Temperatures dipped below freezing in some areas of northern Iowa over Mother's Day weekend, causing concern that some farmers may need to replant corn and soybeans in one of the earliest planting seasons in many years.

The weekly Iowa Crops and Weather Report, released May 10 by the Iowa office of USDA's National Ag Statistics Service, cites temperatures in the 28 to 30 degree range overnight on May 8-9 in areas of northern Iowa.

"The concern isn't so much the cold snap over the weekend as the cold, wet weather that is forecast for the rest of this week," says Roger Elmore, Iowa State University Extension agronomist. The National Weather Service is forecasting lows in the upper 30-degree range for the Mason City area in northern Iowa this week, along with some rain.

Iowa corn crop now 93% planted, beans 44% planted

A few farmers have reported leaves of young corn plants getting nipped by frost over the weekend. But the plants are young and the growing point is still under ground, so those plants are expected to recover and re-grow new leaves. But corn and soybeans can run into problems when cold, wet weather prohibits the seedlings from growing. Sitting in cool, wet soils makes them more susceptible to seed rots, seedling diseases and stand loss.

Most of the corn that was frosted was less than 3-leaf growth stage corn, notes Elmore. The growing point is still below ground so the corn should recover—although there is a chance that seedling rot could infect the seedling. Cool, wet conditions create more risk of seedling rot and slow the recovery. So hope for warmer weather. Elmore recommends waiting a few days before making any decisions. Before deciding to replant, evaluate stands for new growth, and dig some plants to check the health of the growing point.

The weekly statewide survey results released May 10 show that 93% of Iowa's 2010 corn crop was planted as of May 9. Also as of Monday, 44% of Iowa's soybean acres are now planted, well ahead of average. Nationwide, 81% of the corn and 30% of the soybeans are planted as of May 9, says the USDA report.

Near-perfect weather for planting comes to an end

"The run of near perfect planting weather has come to an end, but most farmers remain well ahead of their normal pace for getting their crops in the ground," says Harry Hillaker, state climatologist with the Iowa Department of Agriculture in Des Moines. "However, the sporadic heavy rains, high winds and freezing temperatures certainly cause some concerns for farmers across the state."

The weekly weather and crop report is available on the Iowa Department of Agriculture site at www.IowaAgriculture.gov or on USDA's site at www.nass.usda.gov/ia. Following is a summary of the report released May 10.

Colder temperatures, and frost create re-plant concerns

The past week saw scattered rain showers, high winds, colder temperatures and wide-spread frost. Temperatures dropping into the high twenties in northern Iowa and low thirties in Southern Iowa during the overnight hours led to frost and decreasing soil temperatures. This caused concern that re-planting may be necessary. Lower temperatures also caused the emergence of newly planted crops to slow.

Although inclement weather slowed progress, farmers were able to continue with field work as conditions permitted. They continued to plant corn and soybeans as well as spraying when the winds subsided. Hay conditions are being reported in good condition with some possible damage from the frost over the weekend. Pasture growth slowed with the cooler temperatures, but still allowed livestock to graze.

There were 4.1 days suitable for fieldwork during the week, compared with 3.1 days last week. The days suitable for fieldwork ranged from a low of 2.5 days in southeast Iowa, where some reports indicate that there have been zero days suitable, to 4.7 days in west central and central Iowa. Topsoil moisture rated zero percent very short, 2% short, 82% adequate, and 16% surplus across the state. Subsoil moisture rated zero percent very short, 1% short, 81% adequate, and 18% surplus.

Field Crops Report: The report released May 10 shows Iowa corn acreage planted was 93% complete as of May 9, increasing 9% from the previous week. Corn planting progress is 11 days ahead of last year and the 5-year average. Corn acreage emerged was 48% as of May 9, well ahead of the 21% last year and the 5-year average of 17%.

Soybean acreage planted was 44% complete in Iowa as of May 9, compared with 19% last year and 17% for the 5-year average. Early planted soybeans have begun to emerge. About 90% of the expected oat acreage has emerged, ahead of last year's 70% and the 5-year average of 68%. Oat condition rates 1% very poor, 1% poor, 14% fair, 66% good and 18% excellent.

Livestock and Pasture: Pasture and range condition rates 1% very poor, 3% poor, 21% fair, 56% good and 19% excellent. There have not been any unusual livestock conditions or concerns.