Stalk lodging in corn occurs when the stalk weakens and breaks at some point below the ear (Figure 1). When this occurs, it results in harvest losses and slows down harvesting considerably. Grain moisture levels may also be unacceptably high in lodged corn.
Figure 1. Stalk rot in corn at Kansas River Valley Experiment Field, 2016. Photo by Eric Adee, K-State Research and Extension.
Two common causes of stalk lodging are stalk rot diseases and corn borer damage. Stalk rotting diseases in Kansas include charcoal rot, Fusarium, Gibberella, anthracnose, and Diplodia. Stalk rotting diseases are present in the soil or on old crop debris every year, but disease only develops when certain other factors predispose the plants to disease infection.
What are the common causes of stalk lodging in corn in Kansas?
Carbohydrate depletion in the stalk during grain fill. High-yielding, “racehorse” hybrids tend to produce superior yields at the expense of late-season stalk integrity. These hybrids translocate a high percentage of carbohydrates from the stalks to the ears during grain fill. The latter is reflected in a substantial reduction in the stalk diameter from flowering until maturity (stem shrinking process). This weakens the lower stalk until it eventually breaks over, possibly after becoming infected with a stalk rot disease. However, this does not mean producers should stay away from these hybrids. These hybrids have to be managed well. They should be harvested early, shortly after physiological maturity. This may mean harvesting the corn at about 20-25 percent grain moisture. Early harvest can result in discounts for high moisture, but it is better than leaving those hybrids in the field so long that stalks break.
Hybrid differences in stalk strength or stalk rot susceptibility. Some hybrids have genetically stronger stalks than others do. This is often related to a hybrid’s yield potential, as mentioned above, and how it allocates carbohydrates during grain fill. However, there are genetic differences in stalk strength for other reasons, including better resistance to stalk rot diseases. If a field of corn has stalk lodging problems, it could be partly due to hybrid selection.
Poor root growth and other stresses. Cold, waterlogged soils, severe drought (a critical factor for this season), and soil compaction can all result in short, inadequate root systems and crowns that are damaged to the point that water and nutrients cannot effectively move through them. Under these conditions, the roots may not extract enough water and nutrients from the soil to support plant growth and carbohydrate production. When carbohydrate production is below normal during any part of the growing season, the ears will continue to take what they need during grain fill, which can leave the stalks depleted even under average yield conditions. The developing ear always has priority for carbohydrates within the plant.
Tar spot of corn. Tar spot is an emerging disease in Kansas that can affect stalk rot (Figure 2).
Any factor that results in poor leaf health will reduce carbohydrate production. When carbohydrate production from photosynthesis is inadequate due to loss of green leaf area in the leaves, the plant will mobilize reserves from the crown and lower stalk to complete grain fill (see carbohydrate depletion above).
Figure 2. Premature leaf death caused by severe levels of tar spot on corn. Photo courtesy of Rodrigo Onofre. K-State Research and Extension.
Many hybrids lack good resistance to tar spot, and producers should be ready to apply a fungicide when the disease is active and in the corn canopy. More information tar spot, including the best time to apply fungicide, can be found in a companion article in this issue of the Agronomy eUpdate.
High plant density. Plants become tall and thin when supra-optimal populations are used, which results in thin stalks with inadequate strength (Figure 3). In addition, plant-to-plant competition for light, nutrients, and water enhances the competition for carbohydrates between the stalk and ear within the plant, thus reducing the vigor of the cells in the stalk and predisposing them to invasion by stalk rot.
Nutrient imbalances and/or deficiencies. Nutrient imbalances and/or deficiencies predispose corn plants to stalk rot and stalk lodging. Both potassium and chloride deficiency have been shown to reduce stalk quality and strength and stalk rot resistance. High nitrogen levels coupled with low potassium levels increase the amount of premature stalk death and create an ideal situation for stalk rot and lodging. Soil chloride levels should be maintained above 20 lbs per acre.
Figure 3. High plant density corn presenting late-season stalk lodging. Photo by Ignacio Ciampitti, K-State Research and Extension.
Corn rootworm and corn borers. Damage caused by the corn rootworm and the European corn borer can predispose the corn plant to invasion by stalk rotting organisms, as well as lead to outright yield loss.
Mid-season hail damage. Similar to the damage caused by insects, the physical damage caused by mid-season hail can set up the plant for invasion by stalk rotting organisms. Stalk bruising and the resulting internal damage may also physically weaken corn stalks, making them more likely to lodge later in the season.
Rodrigo Borba Onofre, Extension Row Crop Plant Pathologist
Ignacio Ciampitti, Farming Systems