Rosette disease of groundnut is transmitted by an aphid. Aphids are tiny insects that feed on the sap of plants and can transmit viruses and other diseases from plant to plant. In the case of groundnuts, the aphids spread the rosette virus from infected plants to healthy plants as they feed on them. The virus then spreads throughout the plant, causing stunting, yellowing of leaves, and the characteristic rosette or bunching of leaves at the top of the plant. If left unchecked, the disease can significantly reduce the yield of groundnuts. Therefore, it is essential to take preventive measures to control the spread of aphids and the disease they transmit.