How do I control woody weeds?

FAQ
Question: 

How do I control woody weeds like honeysuckle, tree of heaven, or mulberry?

Answer: 

Woody weeds are trees and shrubs that have woody plant tissue.  They are perennial and typically classified as eudicots, although some may belong to other plant groups like 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

Some woody weeds can be controlled by pulling and digging.  This method is best for small, newly emerged trees and shrubs and is done more easily after a soaking rain or deep watering.  Utilize a trowel, spade, or weeding tool to dig and pull the plant out of the ground.  A 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 be sure to utilize a tool with good gripping strength.  A spring-loaded needle-nose pliers is good option.

Mowing

Mowing or cutting off woody weeds can provide temporary improvement in garden appearance, but stumps left behind frequently resprout.  Often the plant that regrows is bushier with more stems and even more difficult to manage.

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 completely eradicate the weed.  Both selective and non-selective herbicides work on many woody weeds.  You can utilize a broadleaf selective herbicide like triclopyr, dicamba, 2,4-D, picloram, or products that are a combination of these active ingredients.  Non-selective herbicides like glyphosate and imazapyr are also effective on woody weeds.  Some of these herbicides, such as picloram and imazapyr, have a higher potential of off-target damage as they are highly mobile and/or long-lasting in the soil.  Use all herbicides with care as any of them can cause damage to nearby plants if applied incorrectly.  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 like buckets or boxes to further reduce problems with drift. Herbicides must be used according to label instructions on the package.

There are several herbicide application techniques that can be used to control woody weeds.

Foliar Application

Foliar applications spray herbicide on the leaves of the plant.  This application method is best for smaller plants and often requires more than one application for complete control.  Complete coverage of the foliage is necessary to be effective but the application must be done carefully as there is a higher risk of overspray and/or drift to desirable plants nearby.  Triclopyr and glyphosate work well for this type of application.  Applications can be made anytime during the growing season but late summer and fall applications are often more effective than those made in spring or early summer.

Cut Stump Application

Cut stump applications involve cutting the woody plant off near the base and applying the herbicide directly to the cut surface as quickly as possible after the cut has been made and the sawdust has been brushed aside.  Utilize a sprayer, squirt bottle, or foam brush to apply herbicide to the entire cut surface of smaller stumps and the outer ring of stumps larger than three 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 and picloram can be used for this application method as directed on the label.  Use these products with great care as they move readily in the soil affecting nearby desirable plants and can remain active in the soil for a long time impacting existing and new plants in the areas for months to years later.

Applications can be made anytime 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 frequently needed, especially for certain difficult-to-control species like 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 bark and living tissue or sapwood of the tree.  Fill the “cup” created by this cut with herbicide solution without overfilling as any herbicide that is allowed to run out is wasted and could negatively impact nearby desirable plants.  The recommended spacing and number of cuts is outlined on the herbicide label.  It is typically one “hack” for every inch in diameter of the tree and evenly spaced every 1 to 2 inches around the circumference of the trunk at a height comfortable for the applicator but below the lowest living branch. 

Glyphosate, triclopyr, 2, 4-D, dicamba, imazapyr, and picloram can all be used for 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 any time during the growing season.  Late season applications tend to be 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 get or only available for licensed applicators.  Applications are not effective on some species, especially those with thick corky bark and larger trees greater than 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.