mm wrote:

Does concentrated Round-up weaken and go bad as quickly as the stuff
sold for immediate application?

I have been using Roundup for many, many years and here's my
experience:
Roundup, as it comes in the container you buy, will last 2-3 years
before it starts to weaken. However, once you dilute it to specs for
spraying, it is only good for 2-3 days.

The original Roundup was a great product, but it had to be mixed with a
surfactant (soap) to get it to stick to the leaves. Mixing reduced the
use time to 2-3 days. Then Roundup decided to add the surfactant at
the factory (Roundup Ultra) (Increased price). But it didn't work
nearly as good as the original product because of the mix. So they had
to increase the strength to make it last longer (another price
increase). I now buy a generic brand because it's cheaper and works
better than Roundup.

A 4-oz. bottle came included with something else I wanted to buy, but
in order to mix it, I want to put on gloves and long pants (do I need
that?) and so it's been more than a year and I've never gotten around
to doing it.

The ingredient in Roundup is little/no toxic to humans. I even had a
salesman tell me you could drink it with no ill effects (but how many
people believe salesmen?). The standard used to measure toxicity is
table salt. Roundup is less toxic than salt. HOWEVER, always follow
the manufacturers directions.

I"m thinking it might have been cheaper in the long run to buy it
already diluted.

Depends on how much you use and how fast you use it.

Bob