“Plant height is the best visible indicator of how well the plant has been able to take up the water it needs to expand cells,” Nafiziger explained. “Cell expansion is sensitive to water supply, so shortened internodes are one of the first things we notice on plants that have struggled to take up enough water to keep growing.”

This year, many fields have plants only 5 to 6 feet tall at tasseling, several feet shorter than normal. These plants may grow some after tasseling, but will reach full height by the end of pollination. Some of the fields in the driest areas have tried to pollinate while the plants were still very short.

Most of these fields will produce low yields; some may produce no yield at all. Short plants may not be able to form the complete canopies needed for maximum yield because, if they have had trouble getting enough water to elongate their stalks, they may have shorter-than-normal leaves.

Even if the leaf area is normal, leaves may be stacked more closely together on short stalks, allowing for less interaction among neighboring plants and less flexibility of leaf movement.

Hence, the plants’ ability to form the complete canopy that is needed to intercept nearly all of the sunlight is reduced. This problem is coupled with ongoing water stress that limits photosynthetic rates.

Is there anything we can do to help the crop get through this dry period?

Not much, according to Nafziger. “When water is clearly the major limitation to plant function, we would expect little or no response to anything we can apply that’s not water.”

As an example, he does not think that applying fungicides to reduce respiration and increase the plant’s sugar supply is likely to help much.

“Strobiluron fungicides do act by reducing respiration, some of which is considered wasteful,” he explained. “But plants that are not photosynthesizing well do not have much sugar to respire away, so reducing respiration probably won’t do much good.” Moreover, fungal diseases that would respond to fungicides are not a threat in most fields today.

By the same token, applying products said to reduce the “ethylene effects” in stressed plants is unlikely to have a positive effect when there is not enough water to keep open the stomata, which they need to do to allow photosynthesis to take place.

Protecting the crop from anything that reduces effective leaf area, such as applying insecticides if enough insects are present to do damage, can help the corn to retain its potential to fill grain if there is rainfall. Foliar nutrients are unlikely to be of much benefit, and the good canopy color in most fields indicates adequate nutrient levels.

While the focus has been on corn, soybean plants are also showing stress effects. Soybeans planted around April 20 at Urbana are now about 24 inches tall and at stage R2 or full flower. With fair-to-good growth and warm temperatures, soybeans are moving quickly into flowering, with 11 percent blooming by June 24.

“An early start to soybean flowering is generally positive, but we remain concerned about how water shortages might affect soybean pod formation,” Nafziger said.

The period over which new flowers appear will last for up to a month as the soybean plants continue to increase node numbers and stem height, and can even recur if stress is relieved after that. This longer flowering period makes the soybean crop better able to set pods and to start filling seeds even if there is some stress during July.

“But if we continue with little or no rainfall, abortion of flowers or of pods will likely continue,” said Nafziger. As with corn, applying materials promoted to reduce stress in soybeans is not likely to do much good as long as water supply remains inadequate.