how much glyphosate to kill this grass?

farmerjoe4October 10, 2013

I have a 20-year old ornamental grass I would like to kill with glyphosate, but I'm not sure how much I need to buy. The plant measures 4 feet across, 3 feet tall.

Would a pint of 18% concentrate be enough? (16oz)

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gardengal48

It tells you on the package label exactly how to mix and apply - 6oz (12 tbs) per gallon of water. This covers 300 SF. A pint should cover 2 and 2/3's applications.

My suggestion would be to cut the grass off about half way - 18" or so - then apply the glyphosate solution to the 'stump' of the grass. The kill may not be immediate. Glyphosate sometimes takes time as well as more than a single application to be effective. And we are getting rather late in the season for it to be performing at its optimum efficiency.

You could always dig the grass up. You are going to have to anyway if you want to replant in the same spot, as that rootball will be present for the foreseeable future :-)

    Bookmark   October 11, 2013 at 5:04PM
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donn_(7b-8a)

I've recently ended a several year experiment, during which I fooled around with a wide variety of generic glyphosate concoctions, in an attempt to save money. I tested different concentrates, mixed with different detergent surfactants, all to avoid supporting Monsanto.

I now use Roundup ProMax only. It's the most effective and cost efficient solution out there.

That said, different ornamental grasses react in different ways to Roundup (or any glyphosate treatment). I've found it takes longer, and requires more treatments to kill a broad leaf grass than a fine leaf grass. It also takes more to kill an older grass than a younger one, and, as GG48 points out, if the grass is not in its active growth season, you may be butting your head against the wall. Dormant or semi-dormant plants don't have a lot of transpiration going on, and if they aren't moving water around, they won't move herbicide either.

    Bookmark   October 11, 2013 at 9:15PM
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lazy_gardens

Cut the mature grass back close to the ground ... then when it starts sending up fresh tender shoots, spray them.

Repeat this as needed until the roots are no longer sending up shoots.

    Bookmark   October 22, 2013 at 3:18PM
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