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Early fall frost

corn field with brown leaves
Figure 1: A mid-September frost affects corn in Dakota County. The field’s lower elevations show increased upper canopy damage.

Frost can mean yield loss for corn producers, although the severity of frost damage greatly varies based on local climate conditions, crop maturity and topographical features.

A corn killing freeze occurs when temperatures dip to 32 degrees Fahrenheit for four hours or 28 degrees for minutes. A frost or killing freeze can still happen with temperatures above 32, especially in low and unprotected areas when there’s no wind.

Symptoms of frost damage and severity

Frost more easily damages corn leaves than stalks. In addition, leaves above the ears are more susceptible to injury than leaves below the ear.

Frost-damaged leaves initially appear water-soaked (Figure 2). They’re light green to gray after drying and later turn brown.

Wait a few days before scouting fields to assess the frost’s impact. If the frost is not severe enough to cause the kernel black layer to prematurely form, kernels will continue to accumulate dry matter by translocating sugars from the stalk and remaining green leaf area.

corn plant with wilted leaves
Figure 2: Frost damage near Nicollet on Sept. 13, 2014. Note how the corn leaves appear water-soaked.

How frost affects corn

Due to the variable nature of natural frost, yield loss estimates are quite difficult to come by. Yield and quality reductions depend on the crop stage when frost occurs and the frost’s severity.

Frost damage to corn reduces grain and silage yields, grain test weight and silage quality (Table 1). If frost damages leaves above the ear, but leaves below the ear are unharmed, then expect yield losses slightly less than those listed in Table 1, which only shows leaf damage.

Photos: How to tell a corn plant’s development stage and whether it’s reached black layer

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Jeff Coulter, Extension agronomist; Dave Nicolai, Extension educator and Phyllis Bongard, Extension communications specialist

Reviewed in 2018

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