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Weed control, management, ecology, and minutia
Comments:
by George Atcherson
on April 15, 2020 at 10:05 AM
Does Glyphosate kill Wooley distaff thistle?
Reply by Brad Hanson
on April 15, 2020 at 10:14 AM
George,  
Glyphosate should control woolly distaff thistle. Here's a link to an excerpted report on the species:  
http://wric.ucdavis.edu/information/crop/natural%20areas/wr_C/Carthamus.pdf  
 
That report was excerpted from this excellent resource Weed Control in Natural Areas in the Western United States:  
 
https://www.cal-ipc.org/resources/library/publications/weedcontrol/
Reply by Guy B Kyser
on April 15, 2020 at 10:16 AM
Also see this blog post.  
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16522  
We tested a bunch of selective herbicides because we wanted to control the thistle, but not damage the forage grasses.
by Kris
on September 18, 2021 at 8:30 AM
The above mentions that Milestone continues to be active for some time after application. Is there a rough estimate of how long the product stays active? A week? A month?
Reply by Bradley Hanson
on September 19, 2021 at 9:54 AM
Kris, the answer to length of herbicidal activity in soil is usually "it depends". That's true here as well.  
 
One source I read indicates "depending on the rate applied and weed species, aminopyralid can also provide residual activity on some germinating weed seeds and emerged seedlings". That same source described the soil half-life in field studies in North America of 6-72 days. Half life in soil can be highly variable depending on soil conditions (especially moisture, temperature, organic matter, and pH).  
 
I'd interpret that as likely to provide reasonable levels of "control" of sensitive weed species for a few weeks or a month. By the same token, tiny amounts might persist long enough to cause "symptoms" (maybe or maybe not enough to kill) extremely sensitive species for longer than that (that's why several herbicides in this class have warnings about composting material that might have residues).
 
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