I have received many calls concerning burndown over the past couple of weeks. The warm weather we have experienced recently has most farmers itching to get started. Research has shown that the optimum time to burndown winter vegetation is 4 to 6 weeks prior to planting. This is primarily to reduce the risk of insect damage to seedling crops. Think of it this way, winter vegetation in the field is like a buffet for the worms. Removing the buffet 4 to 6 weeks prior to planting will cause the worms to die or move on to another food source. If a crop is planted into green or dying vegetation, the possibility of those worms feeding on the seedling crop is very high. Also, removal of winter vegetation 4 to 6 weeks prior to planting reduces the risk of physical competition between the weed and the crop. Corn, for example, is determining its yield as it is spiking and if growth is hampered by any physical competition, i.e. weeds, then yield will be reduced. Acreage that had a burndown application greater than 6 weeks prior to planting may need to be sprayed again prior to planting, especially if a residual herbicide was not applied with the burndown. The take home message is simple, plant into a clean, weed-free seed bed.
Use of residual herbicides tank-mixed with the burndown application is pretty common. Many herbicides utilized for residual control in a burndown application need to contact bare soil to provide residual. If a field is completely covered by winter vegetation (cannot see much bare soil), that vegetation will intercept the burndown application cocktail, thus the “residual” herbicide may only act as a foliar herbicide and offer little to no residual herbicide. Metolachlor or S-metolachlor are examples of herbicides that are tightly bound by plant biomass, so don’t expect residual control if it doesn’t reach the soil surface.
Research has shown that glyphosate plus 2,4-D at 1 lb ae/A is the best broad spectrum burndown treatment. Notice I wrote 1 lb ae/A, not 0.5 or 0.75 lb ae/A. For a 4 lb ae/gal 2,4-D formulation, 1 lb ae/A of 2,4-D equals 1 quart/A. In my opinion, this holds true no matter if you add another herbicide like Sharpen, Goal, LeadOff, etc. to the burndown application. Essentially, if you are going to make the trip to apply the herbicide, why not apply enough 2,4-D that research has shown will kill almost all of the winter weeds Louisiana farmers deal with.
If a producer does not want to or can’t use 2,4-D in their burndown application, then the choice of burndown herbicide depends upon weed spectrum. I’m not going to go through every scenario because there can be many options. Give your local county agent a call for help in this situation.
In conclusion, the main item all consultants and producers need to strive for with burndown is to ensure that any crop is planted into a weed-free seedbed. Good luck and please call us if you need any help.
The Projected Rice Farm Cash Flow Model was developed to assist producers in planning for the 2017 crop year. The model is an Excel spreadsheet which allows rice producers to enter projected acreage, yield, market price and production cost data for 2017 to estimate net returns above variable production costs and to easily evaluate the impact of changing percent of base planted on net returns.
LSU AgCenter Extension Agents in rice producing parishes conduct a survey every year to determine the rice varieties which are grown in their respective parishes. The data is then broken down further into rice classes including long grain, medium grain, special purpose, hybrid, and Clearfield rice acres. In addition, information about planting methods, reduced tillage acres, and ratoon rice production is included in the survey. Graphical parish maps and pie graphs are also provided. This information can be found on the LSU AgCenter’s website by clicking the following links: Tabular Data & Parish Maps or a complete summary by clicking the image below.
Assessment of Weed Control Programs and Post-harvest Weed Control in Problem Fields.
Josh Copes, Donnie Miller, and Daniel Stephenson
Assessment of weed control programs.
With corn harvest underway and soybean and cotton fields approaching maturity, this is a great time to evaluate this year’s weed control programs. Things to consider include: what herbicides were applied, when they were applied in respect to crop and weed growth stages, what were weather conditions like before and after application, and what weed species are present after final weed control efforts. In addition, knowing which fields contain glyphosate-resistant weeds and other difficult to control species that escaped control can help us better plan and budget for more effective herbicide programs. These factors will help critically evaluate weed control programs and may offer insights into becoming more effective at herbicide selection, improving application timing, and how environmental conditions may dictate the need for more aggressive weed control tactics in certain fields.
Post-harvest weed control.
The time period from corn harvest and the first killing frost can range from 1 to 4 months. The average first frost date in North and Central Louisiana is November 15 and 25, respectively. A lot of money and effort is spent in controlling weeds during the growing season to negate yield loss. With the extended window from harvest to first frost, weeds will continue to emerge and produce seed. Timely weed control practices following harvest (post-harvest weed control) can reduce weed seed return to the soil, thus ensuring fewer weeds to fight in future cropping seasons. Post-harvest weed control is especially important in fields containing herbicide resistant weeds. A good example to illustrate the importance of post-harvest weed management is the ability of glyphosate-resistant Palmer amaranth to produce mature seed in as little as 30 days after emergence during late summer and early fall. Many other grass and broadleaf weeds are capable of setting viable seed in a similar time frame.
For weeds that are present in the field at harvest time, mowing and/or tillage should be conducted as soon as possible upon harvest to ensure viable seed set is eliminated or reduced. Rainfall will influence subsequent germination of weed seed and therefore the need for additional weed control. Furthermore, rainfall following cultivation could increase weed seed germination, however, if the weeds are controlled the soil seedbank would be reduced.
