloram is a restricted-use herbicide that is not recommended for home landscape use as it has a high potential to damage nearby plants because it is mobile and persistent in the soil.
Use all herbicides with care, as any can damage nearby plants if misapplied. Consult the label carefully, as not all herbicides are labeled for all garden settings. Always apply herbicides when winds are calm and temperatures are cool to prevent drift and damage to desirable plants. Protect garden plants with barriers such as buckets, boxes, or plastic sheeting to further reduce drift problems. Herbicides must be used according to the label instructions on the package.
Several herbicide application techniques can be used to control woody weeds.
Foliar | Cut-Stump | Hack & Squirt | Basal Bark
Foliar Application
Foliar applications involve spraying herbicides onto plant leaves. This application method is best for smaller plants and often requires multiple applications for complete control. Complete coverage of the foliage is necessary for effectiveness. Still, the application must be done carefully, as there is a higher risk of overspray and/or drift onto nearby desirable plants. Boxes, buckets, or plastic sheets can be used to protect nearby plants from overspray. Triclopyr and glyphosate work well for this type of application. Applications can be made at any time during the growing season, but late-summer and fall applications are often more effective than those in spring or early summer.
Cut-Stump Application
Cut-stump applications are preferred for treating woody weeds as they significantly reduce the amount of herbicide used and the risk of overspray that can negatively affect nearby plants. This application method involves cutting the woody plant near the base and applying the herbicide directly to the cut surface as quickly as possible after the cut is made and the sawdust is brushed aside. Use a sprayer, squirt bottle, or foam brush to apply herbicide to the entire cut surface of smaller stumps and to the outer ring of stumps larger than 3 inches in diameter. Only the outer ring of larger stumps needs to be treated because the living tissue is only found in the outer ring of larger trees. Only use enough herbicide to thoroughly wet the cut surface and avoid runoff.
Applications of glyphosate and triclopyr at higher concentrations can work well for this application method. Glyphosate should be at 20% active ingredient, and triclopyr should be greater than 8% active ingredient. Imazapyr can be used for this application method as directed on the label. Use this product with great care, as it moves readily in the soil, affecting nearby desirable plants, and can remain active for a long time, impacting existing and new plants in the area for months to years.
Applications can be made at any time during the growing season, although late-summer and fall applications tend to be slightly more effective.
If the stump resprouts, cut and treat again, or apply a foliar spray to the new growth. Multiple applications are often needed, especially for difficult-to-control species such as mulberry and trumpet creeper.
Hack and Squirt Application
The hack and squirt application method is a good option when trees are too large or difficult to cut down, and there is no concern for dead standing trees from a safety or aesthetic standpoint. With a hatchet or machete, cut into the bark several inches at a downward angle of about 45 degrees. The cut should be about 2 inches long and must cut through the tree's bark and living tissue or sapwood. Fill the “cup” created by this cut with the herbicide solution without overfilling, as any herbicide that runs out is wasted and could harm nearby desirable plants. The recommended spacing and number of cuts are outlined on the herbicide label. It is typically one “hack” per inch of tree diameter, evenly spaced every 1 to 2 inches around the trunk's circumference, at a height comfortable for the applicator but below the lowest living branch.
Glyphosate, triclopyr, 2,4-D, dicamba, and imazapyr can all be used with this application method. Consult the label for recommended concentrations. The hack and squirt method is effective any time of year except during periods of heavy sap flow in the spring.
Basal Bark Application
Basal bark applications are made with oil-soluble herbicides and are effective on trees with a stem diameter of four inches or less and on those species with thin, smooth bark. Oil-soluble herbicides are necessary to penetrate the waxy coating on the bark. Apply the herbicide directly to the bark around the entire circumference of the bottom 12-18 inches of the trunk. Herbicide injury will not be observed for several weeks to months after treatment. Applications can be made at any time during the growing season. Late-season applications are more effective than early-season applications made when trees are flushing out new growth.
Basal bark applications have limited use for homeowners. Appropriate oil-based herbicides may be difficult to obtain or available only to licensed applicators. Applications are ineffective on some species, especially those with thick corky bark and larger trees over 4-6 inches in diameter. Additionally, this method can only be used where there is no concern for dead standing trees from a safety or aesthetic standpoint.