I am beginning to get reports that corn is lodging this year. What is particularly alarming is that stalk lodging is occurring in fields with hybrids that typically have very strong stalks. And, even more perplexing, when stalks are split open, they appear to look healthy however the pith is gone right above the node where the stalk lodged over. Many farmers are asking how this can happen.

Typically, weaker stalks result from smaller root systems. This leads to less nutrients going into the plant to satisfy the high demand for carbohydrates of the grain. If the roots bring in less nutrients than the demand of the grain then the grain will pull the carbohydrates it requires from the leaves and stalk. This creates hollowed out pockets above the nodes, which weaken the stalk, and predispose stalks to lodging whenever we get strong winds.

Below, I have put together some talking points that can be helpful in diagnosing weak stalks that may be found in your fields this harvest season.

The most effective management practice at this point in the season is to monitor fields and determine the level of weak stalks in the field. Randomly walk each field and test stalk strength of 50-100 plants by squeezing the stalk at the lower two internodes. If the stalk collapses between the thumb and forefinger of 25 or more plants, weak stalks have advanced to problem levels. These fields are at high risk to wind damage and should be harvested first to decrease lost yield from unharvestable ears.

#1 Wet Spring (late planting, small roots, side-wall compaction, N loss, and poor potassium uptake)
Corn plants have smaller than normal root systems this year. Later planting did not allow the plants time to generate roots that will reach water deep in the soil profile. In addition, when soils are wet, sidewall compaction at planting time can cause nutrient deficiencies later in the season, particularly nitrogen and potassium.  We probably lost some applied nitrogen due to wet conditions early. In essence, the plant will do all it can to “pump” carbohydrates into the kernels, sometimes at the expense of the health and maintenance of other plant parts including the roots and lower stalk.

#2 Dry periods (drought) during grain fill
Fields subjected to several weeks without rain will stress the plant and cause the plant to move nutients from the stalk into the ear to fill the grain.  This weakens the plant to the point that lodging can occur. Additionally, pathogens can invade and infect the plant causing premature plant death, dropped ears, lightweight grain and encourage the development of stalk rot.

#3 Cooler temperatures and cloudy conditions during grain fill
Cooler temperatures and cloudy days during grain fill can reduce sunlight to the leaf area that provides carbohydrates to the developing kernels. As a result, the corn plant draws reserves from the stalk tissue. The mobilization of nutrients our of the stalk creates hollowed out pockets which weaken stalks and can predispose the plant to stalk rot diseases.

With late plantings and a wet spring, this year has created disease conditions in areas with:

• Wet, humid soils combined with recent high temperatures
• Fields with high residue
• Reduced or no-till ground

Anthracnose is among the diseases that thrive in these conditions. It’s caused by a fungus and can affect the plant at any stage of growth. Look for these symptoms: leaf blight, stalk rot, top-kill of the stalk, and kernel rot. The disease causes the most problems at the leaf blight and stalk rot stages.

ABOVE: Anthracnose leaf blight (Ohio State University)

ABOVE: Anthracnose stalk rot (Ohio State University)

Grey Leaf Spot can be easily confused with other types of disease in its first stages of development. The tell-tale sign for this disease is small lesions surrounded by yellow rings or halos. The fungus will begin in the lower leaves and move to the top of the plant. Lesions travel through the tissues in the leaf, elongating and eventually merging together. The plants then become much more susceptible to other disease such as stalk rot.

ABOVE: Gray Leaf Spot

Northern Leaf Spot is a fungal disease that, like Grey Leaf Spot (GLS), is identifiable by its narrow elongated shaped lesions surrounded by a pigmented border. The disease will spread to all parts of the plant including leaves, sheaths, husks, and ears. Spores are released and are capable of traveling and infecting neighboring fields.

ABOVE: Northern leaf spot (Ohio State University)

For each of these specific diseases, I recommend control methods of fungicides or resistant/tolerant hybrids. For more information on these and other mid-season corn diseases, Purdue University’s Desktop Reference link is a great resource.