LISA RATHKE

Associated Press

MONTPELIER -- The Vermont Agency of Agriculture is trying to figure out how trace levels of two persistent herbicides got into both bulk and bagged compost, damaging some vegetable plants. Authorities said humans weren’t believed to be at risk.

The Health Department is advising gardeners to make their own decision about whether to consume produce grown in the affected compost from the Chittenden Solid Waste District.

Trace residues

"We just want people to be aware that even if their plants don’t look like they’re affected, they could still have some trace residues of these herbicides, and if that’s something that’s important to them, they need to make their own decision," Sarah Vose, the Health Department’s state toxicologist, said Friday.

The Health Department doesn’t expect that the low levels of the herbicides -- clopyralid and picloram -- would cause consumers any harm, she said.

The Green Mountain Compost was tested after customers and staff reported last week that certain vegetable plants showed signs of leaf curling and distortion consistent with herbicide exposure.

The district has since stopped selling its compost products and is notifying all customers known to have bought bulk or bagged compost. At first, CSWD thought the contaminated compost was bought between mid-April and the end of May. But the contamination has turned up in samples of compost made at the district’s old facility in Burlington in July 2011.

"We are working with the Vermont Agency of Agriculture to determine how these herbicides, which are regulated by the state, have entered feedstocks to our compost program in apparent violation of their label requirements and how to prevent it from occurring in the future," district General Manager Tom Moreau said.

The two herbicides aren’t widely used on food crops in Vermont and are intended to control thistle, clover and other weeds on nonresidential turf or rangeland.

The Vermont Agriculture Agency has checked the reports of commercial pesticide use collected by the state and found no source of the two herbicides.

Picloram is a restricted-use herbicide, meaning that it can only be used by licensed applicators. Clopyralid isn’t restricted in Vermont, but the state said the manufacturer canceled residential use of it on lawns in 2002.

Signs of herbicide exposure include cupped leaves, twisted stems, distorted growing points and a reduced fruit set on broadleaf plants such as tomatoes, potatoes, eggplant, beans, peas, peppers and sunflowers.

Home gardeners with health concerns related to the compost can call the Health Department on weekdays at 800-439-8550; commercial gardeners are asked to call the Agriculture Agency at 802-828-6531.

Gardeners who notice leaf curl or similar damage on their plants after using compost from CSWD are asked to consult the plant diagnostic clinic at the University of Vermont Extension Service at 802-656-0493 or http://pss.uvm.edu/pd/pdc.