Skip to content

Late Season Flood/Storm Events in Louisiana Soybeans

Late Season Flood/Storm Events in Louisiana Soybeans published on No Comments on Late Season Flood/Storm Events in Louisiana Soybeans

Over the next few days, producers across the state will begin to assess damages to soybeans brought upon by tropical system Harvey.  Unfortunately, there is no cookie cutter answer to how a system like this will affect every grower.  The main distinction of how varying situations will need to be assessed is the growth stage of the soybeans at the time the event occurred.

The lack of available oxygen for plant processes is the main concern in flooded fields. Oxygen is required for many essential plant processes including respiration, water uptake, root growth, and nodulation.  When flood water covers a field, the oxygen concentration drops quickly and can be depleted in as little as 24 hours.  However, depending on additional factors, soybeans can survive flooded conditions for up to 96 hours.

Temperature: Higher temperatures (ambient and water) will accelerate plant respiration, leading to a depletion of oxygen sooner than cool temperatures with cloudy weather.

Water movement: Even moderate water movement can increase aerification and allow oxygen to the plant roots.

Soil type: Flooding is potentially worse on poorly drained clay soils due to the reduction in hydraulic conductivity (the speed at which water can move through and out of the soil) compared to coarse soils.

According to research conducted in Baton Rouge in the late 1990s, the most sensitive growth stages of soybeans to flood stress are the early reproductive stages of R3 to R5 with yield reductions as high as 93% and 67%, respectively, when flood water remained for seven days (Linkemer et al., 1998).  The lack of oxygen associated with flood waters reduces the plants ability to develop additional plant material due to a reduction of photosynthesis and respiration.  At R3, the loss of yield is caused by a reduction in both the number of pods and seed size while the yield reduction at R5 is attributed mainly to seed size.   The same study showed little loss in yield for soybeans flooded after R6 as this rapid seed fill stage is believed to be protected against temporary stresses (Linkemer et al., 1998; Westgate et al., 1989).

R5 Soybeans in standing water. Soybeans are most sensetive to flooding at growth stages R3 to R5. Todd Spivey

R8 soybeans in standing water. Todd Spivey

 

The yield losses discussed in these studies however, only refer to direct reductions of seed number and size by the plant.  The studies presented do not account for yield and quality reductions caused by outside factors associated with these type of weather events.  Late season flooding followed by warm conditions can become conducive to several fungal diseases such as aerial blight, anthracnose, pod and stem blight, and soybean rust.  It is important producers continue to scout fields for an increase in disease incidence in the coming days.

Consideration should also be given to the possibility of seed rot and seed sprouting.  Sprouting can occur in seed that have previously dried down to below 50% moisture before experiencing extremely wet weather.  Additionally, ease of harvest can be reduced with soybeans that received an application of gramoxone just prior to the storm.  As the leaves desiccate and are removed from the plant the stem can still imbibe water.  With no leaves to aid in moving the water out of the stem, the stems will not dry down and producers can see an increase in green stem incidence in many fields.   

 

Linkemer, G, J.E. Board, and M.E. Musgrave. 1998. Waterlogging effects on growth and yield components of late-planted soybean. Crop Sci. 38:1576-1584.

Westgate, M.E., J.R. Schussler, D.C. Reicosky, and M.L. Brenner. 1989. Effect of water deficits on seed development in soybean. II. Conservation of seed growth rate. Plant Physiol. 91:980-985.

Use of Harvest Aids in Louisiana Soybeans

Use of Harvest Aids in Louisiana Soybeans published on No Comments on Use of Harvest Aids in Louisiana Soybeans
Todd Spivey, Sebe Brown, Josh Copes, Donnie Miller, Boyd Padgett

Over the last several weeks, we have received numerous calls about soybean harvest aid timing, products, and general recommendations.  The use of harvest aids in Louisiana soybeans is a common practice, with timely applications improving seed quality and harvest efficiency while potentially resulting in a soybean harvest 10 to 14 days earlier when compared to non-treated beans.

