KANSAS CITY — Voluminous late-winter snow and a precipitation-heavy spring have shortened the window for producers to seed spring wheat and row crops, and planting progress lagged the average pace across the farm belt. The corn crop was the biggest concern.

“Corn pollination is typically in July if the crop is planted on time, so you tend to hit pollination ahead of the hottest part of the summer,” said Paul Meyers, vice-president of commodity analysis with Foresight Commodity Services, Inc. “When you’re planting corn at the end of May or the first couple weeks in June, then you run the risk of some hotter, drier weather during the pollination period.”

In its weekly Crop Progress report, the U.S. Department of Agriculture indicated corn planting in the 18 principal producing states, which accounted for 92% of the 2018 corn acreage, was 58% completed by May 26, compared with 49% a week earlier, 90% a year earlier and 90% as the recent five-year average for the date. Planting in Iowa on May 26 was 76% completed compared with 95% a year earlier and 96% as the five-year average. In neighboring Illinois, planting was 35% completed, drastically lower by comparison with 99% a year earlier and 95% as the 2014-18 average for the date.

“In particular, Illinois — one of the two largest producing states — is running 60 percentage points behind normal, so that’s a concern,” Mr. Meyers said. “Some of those acres won’t get planted, some of them will shift to soybeans, some of them will have crop insurance and probably take prevented planting.

“Most parts of the Corn Belt, really it’s just a rotation of corn and soybeans, so that’s where the acres will most likely go.”

Skipping corn in the rotation wasn’t expected to be detrimental to the soybean crop, whereas “corn-on-corn acres tends to create a slight drag on yields,” he said.

Soybean planting progress also lagged the average pace. The U.S.D.A. indicated the soybean crop in the 18 largest producing states, which accounted for 95% of the 2018 soybean planted area, was 29% seeded by May 26, compared with 19% a week earlier, 74% a year earlier and 66% as the 2014-18 average for the date. South Dakota was the furthest behind the average pace. The crop there was 6% planted by May 6, compared with 56% a year earlier and 64% as the five-year average. In top-producing Illinois, the soybean crop was 14% planted, far behind 89% a year ago and 70% as the average. Soybeans were 32% planted in Iowa (77% as the 2014-18 average), 35% in Minnesota (77%), 56% in Nebraska (74%) and 46% in North Dakota (65%).

Spring wheat planting progress was in better shape than corn or soybeans last week. North Dakota producers were on track to potentially complete seeding within the week. Although recent northern Plains rains have skirted North Dakota, the area featured adequate soil moisture to allow the crop a strong start.

The U.S.D.A. said the spring wheat crop in the six major production states, which accounted for 99% of 2018 spring wheat acreage, was 84% completed by May 26 compared with 70% a week earlier, 89% a year ago, and 91% as the recent five-year average for the date. The North Dakota crop was 82% planted by May 26 compared with 66% a week earlier, 89% a year ago and 87% as the 2014-18 average for the date. Of the six states, all were within five percentage points of the five-year average except South Dakota, which was 79% planted compared with 97% as the average.

South Dakota planting progress was limited by wet conditions stemming from a wet winter and spring. In mid-March, Winter Storm Ulmer set wind and pressure records in the mountain west and went through “bombogenesis” — a 24-millibar drop in atmospheric pressure in 24 hours or less — en route to the central Plains bringing blizzard conditions from Colorado to North Dakota. In the aftermath of the bomb cyclone, South Dakota was among six Midwestern states plagued by record river flooding from rapid snowmelt. Ice jams were common, and record-high river levels sometimes sent giant ice slabs out into roads and fields.

Less than four weeks later, Winter Storm Wesley blanketed the state again. Twenty-five inches of snow over three days set a record in Watertown, S.D., while Huron’s 18 inches and Mitchell’s 16.2 inches each set two-day records. 

For a time, winter seemed unwilling to let go a full two months into spring. A May 21-22 snowstorm covered the area surrounding the Black Hills, dropping 20 inches in Lead, S.D., and 10 inches in Spearfish, S.D. East of Rapid City, S.D., which notched record snowfall for the date, much of the rest of the state was drenched in spring rain. Runoff and continued rain caused creeks and rivers to top their banks again in western South Dakota.

“Farmers are looking for a break in the weather, and it’s very unusual to go seven weeks where they haven’t been able to get much field work done, as some of these areas have,” Mr. Meyers said.

But the late-June acreage report might lack precision considering the delayed planting season might push producers’ decisions on seeding past the early-June survey period.

“We may have to wait until August for some of those states to get a better indication of what the acreage is going to be,” Mr. Meyers said.