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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.



May 9, 2013

Here is an interesting post from Richard Jauron, the answer line person in Horticulture here at ISU.  If you have been following the blog, you know that Richard has been experimenting with Tenacity (Mesotrione) for the control of nimblewill in his lawn.  That experiment has been going on since 2011 and he has had good results and has nearly eliminated his nimblewill. 

Here is another observation from his work.  He has Virginia bluebells (Mertensia virginica) in the beds at the edge of his lawn.  The nimblewill and the bluebells both spread by seed and they have been merging at the edge of the bed in recent years.  The bluebells flower in early spring and the foliage then dies back by the end of June.  He last spot treated with Tenacity in August after the foliage of the bluebells was gone.

The bluebells are just coming up this spring and are in full bloom.  Where he sprayed the tenacity, the bluebells are emerging with damaged, white leaves and stems.  This is the first report that I have seen indicating damage from Tenacity to this species.

Here are the healthy Virginia bluebells on May 8, 2013.



Here are the bluebells in areas spot treated with Tenacity.