Potato virus Y (PVY) is considered one of the most serious viral diseases that affect solanaceous crops such as potato, tobacco, pepper, and tomato worldwide. The disease has become more prevalent in some regions in recent years. Symptoms vary from mild to severe depending upon the host crop, the host variety, the virus strain and environmental conditions. It is sometimes called "common mosaic" due to the light and dark green mottling and mosaic patterns on leaves of susceptible hosts. Some strains can cause leaf necrosis, yellowing and distortion in some potato and tobacco varieties.

There are four known strains of PVY. Most research into strains has been conducted on potato and tobacco. Some varieties of potato are tolerant to certain strains of the virus while others cultivars are significantly impacted.

  • PVYO is the 'original' strain which causes a range of symptoms in most host plants depending upon the cultivar and climate conditions. It does not cause tuber necrosis symptoms in potatoes.
  • PVYN causes 'necrotic' or dead spots on veins of tobacco leaves (Figure 1) but not on potato leaves.
  • PVYNTN is a new strain thought to be a variant or sub-strain of PVYN that causes necrotic lesions and veins on tobacco as well as necrotic flecking and ringspots in the tubers of susceptible potato varieties. Often PVY strains that cause flecks and ringspot symptoms in the tubers resulting in the loss of yield quality are correlated with foliar.
  • PVYN:O is a new strain that has characteristics of both PVYO and PVYN and thought to be a cross between the two strains.

Figure 1. Symptoms of PVY on tobacco leaves.

Symptoms are variable on infected pepper plants and often appear as systemic dark green bands along veins of leaves that develop into a mottled dark and light green discoloration. Often severely infected plants will develop necrotic lesions along the leaf veins, petioles and stems. Fruit on infected plants may display a mottling and necrotic brown spots. Occasionally severely infected plants will appear stunted, with distorted leaves that may produce small fruit.

Leaves of infected tomato plants develop dark green bands along veins with slight mottling and occasional leaf distortion. However, depending upon conditions, age and cultivar of the tomato plant and the strain of the virus, more severe symptoms may develop in the field including dark brown necrotic lesions between veins on leaves. Terminal leaflets may also become brown and dead. Plants that have been infected for some time often appear droopy due to petioles and leaves curling downward. No tomato fruit symptoms have been reported.

The virus can be introduced into a region on infected propagation material like potato tubers or solanacious vegetable crop transplant seedlings. Once the virus is introduced into the region, aphids including cereal, soybean and green peach aphids acquire the virus through feeding-related activities and then transmit it to nearby healthy plants. The acquisition and transmission of the virus by aphids can happen in very quickly. Once the aphid has transmitted the virus, it no longer carries it until it feeds on another infected plant and acquires it again.

Plant Certified, Virus-tested, Virus-free transplants and tubers

Growers should plant only virus-free vegetable and tobacco transplants or certified virus free potato tubers.

Scout and Inspect fields for symptomatic plants

Susceptible crops should be visually inspected frequently throughout the season.

Scouting fields early and removing infected symptomatic plants if practical will reduce the spread of this virus to other plants and fields in the region.

Manage aphid vectors

Once established in a region PVY is spread by aphids moving through the susceptible crop and from one crop to another. Applying knock-down insecticides has not been a successful strategy for controlling the spread of non-persistent viruses such as PVY. Knock-down insecticides may kill aphids that have formed colonies in a crop but will not kill migrant aphids that land in the crop between spray applications. Aphids that enter the crop after spraying knock down insecticides often become agitated by spray residue, probe more frequently, and disperse to adjacent plants. This in turn, can increase the spread of the virus. However, it is important manage colonizing aphid pests in susceptible crops when populations approach or exceed established economic thresholds.

New anti-feeding insecticides may reduce aphid feeding on infected plants and have been shown to reduce the transmission rate of PVY. Some refined crop oil sprays have been shown to remove the virus from the aphid's stylet reducing the spread of non-persistent viruses such as PVY.

Manage alternative weed hosts

Control weed hosts such as nightshades, purslane, pigweed, dandelion, chickweed, lambsquarters and others in and around fields of susceptible crops.

Plant susceptible crops away from each other

The further susceptible crops are planted away from each other, the less chance PVY will be transmission by aphids from one crop to another if introduced into a region. Growers should also avoid planting susceptible hosts near urban gardens.

Plant resistant varieties when available

Planting PVY resistant varieties when identified and available is the best way to manage PVY. Remember that tolerant varieties can still become infected and carry the virus from which aphids can acquire and spread to nearby susceptible varieties or other solanacious crops. When planting tolerant varieties, avoid planting near other susceptible crops.