This edition covers current crop progress and issues, recommended fungicide rates and timings, shortage of Sercadis, and stink bug BMP’s.
Rootless corn has appeared in many fields during the early part of the 2016 growing season in Louisiana. Most are all of the nodal roots are missing in corn that is at the V1 to V2 stage. Existing nodal roots may be stubby and not anchored to the soil. Without an adequate root system, affected plants may be lodged, wilted, stunted, or even die (Figures 1 and 2).
Rootless corn phenomenon is currently attributed to the excessive amounts of rainfall which has eroded the soil near the plant base and/or the strong winds we have experienced breaking the upper roots and hindered the establishment of a strong root system.
Also, many fields currently have a hard packed soil surface from heavy rainfall which has hindered the establishments of the nodal root system penetrating into the soil. Other situations where rootless corn syndrome can occur are under hot and dry conditions on the soil surface, planting too shallow, compacted soils, and loose or cloddy soils.
These symptoms are unlike any associated with herbicide or insect feeding injury. Several sets of roots may not have formed below-ground, the crown may appear to be at or above the surface.
The important thing to remember is that roots will not develop in dry soil. They will not grow toward moisture. Plants can recover if rainfall is received which will soften the soil surface and promote nodal root development. Also, row cultivation may encourage root development if moist soil is thrown around the bases of the plant.
Cover crops can provide producers a variety of benefits from nutrient cycling and soil cover to nitrogen fixation and pollinator food sources. Cover crops come in many varieties including grasses, legumes and brassicas, however; cover crops maintain a “green bridge” throughout the fall and early spring that may facilitate the movement of pest insects into above and below ground plant structures.
Seedling corn, in Louisiana, is often adversely affected by many factors including excess moisture, cold temperatures and a complex of above/below ground insect pests. The complex of underground insects includes southern corn rootworm, wireworms and white grubs, while the above ground complex includes sugarcane beetles, chinch bugs and cutworms. Most of these insects require a food source that is present in fields for them to successfully overwinter and subsequently begin reproduction when temperatures begin to warm in the spring. The inherent benefits of cover crops often include the presence of large volumes of biomass and an abundant root structure that anchors soil or penetrates a hard pan. Yet, these attributes make cover crops an ideal source for the buildup of yield limiting insects.
Insecticide seed treatments (ISTs) are neonicotinoid based insecticides that coat the outer layer of the seed offering protection from below and above ground early season insect pests. The systemic nature of ISTs make these compounds water soluble and facilitate the vascular movement of the insecticide into the plant tissue. The value of ISTs in Louisiana varies among crops and environmental conditions, most agricultural commodities will usually not benefit from ISTs when planted under optimal environmental conditions (adequate soil temperature, optimal soil moisture and low pest pressure). However, insecticide seed treatments will typically produce an economic benefit when conditions are sub-optimal including very late or early planting, reduced tillage field arrangements, double cropping systems (soybeans behind wheat), pests that are present every year and consecutive plantings (i.e., corn behind corn). In addition to the above mentioned situations, data from the LSU AgCenter’s Macon Ridge Research Station confirmed the need of an IST when corn is planted behind cover crops (Figure 1). A statistically significant increase in yield was observed in corn treated with Poncho 500 IST in Berseen Clover, Crimson Clover and Hairy Vetch while a significantly lower yield was measured in corn planted behind Tillage Radishes treated with the IST (Figure 1). No fungicide seed treatment was used in this study. The measurable difference in yield may be due to the presence of below ground insects that also produced a notable decrease in vigor (Figure 2). Unfortunately for producers, there are no rescue treatments available for below ground insect injury in corn or any other agriculturally managed crop in Louisiana. Therefore, the use of an IST can help safely and effectively control below above and below ground insect pests in corn planted behind cover crops.
Aside from the use of ISTs, there are other management practices that can be done to minimize the effects of pest insects, from cover crops, on corn. Burning down cover crops in a timely fashion (6 weeks before planting) will provide enough time for available biomass above the soil to dessicate and force any harbored insects off of the plants. Yet, this timing may not allow enough time for below ground insects to cycle out or succumb to a lack of forage. Earlier burn down timings and the use of minimum tillage may allow enough time for insects to cycle out or be physically removed or destroyed with implements. If you elect to destroy your cover crops earlier than intended, check with your local NRCS representative or LSU AgCenter county agent to ensure enough time has passed that your preplant intentions are met (ie. Nitrogen fixation, nutrient cycling, etc.).
