Papaya Mosaic Virus
Symptoms of infection are concentrated in young leaves and include a mild leaf mosaic pattern and a slight deformation. Dark green blister-like patches appear on otherwise yellowish-green leaf blades. At later stages of the disease, leaf veins can show signs of clearing, petioles are somewhat shorter and leaves curl downward while adopting an upright position. Other plant parts (stems, flowers) are not affected. Plants show a moderately stunted growth, something that only becomes apparent when directly compared to healthy plants.
The virus affects papayas as well as other crops, for example those of the cucurbit family. It is spread from plant to plant by aphids or mechanical injuries. Other ways of disease transmission is through grafting of infected planting material or via mechanical plant injuries. It is often associated with other viral diseases and symptoms can vary slightly in those cases. This virus is actually of minor importance in papaya but if the right conditions are met, it can lead to yield losses.
Disinfect working tools or heat them in an oven at 150°C for 1 hour to kill the virus. Working tools or gloves can also be dipped in 0.525% sodium hypochlorite and then rinsed in water. Bio-fungicides based on Verticillium lecanii can also help to control aphid populations. Insecticidal soaps might be effective at the beginning of an infection.
Always consider an integrated approach with preventive measures together with biological measures if available. There is no chemical treatment for viral infections. Aphids can be controlled through a series of chemical products such as cypermetrhin, chlorpyrifos, imidacloprid, pirimicarb or carbosulfan.