Way Too Early Prediction: Weak Corn Stalks this Fall

Chad Lee, Extension Agronomist, University of Kentucky
Carrie Knott, Extension Agronomist, University of Kentucky

The 2015 growing season has been wetter than normal with reasonable temperatures. Over 80% of the corn crop and over 70% of the soybean crop are rated good to excellent in the most recent USDA crop progress report. This should be a time to celebrate and enjoy the good fortunes to this point.

We could see weak corn stalks this fall. It's still too early to predict, but several factors make me think it could be an issue. Below are reasons why we could have weak stalks

Reasons to scout corn for stalk strength

Excellent yields are expected in many corn fields this growing season.  Along with that good news comes concerns over stalk strength.  Plants in many fields have heavy ears, along with shallow roots because of abundant rainfall.  Many of these plants could topple easily as they mature, especially if a late-season storm with high winds blows across the field.  Plus, several extended periods of cloudy weather during grain fill may have increased the risk of stalk weakness in some fields.  This is because, when the corn plant is filling grain, if leaves cannot meet the carbohydrate demand of the grain, the plant may “cannibalize” carbohydrates in stalks in order to fill the grain.

Similarly, infectious diseases may play a role in increasing stalk weakness, by depriving the plant of healthy foliage necessary to maintain stalk strength through crop maturity.  Gray leaf spot (Figures 1-2) is prevalent this year, although levels generally appear to be low to moderate.

Figure 1. Lesions of gray leaf spot, viewed by holding up to the sky. Some hybrids develop an obvious yellow border around these infections, as shown here.

Figure 2. Lesions of gray leaf spot in a highly susceptible variety. They are often described as "match-stick" lesions.

  

I have also observed scattered fields with significant damage from northern leaf blight (Figure 3).  Given the generally mild, wet weather this season, this isn’t surprising.

Figure 3. Lesions of northern leaf blight, with high levels of control by a strobilurin fungicide

Although southern rust has been present in Kentucky for over a month, some cool weather experienced in recent weeks has helped suppress disease activity.  This disease may still contribute to weakened stalks in some late-planted fields, but in general, it appears we have “escaped” widespread damage from this disease this year, especially if cool nights predominate.

Scouting for stalk lodging

Check for stalk weakness by walking the field and pushing plants about 1 ½ feet from vertical.  Those that fail to spring back exhibit lodging potential.  If 10-15% or more of the field show lodging potential, it may be wise to schedule that field for early harvest, before it is laid down by strong winds.