A shallow flood in rice fields offers farmers another means of managing rice water weevil, according to research by the University of Arkansas System’s Division of Agriculture.

With production costs rising, rice farmers wanted to know if agricultural practices could reduce rice water weevil infestations, said John Bernhardt, an entomologist at the Division of Agriculture’s Rice Research Center near Stuttgart, Ark.

“Most years, rice water weevils are our No. 3 pest,” Bernhardt said. “They’re in every rice field in Arkansas and some farmers have a real problem with them.”

Most farmers know which of their fields will have weevil problems, Bernhardt said. They were looking for a practice that could reduce costly insecticide treatments.

Bernhardt said that rice water weevils are attracted to rice fields at the onset of permanent flood. Previous studies had shown that adult weevils lay eggs in plants of all ages, but the highest densities of larvae were found in areas with a deep flood.

Researchers established rice test plots at RREC in which the natural infestation of rice water weevils was monitored and the impact on yields measured. The plots had variable flood depths maintained for different lengths of time. No insecticide treatments were used. At three and four weeks after permanent flood, the plots were sampled for rice water weevil larvae.

In his study, Bernhardt said the plots with a 4-inch flood had the highest density of rice water weevil larvae. Rice plots with a 2-inch permanent flood or a 2-inch flood for four weeks before being raised to 4 inches had significantly fewer larvae.

All treatments yielded similar amounts of rough rice, he said. No blast disease — a concern for reduced flood levels — was noted in any of the plots.

“Larvae populations in these fields were reduced about 30 percent in last year’s tests and about 28 percent this year,” Bernhardt said.

“Reduced flood level is not a substitute for chemical control, but, for some people, it can reduce water use and maybe keep weevil populations below the threshold where they will need chemical insecticide,” Bernhardt said.

Bernhardt said he has also conducted tests in which flood was delayed, and this practice also gave some control over rice water weevil populations.

“We think a combination of these two practices will offer significant help in managing rice water weevils,” Bernhardt said.