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Andrew Gabriel

In article ,
writes:
Andrew Gabriel wrote:
Also, higher concentrations often don't work because they
kill the parts of the plant they land on before the plant
can absorb them down into the roots

So, would repeated (eg daily) application of a weaker solution work?

No, it needs time to work, and the right conditions.
It's not an instant drop weedkiller (if that happens, it didn't work).

Generally, you need to apply it when the plants are growing fast,
so it gets carried around the whole plant before it kills it. It
should take at least a week before you see any signs, and could be
several weeks in more hardy plants. It won't work well in the dry
weather we have at the moment, as most plants won't be growing due
to lack of water.

There are some other use cases. There used to be lots of marestail
weed in my garden, coming up between paving stones and stone
chipping areas. Glyphosate doesn't work well on this because the
leaves (filaments) have a coating which doesn't let it through
very well, making it difficult to get enough into the plant. One
way is to walk over the plant after spraying which damages the
leaves and gets more in, but the damaged leaves may then die
anyway before distributing it (and you mustn't walk it over the
lawn!). Turns out the best way to apply to this plant is at the
end of the season shortly before it starts dying down naturally.
It retrieves some of the nutrients from the leaves back into the
deep root system to save for next year, and pulls back some of
the glyphosate too. It's still not much, but now it's trapped in
the root system all winter, and that does kill the roots. It took
a couple of years of this to knock it on the head, but I now
only have to deal with the occasional straggler which pops up
each year, and not a forest of it.

--
Andrew Gabriel
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