Herbicide residue damages crop

herbicide residue

Damage costs growers thousands in potential revenue


Capital Press

Herbicide residue in composted manure and silage has been blamed for severe damage to organic crops in several Washington counties in 2009 and 2010.

The crops were not killed, but the damage cost growers "tens of thousands" of dollars in potential revenue, Colleen Burrows of the Washington State University Extension Service said.

Burrows said the number of acres was small but involved high-value crops such as greenhouse tomatoes. Several home gardeners also reported damage.

Investigations revealed low levels of the compound aminopyralid, a herbicide registered for use on rangeland, grass hay, pasture and some turf applications. The compound causes damage to sensitive plants at levels as low as 10 parts per billion.

The broadleaf herbicide is made by Dow AgroSciences, which voluntarily suspended its sales in Great Britain in 2008 after similar problems occurred there, according to Dow's website. The herbicide was reinstated last October.

Dow spokesman Garry Hamlin said the company has submitted a proposal to the Environmental Protection Agency and will meet with the agency's officials this month.

"We have an idea of how we'd like to solve the problem, addressing the stewardship of aminopyralid," he said.

On the labels now is a pictogram illustrating how the pesticide should be handled.

"The advantage of the product is it doesn't take much, but that means it must be handled properly," he said.

A similar compound, clopyralid, showed up in composted yard debris and manure in Washington state in 1999 and the early 2000s. It is still registered for use on certain crops, roadsides and forests, Burrows said.

The half-life of both herbicides ranges from one week to several months, Burrows said, but high organic matter levels can slow their breakdown, especially in anaerobic conditions, such as manure piles, silage or a cow's digestive system, she said.

In the meantime, the pesticide residue won't endanger the growers' organic certification.

"No growers lost their organic certification, because they did not do anything wrong," Burrows said.

"Manure is an approved input for organic farms," Nathaniel Lewis, organic certification specialist at the Washington State Department of Agriculture, said. The National Organic Program allows composted manure to have so-called unavoidable residual environmental contamination, he said.

"If you apply it, it does not jeopardize an operator's certification," he said.

Asked whether any growers plan to sue over their crop loss, Burrows said, "I have heard some legal mumblings around."

Robin Schoen-Nessa, WSDA area manager for compliance in pesticide management, said similar instances have been reported in North Carolina and the European Union.

How to avoid problems

Colleen Burrows of the Washington State University Extension Service recommended several actions growers can take before bringing manure or compost onto the farm:

* Ask the supplier for information on the origin of the organic matter and intermediate handlers.

* Ask the farm of origin for details of herbicide practices on feed crops.

* Have a contract with the organic matter supplier indicating it is contaminant-free and if it tests positive for contaminants, the supplier will take back the material.

* Perform a bioassay to test for herbicide contamination. This can be done with the plant type to be grown in the material or with a sensitive crop such as peas.

Damaged crops

The following crops were damaged by aminopyralid herbicide residue:

* Peas

* Beans (bush, fava, soy, pole)

* Clover

* Alfalfa

* Vetch

* Lentils

* Tomato

* Potato

* Eggplant

* Tomatillo

* Peppers

* Lettuce

* Raspberry

* Strawberry

* Spinach


Registration changes proposed

Emphasizing that any proposed changes in registration for aminopyralid must be approved by the Environmental Protection Agency, Dow spokesman Garry Hamlin described the company's suggested changes.

The proposed listing would make it illegal for anyone in Washington, Oregon or California -- among several other states -- to move hay or any other forage grass that has been treated with aminopyralid off-farm. A dairy could use aminopyralid on hay that would be used on-farm, but it would be illegal for it to apply aminopyralid to hay to be shipped off-farm.

A supplemental label would allow users in select states to move treated hay off their farms.

"We are very concerned that our proposal not be presented as a reality, falsely implying that EPA has no authority in the matter, since we would like to get these label improvements in effect in time for the coming growing season, and we really did not want to allow any potential for the regulatory review process to be unnecessarily complicated by misrepresentations in public forums," he said.

-- Steve Brown

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