MONROE - Most often, farmers benefit from Mother Nature. Recently, however, Mother Nature has been more frustrating than helpful.

Heavy rains last weekend and more Thursday night have left many farm fields in Green and Lafayette counties - and throughout the state - under water. Agriculture experts say crop losses due to heavy flooding in Wisconsin could reach the tens of millions of dollars.

Green County Agriculture Agent Mark Mayer said fields in the Pecatonica River basin are in the worst shape, with farms along the Sugar River near Brodhead also suffering flooding.

Mayer estimates 5 percent of the county's corn crop and 5 percent of the soybean crop have been lost. That may not sound like much, but it equates to about $5 million worth of crops.

Not included in that amount is the hay crop.

Mayer said heavy winds and rain have packed down the hay, making it difficult to harvest the first yearly hay cutting.

"We're usually done harvesting by now," Mayer said. "We've still got half of it out there."

Keith Blumer is one farmer who still has hay in the field, but that's the least of his worries. His Plain View Stock Farm just north of Albany is home to about 3,000 acres of crops, including 1,000 acres each of corn and soybeans.

"This is probably the most standing water I've ever seen in the years I've been here," said Blumer, who has lived at the farm all his life. "The groundwater is the highest I've ever seen it.

"It's a combination of 30 inches of rain in August (2007), record snowfall and it just keeps going."

Blumer said between 25 and 30 acres of cropland is under water. He has been unable to plant on another 160 acres.

The wet weather will force many farmers to make a difficult decision.

Ben Brancel of the federal Farm Service Agency in Wisconsin works with farmers who have lost crops, buildings and livestock because of storms.

Brancel says farmers also will lose money because of poorer yields on crops planted late because of flooded or muddy fields. Other farmers may choose to switch to less-favored crops with a shorter growth cycle, or not plant at all.

"This has already impacted the yield; there's no doubt about that," Blumer said. "The financial impact could be great, but we won't know until we harvest the crop."

Mayer has seen more extensive flooding in his 23 years as Green County's agriculture agent, but he said this round of flooding may be worse.

Mayer said there is more soil erosion going on because the fields are open. He said it's hard to put a dollar value on soil.

"If you lose an inch of soil, it takes 400 years to get it back," Mayer said. "A lot of Green County is going down the Mississippi River."

Mayer said farmers have to get corn planted by June 20, but even then, it would be for silage only, not grain. He said soybeans could be planted by July 1, but the yield will be much less than normal.

University of Wisconsin-Madison farm management specialist Bruce Jones says lower yields also will put more pressure on food prices for consumers.

Blumer said he is hoping for wind and sunshine to dry out his fields so he can see how extensive the damage is. Mayer said corn and soybean plants that are submerged for 48 hours will not survive.

"Finding out what kind of crop you will get is fun," Blumer said. "That fun part of harvesting is gone already."

- The Associated Press contributed to this report.