Whatcom County organic farmers and gardeners are reporting severe crop damage that appears to be linked to herbicide contamination in the manure and compost they obtain from non-organic farms and dairies for use as natural fertilizer.

The herbicide suspected is known as aminopyralid. It is not believed to pose much danger to humans, other mammals or birds, but it’s tough on broadleaf plants. Farmers use it for weed control in pastures and fields that grow silage crops for dairy cows.

When cows eat grass or silage tainted with aminopyralid, the chemical passes through them unchanged and remains in their manure in concentrations that can still be high enough to damage broadleaf crops if the manure is used to fertilize them.

“It’s killed off most of our potato crop, our salad crops,” said Kirk Hayes, a Whatcom County grower who sells his crops to the Bellingham Community Food Co-op and four other co-ops in the region. “We’ve contaminated about seven and a half acres, it looks like.”

He estimated he has lost about $40,000 worth of sales in the past two months because of the problems.