Symptoms vary depending on the plant species infected and the environmental conditions. In some cases, the virus may be present but the symptoms are hidden or masked. Yellowish patches or light green and yellow mottling can be seen on the leaves and fruits. Longitudinal growth of side branches and leaf stalks is increased, leading to the downward bending of leaves and petioles. Young leaves appear crinkled and narrow and the entire plant is severely stunted and malformed, with a bushy aspect. Flowers may display white streaks. Fruits develop upward-arching bulges that render them unmarketable.
The symptoms are caused by the cucumber mosaic virus (CMV), which affects a variety of species (cucurbits, spinach, lettuce, capsicum and celery 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 an 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.