Early Corn Problems During a Cool, Wet Spring Conditions

Heather Darby and Sid Bosworth, Extension Assistant Professor, UVM Extension - Northwest Region and Extension Associate Professor, Department of Plant and Soil Science, University of Vermont heather.darby@uvm.edu

Cool, wet spring weather generally slows the growth and development of early emerging corn often resulting in a wide array of colors including purple, purplish-red, yellow, white, and even striped.  This off-color corn is not unexpected under such conditions.  Below is a description of some of the symptoms and causes observed in Vermont during cool, wet spring and early summer periods.

Purpling in corn results from the accumulation of a purple pigment called anthocyanin.  During this time of the year, accumulation of anthocyanin in corn is caused by two factors.  The first factor is a genetic response to weather conditions.  Some hybrids will produce anthocyanin (resulting in purple plants) as a genetic response to cool nights following bright, sunny days.  The second factor is restricted root development in conjunction with a buildup of sugars produced by photosynthesis.  These sugars build-up in the leaves and stem of the plant because the roots are not growing fast enough to allow the sugars to move into them.  This in turn triggers anthocyanin production resulting in purple plants.  The cause of root restriction will generally indicate whether or not yield losses are experienced.  If restricted root development is due to cool temperatures then the purpling should disappear as the plant develops and yield losses should be minimal.

If the cause of root restriction continues to affect root growth (e.g. compaction, herbicides, insect feeding) than purpling may continue to affect plant growth and some yield loss may result.  Digging up plant roots and looking for abnormalities such as clubbed (indication of compaction or herbicide damage) or pruned roots (indication of insect feeding) can give some indication of what may be causing restricted root growth.  Phosphorous deficiency can also cause purple color in leaves; however, phosphorous deficiency is not usually diagnosed as the primary cause of purple plants early in the season.

Yellow corn can also be a result of  cool, wet conditions.  Corn plants turn pale green to yellow because they have not been able to absorb enough nitrogen. When soils are cool and wet, the plant cannot efficiently collect nitrogen from the soil.  The good news about yellow corn is that the plant will grow out of it. When warmer conditions arrive, plants will green up and grow normally.  Extra nutrients are not needed.  White corn is occasionally due to herbicide damage from glyphosphate (e.g. Roundup) or clomazone (e.g. Command).  Single, random white plants in a field are generally genetic mutants.

Twisted growth of corn whorls is an oddity growers should look out for as the weather goes from cool to hot.  Twisted growth of corn is caused by the inability of older leaves to relax quickly enough to allow younger leaves to push up through the center of the whorl.  When the whorls eventually unfurl, yellow, crinkly leaves will be seen in the field.  These are the young leaves that were unable to photosynthesize in the twisted whorl.  These plants will green up after a few days of sun.  Generally very little yield loss is associated with twisted growth.

Zinc deficiency symptoms can also be exacerbated by cool weather although it can also show up under a wide range of weather conditions.  Plants are usually stunted and there is a white stripe along the midrib often more pronounced on one side compared to the other.  Symptoms can occur due to low Zn levels in the soil but also will show up when acid soils are limed to a pH of 7.0 causing a sudden reduction in Zn availability.

The weather forecast for warm temperatures and sunshine will likely alleviate most discoloration and malformities of corn plants.  However, keep in mind regular scouting of corn in the early season will help identify problems that are not temporary (i.e. compaction, insect damage).  Refer to Assessing Field Corn Soon After Emergence for more information on early corn scouting.


This site is maintained by Sid.Bosworth@uvm.edu, Plant & Soil Science Department, University of Vermont.

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