In message , Franz Heymann
writes

"sw" wrote in message
...
Nick Maclaren wrote:

In article ,
PA wrote:
thanks every one for your input, I'm still in two minds though....
the bit I don't get is: if no residue is left in the soil, what about
when
the roots of the weeds start to break down wont they release chemicals,
which will be then taken up by whats ever growing?
the trouble is I've got about 450 square meters to clear and its taken
about
an hour to do one properly
and now I'm dreaming of roots

No, because it will be released into the soil, where it will be broken
down by bacteria. Apparently, some breakdown products disappear very
slowly from the anaerobic sludge at the bottom of ponds, but garden
soil has a very different (and much more vigorous) collection of
microorganisms.

I'd thought there was some research suggesting it doesn't break down in
soil quite as thoroughly/quickly as was originally believed? Or is that
more a concern where fields of GM-HT crops are resulting in higher
usage?

Surely if it does not break down pretty smartly, the plants surrounding the
targeted weed would die as well? I have never noticed an effect of this
kind.

Not necessarily, even some of the much more noxious and longer term
active weedkillers are physically adsorbed on clay soils and so rendered
inactive against plants. The same happens to glyphosate too (although it
isn't so important since to work it has to hit the green parts of the
plant).

It doesn't have to be broken down to prevent it working. It just has to
be made physically unavailable or kept locked up in the wrong place.

If you garden on pure peat and sand with no hint of clays you might have
real difficulties with weedkiller persistence (but not with glyphosate).

Regards,
--
Martin Brown

In message , sw
writes
Nick Maclaren wrote:

In article ,
PA wrote:
thanks every one for your input, I'm still in two minds though....
the bit I don't get is: if no residue is left in the soil, what about when
the roots of the weeds start to break down wont they release chemicals,
which will be then taken up by whats ever growing?
the trouble is I've got about 450 square meters to clear and its taken about
an hour to do one properly
and now I'm dreaming of roots

No, because it will be released into the soil, where it will be broken
down by bacteria. Apparently, some breakdown products disappear very
slowly from the anaerobic sludge at the bottom of ponds, but garden
soil has a very different (and much more vigorous) collection of
microorganisms.

ISTR the most potent breakdown pathways are in soil fungi...

But even so glyphosate is only lethally effective when it hits living
green plant tissue. It can hit bark or roots in normal soil without any
effect.

I'd thought there was some research suggesting it doesn't break down in
soil quite as thoroughly/quickly as was originally believed? Or is that
more a concern where fields of GM-HT crops are resulting in higher
usage?

The research which shows it breaking down very slowly was in extreme
environments where *nothing* organic breaks down quickly either because
it is desiccated, deep frozen, deoxygenated or a combination of all
three.

I am no fan of gratuitous GM style use of glyphosate on field scale to
annihilate all weeds. Not least because I fear it will inevitably lead
to the development of resistant superweeds. But for the moment
glyphosate is as close to a safe environmentally friendly weedkiller as
we have ever managed to come. I favour minimum inputs horticulture.

Regards,
--
Martin Brown

In message , Franz Heymann
writes

"Martin Brown" wrote in message
...

[snip]

A few very tough weeds with large deep roots and small tough waxy leaves
can survive it (and for some reason buttercup is partially resistant).

[snip]

Glyphosate is ever so slow in action compared to paraquat. I use both
according to my mood, and (because of my impatience?) I usually have to
apply glyphosate twice before the weeds keel over.

The second application is almost certainly wasted. Have more patience
and the weeds will keel over if you give them time for the waste
products of photosynthesis to build up. Green plants and glyphosate
don't mix.

Typically plants start to show serious signs of glyphosate damage after
about two weeks from application and it may take them another couple of
weeks to expire after that. And contrary to popular belief it may be
more effective to dilute the stuff to weaker than the recommended dose
(unlicensed use) so that it takes out more of the root system. Strong
sunshine, warmth and active growth speed the process up a bit.

Translocating weedkillers like glyphosate take a lot longer than
paraquat but have a more throrough effect. It takes time to permeate
deep roots.

Does paraquat really put paid to a plant, root and all, or does it only
interfere temporarily with the photosnthesis in the leaves?

