Stalk Rot? Precision Irrigation Can Help
This has been a challenging year for many producers with a cold wet spring, followed by drier than normal early season crop growth cycle, then wetter and cooler than normal growing conditions in the later part of the season. The first 10 days of the harvest season were very wet and prevented much harvest progress. When the dry weather came it brought the winds with it. Now many fields are showing considerable lodging which is slowing down the harvest further and decreasing yields because of excessive field losses.
Growers are analyzing the data, looking back at the year, and attempting to figure out what they can do differently to prevent the down corn and field losses we are seeing this year occurring in future years. Most of the lodging has been due to early root/stalk rots followed by high winds. We can’t control the wind but we can look at the plants and our production practices to see if changes are warranted.
The first thing to look at is what causes stalk rot. Although bacterial infections have been increasing, most of the damage we see is due to an opportunistic fungal infection. The infection started because the plant was stressed. Early in the growing season, the plant “made a decision” to produce a certain number of kernels based on the growing conditions at that time. Those kernels all required a certain amount of sugar to reach maturity. Anything that prevented the plant from producing enough sugar to meet the kernel demands required the kernels to take sugar away from that stored in the stalks. The sugar in the stalk acts similar to a person’s white blood cells in their immune system. When that system has been compromised, fungal pathogens can take over and the plant suffers. No different then when people under high levels of stress, end up getting ill.
So, how do we reduce stalk rot? Since most of the stalk rots start in the roots then move up it’s critically important to make sure we keep a healthy root system during the growing season. Roots are the foundation of the plant and without a healthy root system, water and nutrient uptake slow down and the plant get’s stressed. One of the most important factors in ensuring healthy roots is to make sure they have an optimum moisture environment to grow in. Roots will not grow and thrive in a soil that is too dry or too wet. With our irrigation systems, it’s rare that we have fields that are too dry, but fields that are too wet because of over-irrigation are fairly common. (This was very evident in many overwatered soybean fields this year that had higher yielding and much better standing beans in the corners than the irrigated pivot.) For the most part, the pathogens that cause stalk rot are fungi; mold like organisms. Anyone that has ever had mold problems knows what happens when you increase the moisture content of the environment. This year many cornfields had a moist and higher than average humidity environment in August. This was not because we over irrigated for the most part, at least on those using and following their precision irrigation systems agronomist’s advice, but because we had above normal rainfall. That rainfall coupled with lower than normal temps because of reduced sunlight, (National Weather Service at Hastings NE reported 15 days with fog in August which resulted in a 4-degree average temp deficit compared to normal) reduced the sugar production and caused stress on the plant.
It’s not unusual to see distinct spatial patterns with stalk rot and downed corn in the field. For example, you may see much worse conditions on lighter and coarse textured soils. With excessive water, these areas may have leached out their fertility and the plant didn’t have enough during the grain fill period to meet full potential. The heavier textured soil areas are also sometimes worse, depending on field conditions. This is often due to those areas being excessively wet and or compacted and creating an anaerobic, unhealthy root environment, prone to both denitrification and leaching. And, since both heavier and lighter soils are often present in the same field, Variable Rate Irrigation helps tame this variability. A common abiotic cause of lodging in the Midwest are heavy storms that have high winds and driving rains often accompanied by hail that reduces leaf area and photosynthesis, while providing an entry point for pathogen attack. A storm that hit central Nebraska in early August showed the effects of overwatering. Many of the wet areas with compromised roots systems severely lodged because of their unhealthy and limited root development. The pivots that were strategically applying water based on the precision irrigation practice, had very little damage with that storm. Also, lodging can be much worse when stalks are already compromised because of moisture stress (too much or too little), compaction (see photo on left), nutrient imbalances, herbicide damage, or hail. These abiotic stresses reduce the plant’s total green leaf area, which reduces the plant’s ability to use photosynthesis to produce necessary carbohydrates. The physiological remobilization of these carbohydrates from the stalk to the grain, physically weakens the stalk.
Also, diseases such as gray leaf spot, northern corn leaf blight, southern corn leaf blight, Stewart’s leaf blight, yellow leaf blight, and anthracnose similarly reduce the area of photosynthetic leaf tissue, thereby increasing the plant’s susceptibility to stalk rot. Injury to roots, stalks or leaves by nematodes, northern and western corn rootworms and other insects often provide avenues of entry for stalk rot fungi in addition to hail. We can’t control Mother Nature, but we can manage some of the effects and curve balls we are thrown. In the case of managing downed corn for harvest 2017, many problems could be avoided with precision application of water while ensuring a healthy plant, both above and below ground.
There is no sure way to prevent stalk root in a field of corn. But precision irrigation that optimizes the moisture in the root zone can certainly help reduce the damage it causes. For information, see your local Certified CropMetrics Dealer or call 402-512-1850.