Tom's Blog

Friday, November 16, 2012

Not too late for weed control

Despite many cautions to the contrary, it is possible to spray weeds this time of year. In fact, it is an ideal time to use glyphosate, because lots of exotic weeds have an extensive fall regrowth period and are still green. Since most of the native plants have senesced and are brown, they will not be affected. Here is some research from Ohio: Mark Frey et al. "Cold weather application of glyphosate for garlic mustard (Alliaria petiolata) control. Weed Technology 2007, Vol. 21, pp. 656-660.

What can you spray this time of year? Garlic mustard, for sure. Also, dames rocket, motherwort, catnip, hedge parsley, sweet clover. In fact, anything green. We use a foliar spray of 2% glyphosate. (Just be sure you don't spray the fall regrowth of "good" plants such as golden Alexanders or stiff goldenrod.)

Although I haven't seen any research on it, it should also be possible to spray exotic cool season grasses such as smooth brome and bluegrass. Also reed canary grass. Again, foliar glyphosate. In fact, this is a great time of year to spray these bad grasses because all the native grasses have senesced.

The rule is that only plants that are green will be affected. If it isn't green, it won't be hurt. And there is no soil residual with glyphosate.

Yesterday, we sprayed lots of patches of cool season grasses. In addition to those mentioned above, we also sprayed large clumps of orchard grass.

Here is what I think happens when you use glyphosate this time of year: It is absorbed by the green leaves and is translocated to the roots, where it remains in an active state all winter. When the soil warms up in the spring, the herbicide takes over and kills the roots, thus killing the whole plant. Mark some sprayed areas and see what happens to them in the spring!


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