Bluestem as a lawn weed

I have a lot of bluestem grass in my yard this year, more than ever. How can I get rid of it without killing my good grass? I cut it down, and the next day it is up again waving in the wind. - BW

It is interesting that you have a problem with bluestem. We are recommending Little Bluestem as an ornamental (un-mowed) grass in landscapes in New Mexico because it is so well adapted and attractive. However, I can see where it can be a problem. Mowing will not eliminate it quickly. If it is mowed frequently to a short height and the surrounding lawn is in good health, the lawn grass should eventually overwhelm the bluestem. However, quicker ways to remove it include digging (a lot of work) or spot applications of herbicide.

If you choose to use herbicides, it is important to be very careful because you are trying to kill grass growing in grass you don't want to kill. Choose an herbicide labeled to kill grass. Roundup� (glyphosate salt) is an example. It may be applied to the leaves of the bluestem by spraying or by brushing (painting) it on. Spraying will probably kill a spot of the desired lawn grass around the target bluestem. By brushing it on (diluted to the label recommended concentration), you can target the taller bluestem grass without harming the lawn grass. There are special applicators made for "wick" or "brush-on" application. These often have a tube containing the herbicide with a sponge or other absorbent material at the base. The sponge becomes moistened by the herbicide that is then transferred to the grass blades as you wipe the sponge across the grass. Take care to prevent dripping, or the lawn will be injured.

If you don't need to treat a large area or don't want to purchase the special applicator (or can't find one), you can use a sponge and a small container of diluted herbicide. Be sure to wear new (without holes) plastic or rubber gloves. Disposable gloves may be used and then discarded after use. Follow the directions that come with the herbicide you choose to maximize the effect. Some of the bluestem may need to be treated more than once.

The reason this works is that some herbicides are absorbed by green tissues of the plant and translocated throughout the plant. Some of these (like the glyphosate mentioned as an example) cannot be taken up from the roots, so surrounding plants are not injured and there is no residue left in the soil to injure plants later. Since the bluestem stands above the other grasses, it is easy to target them while protecting the desired lawn grass. Once the bluestem grass has become dormant, you must wait until next year; however, if it is still green, autumn is the best time to treat it.

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: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

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