The use of ISTs is a best management practice recommended by the LSU AgCenter and will help ensure your crop is protected from yield limiting insects. The use of ISTs is highly recommended if you choose to plant corn behind cover crops particularly Berseen Clover, Crimson Clover and Hairy Vetch. If you have any questions or concerns please contact your local LSU AgCenter extension service.
By Dustin Harrell
Since writing the article yesterday that discussed estimating nitrogen (N) losses in corn following flooding events (http://louisianacrops.com/2016/03/18/corn-with-all-the-flooding-how-much-nitrogen-have-you-lost/), many new questions have been raised by producers. They are concerned that young corn will need to have the N replaced quickly after the flooding waters drain off fields in order to replace lost N and maximize the yield potential of the corn. This is a valid concern especially if little N is left in the soil after the floods recede or if N has not been applied at all and the corn is reaching the rapid vegetative growth stages. For example, a 200-bushel-per-acre corn crop will take up approximately 200 pounds of N during the growth and development of the crop. Seedling corn, prior to the V6 stage of development (6th leaf collar) will take up very little N, approximately 5% of its seasonal need. However, from V6 to VT (tasseling) corn will take up approximately 60% of its seasonal needs, or about 120 pounds of N for a 200-bushel corn crop. If that N is not available during that rapid growth period (approximately 30 days), then yield losses are certain to occur.
As the flood waters recede, many producers have questions about the best way to replenish the lost fertilizer N quickly to avoid yield losses. Most soils in north Louisiana are too wet to apply N with ground rigs, so that removes the potential to band or knife-in liquid N fertilizers. The only application method currently available to supply a large rate of N is to surface broadcast granular N fertilizer sources such as ammonium sulfate (21-0-0-24) and urea (46-0-0). Urea is less expensive than ammonium sulfate per pound of N; however, it also has the potential to volatilize. The volatility potential of ammonium sulfate is minimal. Volatilization is the conversion of ammonium (a solid) to
ammonia (a gas), which will be lost to the atmosphere. Trials evaluating urea volatility potential of N fertilizers have been conducted at the H. Rouse Caffey Rice Research Station over the past several years. Trials have shown that 30% or more of the N from urea surface broadcast on a dry soil can be lost by ammonia volatilization in a 10-day period of time. Of course, rates of volatilization can vary considerably across soil types. Typically, higher pH soils will have a greater N volatility potential as compared to acidic soil. Treating urea with a urease inhibitor with the active ingredient NBPT or NPPT will protect the urea from volatilization for a given amount of time, depending on soil properties and environmental conditions. In the same studies mentioned above, urease inhibitors greatly reduced ammonia volatility for a 10-day period when applied onto a dry soil. Incorporation of urea into the soil by irrigation or rainfall will minimize volatilization losses. Therefore, if incorporating N into the soil by irrigation or rainfall soon after application is not a possibility, then a urease inhibitor is recommended.
Surface soil moisture will have a tremendous effect on the volatility potential of urea. Typically, urea applied on a dry soil will begin to slowly volatilize initially, but the rate of volatilization really takes off around three days after application. When urea is applied onto a soil that is saturated (without standing water), the rate of volatilization will begin much quicker, and the potential for volatilization losses over a given period of time will be much higher. Figure 1 above, which came from a volatilization trial conducted at the Rice Research Station in 2014, illustrates this phenomenon.
Addition of a urease inhibitor will help in reducing the amount of volatilization losses when urea is applied on a soil without standing water. However, the protection time is generally cut in half. Therefore, the 10-day protection time may only be five days if applied on a moist soil. If the urease inhibitor treated urea is dropped into standing water, the NBPT will not give you any protection.