Timing

If the goal of harvest aid use in soybeans is to promote early harvest and improved harvest efficiency, harvest aids must be applied as timely as possible.  Once seed have separated from the white membrane inside the pod, they have reached physiological maturity and will no longer increase in size.  Any use of a harvest aid prior to the majority of seed reaching physiological maturity will result in a loss in yield.  Table 1 gives the paraquat label requirements for harvest aid application timing in soybean. Research conducted in Louisiana by Dr. Jim Griffin and Joey Boudreaux established that a harvest aid application could be made to soybean without yield penalty as long as soybeans are at reproductive growth stage R6.5 (physiological maturity). They provided a list of procedures to help determine when harvest aids can be safely applied to soybeans:

  1. Begin to scout fields for harvest aid timing when leaves begin to yellow
  2. Collect pods from the top four nodes of the plant at multiple, random locations within a field
  3. Open soybeans from pod, they should shell easily, and look for soybean separation from the white membrane
  4. If soybean separation from the white membrane has occurred for all pods collected, the seed has reached maximum dry weight and harvest aid application can be made without yield penalty

Plant appearance at growth stage R6.5 will vary by variety so close attention should be made to pods collected from the field and if seed have separated from the white membrane (Griffin and Boudreaux 2011 Louisiana Agriculture magazine Vol. 54, No. 2, Spring 2011).

Table 1. Proper application timing of harvest aid in indeterminate and determinate soybean varieties.
Indeterminate Varieties 65% of pods have reached a mature brown color or seed moisture is less than 30%
Determinate Varieties Plants are mature; beans are fully developed, 50% of leaves have dropped and remaining leaves are yellowing.

Products

Producers have several harvest aid options, though the typical harvest aid application consists of paraquat with an additional nonionic surfactant.  With excessive morningglory pressure, growers might consider including carfentrazone (Aim) or saflufenacil (Sharpen) with paraquat to improve desiccation of vines and in situations with high grass pressure, a tank-mix of paraquat with sodium chlorate may be warranted to improve the desiccation of grassy weeds prior to harvest.  Questions have also been received in regards to the use of sodium chlorate to aid in drift reduction of paraquat applications made by air.  The LSU AgCenter has no data to support this claim and only recommends the use of these products together for improved desiccation of weeds and soybeans present in the field.

It is also imperative that producers consider the required preharvest interval (PHI) associated with each product label.  When using multiple products, the longest PHI must be adhered to.  Labeled rates and comments are presented below in the excerpt from the 2017 Louisiana Suggested Weed Management Guide.

Labeled rates and comments of soybean harvest aid products from the 2017 Louisiana Suggested Weed Management Guide

Redbanded Stink Bug Considerations

Producers should also continue monitoring redbanded stink bug (RBSB) populations and should not rule out the inclusion of an insecticide with the application of a harvest aid.  LSU AgCenter entomologists recommend the control of threshold populations of RBSB until the soybeans are out of the field.  This means that many producers could, and should, include an insecticide for the control of RBSB with their harvest aid application (sodium chlorate cannot be tank-mixed with any insecticide).  It is important to keep in mind the restrictions placed upon many of the products at this point in the season.  These restrictions may include total active ingredient restrictions and PHIs.  Acephate, a common recommendation for RBSB control, can only be applied up to 2 lb ai A-1 year-1 in Louisiana.  Other insecticides also have increased PHI such as the pre-mix product Endigo, with a PHI of 30 days.  It is important to read and adhere to the label of all labeled materials prior to use.  When label restrictions prevent the inclusion of an insecticide with the harvest aid, producers should not delay the harvest of soybean so that the seed can be removed from the field as quick as the label allows.

Redbanded Stink Bug Numbers Increasing in Soybeans

Redbanded Stink Bug Numbers Increasing in Soybeans published on No Comments on Redbanded Stink Bug Numbers Increasing in Soybeans

Reports from the field indicate redbanded stink bug (RBSB) numbers are beginning to build in soybeans at the R5 development stage and beyond. Once RBSB colonize a field, native stink bugs often are forced out or are outcompeted, leaving only RBSB behind. The Louisiana threshold for RBSB is four insects per 25 sweeps. RBSB are strong fliers, and routine scouting is essential to detecting an influx of these insects. Furthermore, the presence of immatures signals that RBSBs are reproducing, meaning previously applied insecticidal controls may no longer be active. Recommended insecticides include pyrethroids, neonicotonoids and organophosphates.

