OYDV - Onion Yellow Dwarf
Type: Virus - Potyviridae
Yellow Dwarf is a virus disease that affects the growth of garlic, onions, and shallots. It was first discovered in Pleasant Valley, Iowa adjacent to the Mississippi River in June of 1927. Although the virus is not spread to the seeds, seeds from infected plants are of poor quality. Symptoms of yellow dwarf include yellow streaks and complete yellowing at the base of the true first leaves. The leaves are usually crinkled, twisted, and flattened and usually fall over. The plants will be wilted and dwarf and bulbs are usually underdeveloped and do not reach full size. The virus is spread by aphids. Controlling aphids does not prevent the disease, as they quickly transmit the virus as they move through the field and infect the crop. Use onion seeds rather than onion sets. The best option is to use disease resistant varieties.
PR - Pink Rot
Scientific Name: Phoma terrestris
Type: Fungus
Pink Rot is a devastating soil borne disease that affects the growth of onions and can occasionally affect corn, peppers, spinach, and soybeans. The disease started in North Carolina and the mid-Atlantic region and continues to spread to other areas. The disease affects the roots, where they become shriveled and deteriorate, and then may disintegrate. Symptoms of wilting of the leaves may occur and the leaves turn a pale green and start to die off. Onions infected with Pink Root often show a light pink color, then becoming a darker pink color, and progressing to a purple-brown color. The plant is rarely killed by the disease, but the bulbs never matures fully. The surviving plants are stunted and the bulb size is reduced and becomes soft and non-desirable. Cold weather, drought conditions, insect spreading the disease, nutrient deficiencies, and other diseases, can cause stress to the plant which can increase the severity of the disease. Plan on using a 6 year crop rotation and avoid planting onions in the same location, year after year as the disease can survive in the soil for a long time. The best option is to use disease resistant varieties and/or use a root fungicide for soil based diseases.
TH – Thrips
Type: Insect
The onion thrips is a common insect pest of onions. The insect is present throughout the United States. It is one of the most destructive insect pests in growing onions in Washington State. Besides onions, they feed on numerous vegetables including: cabbage, potato, and tomato. Thrips damage onions by puncturing the leaves and sucking up the sap. The damage causes the leaves to dry up, wither, turn brown, and eventually cause the stalk to bend and break. If thrips are feeding on cabbage, the cabbage will be blistered, scarred, and bronzed by thrips feeding on the leaves. Where many thrips had fed, discolored brownish blister-like areas will be visible. Lacewings, lady bugs, and parasite wasps may help regulate the thrips population. Insecticides have helped in controlling thrips in the past, but its rapid resistance to insecticides has been a problem. The best option is to use thrips tolerant varieties.
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