Researchers fight broccoli blight in Minnesota's fields

Broccoli, often cubed and steamed on children's lunch trays, may have gotten a bad rap over the years. But for the smallholder farms across Minnesota that sell produce at farmers markets and local cooperatives, the knobby green vegetable is king.

"Broccoli is one of our highest-earning crops," said farmer Erik Heimark, co-founder of Maple Ridge Produce in Aitkin County. "I've got a little bit invested into them, and they don't have the labor like I do in green beans and lettuce."

But over the unpredictable growing seasons the last few years in Minnesota — ranging from intensely wet to intensely dry — broccoli has come under attack from black rot, sometimes wiping out whole fields.

So far, Heimark's farm has avoided the scourge. But he fears it's coming.

"Having [black rot on broccoli] for vegetable growers? Oof," Heimark said. "That'd be a big gut punch."

The spread of black rot has endangered enough smaller produce farmers that a state-backed grant is funding the study of more-resistant broccoli varieties.

In an experimental field outside Waseca, Minn., researchers funded by a grant from the Minnesota Department of Agriculture have injected black rot into dozens of varieties of broccoli in a patch near soybeans and corn. They're testing for tolerance to a number of enemies, including black rot, which emerges as yellowing leaves or deformed heads.

Earlier this month, with broccoli knife in hand, Charlie Rohwer, a researcher at the University of Minnesota's Southern Research and Outreach Center,

stood in the field plot. He lopped off a head of broccoli and held the plant up to sunlight, revealing dark fringes on shoots.

The blight, he said, can be ruinous for growers whose customers want picture-perfect vegetables.

"We did the project because there were some growers who lost everything to black rot," Rohwer said.

Broccoli is a crop that still longs for its Mediterranean roots, researchers say. Grown year-round in places such as California, the plant is happiest with cool nights.

Lately, broccoli has had a tough go in Minnesota. In 2018 and 2019, Minnesota growers endured wet seasons. The last two they've contended with fall seasons that were warm and dry — weather beloved by walkers but withering to certain crops.

Enough of Minnesota's 3,000 produce growers were hit by blight to raise alarm. Two years ago, the state Department of Agriculture approved a $34,000 grant to pay for two years' worth of spring and fall broccoli, screening for resistant varieties. Another 80 farmers and gardeners across the region planted mini-trials to chart results.

"Broccoli is the crop that many of us grew up eating — gross, steamed broccoli," said Natalie Hoidal, local foods and vegetable educator with University of Minnesota Extension. But, she said, broccoli deserves an image reboot.

"For one, broccoli is delicious," she said. And second, "it's also an important crop for fresh market growers."

Recent climate extremes, whiplashing between wet and dry, hot and cold, have beat up on Minnesota's broccoli harvest and stymied growers who select seeds months in advance of the season.

"When we talk about hotter weather," Hoidal said, "one of the most important shifts is nighttime temperature. Broccoli is a cool-season crop."

A 2021 report on the first year's growing noted that the hot, dry summer meant "disease pressure was minimal." But as produce growers harvest this fall under statewide drought conditions, they increasingly must grow varieties that flourish in a wide range of weather. Moreover, many of the growers are organic, working without fungicide.

And it's not just broccoli. A range of crops — from tomatoes to peppers to eggplants — need to withstand the seesawing conditions.

"Our yields were a little bit lower this year," said Heimark, who sells at area farmers markets, including in Grand Rapids, Minn. "Basically our June was more like August, and our August was more like June."

In other words, Heimark added, the rules of the vegetable-growing game are being rewritten.