Source: Kraig Roozeboom, Crop Production and Cropping Systems Specialist, Doug Jardine, Extension Plant Pathology, and Scott Chapman, Post Rock District Extension Agent, Kansas State University
With the cool, wet weather in much of Kansas during May, much of the corn planted in April or early May was not looking too good by the third week of May. Emergence was often very slow, and plants that had emerged were growing slowly and did not have the deep green color we like to see. Unfortunately, some fields never emerged adequately and had to be replanted — more than once in some cases in eastern Kansas.
With the warmer temperatures and sunshine in late May and early June, much of the corn has taken off and is now developing quite well. However, reports have come during the week of May 31-June 4 about fields that still do not look quite right. In one instance in Lincoln County, a somewhat eroded, terraced upland field had many plants with interveinal yellowing that looked like a potential nutrient deficiency. This interveinal yellowing, plus a general stunting of the plants, appeared in large patches in the field. The smallest, most severely affected plants (some with purpling) were found in the terrace channels.
It was not until the stalks were split that the likely cause of the symptoms became apparent. The discoloration in the crown area at the base of the stalk in the photograph below is often associated with chilling injury or cold weather crown stress.
Similar symptoms were observed in 2007 when we also had an extended period of cool, wet conditions when the corn was in the V1 to V5 stages.
Several days of wet, cool conditions can limit oxygen availability to the crown, slowing normal growth and causing gray-brown discoloration. The damaged crown disrupts nutrient flow to leaves, causing nutrient deficiency symptoms. Affected corn plants will continue to grow but will be smaller, will yield less, and will be more prone to stalk rot if it is hot and dry in August. Southern-germplasm hybrids are typically more susceptible to this problem than northern-type hybrids.