Viroses of groundnut in Tamil Nadu.
In a survey of rosette disease of groundnut (which was transmitted by grafting and through the vector Aphis craccivora Koch) and mosaic disease (which was transmitted by grafting only) in Tamil Nadu, India, rosette was found in ten and mosaic in three districts. The incidence of rosette disease was 4.92% in bunch and 3.26% in spreading varieties of groundnut and was nearly twice as high in irrigated as in rain-fed crops. The loss in yield varied from 27.0 to 100%. Rosette disease spread in groups round infected plants, and maximum infection was found when the crop was 75 days old. There was a positive correlation between aphid infestation of the crop and the incidence of rosette disease. The initial infection appeared to be caused by the few incoming viruliferous alatae and secondary spread by viruliferous apterae. Close spacing and late weeding were highly effective in reducing infestation and infection and increasing yield. When 0.1% thiometon (Ekatin) or methyl-demeton (Metasystox) was applied in sprays, all the aphids were killed; for control of the vector, four applications at intervals of 15 days from the time when the crop is 30 days old are recommended.