Source: Doug Jardine, Extension Plant Pathologist and Kraig Roozeboom, Cropping Systems and Crop Production Specialist, Kansas State University
Stalk lodging in corn occurs when the stalk weakens and breaks at some point below the ear. When this occurs, it results in harvest losses and slows down harvesting considerably. Grain moisture levels may also be unacceptably high in lodged corn.
When looking for the causes of stalk lodging, many first look at either stalk rot diseases or corn borer damage. In fact, we often find stalk rot disease organisms (charcoal rot, Fusarium, Gibberella, anthracnose, and others) in corn with stalk lodging; and stalk rot is often the ultimate cause of lodging. In most cases, however, the stalk rot diseases were only able to infect the plants because certain other factors predisposed the plants to disease infection. We must look deeper for the primary causes.
What are the most common causes of stalk lodging in corn throughout the state?
- Carbohydrate depletion in the stalk during grain fill. Higher-yielding, "racehorse" hybrids tend to produce super-high 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. This weakens the lower stalk until eventually it will break over, possibly after becoming infected with a stalk rot disease. This doesn't mean producers should stay away from the racehorse 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 30-35 percent moisture. This can result in discounts for high moisture, but it's better than leaving those hybrids in the field so long that stalk lodging occurs.
- Hybrid differences in stalk strength or stalk rot susceptibility. Some hybrids have genetically stronger stalks than others. This is often related to a hybrid's yield potential, as mentioned above, and how it allocates carbohydrates during grain fill. But there are also genetic differences in stalk strength due to other reasons, including better resistance to stalk rot diseases. If a field of corn has stalk lodging problems, it could be due in part to hybrid selection.
- Poor root growth and other stresses. Cold, waterlogged soils, severe drought, and soil compaction can all result in short, inadequate root systems. Under these conditions, the roots may not be able to effectively extract enough water and nutrients from 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.
- Poor leaf health. Any factor that results in poor leaf health, such as gray leaf spot or spider mites, will reduce carbohydrate production during the season. If overall carbohydrate reserves in the plants are low when grain fill begins, stalk integrity will often suffer as the available supply of carbohydrates moves into grain production. Maintaining good leaf health is important in minimizing stalk rots. The more photosynthesis, the less need for the plant to tap stalk reserves. Stay green characteristics in hybrids are highly correlated to stalk rot resistance and reduced lodging.
- High populations. Plants can become tall and thin when populations are too high, which can result in thin stalks with inadequate strength. 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 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.
- 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.