1 - Persistence is the best way to kill perennial weeds.
Yard and Garden May 19, 2012
How can I get rid of tree of Heaven & other invasive runner trees. Also my yard is overrun with bindweed?
-Ann B. Kingston & Hillsboro, NM
The best (and really the only) herbicide effective against the tree of heaven is persistence. If you choose to use chemical herbicides (2,4-D based or glyphosate based) or if you use elbow grease (digging and hand pulling the trees), they will return until you have depleted the stored foods in the roots remaining in the ground. These stored foods are used by the plant to produce new sprouts. This is one of the important differences between perennial weeds that return from a persistent root system and annual weeds that must grow from seeds each year. The perennial weeds may also produce seeds, but the roots more quickly replace plants that you remove.
Manual removal of trees and roots (remove as much as possible) can be effective, but must be done frequently to adequately deplete the food reserves used to produce new growth. If the trees are allowed to grow 2 weeks once they develop new leaves, they will begin feeding the roots, so you must be very persistent. Do not let new sprouts or growth remain more than about 10 days before removal. This will result in withdrawal of stored foods to produce the new growth, but will not allow the new growth to replace those nutrients. In time, the sprouts will become fewer and fewer. Eventually, you can eliminate the trees.
If you choose chemical treatments, you may speed the process slightly. Combined chemical and manual management techniques may be the fastest way to eliminate the trees. 2,4-D based products can be applied to the leaves of small trees and new sprouts. (If you have pets, keep them away from the area for a week or so to allow the chemical to break down, though it is unlikely that they would ingest the tree of heaven sprouts.) To minimize unintended consequences, you can apply the chemical directly to the leaves of the sprouts with a paint brush (after diluting the product according to the label directions). Some glyphosate (and brush and stump killer) products are labeled for "frill application" which means they can be applied full-strength into frills (notches cut just through the bark into the phloem and cambium layers that will carry the chemical into the roots). This is most effective in the late summer/fall when there is more movement of materials downward in the tree, but it can be done now with somewhat less downward movement. With chemical management (or combined chemical and manual management), persistence remains critical. Do not let the sprouts remain more than 10 days before removing them. When using chemical treatments read the label directions, looking for weeds controlled and proper treatment procedures. Follow those directions carefully. If you need help understanding the directions, contact your local NMSU Extension Service County agent.
Regarding bindweed: The same information mentioned above applies It is another perennial weed with extensive roots that quickly produce new sprouts. Removal every 10 days, or treatment with chemicals every 10 days over a period of time will reduce the problem. Seeds will remain dormant for several years, so even after the original plants have died, new plants may develop from these dormant seeds.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: email@example.com, office: 505-865-7340, ext. 113.
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!