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.
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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont.University of Vermont Extension and U.S. Department of Agriculture, cooperating, offer education and employment to everyone without regard to race, color, national origin, sex, religion, age, disability, political beliefs, or marital or familial status
Last modified May 26 2004 01:29 PM