Stalk lodging, by definition, is the breakage of the stalk below the ear. Severely lodged corn leads to increased harvest losses, increased harvest time, increased drying cost, and may result in volunteer corn the following year. Annual yield losses due to stalk lodging in the U.S. range between 5 and 25%. In addition to outright yield losses, grain quality may also decline as a result of stalk lodging.
There are three main causes of late-season stalk lodging in corn. Severe weather is a major cause. Hard driving rains accompanied by strong winds and/or hail can devastate a bumper crop in a matter of minutes. Another major cause is the European corn borer, particularly the second generation, which tunnels into the stalk or ear shank and can cause stalk breakage or ear droppage. Early-planted corn is most susceptible to first-generation attack, and late-planted corn to second-generation attack. Information about controlling this insect pest can be found in the publication E-17, "European Corn Borer," available from your local Cooperative Extension Service educator. The third major cause of stalk lodging, also important from a management standpoint, is stalk rot. Stalk rot decreases the corn plant's ability to resist external stress by weakening the stalk tissue and results in a plant more susceptible to stalk breakage.
The incidence and severity of stalk rot in any given field depends on the susceptibility of the corn hybrid, the presence and virulence of the stalk rot organisms, and an environment conducive to formation of the disease. These three conditions, the host, the pathogen, and the environment, must be present simultaneously in order for the stalk rot to develop. All three can be partially controlled by management. For example, you can choose hybrids with high levels of disease resistance, or you can partially control the growing environment by making appropriate cultural management decisions.
For the purposes of this publication, we will restrict our discussion to stalk rot-induced stalk lodging which occurs after physiological maturity. Physiological maturity is that point in time when the kernels reach maximum dry weight and a layer of black cells forms near the base of the mature kernels. This black layer can be used to identify the occurrence of physiological maturity. Moisture content of the grain is approximately 30-35% at this time.
The objectives of this publication are: 1) to describe the relationship between plant stress, plant sugars, and stalk rot, 2) to provide the corn producer with preventive management options to help minimize the risk of stalk lodging due to stalk rot, and 3) to provide the corn producer with harvest management options when stalk lodging has already occurred.
Predicting the occurrence of stalk rot and stalk lodging is difficult for farmer and scientist alike. Although hybrids vary in genetic resistance against stalk rot organisms, a small amount of stalk rot will occur in every hybrid. Similarly, one field may develop stalk rot while an adjacent one does not. Or part of a field may have severe stalk rot while the rest of it is free of the disease.
A sad fact of life is that almost any kind of plant stress, occurring almost any time during the growing season, can predispose the corn plant to invasion by stalk rot fungi. James Dodd, plant pathologist for the Seed Division of Cargill, Inc., has developed a concept which helps explain the complex relationship between plant stress and stalk lodging. Environmental stress generally affects a corn plant in one or both of two ways. Stress prior to pollination slows the rate of photosynthesis, which, in turn, slows the plant growth rate, resulting in a smaller than normal plant. Stress after pollination, when the plant is fully grown, causes a reduction in photosynthesis.
During grain fill, plants which are smaller than normal or which are under post-pollination stress produce smaller amounts of plant sugars in the leaves than healthy non-stressed plants. Since the developing ear usually has priority over the rest of the plant for receipt of available plant sugars, this deprives the lower stalk and roots of sugars and causes the defense mechanism against stalk rot fungi to break down.
In fact, not only can the lower stalk and roots be deprived of sugars, but sometimes the existing stored sugars in these plant tissues are remobilized to the ear. This makes the stalk rot potential even greater. As the roots begin to die, stalk rot can invade the root tissue, and the plant wilts because of insufficient water uptake. The rate of photosynthesis suffers due to the wilting, and carbohydrate translocation to the grain is increased. As all of the above occurs, stalk rotting organisms begin to decay stalk tissue.
The important point for you, as the manager of a corn field, is to realize that you can take appropriate preventive management steps to minimize plant stress conditions which impose an imbalance between photosynthetic carbohydrate production and sugar remobilization during grain fill. This will help prevent conditions conducive to the development of stalk rot and, subsequently, stalk lodging.
