Oil’s nose-dive is sending farmers a stark reminder: They also need to be energy traders.

Growers have become more vulnerable to energy swings over the past decades as nations from the U.S. to Brazil mandated the use of biofuels.

About a third of America’s corn crop is used in ethanol, while Brazilian millers can use as much as 60% of their cane to make the biofuel. Asia’s palm plantations and Europe’s rapeseed crops are largely dependent on biodiesel demand.

As oil suffers its steepest plunge since the Gulf War in 1991 and the coronavirus spreads across the globe, agriculture markets are feeling the pinch.

“Ever since farmers embraced and promoted ethanol and biodiesel, they have increased their linkage to energy prices,” said John C. Baize, an independent consultant who advises the U.S. Soybean Export Council.

“When energy prices were high, corn and soybean prices were also high,” Baize added. ‘Now with the collapse of oil prices, commodity prices also are low. One cannot accept the higher prices without also accepting lower prices now.”

Oil’s rout — caused by a price war between Saudi Arabia and Russia — is the latest blow to crop markets already hurt by a decline in demand because of the spread of coronavirus that’s keeping people at home.

Markets have become more tied together over the past decades and farmers need to watch everything from crude oil to the state of the global economy.

“The coronavirus and drop in crude will impact demand and economic activity, and this could be dangerous,” said Michael McDougall, a managing director at Paragon Global Markets in New York. “Farmers have to be cognizant of this.”

U.S. ethanol margins were crushed as cheaper crude makes the biofuel less appealing.

Ethanol futures seesawed through the week but ended about 10% lower than they were two weeks ago.

Shares in producer Green Plains Inc. lost half their value last week. Pacific Ethanol Inc., another producer, saw its shares drop nearly 40%. Archer Daniels Midland Co., which is trying to sell its dry ethanol mills, slumped more than 15% through the week.

“Destruction of U.S. demand is heavy on everyone’s mind right now,” said Jordan Fife, domestic ethanol trader at BioUrja Trading LLC in Houston, said.

Sugar futures slumped as lower oil prices boost the incentive for millers in Brazil to produce more of the sweetener at the expense of ethanol. Brazil may produce an additional 6 million metric tons of sugar this year, according to top producer Raizen.

Equities were also hit, with Brazilian sugar and fuel giant Cosan SA falling through the week.

This year’s recovery in sugar prices had already been threatened by slow demand and the sell-off in commodities due to the coronavirus.

Edible oils used in biodiesel production also took a dive.

The sell-off comes as agricultural chemical manufacturers are hoping to see a rebound after last fall’s wet weather hampered demand. Nutrien Ltd., the world’s largest crop nutrient supplier, tumbled more than 30% through the week. Shares in competitors Mosaic Co. and CF Industries Holdings Inc. slid more than 35%.

It’s not all bad news for farmers. Crop prices are still holding relatively well compared with oil, and lower energy costs will help.

Chris Robinson, managing director of agriculture and commodities at TJM in Chicago, is advising clients to take advantage of crude’s plunge to lock in diesel prices.

“At the end of the day, that’s the silver lining to being an energy trader/farmer,” he said.