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.
Here's some of my work:
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
Oh...throw a little household detergent in there as a surfactant...it'll
wet better that'll help.
***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
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
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.
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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