Last night light frost occurred throughout most of Wisconsin. Corn is killed when temperatures are near 32 F for a few hours, and when temperatures are near 28 F for a few minutes. A damaging frost can occur when temperatures are slightly above 32 F and conditions are optimum for rapid heat loss from the leaves to the atmosphere, i.e. clear skies, low humidity, no wind.

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 grain yield losses after frost.
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