Pesticide use rose nearly 11 percent in San Joaquin County in 2010, a reflection of the end of California's drought, state pesticide and local farm officials said.
Much of the increase was due to additional applications of sulfur dust, a material applied during wet weather to discourage powdery mildew and other fungal diseases.
Applications of the potassium fumigant showed the greatest increase, up from 286 pounds used in the county in 2009, as farmers sought an alternative to methyl bromide, which is being phased out because it contributes to ozone depletion in the upper atmosphere.
That needs to change, said Paul Towers, organizing director and spokesman for Pesticide Action Network.
"Unfortunately, California agriculture is stuck on a pesticide treadmill," he said.