While some rain and brief respites from the heat have been welcome, crops in the region are starting to suffer from the early summertime heat.

“Farmers reported crop stress with the lack of rain and heat conditions,” wrote Ben Torrance, state statistician with USDA’s National Agricultural Statistics Service Ohio field office in Monday’s Crop Progress Report. “Corn condition was rated 60% good to excellent, while soybean condition was rated 61% good to excellent, each down from the previous week.”

It has been hot and dry in the Buckeye State. The average temperature last week was 80.2 degrees F, 9.6 degrees above normal. Weather stations reported an average of 0.41 inches of rain, nearly half an inch below normal. More than 60% of topsoil was rated short or very short in the report.

Farther north in Michigan, it’s been really hot and really wet.

“Excessive heat and heavy rain highlighted the variable weather conditions across the state last week,” wrote Marlo D. Johnson, director of USDA’s NASS Great Lakes Regional Office. “Winter wheat experienced lodging from high winds and excess rain in isolated areas as it continued to mature, while corn and soybeans benefited from the rain events.”

Corn is rated 71% good to excellent, while soybeans are 62% good to excellent.

Northeast and mid-Atlantic

In Delaware and Maryland, soil moisture has deteriorated significantly as droughty conditions have officially started to creep in. Topsoil is rated 43% very short on moisture in Maryland, according to the report. More than 50% of corn is either fair or poor. Soybeans aren’t faring much better, with 54% of the crop rated fair or poor.

In Delaware, 48% of topsoil is very short. Corn is rated 57% poor or very poor, while soybeans are 90% fair or poor.

Pennsylvania crops look a little better. Corn is rated 90% good to excellent, while soybeans are 80% good to excellent. Pasture is 70% good to excellent.

LEAF FLIPPING: When soybeans are drought-stressed, the leaves will flip over to show their silvery-green undersides, like in this field in Berks County, Pa. It is a defense mechanism to reflect more light, reducing the amount of sunlight the plant takes in through its leaves.

Eric Rosenbaum, owner of Rosetree Consulting in Shillington, Pa., says most corn he’s seen has reached the six- to seven-collar growth stage, meaning rows around the ear were already set at the five-collar growth stage, although kernels per row won’t be set until just before tasseling.

“So, we’re in a time period where no critical yield determination is occurring,” he says. “If I got to pick what growth stage to have a drought in, it would be this growth stage.”

Wait to sidedress?

If you haven’t sidedressed nitrogen yet, Rosenbaum recommends liquid N over a dry topdress.

“Dry weather N losses are volatilization losses; there's no leaching or denitrification losses when we don't have water,” he says. “Banded liquid applications have low risk of loss, and a stabilizer can further reduce that risk. Products like ESN, Super U and ammonium sulfate would be safe in dry topdress applications, but think twice about a traditional urea application.”

His biggest concern right now is root development.

“Corn that was planted a little on the wet side already dealing with sidewall compaction is now dealing with hard, dry soil,” Rosenbaum says. “I've seen fields goose-necking, just like they would from corn rootworm damage, because waist-high corn plants have a baseball-sized root system. This restricted root system will cripple the plant's ability to uptake water and nutrients,” he says.

On the soybean side, being early this year was likely not better.

“Early beans that were struggling to overcome slug damage are now struggling to grow,” Rosenbaum says. “As with corn, any sidewall compaction created by the planter is an additional hurdle the plants are trying to overcome now. Plants struggling with root growth will also struggle with nodulation and overall nutrient uptake.” 

Leon Ressler, Extension educator of agronomy with Penn State, says he would delay any sidedressing until some rain comes through.

“So, you have nothing to lose by delaying if you can wait,” he says. “I would definitely agree that banding liquid N on corn is the best way to go, and use a stabilizer. This is going to be challenging wherever planting too wet resulted in sidewall compaction, but there really isn’t anything that can be done about that now.”

It might be too early to get concerned about yield losses, but the longer this dry hot streak goes, the more damage will occur.

“Last year, northern Lancaster County had six weeks with no rainfall at all, yet a few contestants in the corn and soybean contest had yields around 90 bushels on beans and over 250 on corn, which was a total surprise,” says Jeff Graybill, Extension educator in Lancaster County. “However, last year the drought ended around June 5 or so. I think the later we have severe stress, the greater the potential for significant yield loss.”

Dry and hot: A potent combo

Mark Jeschke, agronomy manager with Pioneer who is based in Johnston, Iowa, says high temperatures and water stress go hand-in-hand. For example, these five factors tie high temperatures and water stress together in corn:

1. Higher temperatures and transpiration rate. Transpiration is the rate water released from the plant leaves into the environment through evaporation. It's an invisible process that varies depending on weather, soil types and conditions.

“Higher temperatures cause transpiration rate in corn to increase,” Jeschke says. “That places a greater demand on soil water supply. It can accelerate the onset of drought stress.”

2. Water demand from heat can be substantial. And if you grow crops in soils with reduced water-holding capacity, it could lead to big trouble.

“Raising temperatures from 80 degrees F to 95 degrees F causes water demand to double,” Jeschke says.

3. Corn plants close leaf stomates. “Corn plants respond to water stress by closing their stomates,” Jeschke says. “That helps preserve water, but also reduces carbon dioxide intake. Carbon dioxide is needed in photosynthesis.”

What are stomates? They are tiny openings on the leaf surface that allow gas exchanges between outside air and the leaf's internal air system.

Closing stomates is a natural reaction by corn plants, like rolling of leaves. When leaves roll, the goal is to conserve moisture within the plant.

4. Reduced pollination, less net photosynthesis. The biggest impact here is through the interaction of heat and water stress.

Jeshke says it can lead to delayed silking, which can get so bad that pollen may be gone by the time silks emerge, resulting in barren cob or ears with limited numbers of kernels.

5. Vapor pressure deficit. Higher temperatures in the cornfield create a vapor pressure deficit, or VPD, between the saturated interior of the leaf and ambient air.

The greater the VPD, the faster water is pulled out and evaporates. Temperature is the big driver, Jeschke says, and VPD increases exponentially as temperatures rise, even if relative humidity stays steady.

VPD is a measurement that combines relative humidity and temperature into a single variable to describe the evaporative potential in the atmosphere. Air space inside the plant is fully saturated with water at 100% relative humidity. Water vapor moves from higher concentration to lower concentration. So, if relative humidity outside is less than 100%, VPD pulls water out of the plant.