# Glyphosate - residual?



## DCB (Jun 5, 2006)

Hi Guys, recently i've been looking at a few trees - Calistemons for a local Authority. The trees in question show stag heading, chlorosis on various patchy sections throughout the tree. These are street trees which are semi -mature specimens and are at a guess 15 years old. They look like classic cases of poisoning but the trees effected are very random. In the street of approx. 70 trees probably10-15 trees arent looking too good. I do know the local authority do spray for pre-emergence weed control just before the rains once a year. The soil is a very sandy texture and around the base of the trees is grassed. I know no fertiliser is used on the grass. The only thing which i can think of is maybe a build up of Glyphosate which they use for weed spraying can be the cause - any ideas?


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## BlueRidgeMark (Jun 5, 2006)

I'm no chemist, but I have a friend who is one, and I asked him this quesiton a few years ago. Short answer: it's gone in a few days.

Long answer: He works for a small family owned company which makes a crop fumigant. Some years back the EPA was on a vendetta to shut them down, assuming that their fumigant is a carcinogen. When testing on the fumigant showed NO problems, the EPA decided that it must break down into dangerous, long lived toxins. (There was no REASON to think so, but it's effective, so it must be bad, right?) They spent several YEARS researching exactly what happened to their fumigant after it was put in the ground. They did radioactive isotope tracing until they could tell EXACTLY where each atom of their fumigant wound up. Finally, the EPA had to give up - they were clearly on a vendetta, and they were clearly defeated. As a control, they did the same testing with glysophate. Same result. My friend said that it's basically broken down in the soil within a few days. Once the plant that has ingested it decays, the residual there breaks down quickly, too.


Based on that, I'd say that if glysophate is what is bothering these trees, it's doing it during the application, not as a result of a residual effect.


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## gumneck (Jun 5, 2006)

DCB said:


> Hi Guys, recently i've been looking at a few trees - Calistemons for a local Authority. The trees in question show stag heading, chlorosis on various patchy sections throughout the tree. These are street trees which are semi -mature specimens and are at a guess 15 years old. They look like classic cases of poisoning but the trees effected are very random. In the street of approx. 70 trees probably10-15 trees arent looking too good. I do know the local authority do spray for pre-emergence weed control just before the rains once a year. The soil is a very sandy texture and around the base of the trees is grassed. I know no fertiliser is used on the grass. The only thing which i can think of is maybe a build up of Glyphosate which they use for weed spraying can be the cause - any ideas?



DCB

Glyphosate is not the chemical you would be concerned with. You said they use a preemergent. Glyphosate(roundup or glyphomax) works as a contact. A preemergent would be something similar to Surfan. Its basically spread out prior to weeds emerging. With a "very sand" soil as you mentioned, it could be their preemergent is not formulated for that species.


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## Elmore (Jun 5, 2006)

*glyphosate moderately persistent in soil*

http://www.cetos.org/articles/corralroundup.html

"Because Roundup® is highly persistent once on the ground (the time it takes for half the chemical to disappear ranges from 24-249 days), Roundup® will be present long after a single spray operation is completed. Final degradation depends on active soil cultures of microorganisms, some of which are abolished by the chemical in the first place."

and/or : 

http://extoxnet.orst.edu/pips/glyphosa.htm

"Environmental Fate: 
Breakdown in soil and groundwater: Glyphosate is moderately persistent in soil, with an estimated average half-life of 47 days [58,11]. Reported field half-lives range from 1 to 174 days [11]. It is strongly adsorbed to most soils, even those with lower organic and clay content [11,58]. Thus, even though it is highly soluble in water, field and laboratory studies show it does not leach appreciably, and has low potential for runoff (except as adsorbed to colloidal matter) [3,11]. One estimate indicated that less than 2% of the applied chemical is lost to runoff [99]. Microbes are primarily responsible for the breakdown of the product, and volatilization or photodegradation losses will be negligible [58]. 
Breakdown in water: In water, glyphosate is strongly adsorbed to suspended organic and mineral matter and is broken down primarily by microorganisms [6]. Its half-life in pond water ranges from 12 days to 10 weeks [97]. 
Breakdown in vegetation: Glyphosate may be translocated throughout the plant, including to the roots. It is extensively metabolized by some plants, while remaining intact in others [1]. "


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## Ekka (Jun 6, 2006)

DCB, you are in Perth.

WA is reknown for Phytophthora, sounds similar.

I doubt it was herbicide, the grass around the trees is still green. Are you with the council?

Time for soil and foliar tests. This could be the beginning of something big. 

http://www.deh.gov.au/biodiversity/invasive/publications/p-root-rot/index.html


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## DCB (Jun 6, 2006)

Thanks guys, i realise Glypho is a knockdown but wondered if anyone had come across a similar problem. As everyones back at work today i asked the local park supervisor about their spraying practises and on two occasions they have used a mix of simazine with the glypho so this could be the problem.
I originally thought of phytophra, the symptoms are similar but it is very random. The area which they spray is approx. 100 - 200ml from the actual kerb(roadside) to stop weeds etc encroaching onto the roadway. I did inject one lot of calistemons with fosject but didnt have much success.


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## DCB (Jun 6, 2006)

Thanks Elmore, are you saying that if the soil is basically gutless (mimal microbial activity) then the glypho is present for an extended period? Our soil here in perth is a very grey sand that has absolutely no substance whatsoever. Would the ph of the soil have any bearing on the longevity of the Glypho?


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## Elmore (Jun 6, 2006)

DCB said:


> Thanks Elmore, are you saying that if the soil is basically gutless (mimal microbial activity) then the glypho is present for an extended period? Our soil here in perth is a very grey sand that has absolutely no substance whatsoever. Would the ph of the soil have any bearing on the longevity of the Glypho?



I didn't say that...those web site articles indicate that it is persistant in the soil unless broken down by microbes or leached out. I don't think that it is active though.


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## NOMOREGEARS (Jun 28, 2006)

*Round-up*

I do have to agree that the Glyphosate is somewhat persistent in some form. From what I've read, it can fix certain nutients into the soil. I've been talking to a Wildlife biologist who is concerned about the possible correlation between round-up use and "copper fixing" in the soil (copper deficiency is prevalent in chronic wasting disease). Jury is still out on this one. I do not believe it just goes away. If you do get a chemical analysis done I would be interested.


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