MOUNT HOREB, Wis. — Wisconsin farmers are contending with diesel prices averaging about $6.50 a gallon as harvest-season fuel use adds to the strain on already narrow budgets, U.S. Sen. Tammy Baldwin said during an Oct. 2 visit to a farm near Mount Horeb. The state’s average diesel price was up about $3 per gallon from a year earlier, a rise of nearly 90% — the largest increase of any state over that period, according to fuel-price analyst Patrick De Haan. Disrupted tanker traffic through the Strait of Hormuz amid the United States’ war with Iran has contributed to the increase. Darren Kittleson, a fifth-generation farmer who raises Akaushi cattle at Generations Beef on Brunkeberg Kviteseid Farms, said most of the farm’s equipment runs on diesel, leaving little ability to avoid the higher prices. “Our margins are so thin,” Kittleson said. “Just a few cents makes a big difference in a lot of areas.” Fuel costs also show up in the price of fertilizer, waste removal and deliveries, he said. Suppliers and service providers have added fuel surcharges, spreading the impact beyond the farm’s own machinery. Baldwin said some farmers had locked in lower fuel prices for spring planting through contracts signed before the war began Feb. 28. But those arrangements are expiring, and farmers she has spoken with expect to face higher costs during harvest and in the next growing season. Suppliers, she said, will also seek to recoup losses. The squeeze affects an industry central to Wisconsin’s economy. Agriculture and food processing generated $116.3 billion in revenue in 2022, about 14% of the state’s total, according to a University of Wisconsin-Madison report. Wisconsin had more than 58,000 farms that year, including about 2,500 in Dane County; 95% of the county’s farms were family-owned, UW-Madison Extension data shows. Baldwin tied farmers’ fuel bills to a wider set of challenges, including tariffs, trade disputes and uncertainty in agricultural markets. She called for an end to the war, saying she had voted 12 times to end hostilities but had not secured enough support in the Senate. She also urged a shift toward biofuels, including biodiesel for farm machinery, as a way to reduce reliance on foreign oil and limit exposure to supply disruptions. Reliance on fossil fuels, she said, leaves both the economy and farmers vulnerable when global oil shipping routes are disrupted.