From: "Torsten Brinch" <iaotb@inetdotuni2.dk>
Newsgroups: sci.agriculture
Subject: Re: spraying off set-aside (UK)
Date: Wed, 12 May 1999 00:27:08 +0200

Oz skrev i meddelelsen <7IT7PDAFHJO3Ewji@upthorpe.demon.co.uk>...
>In article <1drnk9l.12j9n576sds4mN@amitiel.demon.co.uk>, sarah
><swroot@copy.amitiel.demon.co.uk> writes
>
>>Several areas of local set-aside are glowing an interesting shade of
>>orange, which I take to mean they've been sprayed off with glyphosate.
>
>Indeed so. 'Autumn colours' as Torsten likes to call it.  :-)
>
>>On closer inspection it's clear that the spray has killed the monocot
>>volunteers from last year's crop (wheat, I think).
>
>They are particularly susceptible.
>
>>Thistles, volunteer
>>OSR and other weeds display some distorted leaves but appear to remain
>>reasonably healthy and are continuing to grow - the OSR is starting to
>>set seed.
>
>Could be. Thistles and OSR have thick cuticles and very waxy leaves so
>it's often hard to get a lethal dose into the plant. Indeed this is used
>for selectivity for some pesticides. Cyanazine will kill charlock (a
>very close relative) in OSR simply because it has no thick waxy cuticle.


I agree with all the above, but on this,

>NB The distortion is probably nothing to do with the glyphosate.

I disagree --  in the situation Sarah describes,
the distorted leaves are very likely to be from glyphosate treatment.
In fact I can't imagine the thistles standing there amidst orange
dead monocots, while _not_ displaying some degree of
glyphosate damage....

It is important when observing sublethally glyphosate poisoned
plants to distinguish between the acute effects  (which may
produce dead greyish drying edges or tips of directly hit leaves
on thistles and consequently  some deformation) as opposed
to the long the chronic effects on the plant growth in the months or
years thereafter. Thistles will rarely display visual effects
beyond the season of treatment, though.

The long term chronic effects on thistles will appear with the
growing tip as brightening and shorthening of  newly formed
leaves. There  will be deformation, but due to the curlyness of
the leaf and rim  of most thistles, leaf deformation from glyphosate
poisoning is less obvious in thistles than in most other species.


Best regards,

Torsten Brinch

From: "Torsten Brinch" <iaotb@inetdotuni2.dk>
Newsgroups: sci.agriculture
Subject: Re: spraying off set-aside (UK)
Date: Thu, 13 May 1999 11:24:03 +0200

sarah skrev i meddelelsen <1drpevk.17y43xg1wg1beoN@amitiel.demon.co.uk>...
>Oz <Oz@upthorpe.demon.co.uk> wrote:


>> Yes, that's typical BLW glyposate symptoms. Personally I wouldn't
>> describe the plant as being distorted (that tends to strongly imply
>> hormone weedkiller-type distortion) but 'affected'. As Torsten has said
>> you can now take a peek and spot drift damage now you have an eye for
>> what you are looking for. The chage in colour can be quite subtle and
>> you should check definitely unaffected plants for natural colour changes
>> of new growth. You may even be able to deduce the wind direction on the
>> spraying day.


Distortion is the wrong word, if it tends to imply hormone weed killer
distortion. The malformation with glyphosate is different from that, in that
it is so extremely apical -- in most cases the malformation resulting from
glyphosate is more like a lack of development (miniaturising the new
growth), and especially lacking development of the outermost parts
of new growth. This produces somewhat cupped, and/or ragged-edged
leaves, as if the leaf rim becomes to 'short to fit' so to speak, or badly
developed or dropping flowers and buds.

>There is some distortion of the younger leaves also.
>As far as wind direction goes it's a reasonably large field - sadly the
>route which includes the likely downwind boundary is not possible before
>work with our aged dog.

>Certainly the degree to which the plant is affected appears to be
>indicated by colour changes. The monocot volunteers on the more recently
>sprayed field turned bright orange yellow within days, but the wild oats
>are still (in some areas) primarily green with red stripes.


The orange-reddish hues after glyphosate treatment should be generally
taken as signs of acute lethal damage. Glyphosate must affect degradation
of chlorophyll in that case (makes sense, as glyphosate interferes with an
important biochemical pathway situated within chlorplasts).  Some
monocots (right, e.g. wild oats) may put  on display a color change to deep
(bluish) red (rather than orange) in longitudinal stripes along leaves. Such
color change is much like what can be seen with monocots in certain types
of soil nutrient imbalances.

But generally with severe sublethal damage, a paler green is the color
change to expect, and freakily not at the spray exposed parts, but on new
growth only. If apices are severely affected they may become so malformed
and pale that apices die off, and the plant will then attempt to produce new
apices below, until at pale continous regrowth is viable (or the plant dies)

Milder longterm sublethal damage may eventually not display
color changes at all, while the shorthening and malformation  of growth at
apices persist. These latter changes are the  last visually observable signs
of long term glyphosate poisoning in plants. As the  plant eventually grows
through a poisoning episode, visual signs of damage will disappear,  while
the perturbation of plant biochemistry is probably still measurable
as increased levels of shikimate from the adversely affected biochemical
pathway.


Best regards,

Torsten Brinch