Corn Lodging Problems Are Not Just Caused by the Weather
Back when I was based in Luzon as a corn agronomist, the first thing that comes to mind when I hear typhoons crossing the northern part is the potential destruction it can bring to many corn areas along with other crops- in the form of floods and crop lodging.
The latter is a very big problem in both low-lying and elevated areas, while the former can only happen along river banks and soils with poor drainage. Flooding is another story, by the way, since no corn can survive under water. Even in the absence of typhoons, strong rains and high winds in some parts of Mindanao can also topple corn plants and lead to serious yield losses. Whirlwinds oftentimes have been reported in the south. Although they’re not as strong as typhoons, the force they bring is enough to cause lodging among taller corn plants and with mature ears.
Scenarios like these happen each season and year, and it is easy to blame the weather. But is this always correct? Yes, high winds can cause stalks to break and roots to give in but more often than not, these problems can only be a confirmation of the stress conditions the corn plants have undergone. Pagdapa in Luzon and hapay in the south can tell us a lot of things other than the hybrid’s genetic defect for poor standability. This article will try to deal with stalk problems in corn and how to deal with it.
Through the process of photosynthesis, plants produce sugars or food by trapping sunlight and carbon dioxide. As soon as these foods are manufactured, plants direct them to actively growing organs. In the early stages, plants move and store them in the roots, converted as structural carbohydrates and proteins in the developing root tissues. As the plant grows, these foods are stored temporarily in the stalks.
During ear development, the plant is pressured to supply great levels of carbohydrates to the ear. If the demand of the developing kernels exceeds the supply produced by the leaves, the stalk and root storage reserves are tapped. In many studies, about 60%-70% of carbohydrates in the stalk are translocated to other parts of the plant but mainly to the ear. This process begins approximately two to three weeks following silking. Extraction of stalk carbohydrates in greater rates can occur with more environmental stresses just to ensure that grain fill rates are preserved at the expense of the stalk.
As stalk and root carbohydrates are mobilized to the ear, these organs begin to collapse and soon lose their defense to soil-borne diseases. With the warm tropical climate that we have, fungi invade and infect the plant. It begins with root rots and then the pathogen moves to attack the stalk. Strictly speaking, although pathogens play a key role in stalk rot development, it is primarily the inability of the plant to provide sufficient food to the developing ear that triggers the process.
Fungal growth in the plant’s vascular tissues can restrict water supply to the plant,_ and as such wilting and premature death of the plant can happen. Discoloration of the lower stalk becomes more and more evident as the deterioration from within ‘progresses. At this point, the plant becomes susceptible to lodging as the structural integrity of the stalk has been greatly diminished. It is here where high winds can provide the force to topple the stalks and somehow confirm the problem that has taken place.
Many corn growing areas in the country can be found among stressful environments where diseases abound and drought conditions prevalent. The upper vega of Cagayan Valley is one such environment where low soil fertility and micro-environment effects heightens the problem on stalk quality in multiple fields. High insect pest pressure and reduced sunlight can likewise lead to poor stalk quality. Even good growing conditions can lead to stalk problems when followed by a less fa- Drought conditions. It was well-favorable environment.
This means that the growing environment has a critical effect on the ability of the plant to provide sufficient food to the developing ear and at the same time preserve the integrity of its stalks and roots. Almost any stress applied to the plant will reduce photosynthesis and its product, which in turn can lead to poor stalks. Here, you will notice that weather effect is just one part of a bigger problem. Let’s briefly tackle each of these stress conditions and why it can lead to serious stalk problems.
Drought conditions. It was well documented that under drought conditions, photosynthesis slows down. Water, which is a vital component during photosynthesis, directly affects the carbon dioxide and oxygen exchange. In addition, when leaves start to roll into “onion leaves” under water stress, the effective leaf surface for collection of sunlight is reduced.
If water was withheld from plants at certain grain-fill stages, photosynthesis can eventually shut down. Grain development, if any, will then depend entirely on the food (carbohydrates) that the stalks had stored previously. Consequently, the stalks and roots shall weaken and lead to infection.
