Please click the picture below to view the effects of weathering on grain sorghum by Dr. Dan Fromme.
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.
If you have any questions please contact us.
Southern Corn Rust Confirmed in Louisiana
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.
Please see the article below by Dr. Dan Fromme on the impact of flooding on Louisiana corn.
by: Dustin Harrell
Blast found in Jupiter
Many things have happened over the past couple of weeks in regard to the Louisiana crop. Probably the most important is that leaf blast has been identified in two Vermilion Parish rice fields. Both fields are growing the medium grain variety Jupiter, which is considered moderately susceptible to blast. One field is approximately at the mid-tillering growth stage of development and the other is almost at green ring. With the early sighting of leaf blast in Jupiter many questions have arisen regarding fungicide applications for blast. The most often asked questions are: How bad does the leaf blast have to be before deciding to trigger a two fungicide application strategy to control the blast? If you do decide to apply two fungicide applications, what timings are recommended? These are excellent questions, and Dr. Groth has quickly put together information regarding these blast questions plus a whole lot more…
Leaf blast has started to show up in the area on the variety Jupiter. Blast disease is caused by the fungus Pyricularia grisea and is one of the most important diseases of rice in the world and the Mid-South. Yield losses as high as 90 percent have been observed in Louisiana because of this disease. Blast can infect rice from the seedling stage to near maturity. The leaf blast phase most commonly occurs between the seedling and late tillering stages. Leaf spots start as small white, gray or blue-tinged. They enlarge quickly under moist conditions to either oval or diamond-shaped spots or linear lesions with pointed ends with gray or white centers and narrow brown borders. Leaves and whole plants can be killed under severe conditions. The most important aspect of leaf blast is that it provides inoculum for infecting the panicles. Fungicides are not normally used at this stage unless you are losing the stand. The best control method is to restore or deepen the flood so all of the soil in the field is covered with water.
Scouting for blast should begin early in the season during the vegetative phase and continue through to heading. Scout the entire field, examining plants at several different locations. Blast is more commonly found in fields where (a) the field has a history of disease, (b) the variety is susceptible, (c) high nitrogen rates are used, (d) the field has sandy soils, (e) the rice was planted late (late-planted rice is more likely to encounter foliar disease problems than early-planted rice), (f) along the edges of tree lined fields, most importantly (g) the rice is growing under upland (no flood) conditions. Draining for straighthead and water weevil control may increase the incidence and severity of blast. These conditions should be avoided whenever possible. Also, as the percentage acreage of blast-susceptible varieties increases, the probability of an epidemic increases because more wind-borne spores pass between fields.
Correct identification of rice leaf blast is critical (Figure 1). Several diseases and disorders have similar symptoms, but control practices are not justified for these other diseases. There is a lot of diversity of lesion type so examine several different lesions at several different locations in the field. If identification is in doubt, leaf samples can be placed in a moist chamber to induce sporulation and identified by spore type (Figure 2) under a microscope.
Figure 1. Correct identification of leaf blast is critical to effective disease control.
Figure 2. Blast spores.
If leaf blast is in the field or has been reported in the same general area, and if the variety is susceptible, fungicidal applications are advisable to protect the head from rotten neck and panicle blast. The only fungicides that have activity against blast are the strobilurins Trifloxystrobin and Azoxystrobin. Trifloxystrobin containing fungicides (Stratego and Gem), are slightly more effective against blast than Azoxystrobin (Quadris, Quilt, and Equation) but they are all effective. I am not sure if Gem is commercially available. Most of the time leaf blast should not be sprayed unless it is killing the rice plants. Normally a single application will control blast on a susceptible or moderately susceptible variety. The rice should be sprayed at 50-70% heading to protect the neck and panicle branches. If a variety is very susceptible or leaf blast is still very active on susceptible varieties two applications are needed, one at 2-4 inch boot to reduce the inoculum in the field and the second to protect the head. Remember as little as a 5 day delay in the heading application can greatly reduce control.
May 28 Southwest Rice and Soybean Field Day, Fenton. (morning)
May 28 Vermilion Parish Field Day, Lake Arthur. (afternoon)
June 16 Acadia Parish (Rice Research Station South Farm) Field Day, Crowley
July 1 Rice Research Station Field Day, Crowley.