Factors that can cause environmental stress and increase the potential for stalk lodging in a corn crop include high plant populations, extremes in soil moisture, nutrient deficiencies and/or imbalances, insect damage, cropping sequence, and hybrid susceptibility. These factors can increase the incidence of lodging directly or indirectly by influencing the amount of stalk rot that occurs.
Cause. Plant population levels that are too high decrease the amount of light in the crop canopy and cause the corn plants to become tall and thin. The physical strength of the corn stalk under these conditions is significantly reduced. 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.
Control. In order to prevent stalk lodging, use seeding rates which promote high yield without causing unnecessary competition for light, nutrients, or water. Proper plant population levels will also increase the efficient utilization of the soil water that is available. For most situations in Indiana, this would mean a final plant stand between 20,000 and 24,000 plants per acre for dent corn and between 28,000 and 30,000 plants per acre for popcorn. Plant populations lower than these levels will further reduce stalk lodging; however, grain yields may also be less than optimum.
Cause. Extremes in soil moisture can increase the occurrence of stalk lodging. Excessive soil moisture retards root growth and development, leading to a less than optimum root system which cannot adequately support plant growth. On the other hand, drouthy conditions stress the crop and enhance the development of stalk rot by reducing movement of sugars to the root system.
Control. Good drainage, natural or man-made, is important for minimizing plant stress due to water-logged soil conditions. Well-drained soils warm up faster than wet soils in the spring, provide for improved root growth and development, reduce the potential for denitrification of soil nitrogen, reduce runoff of rainfall, and allow improved timeliness of field operations.
The potential for stalk lodging can be reduced by early planting because of more efficient utilization of late-spring and early-summer solar radiation and rainfall. In addition, early-planted corn will usually be shorter than that planted later and will stand better later in the season. An additional benefit to early planting is the yield advantage over corn planted later in May.
Where it is practical, irrigation can reduce the potential for drought stress and consequently can reduce the incidence of stalk rot and stalk lodging. If you do irrigate, you should continue to provide water as needed during the complete grain filling period (50 to 60 days after silking) until physiological maturity is reached. Information on irrigation scheduling can be found in NCH-20, "Irrigation Scheduling for Corn-Why and How," available from your local Cooperative Extension Service educator.
Cause. Nutrient imbalances and/or deficiencies predispose corn plants to stalk rot and stalk lodging. For example, high nitrogen fertility levels coupled with low potassium levels enhance the potential for stalk rot. High nitrogen levels enhance lush vegetative growth, while low potassium levels increase the amount of premature stalk death. Together, these conditions produce an ideal situation for stalk rot and lodging. Conversely, low levels of soil nitrogen may result in less vigorous plants which put all their available energy into producing grain. This leaves the stalk vulnerable to stalk rot organisms and, ultimately, stalk lodging.
Control. Proper use of soil tests can reduce the risk of stalk lodging by encouraging the maintenance of balanced soil nutrient levels. Phosphorus and potassium applications should be based on well-conducted soil sampling and analysis.
Cause. 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. Corn rootworm larvae decrease the amount of water and nutrient uptake by feeding on the roots, whereas the European corn borer damages the stalk by feeding on the pith and the vascular tissue. In either situation, the corn plant is placed under physiological stress, which favors both stalk rot development and stalk lodging. These insects can also encourage the development of stalk rots by reducing the photosynthetic area of the plant, causing wounds through which pathogens enter stalks and roots, and carrying disease inoculum into tissues.
Control. It is to your advantage to minimize the risk of damage by these insects. In corn following corn, seriously consider the use of a soil-applied insecticide for control of corn rootworm larvae. Growers who rotate corn and soybeans annually will seldom need to use a rootworm soil insecticide. Corn borer damage can be reduced by avoiding, if possible, extremely early or late planting. Additional information about controlling these insect pests can be found in the publications E-49, "Managing Corn Rootworm," and E-17, "European Corn Borer," available from your local Cooperative Extension Service educator.
