The effect of sowing date and spacing on rosette disease of groundnut in Northern Nigeria, with observations on the vector, Aphis craccivora

SUMMARY In Northern Nigeria, groundnuts planted in June outyielded those planted in July, and, in rows I yard apart, plants spaced at 9 in. gave a heavier total crop than those at 18 in. In two experiments, early sowing reduced the number of rosetted plants per acre; close spacing merely reduced the percentage of plants infected. There was a correlation between the total of aphid‐infested plants during the growing period and the number of diseased plants. Late‐sown crops support more Aphis maccivora, both apterae and alatae. The principal host of the vector during the 6 months dry season is Euphorbia hirta, whereas in East Africa groundnut is the principal host throughout the year. A list of predators is given, with observations on relative numbers of syrphid larvae and aphids.