Herbicides sprayed in pastures to eradicate invasive Canada thistle and members of the knapweed clan are taking an unintended toll on vegetables found in almost any home garden or commercial grower’s field in La Plata County.
Complaints about the herbicides are legion, so much so that La Plata County commissioners have scheduled a workshop today to hear a presentation by Darrin Parmenter, horticulturist with Colorado State University Cooperative Extension in Durango.
“I’ve received a couple of hundred complaints, inquiries or photos of plants a year for the past four or five years,” Parmenter said last week. “There’s a pretty decent consensus that it’s herbicides, not a virus or an insect.”
Phil Shuler, a professor and Public Health Program coordinator at Fort Lewis College, said herbicide carryover is a national problem.
“The issue came to my attention when gardeners in the area began reporting unexpected problems with vegetables that could not be clearly attributed to disease,” Shuler said in an email.
The culprits are three classifications of herbicides, probably the best known of which was registered in the United States in 2005 by Dow Chemical Corp. under the brand name Milestone.
In the pasture, Milestone makes short shrift of the broadleaf weeds that reduce hay production and degrade rangeland but spare the grass.
Unfortunately, horses and cattle feed on grass or hay sprayed with Milestone, which doesn’t decompose over time. When the manure is mixed with hay to make compost, the still-“hot” herbicide goes right along – full strength.
When the compost is used with broadleaf vegetables such as tomatoes, potatoes, peppers and spinach, the herbicide picks up where it left off, attacking any broadleaf it meets.
Dow Chemical is up front about the problem.
A Dow Agrosciences website alerts Milestone users about characteristics of the herbicide: It doesn’t degrade in plants, it takes three days to pass through a grazing animal’s digestive system, and manure may contain enough aminopyralid to injure broadleaf plants, including vegetables and ornamentals.
La Plata County Commissioner Gwen Lachelt said scores of complaints have come in about Milestone.
“No one reads the label,” Lachelt said. “We’re trying to build awareness.”
Linley Dixon from Adobe House Farm recalls that upon arriving in Colorado, she felt extremely fortunate to find 6-year-old composted horse manure to use on her organic vegetables.
She started tomato seedlings in her window using the compost. The plants barely germinated, she said, and those that did died within weeks.
Dixon, who has a doctorate in plant pathology, began to investigate and experiment for months in her greenhouse. She concluded that the evidence ruled out a virus. It had to be the soil.
Terry and Jim Fitzgerald, Bayfield growers of produce for farmers markets, threw out hundreds of greenhouse plants in 2010. They sent samples of withered plants to the Colorado State University laboratory for analysis.
Terry Fitzgerald said last week that the laboratory could determine only that it wasn’t a virus that created havoc in the greenhouse.
Fitzgerald thinks the herbicide could have drifted from a nearby gas-well site to contaminate a spot where she gathered soil for greenhouse plants.
Gabe Eggars, garden manager at Twin Buttes Gardens off U.S. Highway 160 west, quit using manure years ago. Twin Buttes relies on cover-crop techniques and liquid organics as nutrients, he said.
Travis Custer at San Juan Mycology in Mancos has joined efforts to find a way to neutralize injurious herbicides. Custer said last week that mushroom therapy is showing promise.
“We want to further research based on a model already established,” Custer said. “We need $10,000 to set up our project.”
Donations can be made at www.harvestfunders.com. The website includes a video in which Custer describes the need to combat the toll that herbicides take on the environment.
“Some mushrooms appear to have the ability to degrade some of the complex chemicals in soil resulting from the application of some modern herbicides,” Shuler, the FLC professor, said. “I suspect it may take years of research to determine the effectiveness and practicality of using mushrooms to degrade herbicide residue in soil.”