Generally the plant appears dwarfed, and has a wilted appearance. Do not confuse virus symptoms with those of normal-shaped leaves with alternate yellow/green bands caused by genetic or vegetative mutations.
The Onion yellow dwarf virus (OYSV) is not spread by seed, but infected bulbs (transplants, volunteers) always produce diseased plants and serve as sources of contamination for following seasons, especially when aphid populations are high. Therefore, plant disease-free transplants and rotate out of onion production for at least three years. Other disease management recommendations include isolation from other susceptible crops or volunteer onions, and insect control.
This disease is caused by a virus that is transmitted by various aphid species, or mechanically to onions and other crops such as garlic, leek and some narcissus species. The first symptoms appear on the youngest leaves, which turn pale and develop many yellow streaks along the veins. Leaves may crinkle and flop over. Symptoms are more pronounced on leaves that develop from an infected bulb or transplant, and the yellow streaks begin at the base of the first leaves and successive leaves as they emerge. Later, there is more pronounced yellowing, and leaves crinkle, flatten, twist, and fall to the ground. Flower stems are shortened, streaked with yellow, and twisted.
Categories: Onion, Diseases, Yellow Dwarf
Date: 04/01/2007