With all that said, if the soil is too wet for ground equipment and your corn needs N as soon as possible, then you must choose between applying granular ammonium sulfate and urea by air. If urea is your fertilizer of choice, then it is best to wait to apply the N (from an N-efficiency standpoint) when the surface of the soil becomes dry. Applications of urea treated with a urease inhibitor will enable applications onto a soil with a wet soil surface without significant N losses for a few days. Expect large losses of N from urea if it is not treated with a urease inhibitor and it is applied onto a soil with a moist soil surface. Expect even greater losses of N from urea if it is applied into standing water.
The rainfall events that occurred last week have caused tremendous damage to northeast Louisiana farm land due to flooding. In addition to the water received from the rainfall events, some farms were inundated with even more water as nearby bayous and rivers overflowed a few days later. Many of the hardest hit farming operations are still trying to save equipment, livestock, and assets from the rising flood waters. Some farming operations situated on higher ground, such as the Macon Ridge, may have been spared from the flooding but were still affected from the excessive rainfall nonetheless. One of the most commonly asked questions I have been receiving lately is: How much of my nitrogen (N) fertilizer have I lost in my corn crop? Unfortunately, the question is not that straight forward to answer. You really have to consider several factors. What N source did you use? Was it surface broadcast, was it incorporated in after application, was it banded in the soil (knifed-in), or was it dribbled on the soil surface? What was the soil moisture like at the time of application? How long after the fertilizer application did the flooding conditions occur? Was a urease or nitrification inhibitor used? Just to name a few.
Let’s begin by considering the N fertilizer source. First, we need to remember that nitrate-N is not stable under flooded, anaerobic (no oxygen) conditions and that it will be converted to a gas and lost very quickly by a process called denitrification. Ammonium-N, on the other hand, is stable under flooded, anaerobic conditions and will not be lost. Many farmers in northeast Louisiana use granular urea (46-0-0) or liquid UAN (urea ammonium nitrate; 32-0-0) as their N fertilizer source. The granular urea will be converted into the ammonium form after application through a process called hydrolysis. Therefore, if the flooding occurred quickly after urea application, most of the N will not be lost because it will be in the urea or ammonium form and will remain stable under flooded conditions. UAN on the other hand is made up of both urea and ammonium nitrate. The nitrate portion of UAN is approximately 25% while urea and ammonium-N make up the other 75%. Therefore, we would expect 25% of the N that is in the nitrate form to be lost very quickly after flooding.
Now let’s consider the amount of time that the fertilizer N was applied prior to flooding. Ammonium can be converted to nitrate under aerobic (oxygen present) conditions by a process called nitrification. The longer ammonium fertilizer was applied prior to flooding, the more of the ammonium will be converted to nitrate through a process called nitrification. The rate of nitrification depends on several factors including soil type, presence of nitrifying bacteria, and the temperature of the soil. Research has shown a wide range of nitrification rates based on the aforementioned soil properties, so for our purposes let’s assume that the average nitrification rate under cooler soil temperatures (<65oF) would be about 2.5% per day and under warmer soil temperatures the average rate would be at least 4.5% per day.
Another thing we have to consider is whether or not a urease inhibitor or a nitrification inhibitor was applied on the granular fertilizer or mixed in with the liquid N fertilizer. A urease inhibitor (active ingredient NBPT or NPPT) will temporarily delay the conversion of urea to ammonium form (urea hydrolysis) and will therefore temporarily delay volatilization losses (conversion of ammonium-N to ammonia, a gas) and subsequent nitrification reactions (conversion of ammonium to nitrate). Nitrification inhibitors (active ingredients nitrapyrin or DCD) will temporarily delay only the nitrification process. Urease inhibitors and nitrification inhibitors will not last forever. Research at the H. Rouse Caffey Rice Research Station has shown that urease inhibitors will typically give you protection for approximately 10 days when applied on a dry soil, approximately five days when applied on a moist soil, and will provide no protection when applied into standing water. Recent research out of northeast Louisiana indicated that nitrification inhibitors can give you protection 10-30 days, depending on the environmental and soil factors involved.
Using the N source, nitrification rate, and the addition of a urease or nitrification inhibitor, we can begin to estimate how much N will be lost under various scenarios.
