Please see the article below by Dr. Dan Fromme on the impact of flooding on Louisiana corn.
Please see the article below by Dr. Dan Fromme on the impact of flooding on Louisiana corn.
by: Beatrix Haggard and Josh Lofton
The drying conditions in recent days have resulted in a percentage of corn finally being planted. While most producers are focused on planting, these intense planting conditions will result in a short window for N fertilization. With this narrowed window between planting and N fertilization, it is time to start thinking about N management. In recent years, conditions at or near fertilization have resulted in high potential loss of applied N. These losses not only are detrimental to the surrounding environments but also to the production system, resulting in insufficient available N supply to the crop. The use of N inhibitors has been an increasingly common production practice in an attempt to minimize in-season losses. While the use of N inhibitors is a valuable tool for potentially decreasing N loss, proper management and proper selection are critical to decrease losses successfully.
Selection of the proper inhibitor is potentially the most critical aspect and can be challenging because of the numerous options available. Determining the right inhibitor varies, depending on N source, N application method, and field/environment.
Chemical names to ask for:
Figure 1. Untreated urea at 240 lbs N/acre.
Figure 2. Super U urea at 240 lbs N/acre (NBPT and DCD).
Urease inhibitors function by inhibiting the urease enzyme, a natural enzyme in the soil system that hydrolyzes urea into ammonium. By doing this, urease inhibitors attempt to minimize volatilization losses during periods favorable to volatilization (dry, windy, urea on surface). When environmental conditions exist, namely moisture, urease inhibitor activity is diminished, allowing the urease enzyme to break down the urea. Urease inhibitors work very well with granular fertilizers because these are frequently surface-applied with limited to no incorporation. With surface application of granular fertilizers, volatilization is the primary potential loss, at least during early season when adequate moisture does not exist. However, these inhibitors are not only beneficial on granular fertilizers. Substantial volatilization can occur with liquid fertilizers that are surface-applied in warm, dry conditions with little soil moisture. When these same fertilizers are incorporated, such as being knifed-in in lieu of surface-applied, as little as 1-5% of applied N is typically lost through volatilization. Therefore, urease inhibitors are most effective when urea-containing fertilizers are surface-applied, whether liquid or granular, without incorporation.
Nitrification inhibitors function by inhibiting the soil bacteria, which are required for nitrification to occur. Inhibiting nitrification keeps more N as ammonium for longer periods of time. This is beneficial because it can limit or minimize both leaching and volatilization losses, both of which occur as nitrate compared to ammonium. These inhibitors have the potential to be the most universally beneficial in high rainfall and irrigated systems especially. However, the benefit of these products has not been widespread in research trials conducted across the Mid-South. A two-year study conducted at the LSU AgCenter, however, did show that these inhibitors can be beneficial in Louisiana systems. The best management of these inhibitors is to know their limitations. Research conducted at the LSU AgCenter as well as other research around the US indicate that these products last only 10-30 days. Therefore, these inhibitors provide early season “protection” of the N fertilizer, but N can still be lost after the nitrification inhibitor has degraded.
Unlike the other inhibitors, coated-fertilizers do not inhibit any process within the soils system but slowly release N from the coated source throughout the season. By slowly releasing N into the soil system, these inhibitors minimize only the amount of N applied that can be lost through individual loss mechanisms. These N sources are promising at minimizing both volatilization, denitrification and leaching. However, few if any coated liquid sources are currently or will be commercially available in the near future. Therefore, these must be used solely on granular fertilizer sources. Additionally, because the fertilizer is slowly available, N available from the applied fertilizer during early season growth is minimal. Therefore, high amounts of residual soil N need to be available, or supplemental N fertilizer needs to be supplied.
Nitrogen inhibitor products have the potential to be very beneficial tools at managing N fertilizer additions in Louisiana production systems. However, if mismanaged, not only do you lose the benefit of applied inhibitors but also narrow the economic potential of the production system. Therefore, time needs to be given to selection of a particular inhibitor to fit the system as well as proper management within the production system.
