Many thanks to Milner Gardens & Woodland’s Gardening Advice line (a partnership between Vancouver Island University’s Milner Gardens & Woodland and the Vancouver Island Master Gardeners Association) for the following response:
Hi Claire,
Thank you for your inquiry about having your garden beds analyzed to determine whether herbicide was used and where you can get this type of analysis done.
Generally the first step would be to do what is called a “bioassay test” with peas, tomatoes or beans in pots in a controlled environment and compare to a commercial potting soil because it could be a saline issue instead of a herbicide issue. Below is a link to the Washington State University recommended process. Because what you describe are the usual plants that are susceptible to it, what you would be looking for is if the leaves are cupped and stem is twisted, then it is likely a herbicide residue. Plants that are unaffected by the herbicide would be single leaf plants this year like corn, grass and onion so if you can see those growing fine that would also be an indicator. https://s3.wp.wsu.edu/uploads/sites/411/2014/12/PDF_Clopyralid_Bioassay.pdf
There are a few labs that will test for a “home gardener” but perhaps as a community organization you might be able to access commercial tests. The labs will have a specific method you need to follow for their test. Your options nearby are:
MBLabs based in Sidney , BC - website is mblabs.com (they do home garden tests) and Caro Analytical Services in Richmond, BC - website is https:/store.caro.ca/contact-us/ (they have some home garden tests listed on the site, but you might want to call about specifics)
The Pacific Northwest Gardeners Handbook recommends asking your source if specific broadleaf herbicides were used on pastures or hayfields that were used to feed the livestock. Most herbicides will carry over into the manure. Don’t spread any more of the manure until you know what you are dealing with. Some residues can break down by further composting for a year or more, whereas a couple of commercial herbicides may still survive the composting process. For the garden itself, if there is any manure on the top that can be scraped away, move it to a pile for composting. There are a variety of remediation options suggested such as growing barley, corn or wheat to take up the herbicide, then disposing of those plants (do not compost). You can also treat the soil with warmth, moisture, wood ash, or activated charcoal to reduce the toxicity and promote the breakdown. Other methods include replacing the soil or putting raised beds on top of the soil.
ttps://www2.gov.bc.ca/gov/content/industry/agriculture-seafood/animals-and-crops/plant-health/plant-health-laboratory
https://content.ces.ncsu.edu/manage-compost-and-soil-contaminated-with-broadleaf-herbicides-in-gardens
Hope this all helps - there’s a lot of information.
All the best,
Carrie and Katherine