Rice crops can be affected at all growth stages, but are most vulnerable during the period of vegetative growth know as tillering. Most common symptoms are: severe stunting, grassy aspect due to the excessive number of tillers, and very upright plant growth. Leaves are short, narrow, pale-green or yellow, with a mottled appearance. A closer look shows numerous dark-brown or rust-colored spots or patches on the leaf surface, which often cover the whole leaf. When infected during the seedling stage the plants rarely reach maturity. Plants affected at a later stage usually do reach maturity but generally fail to produce panicles, thus impacting on yields.
The virus is transmitted by brown planthoppers of the species Nilaparvata (N. lungens, N. bakeri and N. muiri). Both nymphs and adults have to potential carry the virus for long periods and thus infect new plants in a persistent and propagative manner. However, the planthoppers need to feed on an infected plant for at least 30 minutes to pick-up the virus. The disease is mainly found in South and Southeast Asia, China, Japan, and Taiwan, Indonesia, Philippines and India, particularly in areas where rice monoculture is practiced. In favorable conditions, the virus can co-infect plants together with the rice ragged stunt virus, also vectored by N. lugens, and cause severe losses.
Direct treatment of viral diseases is not possible. Neem Seed Kernel Extracts can help to reduce the populations of brown planthoppers and thereby suppress the transmission of RGSV. Natural enemies of planthoppers include water striders, mirid bugs, spiders, and various egg parasitoids wasps and flies. Brown planthoppers can also be held in check by flooding the seedbed for a day, so that insects are drowned.
Always consider an integrated approach with preventive measures together with biological treatments if available. Direct treatment of viral diseases is not possible, but insecticides can be used if critical numbers of planthoppers are found. Products based on abamectin, buprofezin and etofenprox. The application of insecticides is not always successful in controlling vector populations, especially in regions where rice is grown throughout the year