If you have any further questions, please contact your local extension agent or specialist.
Beatrix Haggard, Upland Row-Crops Soil Fertility Specialist – (318)498-2967
Josh Lofton, Agronomist – (318) 498-1934
Josh Lofton and Dan Fromme, LSU AgCenter
Over the past several days Louisiana has experienced some severe weather across the state. Most notable was the severe weather of August 11. Damage from this storm has been felt from northern Louisiana through the rice-growing areas of southern Louisiana. While reports of hail have been sporadic, damage from wind and heavy rains have been the primary concern. Unfortunately, with the rains that have been experienced across the region in the past several weeks, little of the corn crop has been harvested. This means that a large portion of the state’s crop was at risk for this damage. Driving across the state, many fields have been spared damage; however, others have not. Damage includes lodging of the tops of the plants to complete stalk lodging. At this stage in the corn growth cycle, anything short of complete stalk lodging should be of minimal concern, and there should be little effect on final yields. However, greater concern may be warranted for those with more intense lodging.
The next couple of days will determine how damaging complete stalk lodging will be. At this stage, corn lodging will not correct itself as it will at earlier vegetative stages. However, with most modern day harvesting equipment, producers will be able to capture most of what is currently on the ground. Where the problem arises is with the rain associated with the windy conditions. Lodged corn lying in standing water will begin to be an issue as time progresses. Not only will this corn not dry like the rest of the crop, seed sprout will start to develop. This sprouted seed will maintain relatively high moisture, and dockage will be incurred if high rates of sprouted seed develop. Therefore, it will begin to be essential that these spots dry in the coming days.
While it seems the extent of this damage will be minimal across the state, yield losses on affected fields will be more substantial. Conditions will not be fully known for the next several days.
For further questions or comments, contact:
Dan Fromme, Corn and Cotton Extension Specialist, firstname.lastname@example.org
Josh Lofton, Research Agronomist, email@example.com
Primary Author: Clayton Hollier, Plant Pathologist, Department of Plant Pathology and Crop Physiology
Boyd Padgett, Regional Director and Plant Pathologist, Central Region
Trey Price, Plant Pathologist, Macon Ridge Research Station
We have scouted several corn fields concerning reports of southern corn rust (SCR). These reports and field visits reveal an epidemic of southern rust across the state but in particular in the south central and central corn growing regions. Field surveys indicate that SCR has been reported in 25 of 64 parishes and might be in more that have yet to be surveyed. The LSU AgCenter does not recommend an automatic fungicide application to corn. However, when disease epidemics are progressing up to and including the soft dough stage, an application of a labeled fungicide can protect yield and quality and still be economically viable.
Ideally, fungicides should be applied prior to disease onset, but realistically, fungicides are usually applied at or just after onset. Therefore, individuals should make efforts to detect and treat diseases as early as possible to prevent losses to yield and quality. When it is determined an application is needed, a premix fungicide will offer wide spectrum activity (examples are: Headline AMP, Stratego YLD, Quilt, and Quilt Xcel). Follow label instructions for application timings, rates, etc. In most cases, a single application at tassel is justified when disease is present and active. The decision to apply a fungicide should be made on a field-by-field basis. The remainder of this newsletter will address disease identification and management considerations.
Southern corn rust can be found in Louisiana corn fields every year, but its impact on grain quality and yield is dependent on several variables. Although there is some level of resistance, it seems very low. The hybrids considered resistant to SCR in the past are no longer considered resistant, due to new race development found in Georgia four years ago. Therefore, the decision to manage SCR with fungicides should be based on a solid understanding of disease initiation and development. While this disease rarely develops to statewide damaging levels in most years, disease incidence and severity in individual fields may warrant a fungicide application. However, before applying a fungicide, several factors need to be considered. These include disease identification, environmental conditions favoring disease development, and the relationship between disease severity and yield loss.
Southern corn rust is caused by the fungus Puccinia polysora. Initial infections are caused by wind-blown spores. This is a warmer-season rust and, therefore, usually occurs late season and does not always have adequate time to affect yield. However, this rust is very aggressive and if disease epidemics initiate early (prior to or at tasseling), yields could be reduced.
