The 1975 research objectives were: 1) Discovery of the physical and biological factors that allow the build-up of pest populations that cause economic injury to rice plants. 2) Determination of the most effective control of rice invertebrate pests while maintaining a quality of environment compatible with society's needs.

þ Here is what we learned in 1975. The numbers of weevil larvae found on roots of rice plants in June and July do not always closely correlate with yield reductions. In a test at the Rice Experiment Station, however, yield losses were correlated (within 5 to 15%) with the percentage of rice plants having feeding scars on the newest leaves in the 5th week following flooding.

Rice varieties exposed to heavy populations of the rice water weevil ranked from most to least tolerant as follows: 1403; 72-3764; Earlirose; 1349; M5; and Colusa. Yields were reduced 72% in Colusa and only 12% in 1403. This latter variety (equally tolerant last year) was one of the more tolerant varieties in tests in Louisiana.

þ A 10-day difference in flooding dates in May at Davis resulted in greater seed losses and seeding injury by rice seed midges. Seed planting times of 1, 7, and 14 days following these flooding dates showed that seed losses and seedling injury increased with delayed planting.

þ Injury to rice seeds by midge larvae was reduced from 8% for untreated seeds to 2% injury with a Dursban seed treatment at 2 oz. ai (active ingredients) per 100 lb of seed. Treatments with captan, copper, and Mesurol did not reduce seed damage significantly. In spray treatments of flooded fields, Dursban at 0.2 lb ai per acre reduced the seed midge larval population by 98%. Their numbers were not significantly reduced by methyl parathion (0.5 lb), Sevin (1.0 lb), or copper sulfate (5.0 lb). The applications were made 15 days after flooding, about the time when a grower would be reseeding if prior midge injury made it necessary.

þ Bux at 1.0 lb ai per acre and carbofuran at 0.5 lb ai respectively reduced tadpole shrimp by 80 and 90% when applied as preflood granules for rice water weevil control. The entire fields were treated since treating just the margins does not always reduce tadpole shrimp populations enough. Variability in control is probably related to water temperature, rate of hatch of shrimp eggs, and rate of dissipation of the chemical.

 

Injury (as above) to germinating rice seed by midge larvae was reduced in field experiments by treating seed with Dursban. The compound has not yet been registered for this purpose.