Other methods of weed control include the use of herbicides. Herbicide applications should be targeted from late-September through October when the time period from application to first killing frost is shortened. Multiple herbicide applications for post-harvest control of summer annual weeds should be avoided. Residual herbicides such as S-metolachlor, pyroxasulfone, linuron, and diuron, among others, can be applied in the fall following harvest. However, rotation interval restrictions must be followed and length of residual control will be influenced by soil temperature and saturation. Glyphosate plus 2,4-D and/or dicamba or paraquat plus diuron and/or linuron are some choices for late-fall post-harvest applications. Diuron and linuron will offer soil residual; however, if soil temperatures are warm and rainfall frequent, do not expect long residual from these products. Likewise the lack of rainfall to properly activate residual herbicides to minimize weed germination can negatively impact treatment effectiveness. Maximize water volume to ensure good weed coverage as this is critical for good weed control, especially for paraquat plus diuron and/or linuron.
To reiterate, weeds are capable of setting viable seed within 30 days after emergence during late summer and early fall. Post-harvest weed control is especially important when combatting glyphosate-resistant weeds such as Palmer amaranth, waterhemp, or johnsongrass. Problem fields should be identified and receive top priority for preventing seed return. Once harvested these problem fields should be mowed or tilled shortly after harvest to prevent and/or reduce seed set. Fields should then be regularly scouted for emerging weeds and additional control tactics applied prior to seed set. This will require close inspection of weed species to determine when they are flowering. Once a weed species is observed flowering a weed control operation should be implemented. Depending on weather conditions following harvest, weed control tactics may need to be implemented approximately every 3 to 4 weeks until a killing frost has occurred. If glyphosate-resistant Palmer amaranth or waterhemp is an issue, a management tactic (i.e. mowing, tillage, herbicide application) should be done every 3 to 4 weeks.
Trey Price, Extension/Research Plant Pathologist, Macon Ridge Research Station
Based on a tip from an industry representative, southern rust, Puccinia polysora, was suspected along the Atchafalaya River in milk to early dough stage corn. Yesterday afternoon samples were collected from two locations (Woodside and Lettsworth) and confirmed to be southern rust this morning via microscopic examination. Since then, other similar reports have come in from Rapides and Bordelonville. Incidence in these fields is very low (<1%). Given the stage of the crop and low incidence, I would not recommend treating these fields. Current conditions (warm/humid) are favorable for disease development and producers, agents, and consultants should monitor for disease development in their corn fields. It is noteworthy that we have detected southern rust about one month earlier in 2016 than in 2015.
Scouting is key to managing southern rust. First, identify the disease correctly. Southern rust pustules will appear reddish orange and will almost always occur on the upper side of the leaf (Figure 1). In severe cases pustules may appear on leaf sheaths and husks (Figure 2). Common rust, which has been very common this year, will appear more brick red, and pustules will occur on both sides of the leaf (Figure 3). Most common rust has ceased to develop because of the warm temperatures, and pustules have turned brown. There are differences in susceptibility to southern rust among hybrids; therefore, it is important to define disease incidence/severity prior to making management decisions.
If southern rust is not present, fungicide applications are not necessary. If southern rust occurs near tasseling, a fungicide application will likely be needed for management and provide economic benefit (See Table 1 for products and efficacy) as this disease can be very aggressive under optimal conditions. As the crop matures from tasseling stage, a return on fungicide investment becomes increasingly less likely (See Table 2). Application decisions must be considered on a field by field basis taking into account disease incidence/severity, crop stage, prevailing environmental conditions, and likelihood of economic return. If a fungicide application is deemed necessary, using recommended rates and maximum water volumes will increase efficacy. 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. Later planted corn is at higher risk for developing southern rust that requires management.
Table 1. Fungicide efficacy for control of corn diseases.
The Corn Disease Working Group (CDWG), which includes many members from the mid-South including several pathologists from Louisiana, has developed the following information on fungicide efficacy for control of major corn diseases in the United States. Efficacy ratings for each fungicide listed in the table were determined by field testing the materials over multiple years and locations by the members of the committee. Efficacy ratings are based upon level of disease control achieved by product, and are not necessarily reflective of yield increases obtained from product application. Efficacy depends upon proper application timing, rate, and application method to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application. Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in the table. Table includes systemic fungicides available that have been tested over multiple years and locations. The table is not intended to be a list of all labeled products1. Efficacy categories: NR=Not Recommended; P=Poor; F=Fair; G=Good; VG=Very Good; E=Excellent; NL = Not Labeled for use against this disease; U = Unknown efficacy or insufficient data to rank product
1Additional fungicides are labeled for disease on corn, including contact fungicides such as chlorothalonil. Certain fungicides may be available for diseases not listed in the table, including Gibberella and Fusarium ear rot. Applications of Proline 480 SC for use on ear rots requires a FIFRA Section 2(ee) and is only approved for use in Illinois, Indiana, Iowa, Louisiana, Maryland, Michigan, Mississippi, North Dakota, Ohio, Pennsylvania, and Virginia.
2Harvest restrictions are listed for field corn harvested for grain. Restrictions may vary for other types of corn (sweet, seed or popcorn, etc.), and corn for other uses such as forage or fodder.
Many products have specific use restrictions about the amount of active ingredient that can be applied within a period of time or the amount of sequential applications that can occur. Please read and follow all specific use restrictions prior to fungicide use. This information is provided only as a guide. It is the responsibility of the pesticide applicator by law to read and follow all current label directions. Reference to products in this publication is not intended to be an endorsement to the exclusion of others that may be similar. Persons using such products assume responsibility for their use in accordance with current directions of the manufacturer. Members or participants in the CDWG assume no liability resulting from the use of these products.
Table 2. 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.
If you require additional information, please do not hesitate to contact your nearest county agent, research station, or specialist.
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.
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.