The use of premix insecticides, including Endigo ZC and Leverage 360, may offer a degree of repellency not observed with other insecticides. Insecticide efficacy tests conducted at the Macon Ridge Research Station in Winnsboro demonstrated satisfactory control of RBSB while also having a possible added benefit of repellency. However, these insecticides perform best when populations of RBSB have not exceeded threshold. Once RBSB populations have exceeded threshold, the use of tank mixes of either acephate (0.75 to 1.0 pounds per acre) plus bifenthrin (6.4 ounces per acre) or Belay (4.0 ounces per acre) plus bifenthrin (4.0 ounces per acre) may be required to get them under control.

As with most insects, staying ahead of RBSB populations will make season-long control much easier while also reducing injury. Please contact your county agent or me for more information.

Economic Impact of Excessive Rain to Louisiana Agriculture Exceeds 276 Million Dollars

Economic Impact of Excessive Rain to Louisiana Agriculture Exceeds 276 Million Dollars published on No Comments on Economic Impact of Excessive Rain to Louisiana Agriculture Exceeds 276 Million Dollars

Click here to download full report

l-attales-equipment

Louisiana Rice Notes #9 – 2nd Flood Edition

Louisiana Rice Notes #9 – 2nd Flood Edition published on No Comments on Louisiana Rice Notes #9 – 2nd Flood Edition

The 9th installment of Louisiana Rice Field Notes is now available. This is the second flood edition this week.  This edition covers recommendations on how to proceed with harvest with all of the flood damaged rice, a very important proposed changed to the crop insurance “practical to replant” definition and the final planting dates (FPD) for rice, corn, sorghum, cotton and soybeans, and an important flood recovery meeting in Crowley tomorrow.

LA Rice Notes 9T_Page_1
Click to open

 

Soybean Insecticide Seed Treatment Decisions

Soybean Insecticide Seed Treatment Decisions published on No Comments on Soybean Insecticide Seed Treatment Decisions

One of the most important decisions producers must make when planting soybeans in Louisiana is planting date. Soybeans have the utility to be planted in early March to late June. This wide variation in planting dates exposes seedling soybeans to a multitude of insect pests that affect both above and below ground plant structures.

Optimal seeding dates for each maturity group planted in Louisiana are:

  • Group III – April 15–May 10
  • Group IV – April 15–May 10
  • Group V – March 25–May 5
  • Group VI – March 25–April 30

Soybean seedlings possess an exceptional amount of vigor and can tolerate a substantial amount of insect injury during the seedling stage. However, early planted soybeans may also encounter greater amounts of environmental fluctuations that affect air and soil temperature. Cool conditions can negatively affect vigor and under the right conditions stall plant growth and development. The addition of insect injury, to the aforementioned  environmental conditions, increases stress the plant encounters resulting in loss of stand and yield potential. Therefore, the inclusion of an insecticide seed treatment (IST) provides growers a risk management tool when soybeans are planted early.  The primary insect pests of early planted soybeans are bean leaf beetles, wireworms and grape colaspis.

On the opposite end of the spectrum are soybeans planted late i.e. behind wheat or are late due to unforeseen circumstances such as inadequate or excessive soil moisture. These beans are more at risk for insect injury due to the potential for large insect populations to build in neighboring fields and generally more insects present in the environment. As a general rule with all agronomic crops, the later the crop the more insect pressure that will be encountered throughout the season.  This is particularly evident when soybeans are planted into wheat stubble. Wheat stubble is favorable for the development of threecornered alfalfa hoppers and thrips. Thus, an IST is a sound investment when soybeans are planted late.

However, soybeans planted in a timely manner that being within the recommended planting window, under optimal soil conditions and low pest densities will often not benefit from the addition of an IST.  Insecticide seed treatments typically produce the most benefits when environmental conditions are sub optimal as outlined in the prior paragraphs. With the current economic climate and many ag professionals looking at areas to cut inputs, justifying the use of an IST on soybeans when planted under optimal conditions becomes harder to support. Saving the cost of an IST can go to making a stink bug application later season that may provide a greater economic return.

Outside of early or late planted soybeans are situations where ISTs are justifiable. These include weedy fields with incomplete burn down applications, reduced tillage field arrangements, fields with historically problematic early insect pests (wireworms and/or threecornered alfalfa hoppers) and continuous plantings of one crop.  Each field is unique and the use of ISTs as a blanket treatment over every acre may not be justifiable with $8 soybeans.