Conditions favoring development include temperatures between 80 degreesF and 90 degrees F with high relative humidity or abundant rainfall. Once established, the spores can survive, spread and germinate at temperatures up to 104 degrees F.
Southern rust produces small circular to oval pustules and contains orange to light brown spores (Figure 1). Pustules are usually more abundant on the upper leaf surface and may also be found on the leaf sheath and husks when disease is severe.
Risk and Management
Risk to disease is influenced by several factors including genetic resistance, tillage practices, planting date, and environmental conditions. Later planted corn can also heighten risk to SCR.
The first line of defense for managing any corn disease should be selecting a disease-resistant hybrid. Since commercially available resistance is not an option, a fungicide may be needed. However, when SCR is not present a fungicide is not necessary. Another factor to consider is when SCR epidemics initiate relative to crop growth stage. The potential for yield loss is high when SCR develops prior to tasseling and conditions remain favorable for development during the growing season. When the rust initiates after tasseling, the potential for disease loss decreases.
The relationship of yield and defoliation can be found in Table 1 adapted from the National Crop Insurance Service’s Corn Loss Instruction.
Table 1. Estimated % corn grain yield loss due to defoliation at various growth stages.
Adapted from the National Crop Insurance Service’s Corn Loss Instruction to represent the leaf collar growth staging method. Included in the Mississippi State University, Grain Crops Update June 4, 2010, Erick Larson.
This spring has brought us cool weather, wet/dry spells, and now potassium deficiencies. We have mainly been hearing about corn and soybean potassium deficiencies on the Macon Ridge. However, this does not mean that they are not showing up throughout our alluvial soils.
Potassium is very important for water use efficiency in crops. This means that irrigation on the fields showing deficiency symptoms will need to be managed diligently. There are a few reasons that symptoms could be showing up: 1) Dry soils, 2) Compaction, 3) Low soil test K, and 4) Reduced early-season root growth. Potassium cannot be taken up efficiently in the soil without the presence of water, which can cause a deficiency to appear even if adequate potassium was applied to the soil. Compaction can also cause a potassium deficiency to appear because the roots are not able to find enough potassium in the un-compacted soil. If a soil sample is collected and the results show that the soil is low in potassium, then the recommended amount of potassium should be applied after the current cropping season. Lastly, due to some of the weather that was experienced this spring, there could have been reduced root growth in spots affected by standing water or cold weather. This reduced root growth creates a smaller zone of potassium available to the plants.
Deficiency symptoms in corn and soybeans are denoted by edge of leaf necrosis.
Currently, the LSU AgCenter soil fertility research group does not currently have data on the yield benefits of foliar-applied potassium. Furthermore, research throughout the region has shown little to no yield benefits for foliar potassium applications. Additionally, if yield benefits are seen, there is a chance that the cost of application will often outweigh any yield benefit. Therefore, caution should be used prior to any in-season foliar potassium application. If a foliar K is going to be added, follow the label carefully due to the chance of leaf burn.
If you have any questions, please contact:
Beatrix Haggard, Northeast Region Soil Specialist: (318) 498-2967
Josh Lofton, Agronomist: (318) 498-1934
Dan Fromme, Corn and Cotton Specialist: (318)880-8079
Josh Lofton, Field Crop Agronomist, Macon Ridge Research Station
Beatrix Haggard, Soil Specialist, Northeast Region
Dan Fromme, Corn and Cotton Specialist, Dean Lee Research Station
As the weather around the state is finally transitioning from spring to summer conditions, the corn crop has seen abundant growth in the past several weeks. With these increasing temperatures, it can also be expected that the number and severity of thunderstorms will continue to increase. Two major concerns with these increased thunderstorms for the corn crop are wind and hail damage. With the current corn crop beginning to reach critical growth and developmental stages, it is often wondered how much yield loss can be associated with these potential injuries. While the answer to this question seems somewhat straightforward, there are many factors that determine how detrimental the injury will be and how much yield loss can be expected.
