JoAnne Skelly: Stopping cottonwood suckers

We have about 25 48-year-old cottonwood (poplar) trees that give us wonderful shade, shelter the birds and protect us from the wind. Unfortunately, cottonwoods sucker profusely from spreading tree roots. They sprout in the lawn, flower beds, driveway and even the patio. In addition to our old cottonwood trees, we also have an old crabapple and an apple tree. Although they don’t sucker much in the lawn, they sucker like mad at the base of the tree and on any exposed roots.

I cut the cottonwood suckers whenever I see them, but that’s an ongoing endless task. I also have been pruning the suckers off the crabapple and apple three or four times a year in an effort to maintain some control and aesthetic appeal. But, after 28 years of cutting them back, now there are knobby deformed growths the size of my fists at the base of the trees. There is an alternative.

Naphthaleneacetic acid (NAA) is a synthetic plant hormone. It is used to stimulate rooting in the propagation of stem and leaf cuttings, promote development in tissue culture, enhance fruit growth, thin fruit trees, delay flowering and prevent premature fruit drop. The good news is that when NAA is mixed in the proper chemical formulation it also can control suckers from roots and pruning wounds for many kinds of trees including aspens, willows, silver maples, flowering plum, vines and fruit trees to name a few.

A number of manufacturers make ready-to-use products that will stop suckers. The active ingredient in these products is Ethyl 1-naphthaleneacetate. Most labels mention applying during the dormant season up to green tip stage or in summer when suckers are six to 12 inches in height. They warn not to apply during bud swell, bloom or fruit set. One manufacturer claims that an application of NAA stops suckers for six months. Since this compound can be toxic to plants in high concentrations, it is regulated by the Environmental Protection Agency as a pesticide. Therefore, as with any pesticide, it is important to read the label thoroughly, understand it and follow it. Most of the products come in a 16-ounce spray bottle and range from $27 to $49. Expensive? Yes, but the time it saves may be well worth it.

On a different note, remember, with all this hot weather, deep water your trees and shrubs during the coolest time of day and increase the amount of time you irrigate your lawn.

JoAnne Skelly is associate professor & extension educator, emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.