Ian Grettenberger, CE Specialist, Department of Entomology & Nematology, UC Davis

Management of Tadpole Shrimp

We evaluated a wide range of insecticides for tadpole shrimp management using several different study methodologies and varied rates and timings for a number of materials. We demonstrated that some materials hold promise as alternatives to pyrethroids. Our open ring and trash cans+rings trials did provide contrasting results for some materials, such as Pyganic 5.0. Some possibly odd results for the early post-flood timing will be interpreted cautiously. We also tested Vantacor, which is not currently labelled for rice in California, and which contains chlorantraniliprole (diamide). It was highly effective at both timings for the higher rate we tested, which was still a “lower” rate. We had fewer “other” treatments to test for tadpole shrimp this year because of the lack of efficacy demonstrated for candidate insecticides in prior years and few additional, “new” materials to try Evaluating additional materials will be imperative to help shift away from only pyrethroids.

Biological Control of Tadpole Shrimp

We tested biological control as a management tactic for tadpole shrimp this past year, using mosquito fish. In one of the two trials, the fish suppressed the shrimp when examining counts summed across the season. In the other trial, there was generally no effect of the fish treatments on tadpole shrimp abundance. We also did not see an effect of fish on plant measurements. While mosquitofish will clearly consume tadpole shrimp and suppress their populations, their effects may be inconsistent or it may require high stocking rates of fish to appreciably affect tadpole shrimp abundance. Getting fish into the fields quickly will be critical to make this a viable tactic.

Rice Seed Midge

In the first year for our team, and for the first time in a while in California, we tested the efficacy of various insecticides against rice seed midge. We built off the methods of prior trials and used delayed flooding and planting to create conditions conducive to rice seed midge populations. We found substantial variability among treatments in how they affected midge populations. Notably, management of tadpole shrimp and rice water weevil may run counter to management of rice seed midge. We saw that Warrior II may have even flared rice seed midge populations possibly by disrupting natural enemy control. Some rates of Belay and Dimilin, along with Vantacor, appear to be the most promising treatments of the ones we tested for managing rice seed midge.

The rice water weevil light trap at the RES has been catching very few weevils in the past several years. This past year appeared to be another lowpressure year for the industry.

We remained informed of possible new and invasive arthropod pests that could affect California rice. This includes continued monitoring of brown marmorated stink bug and the channeled apple snail. No new rice pests were found in California rice fields, and we hope that this trend continues into the future.