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Weed control, management, ecology, and minutia
by Frank Peters
on November 6, 2017 at 7:37 AM
Do you know the ppm of 24-D and Dicamba in the compost?
by Brad Hanson
on November 6, 2017 at 8:12 AM
Hi Frank,  
I think this issue was not confirmed as either 2,4-D or dicamba - to answer your ppm question, they'd have needed laboratory analyses done. Instead, the symptoms were "consistent with those caused by growth regulator herbicides". The bioassay with activated charcoal helped narrow the problem down to a soil-related issue (vs drift, for example).  
Here is a link to a useful herbicide symptomology database at UCIPM  
by Mike Mellano
on May 4, 2019 at 8:39 AM
I was wondering if you knew the total make up of the potting mix and how much could have been contaminated compost? I guess heat from composting isn’t enough to break down these materials but seems that you would need a lot of contaminated material in the compost to cause an issue. I’ve seen a few people questioning this type of issue with herbicides from manure based composts on field crops. Seems like a long shot to me. What do you think? Seems that they’d need to spread a lot of compost to crest the issue and then salts would be a bigger concern.  
How much charcoal was added in the bioassay?  
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