2015 Soybean Variety Yields and Production Practices

2015 Soybean Variety Yields and Production Practices published on No Comments on 2015 Soybean Variety Yields and Production Practices

By:

Dr. Ronnie Levy: LSU AgCenter Soybean Specialist

2015 Soybean Variety Yields and Production Practices


For more information please contact Dr. Ronnie Levy at rlevy@agcenter.lsu.edu

Black Root Rot Suspected in Louisiana Soybean

Black Root Rot Suspected in Louisiana Soybean published on No Comments on Black Root Rot Suspected in Louisiana Soybean

Assistant Professor, Field Crop Pathology, Macon Ridge Research Station

Over the past two weeks, I have received many phone calls and conducted numerous field visits concerning black root rot of soybean. The suspected causal agent is Thielaviopsis basicola, which has primarily been described as a seedling disease of cotton. In 2009, the disease was described as a disease of vegetative soybean in Arkansas (http://www.apsnet.org/publications/plantdisease/2010/September/Pages/94_9_1168.1.aspx) and has been mentioned as an issue in Mississippi over the past several years (http://www.mississippi-crops.com/2014/08/01/soybean-disease-update-august-1-2014/). Information concerning late-season (R5-R6) symptoms and epidemiology of black root rot is limited.

During pod fill foliar symptoms of black root rot become obvious in soybean fields (below, Plate 1).

BRR1

These symptoms are easily noticed from the turnrow, and upon closer inspection, interveinal chlorosis is evident with leaf veins remaining green (Plates 2 & 3). Inspection below the canopy in the center of the affected area will usually reveal one or several plants that died earlier in the season (Plate 4).

Plate 2. Interveinal chlorosis caused by black root rot.
Plate 2. Interveinal chlorosis caused by black root rot.
Plate 3. Interveinal chlorosis.
Plate 3. Interveinal chlorosis.
Plate 4. Soybean plant death caused by BRR.
Plate 4. Soybean plant death caused by BRR.

Apparently, these dead plants go unnoticed because the death occurred during vegetative or early reproductive stages, and adjacent plants quickly covered them. Surviving, infected plants adjacent to the dead plants will be stunted and displaying these foliar symptoms (Plate 5).

Plate 5. Dead plants (left), stunted plants (center), and healthy plants (right) from a field affected by black root rot.
Plate 5. Dead plants (left), stunted plants (center), and healthy plants (right) from a field affected by black root rot.

Affected plants may snap-off at the soil line when pulled. When plants are excised, roots are black in color (below, Plate 6).

OLYMPUS DIGITAL CAMERA

Splitting stems near the crown will reveal white fungal growth in the center of the stem (below, Plate 7). Additionally, infected black plant stems from the previous season are often observed near infected roots.

OLYMPUS DIGITAL CAMERA

We have isolated what appears to be Thielaviopsis basicola from diseased roots using a selective medium, and are currently working to confirm identity and pathogenicity. The effects of fungicide seed treatments and in-furrow sprays are unknown. Varietal susceptibilities are currently unknown; however, the official variety trial at Dean Lee Research Station is significantly affected by black root rot and will be rated in an attempt to identify sources of resistance. Additionally, greenhouse screenings may be conducted this winter to corroborate rating information.

This fungus has a broad host range and survives in the soil for long periods of time. Apparently, conditions have been optimal for disease development this year. Incidence in most fields has been <1%; however, in some fields that have been planted to soybean continuously for several years and in a minimum/no till program, incidence has been as high as 10%. This does not necessarily translate to a 10% loss, as affected plants will have the ability to produce some seed depending on disease severity. Anecdotal evidence indicates that rotation to corn will lessen disease incidence. Other diseases/conditions that we have seen this year that may be confused with black root rot include: red crown rot, sudden death syndrome, and triazole burn (Plates 8, 9, 10, and 11).

Plate 8. Foliar symptoms of sudden death syndrome and/or red crown rot.
Plate 8. Foliar symptoms of sudden death syndrome and/or red crown rot.

 Plate 9. Red crown rot fruiting structures on soybean.

Plate 9. Red crown rot fruiting structures on soybean.

Plate 10. Whitish to bluish spore masses produced by the fungus that causes sudden death syndrome.
Plate 10. Whitish to bluish spore masses produced by the fungus that causes sudden death syndrome.

