Information from 2001 Missouri Rice Research Update, February 2002.


Michael L. Boyd- Assistant Professor of Entomology / State Extension Entomology Specialist

Syngenta has expanded its Karate 2.08CS label to target rice stink bugs.

The rice water weevil (RWW) is an important insect pest in Missouri rice fields. Adult leaf feeding damage is rarely of economic importance; however, larval damage to developing plant roots can reduce plant vigor and yields by interfering with the plant's ability to take-up nutrients and water. Severely damaged plants also are more prone to wind damage because the pruned roots no longer provide anchorage in the soil. In 2001, we conducted a field trial at the Missouri Rice Growers' Research and Demonstration Farm to evaluate varietial response to RWW infestations.

Materials and Methods:
Five commercial varieties (Bengal, Cocodrie, Cypress, Drew, and LaGrue) were selected from representative maturity groups (very short, short, and medium). Rice was planted on May 16, 2001 at a seeding rate of 80 lbs. per acre. A split-plot design of treated (Icon 6.2FS) and untreated seed for each variety was used in this trial. Rice was planted in strips (10 ft. in width x 150 ft. in length), and then subdivided into four plots. Plant stand counts and height measurements plus RWW adult leaf scar counts were taken on June 14th. Plots were fertilized (145 lbs. nitrogen per acre) on June 18th and flooded on June 19th. RWW larval populations were evaluated by taking three 4-inch core samples per plot on July 3rd and 19th. Because of water-logged soil conditions, a small-plot combine could not be used to harvest the plots. Three subsamples (3 ft. in width x 15 ft. in length) were harvested by hand from each plot and then mechanically processed.

Results and Discussion:
There were no significant differences among varieties with respect to RWW larval infestations on either sampling date (Table 1). There was a substantial reduction (64.3 to 86.1%) for all five varieties on the second sampling date in treated vs. untreated plots. In the treated plots, the lowest and highest RWW infestations were in Cypress and Drew plots, respectively. The yield impact of these RWW infestations was inconclusive because of the inability to mechanically harvest the plots and the extensive seed damage caused by rice stink bug infestations.

I would like to thank the Missouri Rice Research and Merchandising Council for its financial support. I also appreciated the valuable assistance of Dr. Donn Beighley, Missouri Rice Research and Demonstration Farm manager, and his crew this year. Finally, I want to acknowledge the help provided by these student workers: April Brands, Robert Harper, and Angela (Shelly) Kellams.

Table 1. Rice water weevil (RWW) populations and varietial yield response in Missouri (2001).
Variety Avg. # RWW1 / 3 core samples Yield
Lbs. / plot3
July 03July 19
Bengal 0 0 2.00 11.25 --
Cocodrie 0 0 1.25 9.00 --
Cypress 0 0 1.50 5.25 --
Drew 0 0 2.50 17.00 --
LaGrue 0 0.25 2.50 7.00 --

1 Total number of RWW larvae and pupae per plot.
2 Seed was treated with Icon 6.2FS.
3 Plots were not mechanically harvested because of water-logged conditions. Harvesting plots by hand proved inconclusive because of numerous blanked heads in the samples. Plots were heavily-infested with rice stink bugs.