Dustin Harrell Rice Specialist & Research Agronomist (337) 250-3553 firstname.lastname@example.org
Don Groth Rice Pathologist (337) 296-6853 email@example.com
Eric Webster Rice Weed Specialist & (225) 281-9449 firstname.lastname@example.org
Assistant Southwest Regional Director
Steve Linscombe Senior Rice Breeder & Southwest Regional Director (337) 296-6858 email@example.com
Mike Stout Rice Entomologist (225) 892-2972 firstname.lastname@example.org
Mike Salassi Rice Economist (225) 578-2713 email@example.com
Josh Lofton and Beatrix Haggard- LSU AgCenter
The 2015 corn season has started off very challenging for the majority of the state. Much of the corn that has been planted was planted later within the optimum window, while several producers are still trying to decide on whether to plant the final intended acres (A great article about late-planted corn was recently published by Dr. Erick Larson at MSU http://www.mississippi-crops.com/2015/04/07/are-we-going-to-get-this-corn-crop-planted/). While corn that was planted on time is up and most has a pretty good stand, new challenges are arising with N fertilization in the wet conditions around the state. Much of this corn is between the V2 to V6 leaf stage and has good growth. However, only a limited number of acres have had any measureable N applied. This has increased interest in aerial application of part or all of the intended fertilizer as urea. While these applications have the potential to be very beneficial and common – especially in the delta of Mississippi on high clay ground, according to Dr. Bobby Golden at MSU – correct decisions and appropriate management are needed to get the most benefit.
The first thing that needs to be decided is whether the crop needs this shot of fertilizer or if it can be delayed until the ground applicator is suitable. Aerial application will be more costly per acre than ground applications. The best way to determine if the crop needs this application will be the crop itself. Symptoms of N deficiency are an overall pale crop and shortened growth. However, these symptoms are also associated with cold and/or wet conditions. While poorly drained soils and N deficiencies can be highly associated with each other, field pattern can be a way to determine if the crop as a whole is stressed or just low areas (i.e., is the short, pale corn in a localized area or across the field).
Once areas have been identified as not just localized areas of poor drainage, other issues must be addressed. One such issue is whether the crop is suffering from an N or S deficiency. These two are often confused with the other. Typically, location on the plant can be used to gauge whether N or S is the most likely culprit, with N traditionally being on lower, older growth and S being on the new growth. However, in young, developing plants these traditional deficiency locations are not 100 percent. While determining if an N or S deficiency is present is critical, often these two will probably be present in most Louisiana systems. Additionally, if no S has been put out, then managing for both N and S will probably be necessary, especially if substantial time will pass before successive fertilizer applications.
The next factor that needs to be determined is how much N to apply. This decision will be entirely based on the farm operation. There are pros and cons for both urea and UAN, but both can be used to produce optimum growth and productivity. In this regard, producers can apply their entire intended N applications as urea aerially. Though expensive, this provides the luxury of not having to fit in another application when drier conditions arrive (especially as further planting of grain sorghum, soybeans and cotton are probably also intended). On the other hand, if UAN has been purchased and is the intended fertilizer for the majority of the N management, a smaller application can be applied as urea to provide some flexibility until drier conditions exist. These applications should include at least 50 to 100 lbs of N per acre (as urea and ammonium sulfate) and anywhere from 10 to 20 lbs of S per acre (as ammonium sulfate). This ensures adequate N and S for the stressed crop. However, if making these applications, it is important to readjust further N application to account for this additional application. Additionally, splitting N applications into a couple smaller applications can minimize N losses associated with the current adverse environmental conditions being experienced.
The final management decision that should be made is whether or not to treat the aerially applied urea or not. This decision often comes down to economics rather than agronomics. From an N management perspective, the application of urease inhibitors (NBPT) on aerial applied (without incorporation) should be the standard. This is due to the fact that up to 50 percent of applied urea can be lost through volatilization if the conditions are unfavorable. Furthermore, the application of a nitrification inhibitor (DCD or nitrapyrin) may also be warranted, but this has little to do with the application and environmental conditions now and more to do with soils and environmental conditions that will be experienced in the upcoming season. Further details are provided in the following link: http://louisianacrops.com/2015/04/06/choosing-to-use-n-inhibitors-or-not-in-mid-south-corn/.
Even though this corn season has had a challenging start, overall this current crop that has been planted shows promise. Therefore, management decisions should be taken that will help maintain this potential. However, with current prices, inputs must be warranted prior to application r to ensure return on the investment. Therefore, producers must watch their crop and weather on these applications. For further questions or comments feel free to contact:
Beatrix Haggard, state soil fertility specialist, firstname.lastname@example.org
Josh Lofton, field crop agronomist, email@example.com
by: Dustin Harrell
PDF version – Rice Notes 4_April 17
Rain, Rain and More Rain…
Over the past 10 days all we have seen is rain, rain and more rain. Very little rice has been planted in Northeast Louisiana. In Southwest Louisiana however, I would estimate that 90 to 95% of the rice has been planted and most of that rice has emerged and is moving along nicely. In fact, when the rains first started last Friday, many producers’ fields in Southwest Louisiana had already been flushed or were in need of flushing because they were low on soil moisture. So the rains were initially a welcome reprieve. The problem is that the rains never let up. Over the weekend at some locations received over 5 inches and even more throughout this week. The rain really stopped pretty much all field work this week. However, in many cases it has not stopped rice growth because the weather has been warm and the sun has come out from time to time. If we look at the temperatures and rainfall at the Rice Research Station in Crowley, you will see that it rained six out of the last seven days with a total rainfall of 6.4 inches.