When looking from a turn-row at a field that has been dam
aged by wind itmay appear that all wind damage is similar; however, this is far from the truth. Root lodging appears as the entire stalk has been blown over at the ground level with the roots appearing to be dislodged from the soil surface. This occurs when soil from heavy rainfall events becomes saturated and the roots can no longer support the corn stalk. While this may appear to be very detrimental to the corn crop, oftentimes, given good growing conditions following the event, the crop will reroot and the crop will continue to grow upward. In later growth stages, these stalks can be identified with having a more “goose necked” appearance. While the damage this lodging will have on yields will not be understood until harvest, root-lodged corn often looks worse immediately following the lodging event than the related yield damage; this is especially true prior to reproductive growth.
Snapped corn is a more severe effect of wind damage (often referredto a “green snap”). This effect can be seen after the emergence of the growth point from the soil surface. However, it is more common during late-vegetative or early-reproductive growth when high biomass is paired with high winds. Unlike root lodging, it is unlikely a plant that has experienced green snap will recover from the injury. However, the overall effect on field scale yield will vary based on how widespread the damage is and what stage the crop was when damage occurred. Studies from Iowa State University indicated that when green snap occurs early in the season, prior to V8, yield losses expected should be less than 15 percent. This is due to the ability of many of our modern corn hybrids with flex to adjust seed set. Prior to V8 stage, both ear size and kernel set, which occur from V8 through V14, have often not been fully determined. Therefore, with decreased surrounding competition, these plants have the potential to produce larger ears to compensate for the losses. However, when snapped corn occurs during late-vegetative or early-reproductive stages, both the severity and the yield impact are often higher with as much as 50 percent yield loss expected in severely damaged corn.
Hail, in addition to tremendous rain potential and damaging winds, can also be a damaging aspect. Hail damage can be very disheartening since the visual damage is often worse than it really is. With this being said, it is best to not attempt to evaluate a hail-damaged field the day of or the day following the event. Corn has an amazing ability to recover from damage, especially during early-season growth. Evaluation of these fields should be delayed until favorable growing conditions with adequate moisture have returned. This will allow the manager to determine which plants have recommenced growth and which have not. After these conditions have returned, managers can cut down the center of the stalk and look at the growing point. When determining the yield reduction of hail damage, two aspects should be considered: 1) stand loss and 2) reduction in photosynthetic leaf area. During early-season growth, if the growing point is firm and white, these plants are likely to survive; however, if the growing point has lost firmness or has turned brown or light grey, severe damage has occurred and the plant is not likely to survive.
The primary loss of yield due to hail damage comes from loss of leaf area. However, determining leaf area damage can often be challenging. Two critical aspects in determining how this reduction in leaf area can influence yield are: 1) percent defoliation and 2) growth stage in which the damage occurred. Determining the percent defoliation is probably the most challenging aspect. Often, even minimal to slight defoliation can appear to be severe defoliation. Evaluate damaged leaves compared to undamaged leaves to try to minimize the bias nature of this estimate. Once percent defoliation is determined, growth stage at which the event occurred will be needed. Often, following a hail event, growers and managers will scout the field the day of the event or the day following and growth stage should be evident. However, if time occurs between the hail event and scouting, in general, corn leaf emergence occurs at 1 leaf per 80 GDD prior to V10 and one leaf per 50 GDD after. Once these two aspects are determined, Table 1 can be used to assess potential yield reductions due to loss of photosynthetic tissue.
Table 1. Estimation of percent grain yield loss associated with leaf area defoliation. (Adapted from National Corn Handbook, Climate and Weather, Vorst 1993).
Damage from severe storms can be a very disheartening time. Luckily, the damage is rarely widespread, and therefore field- and farm-scale yield losses will be minimal. Currently, there have only been scattered reports of either hail or wind damage during the 2014 season, but we can expect storms to continue throughout the year.
