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Managing disease risk in BC’s 2011 potato crop

Potato growers in British Columbia’s Lower Mainland suffered devastating crop losses in 2010 when record-setting rains at the end of August made it all but impossible to harvest crops.

Potato growers in British Columbia’s Lower Mainland suffered devastating crop losses in 2010 when record-setting rains at the end of August made it all but impossible to harvest crops. The rains continued at regular intervals through the month of September and into October. This effectively shut down harvest from Richmond to Agassiz. Some growers lost everything, and overall, more than half of the Fraser Valley potato crop was lost.

“It goes without saying that potatoes should not be replanted in fields where the 2010 crop was left in the ground,” says Dave Ormrod. “Of course, not all growers will be able to find sufficient alternative acreage. With the recent decline in processing vegetable acreage, suitable land for potatoes is in short supply.”

Dave Ormrod is a consulting plant pathologist who farms in Langley. He presented some practical advice on how to manage the challenges that growers will face in the coming year during the recent Horticulture Growers Short Course in Abbotsford, B.C.

“The last time a major disaster similar to this occurred was in 1997,” says Ormrod. “The total crop loss that year was also about 50 per cent, but it was different in that half of that loss was due to late blight with the remaining half due to wet soil.”

“If there was anything good about 2010, it’s that most of the fields were top-killed before the rain came, so there wasn’t an opportunity for late blight to get established,” he adds. “If a field was not top-killed before the rains, look for alternative crops next season, to avoid late blight.”

Late blight thrives in wet weather conditions with cool to moderate temperatures, conditions that typically characterize spring in the Fraser Valley. Monitoring for early symptoms and keeping on top of weather conditions will be critical for disease management.

“For the best-drained of the unharvested fields, expect lots of volunteers. These must be destroyed in whatever way you can, regardless of whether or not you are planting potatoes in the field again,” says Ormrod. “Volunteers left to grow unattended can serve as a source of late blight, viruses, aphids and flea beetles for nearby fields and for future years. Do your best to kill any volunteers as soon as the weather allows and keep it up throughout the growing season.”

Ormrod also cautions growers to be vigilant for Pythium rot and pink rot in the most poorly drained unharvested fields. Although these fields will not likely have many volunteers, there could be high levels of Pythium and pink rot as a result of the rotting tubers in the soil.

“If you must plant potatoes into any of these fields, consider planting whole seed if you are able to get enough. Also, don’t plant any seed with a high level of Fusarium infection,” he says. “Using whole seed or top-quality fungicide-treated seed-pieces will help to prevent losses due to seed-piece decay in the event that it rains shortly after you plant.”

Ormond calls the fall rains of 2010 a wake-up call for the future of the potato industry in the Fraser Valley. The scale of the losses has put many growers in a position where their credit and equity is strained. Another event like this in 2011 would likely force many growers out of business. Looking to the future, Ormrod says that making the investment to improve field drainage is the best way to stabilize the industry and manage the risk of a loss like this happening again.

“Dairy farmers learned a long time ago that you cannot grow sufficient quantities of good-quality forage on poorly drained clay soils in the Fraser Valley,” says Ormond. “Meanwhile, potato growers have been using poorly drained fields in the hope that they can plant and harvest during the dry season from mid-May until mid-October. If the dry season can no longer be relied upon, this philosophy of keeping your fingers crossed while growing potatoes is likely to fail.”

The market realities for dairy farmers and potato growers are significantly different. In contrast to the reliable income of a supply managed sector where most farmers own their land, potato growers rely on market values, and often grow their crops on leased land. The question of who pays to install tile drainage, level fields, or maintain perimeter ditches hangs between growers, landowners and various levels of government. In the meantime, spring is around the corner, and there is another crop to get in. ❦