During that same time, it has been fairly warm with a mean daily temperature of 71.5oF. Often we use accumulated DD50 units to help predict rice growth and development. DD50 heat units are an estimate of accumulated daily heat units above 50oF and are an estimate of a day’s thermal quality for growth. It is calculated by taking the average of the daily high and low air temperature in oF and subtracting 50oF. The short of it is that the more DD50 heat units we accumulate the faster the rice will grow and develop. Typically, we would estimate that seedling rice will grow a new leaf somewhere between every 100 to 175 accumulated DD50 heat units. At the Rice Research Station from last Friday (April 10) to this Thursday (April 16) we received approximately 151 DD50 heat units. Most of my research plots moved from 2- to 3-leaf rice to 3- to 4-leaf rice this week. All of this is to say that even though we field activities have stopped this week rice growth and development has not. Of course, all of this DD50 discussion assumes good growing conditions for rice and not for rice which has been submerged under water.
This brings me to the most ask question I have received this week. When seedling rice is submerged under water, how long can it survive? Well this is a question that really does not have an exact answer and does not (as far as I know) have research based information to base the answer on. Typically, the survival of a seedling would be related to several things including how deep the water was over the rice, variety or hybrid grown, water temperature, the “health” of the seedling prior to submergence, and so on. So with all of these different variables in play you can see that this question would not have a one size fits all answer. So to answer this question I polled all of the best rice farmers, consultants, and researchers I could to find the consensus was that under the current temperatures that we have and if the flood was not very deep over the top of the seedling we would feel confident that the rice could survive 5 to 7 days. After that time, the stand would probably start to thin.
So if the rice in the area was growing this week, assuming it was not under water, we can assume that the weeds were also growing. Which brings me to the next group of questions I was asked this week. All of which were related to herbicide applications and wet conditions. There are several scenarios that I was asked and so I wanted to share a few thoughts on the subject. One is that photosynthetic inhibitors herbicides, like propanil, need good growing conditions, good weed contact, and need to be rainfast prior to the next rainfall event to work best. So if the weeds are small, and covered with water, or you are not sure how long you will have before the next rainfall event, you may want to hold off on the application until conditions are more favorable for the herbicide activity. After all, you are paying for the herbicide and the application costs, so you may as well get the most of what you are paying for. Another situation, I would caution you about is applying Command treated fertilizer into a standing flood when you are expecting even more rain. The Command treated fertilizer and the herbicide can move in the water during standing water conditions in the field when the application is followed by high winds. In this scenario, the Command can move from the high side of the field to the low end or even from the top cut of a field to the bottom cut of a field. In these situations the Command would be concentrated (higher than the labeled rate) on one side which could damage the rice and would be diluted (lower than the labeled rate) on the other side of the field, which would provide poor residual weed control. The same thing could occur where you apply the Command treated fertilizer into standing water, raising the flood yourself followed by wind and water movement.
10 Things you need to know about rice sheath blight
- Current rice varieties range from moderately resistant to very susceptible.
- Sheath blight is a soil-borne disease and is not transmitted by wind-borne spores. The pathogen moves up the plant and from plant to plant by surface hyphae.
- The thicker the rice, the more severe sheath blight is.
- The more nitrogen fertilizer used, the more severe sheath blight is.
- The sheath blight pathogen also causes aerial blight in soybeans and attacks many other crops and weeds, making it difficult to eliminate in a field.
- If sheath blight is detected in 30% or more of the stops in a field while scouting susceptible and very susceptible varieties, fungicide applications are advised to reduce damage. For moderately susceptible and moderately resistant varieties, the percentage increases to 50%.
- The best timing for a sheath blight fungicide application is at the boot growth stage (2-4 inch panicle).
- Fungicide applications to suppress sheath blight should be applied before 50%-70% heading. Application as few as five days after this growth stage will provide poor control of sheath blight. Allow time to obtain a fungicide, schedule the application, and adjust for poor weather conditions.
- Under heavy sheath blight pressure or when growing very susceptible varieties, two applications may be needed to effectively suppress sheath blight.
- Fungicide-resistant sheath blight pathogen populations have been found in south central Louisiana and are spreading rapidly. A sound fungicide resistance management system is needed.
Did you know… that according to the USDA – National Agriculture Statistics Service, the United States produced approximately 221 million hundred weight of rice in 2014? That rice has a value of approximately 3.1 billion dollars. Well, did you know that the population of China can consume that much rice in approximately 12 days! With that in mind, how important do you think the China market would be if we could gain access to it for U.S. grown rice? Just a little food for thought!
Louisiana Rice Notes is published biweekly to provide timely information and recommendations for rice production in Louisiana. If you would like to be added to this email list, please send your request to firstname.lastname@example.org.
This Information will also be posted to the LSU AgCenter website where additional rice information can be found. Please visit www.LSUAgCenter.com.
May 28 – Southwest Rice and Soybean Field Day, Fenton.
June 17 – Acadia Parish (Rice Research Station South Farm) Field Day, Crowley.
July 1 – Rice Research Station Field Day, Crowley.