Apr. 25—Maine farmer Ryan Guerrette irrigated his 1,200 acres of potatoes in Caribou more often in the past few years, when more severe rain or drought conditions threatened the state's premier food crop.
Guerrette Farms is in the heart of Aroostook County in the northernmost part of Maine, which has the largest concentration of potato farms in the state. Farmers there produce most of the 56,000 of acres harvested in the state worth a total of $540 million in sales and employing 6,100 people.
Most still dry farm without supplemental irrigation, putting them at risk of a drought such as the one in 2020 that decimated 30 percent of the state's potato crop. Irrigating is expensive, Guerrette said, costing $5 per gallon for up to 3,000 gallons of fuel per day on his farm on top of the irrigation equipment. But more growers are looking at it as an option, with about 25 percent of the potato acreage being irrigated, according to the Maine Potato Board.
So far, climate change has brought mixed news for farmers like Guerrette. It is linked to warmer temperatures and drought, but also brings more frequent and intense rainfall that can damage crops with rot or soil erosion.
Clockwise from left: Climate change means Rob Johanson's field is often either too wet or too dry; An old truck door advertises Goranson Farm in Dresden on Wednesday, April, 20, 2022; Organic Adirondak Blue potatoes glisten in a wooden bin after being washed at Goranson Farm; Johanson stands next to an intake hose he uses to pump water from the Eastern River for crop irrigation on his farm. Credit: Troy R. Bennett / BDN
As temperatures have risen, the annual number of potato plant growing degree days in Aroostook County has increased by more than 20 percent since 1970, according to an analysis by Climate Central, a nonadvocacy science and news group. Growing degree days, which estimate the development of plants and insects during the growing season, indicate to farmers how fast heat accumulates and how their crops will grow.
That extra warmth has helped add an extra week to the end of the typically short Maine potato growing season. But it comes with a suite of challenges, including heat stress, unpredictable rainfall, pest pressure and warmer nights that don't let potato plants cool off.
"There is a decent financial margin if everything works right," said Guerrette, who is president at the Caribou farm. "Now if the weather starts playing games with us, well, you can only do so much."
Getting an extra week on a 1,000-acre farm is tremendous, said Daniel Corey of Daniel H. Corey Farms in the Aroostook County town of Monticello. He was able to plant up to 20 percent more potatoes last year during a bountiful Maine season in which growers shipped their products by train to western states experiencing a drought. Maine ranks fifth in its area of potatoes planted and harvested, with Idaho ranking first and Washington state second.
Nighttime temperatures have warmed about 2.5 degrees Fahrenheit in Maine's potato growing region since 1970, slightly less than in central Washington, which ranks second in U.S. potato production. Across the potato-growing areas of top producer Idaho, nights are warming between 3 and 6 degrees.
Warmer weather also means higher energy costs to store harvested potatoes and keep them cool so they don't spoil. The longer season puts the crop at risk of an early frost during the harvest in October.
Potatoes are hardy and do well in Maine, where summer days of 70-75 degrees Fahrenheit and cool nights of 50-60 degrees suit them. They grow well with one inch of rain per week, but heavier rains that soak the ground for long periods can cause rot and promote disease.
"There's not much you can do to pump water out of the field," said Rob Johanson, co-owner of Goranson Farm, an organic farm in midcoast Dresden that grows a little over five acres of potatoes on its diversified 80-acre farm.
During one heavy rain event eight years ago, Johanson said he lost about 100 feet of the 975-foot-long rows of potatoes he had planted. With climate change, the extremes of extended wet and dry periods happen more often, so he also finds himself irrigating more and sooner than he had in the past.
"How much of the potato production is impacted depends on the magnitude of these changes and on how variable and inconsistent they are," Gregory Porter, professor of crop ecology and management at the University of Maine in Orono, said.
Porter and his colleagues have been developing new varieties of potatoes such as drought-resistant varieties that Corey and other farmers are testing in their fields.
Potatoes are a cool-season crop. When it gets too warm, they breathe more and use more sugar, decreasing their productivity. Under higher nighttime temperatures, they also get more stress-related defects and the soil remains warmer, affecting quality, Porter said.
He said that heat stress can lower the starchiness needed for fries and chips, for which most of Maine's potatoes are destined. It can cause an uneven sugar distribution, creating unwanted dark spots when the potato is fried.
The potatoes, which give off heat, are also harder to cool down when harvested to avoid rotting. He said growers are adapting with better storage technologies, new potato varieties and longer crop rotations.
Although Maine farmers can have a more productive year when there are more growing degree days, "we must temper that optimism," Porter said.
"There is still a lot of variability and uncertainty that growers have to be very concerned about," he said.
Corey said other downsides to the changing climate include northern Maine not experiencing the deep spring freezes anymore. Potatoes left in the field from the fall harvest are not being killed off, more insects are overwintering and he is seeing more soil-borne diseases.
"I haven't seen this many transient aphids since we've had this warm spell," he said. "We have potatoes coming up into our grain fields and russets coming into my red potatoes, which we can't have."
Years with more growing degree days can create an insect boom, said Rachel Schattman, a professor of sustainable agriculture at the University of Maine in Orono. Warmer weather can allow insects to live longer and reproduce more often, just in time for crops to become hospitable hosts.
At the end of the season the "increase in growing degree days and wetter conditions is also prime time for plant diseases," she said, creating a situation where fungal and bacterial diseases can wipe out entire crops.
Erosion control also is a problem, said Bill Sheehan, director of the northern office of the Maine Department of Environmental Protection. The intensity of storms has increased for at least the past 10 years, causing erosion events and small tornadoes. Culverts put in 120 years ago are failing and other erosion-control methods need to be updated.
Unpredictable rainfall will make water management crucial in the coming years, Schattman said. Farmers will need to make important decisions on when to turn the water on and off.
"We're seeing this need for farmers to be able to be really nimble," she said.
To survive, farmers need consistent yields from year to year, and that is difficult with the changing climate, Johanson of Goranson Farm said.
"The vagaries of the weather these days makes it very difficult," he said.
Porter said farmers already are adopting new technologies, including new and hardier potato varieties, supplemental irrigation, longer crop rotations and better storage technology to try to maintain the crop quality through the changing environment.
"We're likely to remain a very strong and productive potato-producing area into the future even with these climate change scenarios," Porter said.
This story was produced through a partnership with Climate Central, a nonadvocacy science and news group.