Quackgrass (Elymus repens) is known for its long clasping auricles and its extensive rhizome system. It is one of the most persistent and difficult to control weeds in cool-season lawns. Rhizomes give this species an ecological advantage over other grasses during extended dry periods. While Kentucky bluegrass also has a rhizome system, quackgrass has a more extensive system and will out compete Kentucky bluegrass in dry years.
This was the case in this year's drought in the Midwest. Lawns went through an extended period of dormancy that in many areas lasted for months. This fall, we are seeing Kentucky bluegrass lawns recover. But wherever there was quackgrass in the lawn, it has gained an even bigger foothold.
Last week, I was asked to look at a lawn that one of my students cares for through his lawn care service. It had been a mostly Kentucky bluegrass lawn up to this year, but following the drought, nearly everything that is recovering is quackgrass from the rhizome system.
Roundup will kill it, but the problem is that Roundup generally does not translocate through the entire rhizome system. When you reseed, there is always some living rhizome tissue and quackgrass returns. I generally recommend repeated applications of Roundup, followed by sodding. Even that extreme treatment generally fails, however, and the quackgrass returns.
Figure 1. Long clasping auricles of quackgrass.
Figure 2. Quackgrass rhizomes.
Figure 3. Lawn in central Iowa that is nearly all quackgrass following the drought of 2012.