Protection of Rice from
Invertebrate Pests - 98



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Project Leader and Principal UC Investigators

Larry D. Godfrey, Extension Entomologist, Associate Entomologist, Department of Entomology, University of California, Davis

Terry D. Cuneo, Postgraduate Researcher, Department of Entomology, University of California, Davis

RWW.jpg (21135 bytes)Research to protect rice from invertebrate pests is concentrated on the Rice Water Weevil (RWW). With the pending loss of Furadan® as a management tool, attention is focused on three new chemicals in the registration pipeline — Dimilin®, Warrior® and Icon®. New biological control products have also entered the scene. In the summary below entomologists report on these and other developments to control RWW.

RWW Flight

The springtime flight of adult RWW has been monitored at the Rice Experiment Station for more than 35 years. Last year's flight continued a downward trend. Approximately 1,085 RWW were captured in 1998, compared to 2,500 RWW in 1997 and 5,500 in 1996. The record was more than 60,000 RWW in 1969.

Invertebrate1.jpg (222727 bytes)The effects of El Niño were apparently significant. RWW adults fly predominantly on warm, calm evenings, conditions that did not exist until late April. Flight peaks occurred April 27, 28 and 29. Little rice had been planted by then, so adult RWW survived on levee weeds. Ninety percent of the flight was complete by April 29.

New chemical controls

Twenty-six treatments involving numerous formulations of eight chemical insecticide ingredients were tested in aluminum ring plots at the Rice Experiment Station. Three of the materials — Dimilin®, Warrior® and Icon® — are in the registration process as replacements for Furadan®. These were compared to Furadan® in two-to-10-acre grower field tests at 11 locations.

A key question is whether these products will provide efficacious RWW control when applied only to field borders. Economically damaging RWW populations generally occur only within the first 30-50 feet of the field adjacent to levees. Border versus full-basin treatments of Dimilin® and Warrior® were examined at four and six sites, respectively. Icon® was also tested in another experiment on two grower fields. All three products successfully controlled RWW in 1998 testing; preliminary results indicate that border treatments are also effective.

Two pyrethroid products, three experimental preplant compounds and an Icon® seed treatment were also examined. These additional products could provide application flexibility for growers and further possibilities for registration. First year results with several treatments showed excellent RWW control.

The influence of application timing on Dimilin 2L efficacy was also studied. Applications at first rice emergence through water, 50 percent emergence and five days after 50 percent emergence performed better than later applications.

Entomologists also examined the efficacy of two biorational products — Novodor®, a bacterium, and Mycotrol®, a fungus. Applied at the three-to-five leaf stage they gave 77 percent and 74 percent control, respectively, compared with 83 percent control for Furadan®. Further testing is recommended.

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RWW biology

The pattern of RWW egg-laying is important for determining the timing of post-flood applications. Since neither Dimilin® nor Warrior® are effective against RWW larvae, they must be applied before significant egg deposition takes place. Research last year showed that egg deposition can start as early as the one-to-two leaf stage and peaks at the three-to-four leaf stage. On average, most eggs were deposited from nine to 32 days after seeding.

Significant field-to-field variation in egg-laying was also noted. Over about the same four-week period, egg laying in one field took place at a constant rate from the one-to-six leaf stage, whereas in another field it was completed by the two-to-four leaf stage. This variation is significant because a short-lived treatment such as Warrior® would not persist long enough to prevent late egg-laying. Further study of timing of initiation of egg laying will be critical for post-flood treatments.

Cultural Controls

Previous small plot research has shown that lower RWW larval populations occur during the growing season in areas that were winter flooded. This research was extended to larger plots and grower fields in 1998.

Three locations were examined. Unfavorable winter and spring conditions — most rice fields were flooded — made research difficult. At one location, there were no differences in rice water weevil adult feeding incidence, egg laying or larval densities between winter flooded an unflooded conditions. At a Sutter County site, there was a tendency for a lower RWW infestation in the winter-flooded site than in the unflooded field. Because of the weather, however, the research was deemed inconclusive.

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