How to avoid blight this spring

As this year’s gardening season approaches, local farmers and agricultural experts want to urge home gardeners to be aware of the risk of late blight, a devastating disease that reared its ugly head in the valley last year. Characterized by black colored wounds or abnormalities on the leaf and stem, late blight is the same devastating pathogen responsible for the Irish potato famine of the late 1840s. In the Mission Valley, tons of potatoes were lost last year, Montana State University extension agent Jack Stivers said.

“It can be damaging to our commercial industry,” he said. “Home growers and gardeners can take steps to protect their neighbors and prevent the disease in the Mission Valley so they are not left empty handed in the fall.”

According to Stivers, indications show now that we could be in another cycle where the conditions for late blight might just be prime.

“Even one inoculated plant from a small home garden can sporolate so fast that within days, it can take out the whole valley,” potato farmer Jack Lake, of Lake Farms Inc. said.

Before this past year, late blight was last spotted in Lake County about 10 years ago, Lake said. Most growers learned from that experience that without continual application of the appropriate fungicides, the onslaught of late blight can be devastating. Those who didn’t learn that lesson were hit hard by the outbreak last summer.

“In Montana, we have the growing weather, the soil and are somewhat isolated,” he said. “The million dollar question for us is, ‘where did it come from?’ The more people with gardens makes the inoculum somewhat easier to spread.”

According to Lake, potatoes, peppers, eggplant and wild nightshade can get, and spread, the disease. Prevention and retention using sanitary growing practices is the key to minimizing this devastating disease in Montana, Dr. Nina Zidack, Director Montana Seed Potato Certification Program in Bozeman, said.

The most important step for any home garden is to buy certified seed from a local grower each season and resist the urge to replant seed, especially seed that has been infected.

“Un-certified seed is going to be carrying something,” Lake said. “When you plant your own garden, be responsible and get certified seed.”

Even local growers who did spray fungicides, which must be applied prior to the arrival of the pathogen to prevent germination and penetration of plant tissue, are now taking precautions to preserve their crops.

“We’re not devastated, it’s just a management thing,” Lake said. “We were lucky that we had our fungicide on. Lucky and smart at the same time. It’s a challenge.”

Since the fungus can’t survive on dead tissue, Stivers advised potato growers that if lesions were found their fields or home gardens last year, all vines in a plastic bag to cook and die. This effectively kills the pathogen, while preserving the crop and allowing the skins to thicken as usual. If potato tops are blighted, the fungus can infect tubers causing rot both in the soil and in storage.

“Get [the vines] killed early enough so they’re dead and there is no tissue carrying the fungus,” Lake said. “It can’t translocate through the plant into the tuber; it has to make contact. Sometimes there can be a problem if there’s a crack in the ground during harvest.”

Typical lesions have a necrotic center surrounded by collapsed pale green or chlorotic tissue. Under moist conditions, the pathogen sporolates from a host tissue, producing a white “downy mildew.”

Lesions on stems are water-soaked and dark green to black, commonly infecting the stem at the apex of the shoot or at the juncture of the petiole and the stem.

Steps You Can Take To Help:

1. Plant Montana Certified seed potato stock. Never plant table

stock potatoes in your garden!

2. Plant only tomatoes grown in Montana or light blight free

tomatoes. Ask your dealer to make sure! Inspect all bedding plants and buy only disease free plants.

3. Destroy, kill and bury diseased plants, culls and volunteer potato and tomato plants.

4. Pass the word…to neighbors, farmers & gardeners.

5. Report outbreaks immediately to your local Extension agent

or the Montana Department of Agriculture.

Who to contact for more information:

• Montana Seed Potato Certification: Nina Zidack (406) 994-6110

• MSU Extension: Barry Jacobsen (406)994-5161 / Mary Burrows (406)994-7766

• MSU Plant Disease Clinic (406) 994-5150

• Montana Department of Agriculture: Larry Krum (406) 444-3730

• Your Local County Extension Agent