Public health concerns have prompted the state Department of Pesticide Regulation to end an exemption that let growers apply more of the fumigant Telone than is allowed.
The move is not being well received by some growers, who say that without the exemption they will have to use less effective chemicals, resulting in lower yields and a shorter growing season.
"The state has to do what they think they need to do," said Bob Weimer, who farms 400 acres of sweet potatoes in the Atwater-Livingston area of Merced County. "But I think they are taking an overly cautious view of the product and its potential hazards."
Counties likely to be affected will be Fresno, Tulare, Merced, Ventura, Santa Barbara and Monterey, said Charlotte Fadipe, spokeswoman for the Department of Pesticide Regulation.
Since 2002, the state has annually limited farmers within a 36-square-mile township to a collective 90,250 pounds of the fumigant, 1,3-dichloropropene, which is marketed under the name Telone.
The powerful, but also carcinogenic, fumigant rids the soil of pests and diseases and is commonly used when planting trees, vines or other crops like sweet potatoes.
In many counties, farmers never reach the state's yearly cap on Telone. And what they don't use, they bank for later use. Other counties with rapidly growing industries like citrus, nuts and sweet potatoes routinely go over the cap, using the exemption that had been allowed by the state.
In some cases, the state-approved exemption resulted in nearly triple the amount of fumigant used per township. In Merced, one township applied 246,574 pounds of Telone in 2002 and a township in Fresno/Tulare counties used 179,288 pounds of the fumigant in 2011.
As the amounts rose, so did concerns by state officials. Preliminary data from air monitoring equipment in the San Joaquin Valley found concentrations of the fumigant at levels higher than regulators liked to see.
The state set a benchmark of 0.14 parts per billion as allowable, but they recorded a spike of 1.82 parts per billion in Merced County. The results of a long-term assessment risk is expected to be completed in 18 months.
"As soon as we started to see those numbers we decided that we could no longer allow exemptions," said Brian R. Leahy, director of the California Department of Pesticide Regulation. "We had to fall back to a more cautious approach."
Leahy said all counties will now have to stick to the 90,250-pound cap per township.
Leahy said that while he understands farmers may not like the elimination of the exemptions, they also knew it could happen.
"Every year they have to come and ask for an exemption and we have had to look at the program and see if it is doable," he said. "They have lived with this trigger in place for the last 12 years."
David Robinson, Merced County agricultural commissioner, hopes the sweet potato farmers in his county won't suffer greatly. The tuber is a growing industry in the county, rising to the fifth most valuable crop in 2012. The crop generated a value of $160 million that year. The labor-intensive crop also employs thousands of workers.
"I know there is a concern about fumigants, and if there is a problem we also want to know what is going on," Robinson said. "But this is going to have an impact."
Paul Towers, spokesman for the Oakland-based Pesticide Action Network North America, supported the elimination of the exemptions.
"That is good news, but more needs to be done," Towers said. "Telone is one of those fumigants that poses a serious threat to California, and we should take every step we can to make sure farmers have the tools they need to transfer to less harmful alternatives."
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