Scenario 1. A corn farmer on the Macon Ridge knifed-in UAN at a rate of 200 pounds of N just after planting. The UAN was not treated with a urease or nitrification inhibitor. Saturated soil conditions occurred 12 days after planting and lasted for 2 days. The soil temperature was <65oF. How much N was lost?
Well, we know right away that 25% of the UAN is in the nitrate form and will be lost under saturated, anaerobic conditions. We also know that we have had 12 days for nitrification (conversion of ammonium to nitrate) to occur in a cool soil and that a nitrification or urease inhibitor was not used, so the nitrification rate will be about 2.5% per day.
Therefore, the N loses from denitrification = (0.25 * 200 lb N/A) + (12 days * 0.025 * 200 lb N/A) = 80 pounds of N per acre lost.
Scenario 2: Granular urea (46-0-0) was treated with a urease inhibitor and was applied on moist ground 3 days after planting at a rate of 50 pounds N per acre. A one-half inch rain occurred 2-days later that incorporated the urea into the soil, minimizing volatilization (ammonia gas) losses from the urea. Flooding conditions occurred 15 days later and the field stayed under water for four days. The soil temperature was <65oF. How much N was lost?
This time all of the N is in the urea form to begin with and was protected from volatilization losses prior to the small incorporating rain. However, the urease inhibitor probably only kept the fertilizer in the urea form for approximately 5 days before it was converted into the ammonium form. Nitrification (conversion of ammonium to nitrate) could then occur for about 10 days.
Therefore, the loss of N from denitrification = 10 days * 0.025 * 50 lb N/A = 12.5 pounds of N per acre lost. In addition, I would expect that the corn would not be able to survive this situation and would have to be replanted.
Remember, these N loss estimates are not perfect. There are a lot of factors involved in estimating N loses that were not covered and it could be argued that the rates of nitrification or the time that a urease or nitrification inhibitor could differ depending on the research you use as your source. However, it is a good starting point and should help growers in northeast Louisiana determine how much N will be available in the soil once saturated soils dry and flood waters recede.
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:
- Urease inhibitors – NBPT (N-(n-butyl)thiophosphoric triamide), or NPPT (N-(n-propyl)thiophosphoric triamide)
- Nitrification Inhibitors – Nitrapyrin, or DCD (dicyandiamide)
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 Steve Harrison, LSU AgCenter
As much of the state is just gearing up for harvest of corn, soybeans and grain sorghum, it is time to start preparing for the state’s wheat crop. While wheat planting is still months away, it is this early season management that begins to determine the yield potential for the upcoming season.
Choosing varieties for the upcoming season is potentially your most important decision prior to planting. Most producers agree that grain yield is the most important criterion for variety selection. However, there are many aspects of grain yield that need to be evaluated when selecting varieties. Two-year average yields give some indication of stability. This not only demonstrates the performance of varieties across various growing environments but also attempts to minimize environmental influence on variety performance (i.e. current year was better for early- or late-maturing varieties). Additionally, test weight is important because varieties with low test weight may result in the producer being docked at the mill. Therefore, when evaluating variety yield performance, it is essential to use as many parameters as possible.
Heading day, plant height, lodging and disease susceptibility are also important selection criteria. Heading day allows producers to gauge relative maturity of the individual variety. Early-heading and maturing varieties permit earlier harvest and timelier planting in a double-cropping system, while later-heading varieties guard against damage from a late spring freeze and can be planted a little earlier. Early-heading varieties should be planted in the second half of the recommended planting window to avoid the likelihood of spring freeze damage. Lodging resistance helps in some years. Intense storms can occur during late grain fill and cause severe lodging, which results in lower test weight, decreased yields and lower harvest efficiency. Disease susceptibility is very important in terms of yield and profitability. It should be noted that varieties less susceptible to disease may not always produce the highest yields, especially if disease pressure is not present. However, in high disease pressure situations, the resistance may result in higher yields as well as enhanced profitability by saving the costs of fungicide applications. Therefore, managers and producers must weigh the benefits of disease susceptibility with potential yields.
