Capsicum & Chilli
Symptoms vary widely depending on the variety infected and the environmental conditions. In some cases, the virus may be present but the symptoms are hidden or masked. In susceptible varieties, yellowish patches or light green and yellow mottling may be seen on the leaves and fruits. In some varieties, a clear ring spot pattern or a necrotic line may be visible. Young leaves appear crinkled and narrow and the foliage is dull light green with leathery appearance. The entire plant is severely stunted and malformed, with a bushy aspect, and often nonproductive. If they develop, fruits have numerous brown circular lesions, occasionally with yellow halo.
The symptoms are caused by the cucumber mosaic virus (CMV), which affects a variety of species (crops as well as many flowers, especially lilies, delphiniums, primulas and daphnes). The virus can be carried and transmitted by 60–80 different species of aphids. Other ways of transmission include infected seeds and grafts, and mechanical transfer on worker's hands or on tools. CMV can overwinter in perennial weeds of flowers, and often also on the crop itself, in the roots, seeds or flowers. In primary infections, the virus grows systemically within the newly emerged seedling and ends up in the top leaves. Aphids feeding on these plants carry it to other hosts (secondary infection). The virus uses the hosts vascular tissue for long distance transport between different plant organs.
Application of mineral oil sprays on leaves can deter aphids from feeding on them and can thereby control the population.
Always consider a integrated approach with preventive measures together with biological treatments if available. There are no effective chemicals against CMV, nor any that protect plants from becoming infected. Insecticides containing cypermethrin or chlorpyrifos can be used as foliar spray against aphids.