The major insect pests are the yellow stem borer, the green leafhopper, which is the vector of the tungro virus, and brown planthoppers, which cause hopperburn. Insect control has been attempted by breeding varieties with improved resistance to the pests. Integrated pest management is becoming more popular in view of the problem of insect resurgence from the excessive use of insecticides. The major diseases of rice plants in tropical Asia remain the rice blast fungus and bacterial leaf blight. The existence of many races of the blast fungus makes control difficult.
Blast is a particular problem in upland rice.
The major virus disease is the tungro virus, transmitted by the green leafhopper. The rice weevil and hoja blanca are the main problems in Latin America, while yellow mottle virus and diopsis predominate in Africa. The incorporation of resistance into rice varieties is complicated by the presence of many races of diseases, as in blast, and the existence of biotypes of pests, as in the brown planthopper. Mean farm yields of irrigated rice in many countries are still about 3 to 5 tonnes per ha, but some farmers can obtain twice that. These rice ecosystems must sustain farmers and consumers who so far have received little benefit from modern advances in rice technology.