Pesticide use in California rose in 2010 after four consecutive years of declines, according to a recent report from the California Department of Pesticide Regulation (DPR).

In all, 173 million pounds were reported to be applied statewide in 2010, up 9.5 percent from 2009. The increase was due in part to a 15 percent expansion in treated acreage to 75 million acres. Production agriculture saw the largest increase in pesticide applications, accounting for 12 million of the additional 15 million pounds used over 2009.

“The winter and spring of 2009 and 2010 were relatively cool and wet, which probably resulted in greater fungicide use to control mildew and other diseases,” said DPR Chief Deputy Director Chris Reardon, according to Western Farm Press. “Summer and fall temperatures were also below average, which led to late harvests, more insect damage to some crops and additional treatments.”

Since 1990, the DPR has required all agricultural and pest-control business users to file monthly reports recording the type of pesticide, amount, and location applied. Home and industrial uses are mostly exempt. An estimated two-thirds of all pesticides sold in California each year (mainly chlorine applied to municipal water supplies) go unreported by the DPR.

The DPR report breaks down pesticide usage into three categories. Post-harvest treatments increased by 657,000 pounds, structural pest control jumped by 760,000 pounds, and landscape maintenance saw a 374,000 pound increase.

Sulfur accounted for 27 percent of all pesticide use in 2010, according to the report. It continued to be the most widely used pesticide, both in terms of pounds applied and acres treated. Sulfur is a natural fungicide used mainly to treat powdery mildew on grape and tomato crops in both conventional and organic agriculture. Sulfur use increased by 10 percent, or 4.4 million pounds. It was used on 141,826 acres, 9 percent more than 2009.

The most disheartening aspect of the DPR report for environmentalists was the increase in fumigant use across the state. The pesticide with the greatest increase in pounds applied was 1,3-dichloropropene (1,3-D), a fumigant used primarily on strawberry and almond fields. Its use went up by 2.4 million pounds, or 37 percent. Farmers didn’t have much choice, however, as its alternative – methyl bromide – is being phased out under an international treaty.

The San Joaquin Valley, the heart of California agriculture, was the region that reported the most pesticide use. In terms of pounds applied in 2010, the top five counties were Fresno at number one, followed by Kern, Tulare, San Joaquin and Madera.

The complete report is available at www.cdpr.ca.gov.