Invertebrate Pests-76



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Project Leader and Principal UC Investigators

Glenn Nader, livestock farm advisor, UC Cooperative Extension Butte/Sutter/Yuba Counties


Two chemicals are found to control rice water weevil.

UCD research made chemical control of the rice water weevil available to growers in 1970, when carbofuran was registered for use. A second chemical for this purpose, Bux, was added in 1973. Most rice fields need treatment only along the field margins and adjacent to the levees, reducing chemical and application costs by 70-50%. Fewer plants are injured by the weevil if paddies are large.

Over 113,000 acres were treated with the two chemicals in 1976. Because of the granular formulation, time of treatment, and recommended water management, no adverse effects on fish or wildlife have been noted in the 7 years these chemicals have been used.

Research on the rice water weevil's biological activity and potential for plant injury has contributed some major findings:

  1. The most important period of flight is April 24 to May 24.
  2. As many as 239 eggs may be laid per weevil.
  3. The most damaging period of egg laying with respect to eventual yield losses is when plants are 3 to 5 weeks old.
  4. During this period the adults tend to be most abundant along the margins of the fields and levees.
  5. Adults of the first generation in July are not a serious threat to that season's rice crop.

With hopes of developing nonchemical methods of weevil control, all major commercial varieties of rice in California and several thousand world varieties were tested and examined for resistance to this pest. Complete resistance was not found, taut two sources of tolerance were demonstrated over several years. The most promising variety, 1403, has been crossed with short-stature varieties and is being tested further.

Burning and other selected methods of rice residue incorporation over three- and four-year periods did not alter the populations of water weevils, nor did they decrease the efficiency of the two insecticides used for rice water weevil control.

Effective chemicals are available for control of tadpole shrimp.

Recent research indicates that preflood chemical treatment with carbofuran or Bux for rice water weevil may also control tadpole shrimp, depending on several conditions. Harrowing after application is not necessary for weevil control, and will reduce shrimp control. Parathion effectively controls tadpole shrimp at all stages.

More is known about rice seed midges.

Injury to germinating seeds by rice seed midges is usually not detected until it is too late to replant. No control is yet available, but the conditions leading to greatest injury have been identified. The later in the season a field is flooded, the greater the chances for higher water temperatures and a more rapid development of midge larvae. Delayed seeding after flooding may result in significant injury. Larval populations of midges were high 6-7 days after flooding in late May, with the result that 16% of the rice seeds were injured.

Priorities for additional research are indicated.

The number one project will be to develop acceptable seed or field treatment methods to control rice seed midges. Efforts will continue toward locating better resistance to the rice water weevil. Serious leafhopper infestations became a new problem in several California rice fields in 1976, and research on that problem has been initiated. Economical control procedures for the pests of rice compatible with the protection of wildlife and water quality will continue to be a major research goal.


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