Planting dates for Louisiana wheat depend on location and variety. For southern and central Louisiana optimum planting dates range from November 1 through November 30. The optimum planting for northern Louisiana is slightly earlier, ranging from October 15 through November 15. Early-heading varieties should generally be planted after the mid-date, while late-heading varieties can be pushed a little on the early side of the planting window. The weather in north Louisiana is cooler in the fall and early winter, which slows growth and prevents excess winter growth. It is important that the wheat crop be well-established and fully tillered before going dormant in the coldest part of the winter. Additionally, because of the cooler conditions, the threat for fall pests (Hessian fly, army worms and rust) are decreased earlier in the fall compared to south and central Louisiana. While these dates are the optimum planting window averaged over years, the timing will vary in some years depending on weather patterns. Additionally, if wheat cannot be planted within these optimum windows, planting later than the optimum window would be preferred. Early planting can result in greater insect and fall rust establishment and also makes plants more prone to spring freeze injury due to excessive fall growth and development. Planting too late (more than 14 days after the optimum window) can result in significant stand loss due to slow emergence and seed rotting and can decrease yield potential due to poor tillering and decreased canopy density.
Wheat can be planted by broadcasting seed and incorporating; however, it is preferred that the seed be drilled. Drilling the seed increases the uniformity of depth and stand. If drill seeding, wheat should be planted at a rate of 60 to 90 pounds per acre of high quality seed into a good seedbed with adequate moisture. If the seed is broadcast, seeding rates should be increased to 90 to 120 pounds of high quality seed to account for decreased germination and emergence. This higher seeding rate should be adapted for conditions in which high germination or emergence is not expected, as with late-planted wheat or heavy, wet soils. Late-planted seed should be planted at a higher seeding rate using a drill to ensure rapid, adequate and uniform emergence.
Nitrogen fertilization of wheat can be a challenging aspect of production. Total N application should normally range from 90 to 120 pounds per acre, but this will vary depending on soil type and rainfall after applications. Timing of N application depends on several factors. The wheat crop needs adequate N in the fall and early winter to establish ground cover and properly tiller; however, excessive levels of fall N can result in rank growth and increased lodging potential, as well as a higher probability of spring freeze damage from early heading. If the wheat crop is following soybeans, soil residual or mineralizable N should be adequate for fall growth, and no pre-plant N is needed. However, if the wheat crop follows corn, sorghum, rice or cotton, the application of 15 to 20 pounds of N per acre would typically be beneficial. Where the wheat crop is planted later than optimum, additional N may be necessary to ensure adequate fall growth prior to winter conditions. If the wheat crop did not receive a fall application and appears to be suffering from N deficiency in January, the initial topdress N application can be made early to promote additional tillering. Early spring is when the majority of N for the wheat crop should be applied. There is no universal rule on how early spring N should be applied. Each field should be evaluated based on tillering, stage of development, environmental conditions and crop color. A crop that has good growth and good color should not need N fertilization prior to erect leaf sheath (Feekes 5), usually sometime in February. However, first spring fertilizer application should be applied prior to first node (Feekes 6) in order to ensure optimum head development, tiller retention and head size. Crop N stress around jointing (Feekes 6) will result in yield losses. Any additional N applied following flag leaf typically contributes very little to crop yield. Splitting topdress N into two or three applications is common in Louisiana production systems due to the increased risk of N losses often associated with heavy rainfall and our long growing season. Splitting N typically occurs by applying fertilizer N at or just prior to jointing with a second application occurring 14 to 28 days later. About 50 percent of the topdress N is normally applied with the first split, but this may be decreased if the first split is put out early and plants are not well enough developed to take up that much N.
Phosphorus, K, and micronutrients should be applied in the fall based on soil test reports. All fertilizers applied as well as lime should be incorporated into the soil prior to planting. Required lime should be applied as soon as possible because it takes time for the lime to begin to neutralize the acidity of most soils. The application of sulfur is a growing concern in Louisiana production systems, with increasing deficiencies appearing every year. Oftentimes, early spring S deficiencies are mistaken for N deficiencies and additional S is not applied. Because sulfur is mobile, similar to N, the application solely in the fall will not be adequate. Supplemental applications of S with spring N applications are often warranted.
For further questions or comments contact:
Josh Lofton, Wheat Extension Specialist, firstname.lastname@example.org
Steve Harrison, Small Grain Breeder, email@example.com