Biologist Ted J. Crane of UC, San Diego, and entomologist Robert K. Washino, UC, Davis, have discovered a naturally occurring biological control for rice field mosquitoes. In field and laboratory research, they found when mosquito larvae (bottom) brush against naturally occurring flatworms (top) the mosquito larvae become paralyzed and die. The flatworms have difficulty in dispersing into fields not previously planted to rice but, once established, are able to overwinter and control mosquitoes in subsequent years of rice production. (Photo by Cooperative Extension photographer Jack Kelly Clark, UCD. Print is 45X lifesize.)

 The recording of feeding scars of the adult weevils during a high natural infestation this year shows a significant negative correlation with yield. We will attempt to use this information to develop a sequential sampling procedure for determining the need for treatment.

Varieties S6, M5, M9 and L-201 were 100 percent, 50 percent and 25 percent defoliated to simulate injury by chewing insects such as armyworms. The results indicated a significant reduction in yield when defoliation is greater than 25 percent at two to three weeks before average heading.

Studies with a natural infestation and caged crayfish showed that crayfish can reduce stand establishment more than 84 percent.

The aster leafhopper is the most abundant species in rice fields and occurs in greatest numbers between early July and mid-August. Rice plant stands of 6 and 18 plants per square foot resulted in no significant difference in leafhopper numbers, but high populations were correlated with fields containing emerged aquatic broadleaf weeds and sedges.

Carbofuran in greenhouse studies provided excellent control of rice water weevils at 0.5 and one pound active ingredient per acre but did not provide adequate control at these rates in the field. It appears that there are factors breaking down carbofuran in the field between the preplant treatment and the fourth or fifth week after treatment. It is possible that for best water weevil control the initial carbofuran treatment should be four to five weeks after flooding.

Several experimental chemicals were tested for control of the rice water weevil, but only diflubenzuron (Dimilin®) provided consistent control. The most effective rate was 0.25 pound active ingredient per acre applied at about three weeks after planting.

Sevin®, copper sulfate, and parathion were tested at recommended rates for tadpole shrimp control. Shrimp and chemicals were placed in clear water and water containing a heavy silt suspension. The silt suspension did not reduce the level of control.

Baytex® at 0.1 pound active ingredient per acre successfully controlled a natural crayfish population that was causing a serious reduction in stand establishment in experimental plots.

 

Research entomologists from UCD use Rice Experiment Station fields to conduct insect pest control research. Note trap in background used to study flight patterns of the adult water weevil.