 

 Plate 11. Triazole fungicide burn.

Plate 11. Triazole fungicide burn.

For more information on these topics or others, please contact your local extension agent, specialist, nearest research station, or visit www.lsuagcenter.com or www.louisianacrops.com.

Frogeye Leaf Spot Prevalent in Louisiana Soybean

Frogeye Leaf Spot Prevalent in Louisiana Soybean published on No Comments on Frogeye Leaf Spot Prevalent in Louisiana Soybean

Over the past two weeks, many reports of frogeye leaf spot have been coming in from all soybean growing areas in the state. Overall disease severity in susceptible varieties has been light to moderate. The disease is caused by a fungus, Cercospora sojina, and has the potential to reduce yield by reducing leaf area and causing defoliation. Losses of up to 30% have been reported in the past. The disease may also cause discoloration of seed reducing seed quality. When scouting for frogeye, initial foliar symptoms are dark, water-soaked spots (1 to 5 mm) which later progress to lesions with gray to brown centers and reddish margins. Symptoms will be evident usually around R3, but may appear earlier or later. The disease may progress with more lesions developing, which may coalesce resulting in large necrotic areas on leaves. If infection is severe, frogeye may cause defoliation of soybeans. Young leaves are infected more readily than older leaves, and patterns of varying degrees of disease severity may be observed within canopy levels. Closer examination with a hand lens, or sometimes with the naked eye, will reveal gray to black conidiophores (reproductive structures) within the center of lesions. The disease is spread by windblown or rain-splashed conidia (spores) formed on the conidiophores. Conditions favorable for disease development have been prevalent in our current weather pattern of consistent rainfall, high humidity, and warm temperatures.

Figure 1.  Frogeye leaf spot lesions.
Figure 1. Frogeye leaf spot lesions.
Figure 2.  Coalescing frogeye leaf spot lesions (note the gray coloration near the centers of the lesions).
Figure 2. Coalescing frogeye leaf spot lesions (note the gray coloration near the centers of the lesions).
Figure 3.  A moderate infection of frogeye leaf spot.
Figure 3. A moderate infection of frogeye leaf spot.

Frogeye leaf spot may be managed by a number of methods. The first line of defense is planting a resistant variety and pathogen-free seed. Although our data is limited on varietal susceptibility, in 2013, we were able to rate soybean varieties for frogeye at Dean Lee Research Station in Alexandria. Results of those ratings are posted at: http://www.lsuagcenter.com/MCMS/RelatedFiles/%7B271517B6-5563-4FB9-BF4F-3D211119F027%7D/Dean-Lee-OVT.pdf. Another list from our friends in Mississippi and Tennessee is located at: http://www.mississippi-crops.com/wp-content/uploads/2013/07/2013-soybean-short-list-frogeye-responses.pdf. If your variety of interest was not included in these sources, please contact your seed representative for more information.

Sometimes a fungicide application may be warranted for management of frogeye leaf spot in susceptible varieties when disease severity is moderate to heavy and conditions favor disease development. One important consideration when making application decisions is the fact that strobilurin fungicide resistance is likely in this pathogen population, and has been confirmed in 9 parishes in Louisiana. Even if strobilurin resistance has not been confirmed in your parish and if strobilurin fungicides have been routinely applied in the area, it is likely that the majority of the pathogen population has become resistant. In some cases we have seen reduced efficacy of strobilurin fungicides (Aproach, Evito, Gem, Headline and Quadris) on frogeye leaf spot. In our trials in 2013 and others conducted throughout the United States, we have seen consistent reductions in disease severity when using triazole products such as Domark, Proline, and Topguard. Additionally, pre-mixes containing these triazoles have shown reductions in disease severity. Data is limited for Louisiana, and we have trials at several research stations examining fungicide efficacy for these products as well as many others not listed.

Other considerations should include application coverage as it relates to nozzle type and water volume. Fungicides usually require a minimum of 10 gallons/A by ground and 5 gallons/A by air. Hollow cone or flat fan nozzles are recommended to achieve optimum droplet size. When applying fungicides, rotate chemistries to avoid resistance issues and prolong the usefulness of products. Please do not hesitate to contact LSU AgCenter via your parish agent, specialist, or nearest research station for additional information.

Secondary Sidebar