Wet weather continued to vex farmers last week, which means planting of Minnesota’s main crops remains behind schedule.

In fact, some farmers will likely face lower crop yields due to the late start.

As of Sunday, 87 percent of corn, the state’s biggest crop, had been planted, compared with a five-year average of 98 percent, according to data released Monday by the U.S. Department of Agriculture’s St. Paul office.

The state’s second-largest crop, soybeans, was 55 percent planted on Sunday, while the five-year average for that date is 88 percent. As for spring wheat, 92 percent was in the ground compared with a five-year average of 97 percent.

“Cool and wet weather prevailed again in Minnesota for the week ending June 2,” the USDA’s weekly crop report said. “Standing water and muddy fields continued to hamper field work.”

Minnesota farmers were plagued by a long winter and wet spring; they started May with nary a seed in the ground. Then, May turned out to be one of the gloomiest months in decades as measured by cloudy days. The Twin Cities experienced its sixth-wettest March-through-May on record.

Minnesota farmers got a big break in the weather during the week of May 12 to 19. They seeded a vast amount of acres, catching up on long-term averages for planting. But progress since May 19 has slowed significantly.

Late planting can reduce crop yields by shortening growing seasons. For corn, yields decline rapidly for every day of planting past mid-May.

“Does this late planting have an effect? Most definitely,” said David Nicolai, a University of Minnesota Extension crop educator in Farmington.

Due to the late start, corn yields on average should be about 84 percent of maximum, he said. Some corn farmers in the southeastern part of the state have been hit particularly hard by the wet weather.

Soybeans can be planted throughout May without a yield penalty, but the clock starts ticking in June. Nicolai said that U Extension recommends that for soybeans planted after June 10, farmers use a seed that’s tailored to a shorter season. But typically, that seed will lead to lower yields, he said.

The silver lining to all the rain: Minnesota’s parched topsoil has gotten a major recharge. As of Sunday, 63 percent of the state’s topsoil had adequate moisture, while 35 percent had surplus water, according to the USDA. As for subsoil moisture, 72 percent was adequate as of Sunday.