For further questions regarding damage throughout the season, feel free to contact:
Dan Fromme, Corn and Cotton Specialist, 318-427-4424
Josh Lofton, Field Crop Agronomist, 318-498-1934
Dan Fromme, Beatrix Haggard, and Josh Lofton
LSU AgCenter Agronomists
During the past weekend, portions of our corn-producing areas received in excess of 6-8 inches of rainfall, which has created flooding in corn fields. A significant portion of the state’s corn fields are between emergence and the 2-3 leaf stage. Corn is extremely vulnerable to flooding prior to the 6-leaf stage or when the growing point is near or below the soil surface. Two to four days of flooded conditions is the most that corn can survive when it is less than the 6-leaf stage. After about 48 hours of flooding, the oxygen supply in the soil is depleted. With oxygen being depleted, the corn plants cannot perform or sustain important functions such as nutrient and water uptake, which is being impaired and inhibiting root growth.
Air temperature is an important factor for the survival of corn under flooded conditions. When warm temperatures greater than 77 degrees F are experienced, corn may not survive even 24 hours. Cooler temperatures prolong the survival, and once the growing point is above the water level, the likelihood for survival improves greatly.
Also, just because corn plants survive a flood in their early stages of development, there still might be a long-term negative impact on crop development and ultimately yield at the end of the season. An overabundance of soil moisture during the early vegetative stages retards corn root development. The implications occur later on during the growing season when it becomes dry and the root systems are not adequately developed to access available subsoil water. Also, be aware that flooding can result in losses of nitrogen through denitrification and leaching.
Overall, crop injury to flooding of less than 48 hours should be limited. To check plants for survival, the color of the growing point should be white and cream colored. A growing point that is darkening or is softening usually precedes plant death (Figure 1). Be sure to look for new growth three to five days after water drains from the field.
Figure 1. Corn plant in the V2, early V3 stage of growth and the location of the growing point in relation to the soil surface.
Another issue related to flooding is disease problems such as crazy top. This disease develops when soils have been flooded shortly after planting or before plants are in the 4-5 true leaf stage. Saturation for 24-48 hours is sufficient for infection to occur.
In addition to corn growth and development, those producers who have already applied N may have to worry about the amount of fertilizer lost during these saturated periods. While N loss during these saturated events often occurs, the amount of N loss varies highly with environmental conditions and management practices. Nitrogen loss can occur through leaching (downward movement of N within the profile) or denitrification (the gaseous loss of N to the atmosphere). Both loss mechanisms occur on soil nitrate, with very little to no loss mechanisms with the ammonium or urea forms. This makes application source one of the most critical aspects. With most producers applying some form of UAN, at application, 25% of the application rate is in the nitrate form and, in turn, susceptible to loss. Of the other 75%, 25% is in the ammonium form and 50% is urea. While both the ammonium and urea forms are less susceptible to saturated losses, the transformation from ammonium to nitrate can occur very rapidly in most soils. Therefore, application timing is also a critical aspect. Fertilizer that has been recently applied is less likely to have a large portion of ammonium transform to nitrate and, therefore, less likely to be lost. However, application seven to 14 days ago can result in higher levels of nitrate in the soil and, in turn, higher potential loss.
Environmental conditions can also influence the amount of N lost during saturation events. When these events occur in warmer conditions, high N can be lost more rapidly than during cooler conditions. Soil microbes responsible for denitrification losses have increased activity with higher temperatures. Luckily, most of the areas that have experienced these saturated conditions have remained cool. Cooler conditions require these fields to be saturated longer for substantial N loss to occur.
Limited information is currently available on the use of “rescue” N application to account for any potential N losses. Oftentimes, if the system has been saturated for long enough for substantial N loss to occur, corn yield potential will also be negatively affected. While it is difficult to follow these events, the best management would be to allow the corn to bounce back and re-evaluate N needs as the corn recommences growth. If additional “rescue” N application is needed, oftentimes mid- or late-season application will suffice.
For further questions contact:
Dan Fromme, Corn and Cotton Specialist, firstname.lastname@example.org
Josh Lofton, Field Crop Agronomist, email@example.com