Potato Virus Y

Potato virus Y (PVY) is the Big Daddy of potato problems, right up there with early blight. And potatoes aren’t the only plants at risk. Peppers, tomatoes, and groundcherries can all catch PVY. Losses can be as high as 80%. Infected potatoes that make it to harvest don’t last in storage. And who wants to eat an infected potato?

Potato infected with necrotic ringspot (Chrisvis1) CC BY 3.0

Potato virus Y is spread by aphids but not in their saliva. Instead, these microscopic potyviruses stick to aphids’ mouthparts (stylets). As the vector aphids feed, they spread the disease. Your shoes, clothes, and garden tools can also transfer this virus.

Tobacco leaf infected with PVY (R.J. Reynolds Tobacco Company Slide Set, Bugwood.org) CC BY 3.0

The many flavors of PVY

PVY used to be easy to identify, leading to the early removal of infected plants and reducing the spread of disease. Recent PVY virus mutations have made identification more challenging. There are fewer symptoms, so infected plants stay in place longer, spreading disease to nearby plants. 

Tobacco leaf showing mild PVY symptoms (R.J. Reynolds Tobacco Company, Bugwood.org) CC BY 3.0

The most common variations of PVY include PVYO (ordinary), PVYC (uncommon)­, PVYN (necrotic), PVYNTN (tuber necrosis), and PVYN-Wi (a recombinant strain). The tuber necrosis strain can cause potato tuber necrotic ringspot disease (PTNRD).

Potato virus Y symptoms

Brown spots on leaves and tubers are the first sign of potato virus Y infection. Other symptoms vary depending on the plant age and health, environmental conditions, potato cultivar, soil health, virus strain, and other coinfections, such as PVA, PVS, and PVX. 

Chlorosis, curved midribs, leaf crinkling, mosaic, mottling, and vein distortions are early signs of PVY. Infected leaves feel rough (rugose) compared to healthy leaves. The underside of infected leaves exhibits dark lesions and black streaks on the midrib. As the disease progresses, leaf loss and stunting are common. This disease is easily mistaken for calico (alfalfa mosaic virus).

Tomato leaves infected with potato virus Y (Scot Nelson) Public Domain

Potato virus Y management

Chemical treatments are not effective against potato virus Y, so these good cultural practices are your best line of defense:

• Start with certified pest- and disease-free seeds and seedlings.
• Choose a resistant cultivar well-suited to your microclimate.
• Space plants in such a way that minimizes soil exposure, or install a reflective mulch. [The color difference between plant and soil attracts aphids.]
• Plant as early in the season as possible.
• Control aphids with super light horticultural oils.
• Remove and destroy infected plants.
• Start each growing season with new seed potatoes.