Reduced sunlight. In full sunlight, photosynthesis is in full swing. Photosynthetic rate increases directly with intensity of sunlight. In an overcast or cloudy day, the rate can be reduced by 50% compared to a day of full sun. Prolonged cloudy conditions during ear-fill often result in severely depleted stalk reserves.
Reduction of leaf area. Any reduction in leaf area will definitely restrict photosynthesis. Leaf area may be reduced due to strong winds (leaf shredding), disease lesions, insect feeding or mechanical injury. Whenever functional leaf area is reduced prior to completion of ear fill, stalks will be weakened. A Pioneer study in Pangasinan revealed that severe corn borer infestation led to premature crop drying brought about by severe Fusarium and Charcoal stalk rots.
Favorable conditions, stress during ear fill. While you may have thought that favorable growing conditions early in the season can prevent stalk problems, it should be sustained until grain filling. Otherwise, it can have a negative effect in stalks. With a favorable condition during when the number of kernels per ear is being determined (V 10-V 17). the eventual demand for photosynthate will be large. Each potential kernel represents an additional requirement for moveable sugars from the plant. If stress conditions appear during ear-fill. this will render the plant incapable of producing enough sugars and the stalks will suffer.
Moreover, studies have revealed that the number of kernels per ear on stalk rotted plants is often greater than that of adjacent healthy plants. Again, this confirms that the additional demand for carbohydrates by larger ears often results in greater depletion of the stalk and eventual stalk rot.
It is always healthy to be balance. Research studies had proven that the combination of high nitrogen (N) and low potassium (K) often leads to stalk quality problems. Hence, it is recommended to have a 1:1 ratio for N and K,O to minimize stalk rots and stalk lodging.
The role of N is to increase the kernel number and implies the need for more carbohydrates. N also aids in mobilizing carbohydrates out of the stalks and roots into the ear by increasing the rate of translocation within the plant. On the other hand, K is responsible in the building of leaf and stalk tissues and in regulating water movement within the plant. K is also known to prevent premature plant death and has been described to facilitate photosynthesis.
It is widely accepted that there are hybrid differences when it comes to stalks. Some hybrids naturally distribute more of their food reserves in the stalks rather than in the ears. Although this is beneficial in a bad growing season, this trait may not give the best option for farmers in most normal years (unless it is normal to have lodging every time). It is still best to measure yield across locations and years. Too much emphasis on stalks could lead to lower yields in most years.
Other than stalk strength, growers should likewise screen hybrids for tolerance to leaf and stalk diseases which can significantly impact lodging as well. Hybrids with corn borer resistance like 30T80, 30T44, and 30T35 would have lesser entry points for stalk-rotting pathogens.
It has been observed that hybrids with high yield potential are especially vulnerable to stalk or root lodging as the ear develops and becomes weight-bearing on the plant. The following are some practical tips to minimize stalk lodging problems:
1. Choose the best genetics from Pioneer’s line of hybrids with multiple resistance to diseases and insect pests and with superior stalk strength. Talk to your local Pioneer agronomist.
2. Manage your crops using Pioneer’s proven technology recommendations on balanced fertilization and hybrid-specific planting distance.
3. If practical and where available, irrigate your corn fields during grain-filling stages to satisfy your corn’s needs for photosynthates. Growers in Central Luzon and Mindoro have long known the value that irrigation brings to their crops.
4. Consider the following when harvesting in a lodged field:
a. Lodged fields should generally be harvested as soon as possible, which may be earlier than grain moisture would dictate. The goal is to gather the crop before further reduction of stalk integrity or grain quality.
b. In most situations, it is better to harvest lodged fields before the well-standing fields but on a case-by-case basis. If better-standing corn is ready for harvest, it may be more efficient and cost effective in some cases to harvest it first, before lodging increases there.
c. If lodging is extreme, it may not be profitable to harvest the field especially if it is water soaked for more than 2-3 days.
d. Try to look at the cost. Handharvesting of lodged fields will certainly be more expensive if any labor can be made available for you. Just make sure that the field can still give 80% of your normal yield. Losses can be greater in fields with lodging occurring at younger stages.