Originally posted by rary
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Aminopyralid and clopyralid will break down entirely in 6-12 months when in consistent contact with damp soil, under the action of normal soil bacteria.
But they will not be broken down (at least not at any decent rate) by the bacteria found in compost heaps (or manure heaps, which are basically the same decomposition bacteria).
Thus, the weed killer tends to persist in compost and manure.
So if you suspect you have already dug in contaminated manure or compost then the best and quickest way to get rid of the residue is simply to dig that area two or three times over the course of the year, making sure to break up any lumps of compost or manure as small as possible, so that as large a surface area as possible is in contact with the soil. Water the area in dry periods, to prevent it drying out entirely, as the bacteria become dormant if there is not enough water.
Some crops can still be grown on contaminated ground. Sweetcorn (like all grasses) is completely immune. Brassicas and Alliums are reasonably resistant, and thus should be unaffected by mild to moderate contamination (severe contamination will affect even them). On the other end, peas, beans and nightshades (tomatoes, potatoes, peppers, etc.) are most sensitive to it.
Of course, any crop waste created from growing on contaminated ground may itself have traces of weedkiller in, albeit less than was in the soil originally, so you may need to be careful how you deal with the dead plants. They are best either put in the general waste or chopped up finely and dug back into the plot they were grown in, to allow the weed killer to be broken down in the soil.
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