Herbicide Carryover in Hay, Manure, Compost, and Grass Clippings

Publish Date: Fall 09 Oregon State University

Depending on the situation, the herbicides can be deactivated in as few as 30 days, but some field reports indicate that breakdown can take as long as three to four years. Degradation is particularly slow in piles of manure and compost. When mulches, manures, or composts with herbicide activity are applied to fields or gardens to raise certain vegetables, flowers, or other broadleaf crops, potentially devastating damage can occur.

http://smallfarms.oregonstate.edu/sfn/f09Herbicide
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Arty turns 10 this summer.