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WILL TENACITY (MESOTRIONE) KILL QUACKGRASS?

May 27, 2014

Quackgrass (Elymus repens) is the hardest turf weed to control that I know of.  You can identify it by the long clasping auricles on its collar (Fig. 1) and by its extensive rhizome system (Fig. 2).  I get the question occasionally whether the new herbicide Tenacity (mesotrione) will selectively control this species.  The answer is “no”.

Figure 1. Auricles

 Figure 2.  Rhizomes

We just treated the Kentucky bluegrass (Poa pratensis) turf at the research station shown in Figure 3.  The result is that the quackgrass turns white, as can be seen in the picture.  That always gets peoples hopes up, including mine when I first started working with this product.  Unfortunately, the quackgrass always recovers and comes back as bad as ever.  Repeat applications do not work either.  I tried for 4 seasons to kill patches in my own lawn, hoping that my tenacious applications of Tenacity would kill it.  I lost, and the quackgrass was not even reduced in severity by my repeated applications.

Figure 3. Quackgrass turned white by Tenacity.

The only way to control it remains non-selective applications of Roundup (glyphosate).  The rhizomes are very hard to kill and repeated applications of Roundup will be necessary.  If you have this problem and want to get rid of the quackgrass, start now in May by killing the infested areas.  Then repeat apply every time the quackgrass comes back from rhizomes.  You should set a goal of reseeding in mid-August.  

Even a better solution would be to sod over the dead areas.  The rhizomes have a harder time emerging through sod than they do into a newly seeded area.

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QUACKGRASS WAS THE BIG WINNER IN DROUGHT

November 13, 2012

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.

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