   Killing Woody Plant Stumps - April 26, 2006 Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Persistent woody plants can sometimes interfere with your gardening and landscape goals. Examples include: invasive species, trees and shrubs that cause structural damage to foundations and/or plumbing, and clearing areas to create fire defensible space. Initially, you may decide to reduce a plant’s size through pruning. However, if you decide to cut a tree or shrub down entirely, you should also consider killing the underground portion of the plant to prevent regrowth. Many trees and shrubs respond to removal by producing new shoots from adventitious buds at or below ground level. These shoots, called stump sprouts, will regrow vigorously using stored energy from the existing root system and often create a landscape maintenance problem. Stump-sprouting native species include: oak, ash, mesquite, sycamore, mountain mahogany, silktassel, and many more. Pine, shaggy bark juniper, and cypress do not stump sprout. Stump-sprouting non-native invasive woody plants include: salt cedar, tree of heaven, Russian olive, and Siberian elm. Stumps can be removed through mechanical means (digging and/or chipping). This method can be labor intensive and must remove a significant portion of the stump to prevent regrowth. It is also difficult to dig out stumps that have grown along fences, along ditch banks, and under structures. Appropriate herbicides can also be used safely and effectively to kill stumps and prevent regrowth. Herbicides are especially useful where access is limited by slopes, structures, and other features. There are many stump killing products available to homeowners. The most common active ingredient in these products is either triclopyr or glyphosate. Read the labels of these products carefully before purchasing to ensure it is labeled for cut stump application. Once you decide on a product, buy the appropriate amount for your current needs and follow label directions. Any pesticide stored on the shelf of your garage or shed is a potential hazard and has a finite shelf life. Both triclopyr and glyphosate rely on translocation to the root system through the phloem tissue (inner bark). This requires they be applied to the freshly cut surface at the proper strength. I find the safest way to do this is by painting it on with an inexpensive paint brush. Always wear disposable latex gloves, safety glasses, and other recommended personal protective equipment as per product label instructions. My personal experience with this method was using glyphosate on over 100 Siberian elms. For small diameter stumps, I used a cordless drill to make two or three ½ inch deep holes just inside the bark. The holes created small reservoirs for the herbicide and ensured a fresh surface for the herbicide to enter. This treatment was 98% effective. Many woody plants naturally sucker from exposed or disturbed roots. These suckers may emerge from the ground far away from the mother plant. Yet they are directly connected to the mother plant and any herbicide treatment applied to them can be translocated to other individuals sharing that common root system. Never treat sprouts coming off a root system of a tree that you want to keep. Cutting and treating these sprouts with an herbicide can result in exposure of the entire root system. This may ultimately kill non-target trees. Sucker producing tree species include: tree of heaven, honey locust, black locust, hackberry, western soapberry, cottonwood, aspen, poplar, willow, box elder, and others. Also remember that trees of the same species growing next to one another may have a common root system as a result of root grafting. Herbicides are an effective tool to control unwanted woody vegetation. Remember: always follow product label directions. For more information, you can read the new Cooperative Extension publication titled: Cut Stump Application of Herbicides to Manage Woody Vegetation. It is available at Cooperative Extension offices and on-line at: cals.arizona.edu/pubs/garden/az1401.pdf. The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. |