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Controlling Unwanted Trees

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Larry Sagers Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved

Occasionally it becomes necessary to remove shrubs, brush or trees from a landscape. Several brush killer formulations containing the active ingredient triclopyr are available on the market. Herbicide formulations that include either dicamba or glyphosate are also effective against brush. Prevent any herbicide from coming in direct contact with desirable plants.

Before removing a tree, it is best to treat with herbicide. The most effective herbicides for this use are products containing glyphosate, 2,4-D, or a combination of 2,4-D + MCPP + dicamba, usually sold as Trimec.

These systemic herbicides move inside the foliage or stems and the herbicides translocate to the roots, killing the entire tree and preventing reemergence of new sprouts or suckers.

Late summer or very early fall (before leaves begin to change color) is the best time to kill trees. Place herbicide concentrate directly into the trunk by drilling a series of holes around the trunk (¼ to ½ inch in diameter and 1 to 2 inches deep depending on the bark thickness). Make the holes 12 inches or less above the soil surface and fill them with herbicide concentrate. Angle holes downward at a 45 degree angle to act as small herbicide reservoirs.

Use a disposable syringe (without needle) and place the herbicide into the holes. Cap holes with caulk, wood putty or other material to prevent evaporation. It usually requires at least 2 cc of herbicide concentrate per inch of trunk diameter to kill a tree. This means a tree with a 10-inch trunk will have to have a total of at least 20 cc of herbicide concentrate injected in the several drill-holes.

Herbicide can also be applied to a tree by using a hatchet or axe to make a series of shallow horizontal cuts (called frill-cuts) low on the trunk. Make the cuts deep enough to penetrate the outer bark and reach the inner living tissue called cambium. This layer is between the bark and the wood.

Make enough cuts to hold the needed amount of herbicide. Angle each cut downward to create a trough and place the herbicide directly into the cuts in the same dose (2 cc per inch of trunk diameter).

Do not cut the tree down until the next spring. This gives the herbicide time to penetrate deep into the root system. Although herbicide pretreatment is preferred, you can kill the trunks of trees that already are cut down. Painting the cut surface of a trunk with herbicide concentrate is effective, but only if the treatment is done within a few minutes after the tree is cut.

To treat a trunk that has been cut previously and is now resprouting, use the drill-hole or frill-cut technique described for growing trees. Inject herbicide concentrate directly into the trunk as near to the soil surface as possible. Without a large, living tree to send sap downward, herbicide translocation to the roots is more limited, so repeated treatments and/or higher doses of herbicide are often needed.

If an old stump is beginning to re-sprout, cut off all sprouts or suckers and immediately paint them with herbicide concentrate. Then inject additional herbicide into drill-holes or frill-cuts in the trunk.

Ready-to-use herbicide formulations are too dilute to be effective in killing trees. Formulations containing at least 3 to 4 pounds of active ingredient per gallon (greater than 40% active ingredient concentration) work best.

Be careful when treating any trees or trunks with herbicide. It is possible for some herbicides to move to an adjacent tree through unseen root grafts, or by exuding into the soil from roots of a treated tree.

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