| Health News | |
Testing for Clopyralide in Compost
by Mary Jane Butters, from the May 2002 newsletter
Margaret Misner, Manager of the Idaho State Organic Certification Program sent
out a letter in March to all the state's organic growers warning us about the
herbicide clopyralid that might show up in compost, straw mulch, or grass clippings.
Because there is a high tolerance allowed for "public safety," most
laboratories do not routinely measure clopyralid below 50 ppb.
Consequently, injurious levels in straw, hay, and compost are often not detected. Testing for contamination at these low levels is expensive, but there is a simple and inexpensive bio-assay test if you suspect you may have contaminated compost. For every load I receive at my farm, I leave the straw piled away from my crops and check for clopyralid first. Here's how:
Mix one part compost or suspect soil with six parts garden soil known to be uncontaminated. Fill several 4" pots and plant 2 pea seeds of any variety in each. Clopyralid damage, if any, will appear with the second set of true leaves, which may be distorted, curled or twisted, pale or yellowed, and usually lacking the normal leaf shape. At levels as low as 3 ppb of clopyralid, all test plants will show damage and most will die quickly. You can view an article about this at http://seattlepi.nwsource.com/nwgardens/59050_lovejoy21.shtml.
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