Rice is growing rapidly and rice stink bugs seem to know it. Their numbers have increased as the rice starts to approach half-inch internode elongation.
The small yellow bugs shine in rice fields on cloudy days when they seem to sit at the tips of leaves waiting for heads to emerge, which will begin in a couple of weeks.
Rice stink bugs feed on the developing seeds of grass crops such as rice and grain sorghum and on many wild host plants, including johnsongrass, dallisgrass and vaseygrass.
The plants seem to attract rice stink bugs when the reproductive phase of growth kicks in. Most likely the rice plant at internode elongation begins to release plant volatiles or substances that stink bugs can detect, thus attracting them to rice at joint movement.
Rice stink bugs have a history of catching producers off guard every few years and inflicting substantial losses. In 2001, rice stink bugs cost Arkansas producers an estimated $30 million. The loss was due primarily to a reduction in quality of the rice.
Rice stink bugs feeding on rice kernels in the early development primarily reduce yield. Feeding on maturing kernels also causes pecky rice or rice that has some kernel injury, resulting in excessive breaking during milling and processing (thus a reduction in grade).
After 2001, rice producers always lend an ear when rice stink bugs are mentioned. Many have purchased good sweep nets, which are required to sample and determine infestation levels.
Treatment should begin when rice stink bug levels reach five bugs per 10 sweeps the first two weeks of heading following 75 percent panicle emergence.
During weeks three and four after panicle emergence and until maturity is reached, the treatment level is higher and fields should be treated when levels reach 10 bugs per 10 sweeps.
The numbers are lower the first two weeks because that is when yield is most affected. Sampling should be completed before 10 a.m. or done late in the afternoon. Stink bugs tend to move down into the plant canopy during the heat of the day and are more difficult to detect. For consultants who must work all day, I recommend taking the numbers after 10 a.m. and doubling them to account for movement downward.
The pyrethroid insecticides Karate and Mustang Max are recommended for control of rice stink bugs. Karate is recommended at a gallon to 50 to 80 acres. The gallon to 80 acres rate does a good job, especially when populations are close to treatment levels, but rates should be increased as populations increase. Mustang Max is similar with a use rate of a gallon to 32 to 48 acres. Methyl parathion is the old standby and should be used at a half pound per acre or a gallon to 8 acres.
I have seen excellent control from all three materials, but methyl parathion seems to do a better job on adult stink bugs and Karate and Mustang Max seem to perform better against immature stink bugs. From this, I lean toward using a combination of the lowest rate of Karate and Mustang Max plus a lower rate of methyl parathion (0.5 to 0.75 pint) to get the best overall control.
Donald R. Johnson is a retired Arkansas Extension entomologist who consults on rice and cotton production in Arkansas.