Question of the Week – Number Two: September 10, 2010

“What is this weed, and how can I get rid of it?”

I’m already getting the calls. This weed is out of control.

This is KR bluestem, more formally known as “King Ranch bluestem.” It was introduced into the U.S. from southern Europe and South Africa almost 100 years ago as a source of livestock forage and as a means of stabilizing raw cuts along roadsides.

It certainly did all of that, but in the process it became obvious that KR bluestem was also invasive and that it threatened the diversity of native species of plants. It’s not exactly as bad as kudzu perhaps, but it’s along those same lines.

At this point I’m glad I’m a horticulturist! Agronomists who get to deal with KR bluestem in pastures and prairies have a much bigger task than home gardeners will have. For that kind of large-scale control I will refer you to your local offices of the Texas AgriLife Extension. I’ll confine my suggestions to home lawns alone.

Coping with KR bluestem in lawns
It’s been my observation that KR bluestem rarely shows up in really healthy, vigorous home lawns. It’s much more common in lawns that have struggled through drought, lack of fertilizers and infrequent mowings.

Here are my suggestions…

• Mow regularly at the height recommended for the type of grass you have in your lawn. This is especially important in fall, when KR bluestem is setting seeds. Keep the seed heads mowed off on 5- to 7-day intervals. Bag the clippings and compost them completely before using them in your landscape.

• Keep your desirable grass properly watered. Of course, you’ll have to abide by any water curtailments in your city, but at least give your turf a fighting chance to crowd out the invader.

• Fertilize your lawn at least two times per year (mid-April and early September). Apply an all-nitrogen or high-nitrogen food that has as much as half of that nitrogen in slow-release form.

If you do all of that and you still have KR bluestem showing up in your lawn, either spot-treat stronger clumps with a glyphosate-only herbicide spray or, more commonly, dig the clumps out by hand, preferably as soon as you see them starting to grow.

KR bluestem is a perennial grass, so pre-emergent weedkillers won’t have much impact on it. However, if your neighbors have the weed and aren’t doing anything to stop it, you might consider applying pre-emergent granules on the same schedules you see me recommending here for annual grassy weeds in spring and late summer.