Corn Freeze Damage Bill Wiebold

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Corn Freeze Damage Bill Wiebold Powered By Docstoc
					May 26, 2000

          Corn and soybean differ in response to freeze
          by Bill Wiebold

Planting of both corn and soybean occurred earlier than normal this year, and seedlings of
both crops may have been exposed to subfreezing temperatures. One such freeze event
occurred on the morning of May 14. Barb Corwin, director of the MU Extension Plant
Diagnostic Clinic, has received several reports, mostly from the northeastern portion of
Missouri, of frosted corn and soybean seedlings. Normally, plant cells can tolerate air
temperatures below freezing but above 28 degrees F. In-field temperatures can be quite
different from temperatures measured in town, and temperatures at the soil surface can be
several degrees cooler than temperatures measured three or four feet above the soil
surface. Cloud-free nights with little wind allow for radiational cooling and rapid
temperature drops. Because cold air is heavier than warm air, cold air pools in low areas
of the field. Even small depressions can trap the cold air.

A rapid drop in temperature below freezing causes ice crystals to form inside plant cells.
Because water expands with freezing, the ice crystals disrupt cell membranes and cause
cell death. Tissues with frost-killed cells often look watery because cell integrity has been

Both corn and soybean tissues are susceptible to freeze injury. However, the growing
point of corn is below ground for the first three to four weeks of development. The
temperature is seldom cold enough for long enough for the soil to freeze, so the growing
point of corn is protected in all but the most extreme occurrences. Corn should suffer
little yield loss, even if all of the leaf tissue on a V4 plant is destroyed by frost. However,
the field should be monitored to determine if new growth can emerge through the killed
tissue. Unfortunately, a soybean's growing point is exposed from emergence on. Damage
to the growing point of soybean seedlings usually results in plant death. There are
axillary buds on the stem nodes, but these are usually damaged, also.

(Bill Wiebold, 573-882-2001)
Corn photos by: Jenny Smith, Student Assistant, Plant Diagnostic Clinic

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