What is a killing frost in corn?

September 5, 1996 3(24):142

Joe Lauer, Corn Agronomist

Corn will be killed when temperatures are near 32 °F for a few hours, and when temperatures are near 28 °F for a few minutes. Less damaging frost can occur when temperatures are around 32 ° F and conditions are optimum for rapid heat loss from the leaves to the atmosphere, i.e. clear skies, low humidity, no wind, and low lying areas. The stem on a corn plant is a temporary storage organ for material that eventually moves into the kernels. Grain yield will continue to increase about 7 to 20% after a light frost that only kills the leaves as long as the stem is not killed (Table 1).

Table 1. Potential impact of frost on grain yield.
Corn development Killing frost
(Leaves and stalk)
Light frost
(Leaves only)
stage percent yield loss
R4 (Soft dough) 55 35
R5 (Dent) 40 25
R5.5 (50% kernel milk) 12 5
R6 (Black layer) 0 0
derived from Afuakwa and Crookston, 1984

Afuakwa, J.J., and R.K. Crookston. 1984. Using the kernel milk line to visually monitor grain maturity in maize. Crop Sci. 24:687-691.

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