Slowly but surely we are making some planting progress. Each day, I hear about more farmers getting some crops planted.

Up to this point it has been a field by field situation with soil moisture and temperature being the big factors. In the coming week or two, the weather begins to look more favorable for lots of planting to take place.

So keep your fingers crossed that after this weekend, we continue with warmer temperatures and more dry days to keep the planting season moving along.

The acres that have gotten planted earlier should be evaluated due to concern with the wet cold weather of late and the below freezing temperatures in Ohio, between May 9 and 10. Temperatures got as low as 26°F with some areas even receiving snow.

The effect on corn and soybean depends on both temperature, duration of low temperature, and growth stage of the plant.

The soil can provide some temperature buffering capacity, especially if soil is wet. Water is approximately 4x more resistant to temperature changes than air or dry soil, and thus will buffer the soil from experiencing large temperature changes as air temperatures drop.

Deeper planted seeds may also be more resistant to large temperature swings.

Alexander Lindsey and Laura Lindsey, both Ohio State University agronomists, note that one concern we have had is with imbibitional chilling.

Imbibitional chilling may occur in corn and soybean seeds if the soil temperature is below 50°F when the seed imbibes (rapidly takes up water from the soil, usually 24 hours after planting). Imbibitional chilling can cause reductions in stand and seedling vigor.

If seeds were planted into soil at least 50°F (and have imbibed), the drop in temperature is not likely a problem if the plants have not yet emerged from the soil.

So what about corn after germination in these kind of weather conditions?

According to Lindsey and Lindsey, the growing point of corn is below the soil surface until the V6 growth stage, and therefore is protected from low temperatures to some extent.

However, if the soil temperature falls below 28°F, this can be lethal to corn. Temperatures between 28 to 32°F may result in frost damage, and both the temperature and duration will affect the severity of damage.

Between May 9 and May 10, the minimum soil temperature at a 2-inch depth was 38°F at the Northwest Agricultural Research Station in Wood County, 44°F at the Ohio Agricultural Research and Development Center in Wayne County, and 58°F at the Western Agricultural Research Station in Clark County.

What about soybean after germination? Lindsey and Lindsey note the growing point of soybean is above the ground when the cotyledons are above the soil surface.

If damage occurs above the cotyledons, the plant will likely recover. If damage occurs below the cotyledons, the plant will die. Look for a discolored hypocotyl (the “crook” of the soybean that first emerges from the ground), which indicates that damage occurred below the cotyledons.

Since it is probably going to be too wet to plant this weekend, now is good time to assess damage to plants or seeds 48 to 96 hours after the drop in temperatures, as symptoms may take a few days to appear. Additionally, cold temperatures slow GDD accumulation and may further delay crop emergence.

For corn, recent work suggests 50% emergence can be expected following accumulation of 130-170 soil GDDs (using soil temperature to calculate GDD rather than air temperatures) from planting, which may take 5-7 days to accumulate under normal weather conditions.

We can’t forget wheat when assessing our crops. Injury to winter wheat depends primarily on three factors: 1) growth stage, 2) how cold, and 3) duration of cold temperature. Differences in freeze injury among cultivars can usually be attributed to slight differences in growth stage.

At Feekes 8 growth stage (flag leaf visible, but still rolled up), Lindsey and Lindsey suggest the growing point is above the soil surface, but still protected within the crop canopy.

Freeze damage at Feekes 8 growth stage can injure developing heads and damage the flag leaf. Symptoms of freeze damage include yellowing or browning (necrosis) of leaves. Once wheat enters Feekes 9 growth stage (ligule of flag leaf visible), the flag leaf may appear twisted.

As the wheat head emerges, it can get stuck in the leaf sheath, causing a crooked appearance at heading. In OSU research, wheat grain yield was reduced, when the temperature dropped below 25°F for 15 minutes. According to research from Kansas State University, 28°F for two hours can cause moderate to severe reduction in wheat grain yield.

At Feekes 10.5.1 growth stage (beginning flowering), wheat heads are above the plant canopy, resulting in heads and anthers that are exposed with limited protection from the crop canopy. Freeze injury at Feekes 10.5.1 can cause sterility, embryo death, or complete loss of the spike.

At Feekes 10.5.1, spikelets and awns may appear white or bleached in color as a result of cold temperatures (Figure 4). In our research, wheat grain yield was reduced, when the temperature dropped below 28°F for 15 minutes. According to research conducted at Kansas State University, at 30°F for two hours, winter wheat grain yield can be severely reduced.

When assessing potential wheat damage, it is important to assess fields for damage as damage may be more or less extreme depending on the growing environment (landscape features, soil moisture, wind speed, overall condition of the field, etc.). Lindsey and Lindsey suggest waiting about a week to walk fields and look for symptoms of damage.

There is more good information with several pictures of cold weather symptoms at https://agcrops.osu.edu/newsletter/corn-newsletter.

Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for over 30 years, currently serving Clinton County and the Miami Valley EERA.