Crayfish

For the third consecutive year crayfish were associated with reduced seedling establishment. Confined crayfish populations of 1 fish per 8 square feet reduced stands by 62 percent, 1 per 16 square feet by 22 percent, and 1 per 32 square feet by 9 percent.

Chemical control experiments were done with the red crayfish (Procambarus clarki) and the green crayfish (Orconectes virillis). Methyl parathion at 0.5 pound active ingredient per acre (AI/acre) gave 100 percent control of both species. Baytex at 0.1 pound AI/acre gave 100 percent control of the red crayfish but no control of the green crayfish. Parathion (ethyl) at 0.1 pound AI/ acre was not effective on either species.

Tadpole Shrimp

Commercial treatments of suspected resistant tadpole shrimp were studied near Escalon. Copper sulfate at 10 pounds AI/acre provided excellent control, carbaryl at 2 pounds AI/acre resulted in adequate control, but parathion at 0.1 pound AI/acre was not effective. This indicates that tadpole shrimp may have built up resistance to parathion..

Aster Leafhopper and Armyworm

In a 1980 study, aster leafhopper populations of 32 and 69 per plant during the last half of August reduced grain 12 percent. Most of the nymphs and essentially all of the adults were on senescent leaves.

Rice fields at Biggs and Richvale in 1980 averaged a 24 percent loss in yield when armyworms ate 25 to 30 percent of the foliage. Laboratory studies showed that armyworms in the last instar (6th) eat in 6 or 7 days about 75 percent of the total food eaten during the 25 days or so needed for larval development.

Sevin at 2 pounds AI/acre is currently recommended for control of the aster leafhopper and the armyworm.

Water Weevil

Field tests with preplant treatments of carbofuran 0.5 pound and 1 pound AI/acre showed no systemic effect on adult water weevil confined on the rice plants for 72 hours. This supports the belief that field control occurs only in the larval stage. Tests for resistance indicate that the weevil has not developed resistance to carbofuran in the past 13 years.

Several chemicals and formulations were field tested and compared with carbofuran for rice water weevil control. Advantage, an analogue of carbofuran that is safer to use, provided control equal to or better than carbofuran at 0.5 and 1 pound AI/acre.

Satisfactory progress is being made in cooperation with the plant breeders in developing a rice variety that will show resistance or tolerance to the rice water weevil.