Improved Insecticide Efficiency

The 0.5 pound active ingredient per acre rate of carbofuran does not always provide adequate control of rice water weevil larvae when applied as a preplant, preflood treatment. This rate and 1 pound active ingredient per acre were applied as standard granule formulations and compared with two formulations of resin coated granules (0.5 lb. rate). The resin coating was applied to delay the release of the toxicant. A comparison of these four treatments subjected to a natural weevil population 5 feet from the field margin showed the following: 1 pound (standard) -1.9 larvae per plant; 0.5 pound (standard) - 8.2 larvae; 0.5 pound (resin-slow release) - 2.8 larvae; 0.5 pound (resin-slowest release) - 4.1 larvae; untreated - 7.4 larvae. A similar trend in protection was observed in plant growth characteristics and resultant yields.

The commercial formulations (0.5 and 1 pound standard) were applied by airplane, and when yields were compared, the 1 pound treatment averaged 1,025 pounds per acre more grain than the untreated, and the 0.5 pound treatment 242 pounds more. Only the former was significant.

Rice leaf miner attacks occur at the same time as the early infestation of rice water weevils. Because of the possibility of one chemical affecting both pests, carbofuran was tested on aritficial infestations of the rice leaf miner in the greenhouse. Treatments at 1 pound active ingredient per acre preplant, preflood and 0.5 pound and 1 pound postflood (drain and treat 23 days after planting) nearly eliminated mining. A 0.5 pound preplant, preflood treatment (commonly used commercial treatment) showed some reduction in mining but was not significantly different from the mining that occurred in untreated plants.

A greenhouse study was conducted to determine the effects of sterilized and non-sterilized soil on the efficiency of 0.5 pound carbofuran for water weevil control. It was suspected that microorganisms in the soil may play a role in breaking down the carbofuran, but no significant differences in control could be attributed to soil sterilization in this test.

The crayfish Procambarus clarki was again associated with a loss of rice stand in a replicated test using caged and natural infestations of crayfish. The natural infestation caused a 69 percent reduction in stand. A chemical test using Sevin at 2 pounds active ingredient per acre; copper sulfate at 10 pounds and Baytex at 0.1 pound showed that Baytex provided the only effective control.

Army worms damaged many rice fields in 1980, with the most serious damage occurring to plants during stem elongation and grain formation stages. Current UC research has shown that when representative field areas have 25 percent or more of the foliage missing and armyworms are present, chemical control is advisable in these areas to prevent further damage. (UC Cooperative Extension photo by lack Kelly Clark)

Bilological Control of Insects

Insect growth regulators are considered to be selective insecticides that do not endanger wildlife. With proper timing of application they show potential for controlling the water weevil in flooded fields at the time of rice emergence from the water. A greenhouse study with four insect growth regulators showed Dimilin and Bay Sir 8514 to be highly effective at a rate of 0.25 pound active ingredient per acre.

Thirty-six lines of rice were evaluated in the field for tolerance and/or resistance to the rice water weevil. These represent the most promising of several years of crosses at Biggs and in Louisiana. Considerable tolerance was observed in four lines that were the result of crosses made in California.

The biological control agent Bacillus thuringiensis israelensis at one and two pints per acre and Baytex at 0.1 pound active ingredient per acre were ineffective in controlling established populations of seed midges.