Yellow dwarf is caused by Onion yellow dwarf virus. The virus is transmitted by various aphid species, or mechanically to onions and other crops such as garlic, leek and some narcissus species. Aphids can acquire and transmit the virus within seconds or minutes of feeding. The virus survives in a living host, either its aphid vector or a plant host.
Generally the plant appears dwarfed, and has a wilted appearance. Infected plants are easily confused with those of normal-shaped leaves with alternate yellow/green bands caused by genetic or vegetative mutations. 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. The disease is of little concern in the High Plains region.
Biological controls have not been developed for yellow dwarf.
The virus is not spread by seed, but infected bulbs (transplants, volunteers) always produce diseased plants and serve as a source 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.
Insecticides may suppress the Onion yellow dwarf virus aphid vector, but generally are not necessary or effective.
Categories: Onion, Disease, Yellow Dwarf
Date: 12/19/2004