When weather conditions are favorable for Phytophthora infestans, late blight can cause severe losses to Washington’s $450 million potato industry. The fungus likes mild, wet weather and has the capacity under optimal conditions to spread almost explosively.
Between 1845 and 1850, late blight led to the starvation deaths of an estimated 1–1.5 million Irish peasants. Another 1.5–2 million fled Ireland during the great famine. Among the emigrants were ancestors of John F. Kennedy, 35th president of the United States.
Late blight of potatoes was first reported in Washington in 1947. It was 27 years before the next infestation. During the next 16 years the resurgent disease struck seven times. Now it is an annual concern in Washington.
Fortunately, today it can be controlled with fungicides. They are effective if applied in time, but very expensive. In1998, Washington potato growers spent $22.3 million to spray fungicides on their fields. That’s money growers don’t want to spend if they don’t have to, but they can’t afford to gamble that the sprays won’t be necessary. Unchecked, late blight can totally wipe out an entire potato field.
“In 1995, when blight took us apart, I happened to be chair of the Washington State Potato Commission. We growers were pretty smug and we just got hammered,” recalls Farmer Ron Reimann, Pasco. Reimann, who grows about 1,000 acres of potatoes a year, called the WSU Plant Pathology Department for help and found that WSU scientists had published a lot of information that many growers hadn’t read.
The next year, Plant Pathologist Dennis Johnson had an early warning system in place. It is based on a computer model that relates weather to development of late blight. Johnson developed the model with assistance from Statistician J. Richard Alldredge, Program in Statistics.
Since 1996, when mild, wet weather has made Washington potato growers nervous, they have picked up the telephone and dialed a toll-free number. They listen to the latest audio tape report from Johnson, based on data from WSU’s Public Agriculture Weather System and a computer model of late blight development.
“His late blight line is our first line of defense,” Reimann says. Typically, farmers have to apply several sprays during a growing season. “If you can get one extra day out of a spray, it will save you a lot of money. Dennis has saved us a lot of money.”
Andrew Jensen, director of research and technical affairs for the Washington State Potato Commission, says, “The late blight hotline is one of the most highly valued services provided to the potato industry by WSU and the potato commission. That phone number is scratched onto more note pads and programmed into more cell phones than just about any other in the industry.”
In 2000, Johnson’s hotline received 1,762 calls.
“The hotline provides a centralized source of late blight information, and is especially critical when the annual outbreaks begin,” Jensen says. “Growers in the area of the first outbreak reported on the hotline must respond quickly to Dr. Johnson’s recommendations. Not only does a quick response preserve the health of their fields, but it can also slow the spread to the rest of the Columbia Basin.”
“From my perspective, Dr. Johnson’s extension and research efforts are one of the best values the commission gets from its research dollars.”
There are two ways growers can save money through Johnson’s service. First, they save the cost of applying fungicides if the danger of late blight is low. On the other hand, they will save far more money if the report prompts them to spray and that spray saves a crop.
Johnson explains, “part of the difficulty with late blight is that the fungus can practically explode from a very low level of infestation to devastating levels in a very short time. Losing a gamble on late blight can put a potato farmer out of business.
Washington has about 350 commercial potato growers producing this year’s crop on about 165,000 acres. The 2000 crop totaled 108 million hundred- weight of potatoes. Funding from Syngenta Crop Protection and the Washington State Potato Commission help fund Johnson’s program.
