Luis Espino: Armyworms Invade Rice
By Charmayne Hefley, Associate Editor
Larva of the armyworm, Mythimna unipuncta.
Photo by Jack Kelly Clark, UC IPM.
Farmers face many threats to their crops on a daily basis. Luis Espino, rice farm advisor UC ANR Cooperative Extension, Colusa County, said rice farmers are on the lookout for two caterpillar infestations during the year when armyworms invade rice fields. “The first one occurs sometime in June,” Espino said. “At that time all they do is just eat the foliage, and you can usually see it when you walk into a field. Nevertheless, the rice has a very good capacity to recover from that type of injury.” Espino’s UC Rice Blog explains it is difficult to accurately estimate yield losses due to early armyworm damage because it can reduce tillering, delay the crop, and cause uneven maturity.
“Heading” occurs when the rice plant prepares to enter its reproductive phase. The first sign, called the ‘booting’ stage, is when the leaf stem that conceals the developing panicle bulges. Then the tip of the developing panicle emerges from the stem and continues to grow. Rice is said to be at the ‘heading’ stage when the panicle is fully visible. Flowering begins a day after heading has completed. As the flowers open they shed their pollen on each other so that pollination can occur. Flowering can continue for about 7 days. (Source: Rice Development, Ricepedia.)
“The second infestation usually occurs in mid- to late-August when the rice is heading out,” Espino said. “At that time, armyworms can feed on the panicles, [causing the kernels to dry before filling], resulting in blanks [without kernels to harvest] on the panicles and broken panicle branches. That’s when armyworms are more important.”
Espino said that the first infestation this year was relatively large, making it harder for the treatments to control the armyworms as they devastated the rice fields. “There were some areas in fields where the rice was down to the waters,” Espino said. “so all the foliage was consumed, and sometimes only a little stem was left standing.”
During the second armyworm infestation, however, Espino said the rice fields were not as badly affected as they had been in the first attack. “We did see some fields with armyworm injury,” Espino said,“ and some farmers had to treat their fields. The numbers were just so big that the treatments were not controlling them.”