Rice Growers Curb Dumping of Herbicides

Faced with heavy pressure from the public and government, rice growers have sharply reduced the amount of herbicides they dump into the Sacramento River, a state official says.

When Sacramento Valley rice growers began using the herbicide thiobencarb, trade-named Bolero, in 1982, people downstream who depend on the river for drinking water complained that it tasted bad, J. Marshall Lee of the state Department of Food and Agriculture said.

During the same year, “tens of thousands” of carp were killed by high concentrations of another rice herbicide called molinate, or Ordram, Lee said at the annual farm machinery conference sponsored by UC Davis.

Found in Tap Water

In 1986, the pesticide bentazon, sold under the trade name Basagran, was found in the river. Lee said it does not break down during chlorination as do the other two, so the material was found in tap water.

The pesticide residues entered the river through a complex series of surface drains from rice fields. State officials subsequently recommended limits on the amount of Ordram and Bolero in the Sacramento River and classified all three herbicides as restricted materials requiring permits from county agricultural commissioners before they can be used.

To get the levels of the herbicides reduced, growers have been required to retain treated field water for varying periods.

Most Ordram users had to keep treated water on their property for only 12 days last year because the chemical dissipates relatively rapidly.

Bolero was allowed only on properties with approved water management systems, and use was limited to 110,000 acres. That did not prove to be a problem for growers because there was only demand for enough Bolero to treat 104,000 acres, Lee said.

Because chlorination of drinking water doesn’t break down Basagran, the state ordered it retained on rice fields from the time of application, normally in early June, until fields were drained late in the summer for harvest.

Tests taken in the Colusa drain showed that Ordram concentrations fell from 200 parts per billion in 1982 to 47 ppb last year, Lee said.

The reduction in Bolero concentrations was even more dramatic--from 60 ppb to 4 ppb.

Tests taken in the river below Sacramento showed similar reductions.

Less Rice Produced

Lee conceded that some of the improvement stemmed from an overall reduction in Sacramento Valley rice production, which resulted in less use of herbicides during those years.

“But the improvements in the water are greater than what could be counted from declining acreage,” he concluded.

During the 1988 season, Ordram users generally will have to hold the water for 14 days after application. The time can be shortened to four days if the farmer uses preplant incorporated techniques, to eight days if the land is in a non-discharging district and to 12 days if there are approved water management practices for the treated acreage. County agricultural commissioners can authorize emergency releases after six days for growers who can show that a longer holding time threatens the rice crop.

Bolero users still will have to use approved water management practices, but the sales limit will be increased 10% if forecasts show the Sacramento River’s flows will approach historical medians. That is likely because the rainy season has been relatively good so far.

Users of Basagran again will have to hold water until the treated fields are drained at harvest. But Lee said there will be an emergency provision similar to the one for Ordram that will allow growers who can prove a hardship to release field water 10 days after application.