Roundup shelf life

I have about a gallon of premixed Roundup in a two-gallon garden pressure sprayer that I mixed about six months ago and did not use. It has been sitting in my garden shed since June.
With the glorious warm weather we're having in SoCal this weekend I thought I'd hit a few weeds that sprouted during the recent rains, but I don't know if this six-month-old Roundup is still good. I've read the package instructions carefully and it says nothing about storing premixed product. It does say that Roundup becomes inert ("deactivated") when it hits the soil, but nothing about the effectiveness of leftover mix. I vaguely recall some of the groundskeepers at work mentioning that mixed Roundup slowly becomes inert with time, but my memory of those conversations is a bit fuzzy.
It's no biggie to mix up a fresh batch, but as expensive as this stuff is, I'd like to not waste it if it's still good. I thought I'd ask here before calling Monsanto.
Frank
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On 11/26/2011 1:21 PM, Frank J Warner wrote:

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It'll be ok...just wet a little more than normal.
We use it in large quantities (like 55 gal drums) for ag purposes and often may have some left from one season to next. It's not quite as effective even then but for a couple months or so doubt if you'll see any difference.
Oh...throw a little household detergent in there as a surfactant...it'll wet better that'll help.
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wrote:

***Check with <rec.gardens>. They are pretty savvy, and always friendly and courteous.
<Answers.com> said : store in a cool dark place and it can last a year.
The operative word there might be "can". But you also need to take Monsanto's advice with a grain of salt. They might want you to buy more.
HB
HB
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Thanks all.
I used the old Roundup. But it ran out fast and I have a large yard, so I mixed a fresh batch and went over everything with the new mix just to make sure.
Frank
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wrote:

I keep a quart bottle of it mixed and sitting on the back porch windowsill. Been there for many long years winter and summer.
Just as effective when I used a small couple squirts last summer as it was when I mixed it.
Harry K
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On 11/26/2011 11:21 AM, Frank J Warner wrote:

why not just spray it and see what happens? It doesn't go bad.
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I've mixed it and had it sitting for months in a hot garage and it worked fine. Also, I have 3 gallons of the high concentration glyphosate, ie generic Roundup, that I've been slowly using for 10 years and it works fine. Roundup comes in a variety of concentrations and I would strongly suspect that the diluting agent is always water. So, if the concentrate lasts for years, don't see why the mixed would not as well. Also, if there were a date issue, especially with only a few months, how would they be able to sell the ready to use stuff? It would go bad in the supply chain, stores, etc. Would need to have a date on it and it doesnt.
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Well, see, the idea was to avoid spraying twice if I could help it.

So I've heard.
Frank
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On 11/26/2011 2:21 PM, Frank J Warner wrote:

Why not just try it? Its not like the question was "I have an old container of glue and wonder if it will work?"
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Based on my experience today, I'd say the issue is not whether the chemicals will kill but how plugged up the spray hardware has become.
m
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