Assistant Cooperative Extension Specialist University of California Davis, California
Armyworms can be a significant pest of rice in California. Midseason, larvae feed on foliage and later on panicles, resulting in empty rice kernels. Both types of damage can result in yield reduction. In the past few years, several experiments have been conducted to improve on the management of armyworms. Pheromone traps have been used to determine when larvae may be found in fields and sampling intensified. Data collected over two years have shown that there is a relationship between the number of moths trapped weekly and the number of larvae found in the field two weeks later; however, this relationship seems to be field-specific. To improve sampling, defoliation and larval populations were monitored for two seasons, providing an estimate of larval density per defoliation level. Artificial defoliation experiments conducted for three years showed that yield reductions are small when 50% of plant height above the flood water is defoliated; however, when all foliage above the floodwater is consumed, 25% of yield is lost. Finally, insecticide experiments showed that pyrethroid insecticides were ineffective while insect growth regulators were very effective.