Paraquat is much faster acting but is much more inclined to just burn
off the tops by excessive growth in the manner that Alan seems to think
glyphosate works.

It looks great for the gardener requiring instant gratification.

Regards,
--
Martin Brown

"Martin Brown" wrote in message
...
In message , Franz Heymann
writes

"Martin Brown" wrote in message
...

[snip]

A few very tough weeds with large deep roots and small tough waxy
leaves
can survive it (and for some reason buttercup is partially resistant).

[snip]

Glyphosate is ever so slow in action compared to paraquat. I use both
according to my mood, and (because of my impatience?) I usually have to
apply glyphosate twice before the weeds keel over.

The second application is almost certainly wasted. Have more patience
and the weeds will keel over if you give them time for the waste
products of photosynthesis to build up. Green plants and glyphosate
don't mix.

Typically plants start to show serious signs of glyphosate damage after
about two weeks from application and it may take them another couple of
weeks to expire after that. And contrary to popular belief it may be
more effective to dilute the stuff to weaker than the recommended dose
(unlicensed use) so that it takes out more of the root system. Strong
sunshine, warmth and active growth speed the process up a bit.

Thanks for the advice. I will be more patient in future, and I will
certainly follow your suggestion of diluting it a bit more than the
container says, since the stuff is costing me an arm and a leg. Would it be
too greedy to go for a recipe which uses, say, 1.5 times as much water as
recommended on the bottle?

Translocating weedkillers like glyphosate take a lot longer than
paraquat but have a more throrough effect. It takes time to permeate
deep roots.

I used to have an RHS booklet "Gardening Chemicals", alas now on permanent
loan to an unknown friend, in which I am sure that paraquat was also
described as being translocating.
I confess that I don't know precisely what the term means. Could you
describe it for someone who is not entirely ignorant of botanical matters?

Does paraquat really put paid to a plant, root and all, or does it only
interfere temporarily with the photosnthesis in the leaves?

Paraquat is much faster acting but is much more inclined to just burn
off the tops by excessive growth in the manner that Alan seems to think
glyphosate works.

It looks great for the gardener requiring instant gratification.

So I will use it in the places where my better half wants the garden to look
spick and span, and use glyphosate where I actually want to get rid of the
weeds. Both of us are too ancient and decrepit to indulge in much hand
weeding or hoeing.

[Franz Heymann]

"Martin Brown" wrote in message
news
In message , Franz Heymann
writes

"sw" wrote in message
...
Nick Maclaren wrote:

In article ,
PA wrote:
thanks every one for your input, I'm still in two minds though....
the bit I don't get is: if no residue is left in the soil, what
about
when
the roots of the weeds start to break down wont they release
chemicals,
which will be then taken up by whats ever growing?
the trouble is I've got about 450 square meters to clear and its
taken
about
an hour to do one properly
and now I'm dreaming of roots

No, because it will be released into the soil, where it will be
broken
down by bacteria. Apparently, some breakdown products disappear very
slowly from the anaerobic sludge at the bottom of ponds, but garden
soil has a very different (and much more vigorous) collection of
microorganisms.

I'd thought there was some research suggesting it doesn't break down in
soil quite as thoroughly/quickly as was originally believed? Or is that
more a concern where fields of GM-HT crops are resulting in higher
usage?

Surely if it does not break down pretty smartly, the plants surrounding
the
targeted weed would die as well? I have never noticed an effect of this
kind.

Not necessarily, even some of the much more noxious and longer term
active weedkillers are physically adsorbed on clay soils and so rendered
inactive against plants. The same happens to glyphosate too (although it
isn't so important since to work it has to hit the green parts of the
plant).

It doesn't have to be broken down to prevent it working. It just has to
be made physically unavailable or kept locked up in the wrong place.

If you garden on pure peat and sand with no hint of clays you might have
real difficulties with weedkiller persistence (but not with glyphosate).

Martin, your contribution is, as usual, excellent. Thank you.

I would still like to know why it is effective only when absorbed vie the
leaves. Is it because in the leaf is required actively to produce the
actual poison which delivers the coup de grace?

[Franz Heymann]