Cause. Cultural practices which increase the amount of disease or insect pressure can also increase the amount of lodging that occurs in the corn crop. Leaving disease-infected corn stubble on the soil surface through reduced tillage methods can increase the incidence of stalk rot and stalk lodging in monoculture. Continuous cropping of corn also enhances the potential for insect problems such as European corn borer and corn rootworm.
Control. Crop rotation is especially important for disease control when you are practicing some form of reduced tillage. In corn following corn, pathogens can overwinter in the organic debris and infect corn the following year. Rotating corn after other crops can also lead to yield increases of 5-7% regardless of diseases present.
Cause. Beware of the so-called "super-yielding" hybrids available in the marketplace, because these tend to also have very poor stalk strength. Quite often, weak stalks are a result of the plant cannibalizing and remobilizing sugars out of the lower stalk to feed the super-yielding ear.
Control. Corn hybrids which are best adapted to intensive management are those hybrids which lodge the least. Important traits that these hybrids share include resistance to stalk rot, excellent genetic stalk strength, short stature, and quick dry down. Resistance to stalk rot generally means resistance to prevalent leaf diseases and the ability to maintain stalk vigor (stay-green potential) late into the season. Pay strict attention to lodging scores given in yield trials. If you wish to capitalize on the "super yield" of these varieties, plan on harvesting them shortly after physiological maturity (about 30% moisture). An adapted mid- to full-season hybrid will generally provide the best combination of high yield and lodging resistance, especially if the corn remains in the field for any length of time late in the fall.
If, after taking precautions to avoid stalk lodging, it still occurs, you do have some options on how to manage the crop to minimize harvest loss.
Inspect Fields. Producers should inspect susceptible fields regularly during late August and early September to estimate the rate of development of stalk rots which may be present. Observations should be made within the field away from the outside rows. To estimate how much stalk rot is present, pinch stalks near the ground and up toward the ear on a number of plants in a sampling area. A hollow shell that collapses easily indicates advanced stages of stalk rot. Also determine to what extent there is any infestation of European corn borer. Choose your sampling areas to adequately reflect soil types, soil drainage patterns, hybrids, rainfall differences, and soil fertility levels.
Identify the extent of the problem. Is it isolated in only one area of a field, or is it spread evenly throughout the field? Also, is only one field affected, or are all fields affected? Once you have determined the extent of the problem, consider the following harvest options.
Harvest the affected areas first. Do not allow lodged fields to remain unharvested any longer than absolutely necessary. Think seriously about harvesting lodged areas earlier than normal, provided that the grain is physiologically mature.
Harvest the affected areas slower than usual. A ground speed of 2 mph is usually adequate for harvesting lodged corn. By harvesting at a slower speed, your ability to pick up lodged ears that would otherwise be missed will increase. Gathering-chain speeds and snapping-roll velocity should be correspondingly reduced to maintain the normal relationship with ground speed. Obviously, picker- or combine-snouts and gathering chains should be run as closely to the ground as possible to pick up downed corn.
Under severe stalk lodging conditions, harvest against the direction of the lodging. For example, if the corn plants are lodged toward the east, come into the field from the east. Harvesting the field from the west will only lodge the plants further, making it almost impossible to pick up the ears. Some farmers indicate that they adjust the gathering chains and the rolls inward as closely as possible, to adequately grip rotten stalks with no center core. These stalks collapse to a thickness of approximately 1/8 inch when squeezed
While the cultural and harvest management options above will help you reduce the harvest losses you incur during the current growing season, you need to evaluate why certain fields or areas of fields lodged. Think carefully about the causes discussed earlier. Did you make the best choices as to hybrid selection, fertility levels, plant populations, pest control, or cultural practices? If not, which factors can be changed to avoid the problem next year?
For additional information and publications on other aspects of crop production systems, contact your local Cooperative Extension Service educator.
Cooperative Extension work in Agriculture and Home Economics, state of Indiana, Purdue University, and U.S. Department of Agriculture Cooperating; H.A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914. The Cooperative Extension Service of Purdue University is an affirmative action/equal opportunity institution.