Drought-stressed corn - Considerations when harvesting for grain
Corn harvest is slowly beginning in parts of Kansas. Harvest may present some challenges when drought is a major factor.
Drought-stressed corn may have high levels of aflatoxin (see companion article in this eUpdate). Aflatoxin levels may increase during storage if the corn is held very long at moisture levels above 14 percent. Growers intending storage for more than a week or two should have the corn tested for aflatoxin. Corn testing above 100 ppb should probably not be stored long-term.
Ears may drop more easily in corn that has gone through drought, especially during grain fill. Some causes of increased ear drop include:
- The ear shank may not develop normally in stressed conditions.
- Rapid drydown may result in brittle tissue where the ear attaches.
- A “pinched shank” or constriction on one side of the shank may occur. This is usually associated with missing kernels on the bottom of the ear on the same side as the pinch.
- Hybrid differences. For example, some hybrids may have a smaller-diameter shank attachment.
- Fusarium stalk rot (pink stalk rot) may infect the ear shank, causing deterioration of the tissues and greater numbers of dropped ears.
Droughty conditions, especially during grain fill, can predispose corn to a number of stalk rots, which in turn may result in stalk lodging. 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.
We often find stalk rot disease organisms (charcoal rot, Fusarium, Gibberella, anthracnose, and others) on corn with stalk lodging. Although stalk rot is often the ultimate cause of lodging, in most cases, the stalk rot diseases were only able to infect the plants because certain other factors predisposed the plants to disease infection. Such factors include:
* 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 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 early in the season; severe drought; and soil compaction all can result in small, 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 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 plant densities. Plants can become tall and thin when plant densities 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 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 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.
Where corn has been under drought stress, there is increased likelihood for small kernels, dropped ears, stalk lodging, and grain toxins. In this situation, it is especially important that corn is harvested in a timely manner and with a well-adjusted combine after a dry growing season.
Ignacio Ciampitti, Cropping Systems and Crop Production Specialist
Doug Jardine, Extension Plant Pathologist
Stu Duncan, Northeast Area Crops and Soils Specialist