Canadian potato growers should keep an extra watchful eye out for potato virus Y (PVY) this coming season. Though PVY has been a costly issue for decades, winter test results show a concerning increase in the disease in certain regions over the past couple years, likely due to newer, more aggressive PVY strains such as PVYNTN, delayed harvests and higher than normal overwintering of aphids.
PVY impacts both yield and, when infection causes tubers to blister and crack, quality too. Because the disease can be transmitted both in-crop via aphids and at planting via infected tubers, staying ahead of PVY requires a multi-pronged strategy.
First – and I can’t stress enough how important this is – commercial growers buying seed should ALWAYS ask for post-harvest test results for every seed lot they buy. Why the need for such caution? Tuber-born infection causes characteristic plant stunting, mosaic patterning and crinkling of leaves, and necrosis. However, aphid-borne infection, especially if the crop is infected late in the season, can be nearly symptom free. To further complicate matters, some varieties can be susceptible to PVY but don’t express it visually until it is too late. If a commercial grower plants tubers from an infected plant, the disease will multiply in the subsequent year, exponentially compounding the problem.
Seed potato fields/lots that test outside of allowable virus limits will be downgraded (e.g. an E2 with .2% infection rate will be downgraded to an E3; an E2 with .3% infection will be downgraded to an E4). If the infection level is severe enough, the tubers will be decertified and must be sold into a fresh or processing market instead. For specific information regarding virus tolerance levels, refer to the Canadian Seed Potato Field Certification Program.
To further protect yourself from PVY, opt for resistant varieties where possible. Plant whole seed, since planting multiple pieces from a single infected tuber will result in multiple infected plants in a field. Keep up-to-date on insect migration maps where available and scout constantly for all aphid varieties (important note: contrary to popular belief, PVY can be spread by any type of aphid, not solely green peach aphids). As soon as aphids are identified in-crop, keep up a rigorous insecticide application schedule. And, harvest on the earlier side if at all possible. Though it can be tempting to delay harvest in dry or cool years to maximize yield, a later harvest increases both the likelihood and severity of infection, as well as the likelihood of passing infection on to surrounding fields.
A little extra caution can go a long way towards keeping your fields PVY-free.