Persistent herbicides pose garden risks

It’s been anything but a good growing season for some farmers and home gardeners on Whidbey Island this year.

They thought they were doing everything right by using locally produced manure on their crops and sharing it, free of charge, with their friends.

What they didn’t know was that the hay that had been purchased from Eastern Washington to be fed to livestock to make that rich manure had been sprayed with a persistent herbicide.

The result of using this manure was everything from low seed germination to deformed plants, or misshapen fruit to the outright failure of young plants to survive.

The culprit was found to be residues of clopyralid and aminopyralid in the manure and compost produced from the hay.

These herbicides do a great job of killing broadleaf weeds, especially members of the aster family, like dandelions and thistles, but don’t affect members of the grass family, like Timothy grass, wheat and other grains. Because of this, they’re go-to herbicides to treat turf grass and grass family crops.

On the other hand, they’re also lethal at extremely low levels to sensitive plants in the pea and nightshade families, as well as other food crops.

We’re talking about peas, beans, alfalfa, potatoes, tomatoes and peppers, to name a few.

According to the Washington State Department of Agriculture, our state was the first to limit the use of clopyralid after it was found in grass clippings used to make commercial compost in 2002.

Three years before that, Seattle banned it because it had turned up in its mandatory yard waste recycling program. The state ban limited its use to turf grass at golf courses and for some hay and grain growers.

Even then, golf courses were exempt from the ban only if “no grass clippings, leaves or other vegetation are removed from a course and sent to a composting facility that provides product to the public.”

The problem for home gardeners and farmers — even organic farmers — didn’t end there.

In 2010, some Whatcom County farmers’ crops were damaged by compost contaminated by Clopyralid and Aminopyralid.

And now Whidbey Island farmers and home gardeners’ crops have seen similar damage.

Clopyralid can remain active in soil, water and vegetation for years. Its half life can be as short as a few months to over a year, which means only half of it will degrade in that time.

It doesn’t bind strongly to soil particles and remains very soluble in water. This makes it mobile and able to spread easily through soils and into ground water. And it doesn’t degrade in sunlight either.

It will eventually degrade through microbial metabolism in soils and in the sediment in the bottom of bodies of water, yet it will pass completely intact through the digestive systems of livestock.

This is why the manure from animals who have consumed treated hay is an issue for gardeners.

When the state enacted its lawn and turn grass ban in 2002, it wasn’t as common as it is today for manure to be a component in compost.

Now we know we have to be aware of the dangers of persistent herbicide contamination, as these chemicals travel down the food chain.

What can you do to protect your garden from the affects of persistent herbicides?

First, the County Extension advises you know who you’re getting your hay, compost and manure from. If you’re not certain whether persistent herbicides have been used in their production, ask.

And ask at your local feed store or anyone else you get these products from.

Know you’re in the clear if the hay you buy contains clovers, alfalfa or lespedeza.

These are members of the pea family (legumes) and would not have been sprayed because these crops are killed by clopyralid and aminopyralid.

Finally, you can do a bioassay on any manure or compost you have concerns about before you spread it on your crops.

This involves planting peas in a sample of your compost and takes about four weeks.

For more information on persistent herbicide dangers, contact Janet Hall at the WSU Island County Extension at 360-679-7974 or Karen Bishop at the Whidbey Island Conservation District at 360-678-4708.


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