Gardeners: check your potatoes for blight

PALMER — Gardeners should check their potatoes for late blight, a fungus-like disease that showed up earlier this week in the latest crop.

Cooperative Extension Service of the University of Alaska Fairbanks reports it has worked with farmers to stop the spread of the blight in the commercial realm.

“It’s just an isolated incidence and it’s been well taken care of on the farms, but the problem is if it’s gotten into people’s gardens, a lot of gardeners will reuse their seed potatoes from the previous year,” said Stephen Brown, Mat-Su/Copper River District agriculture agent for the service and author of the press release. “Late blight can really hurt the industry and we want to make sure the gardeners don’t contribute to that.”

Indeed, he estimated the damage from late blight that is allowed to spread could run to the hundreds of thousands of dollars. The blight is not harmful to humans, but causes potato plants to die and potatoes to rot in storage.

“Late blight is a fungus-like disease and was responsible for the infamous Irish potato famine of the mid-1800s,” the release says. “It attacks potatoes, tomatoes and other members of the nightshade family including petunia flowers.

“The conditions that favor the formation of late blight are foggy rainy days with temperatures between 50 and 80 degrees. This pretty much describes the summer of 2011 and is the weather we should expect through September. A hard frost and freezing temps will kill the disease.”

Symptoms of late blight include:

• A brown-to-black lesion on the stems or leaves of a plant.

• Gray-white spores on the underside of leaves.

• Potatoes with granular, reddish-brown infections on the outer layers.

The extension office recommends gardeners who find their plants infected kill the plants as well as all potatoes within 100 feet of them. Since it takes a week for the disease to develop, nearby plants that look fine are likely already infected.

“Flame weeders are probably the best way to destroy the plants. Other options include bagging the plants and placing them in a landfill. Do not compost plants contaminated with late blight,” according to the press release.

Gardeners with healthy potatoes looking for protection from the blight can try commercial fungicides containing Chlorothalonil. The extension warns to check labels, though, to make sure it is used properly and that it’s the correct product.

“If the plant you’re a treating is not listed on the label, do not use that product,” the release says. “Prevention options are more limited for organic gardeners, but copper-based products have been shown to provide protection.”

For next year’s growing season, the cooperative extension offers some pieces of advice to keep 2012 blight-free:

• Plant only Alaska-grown, certified disease-free seed potatoes. Don’t use potatoes you pick up in the produce aisle at the grocery store.

• Destroy any diseased plants.

• Be careful with tomatoes. Seeds can’t transmit blight, but transplants can. Make sure to use Alaska transplants.

• Soaker hoses or other irrigation systems that keeps leaves as dry as possible are ideal. Blight thrives on moist leaves in high-humidity environments.

Contact Andrew Wellner at andrew.wellner@frontiersman.com or 352-2270.