Horse farms are considered the most scenic of estates, but most don’t reuse their own manure which contains herbicide residues, but put it out for disposal (collection by composters and avid gardeners). This is where the residue problems start.

An informal study conducted by Woods End during the past 3 years examining quality of Maine manures used for compost, may have mushroomed into a focus on herbicide carryover specific to horse manures. When Vermont reported a case of compost chemical contamination, Woods End alerted the Chittenden compost facility about carryover risk of herbicides specifically in horse manures and their feedstuffs.  “The results of all this investigation are possibly more than anyone can handle” says Brinton of Woods End.   Previously, Woods End found horse manures were usually “bioassay-positive,” but at very low levels. In most cases such residues affect plants to only a small degree and sometimes only with massive applications of composts. “The perception is that there is a big problem”.  In fact, the issue is more complex than most believe. Decades of consensus between EPA and industry have led to allowance thresholds for residues of herbicides in farm byproducts.  Perhaps the real need is to re-quantify the risk based on an assumption that these byproducts are not being  farm recycled (which they are designed for). Most herbicides have 1-2 ppm EPA thresholds in feedstuffs (considered safe in the food chain).  Woods End’s strategy to aid composters and growers is to construct risk-pathways for sources — a process analogous to Identity Protocol used to track grain contamination.  This may lead to feeds and hay/straw being seen as as significant indirect sources of residues for farms, especially equine.  A diverse array of information and data mean that any effort  faces “multiple challenges” one being an (odd) perception of being anti-farming. A combination of re thinking safety levels, performing pathway analysis in the short-term to protect growers, and encouraging sustainability for farms not reusing their own residue-laden manures, will have to be implemented. All this against a political backdrop of reduced regulatory oversight of farmers (and composters).