Volume 11, Issue 7 - August 2021

David Moseley, Stephenson, Daniel O., Brown, Sebe, Price, III, Paul P, Padgett, Guy B., Foster, Matthew, Parvej, Md Rasel, Watson, Tristan, Harrison, Stephen A., Miller, Donnie K.

Louisiana Crops Newsletter Plain Banner.

Applying Harvest Aids in Louisiana Soybean

Daniel Stephenson, Donnie Miller, Sebe Brown, and David Moseley, LSU AgCenter Scientist

Use of a herbicide as a desiccant in soybean has become popular to potentially improve harvest efficiency in Louisiana. Herbicides such as paraquat, Aim, Sharpen, and sodium chlorate are labeled for use in soybean as a desiccant, but paraquat is the most widely used. The paraquat label states at least 65% of pods should be mature (Figure 1) or moisture content should be 30% or less for indeterminate soybean varieties; and at least 50% of the leaves should have dropped and remaining leaves should be yellow for determinate varieties. Table 1 gives the harvest aid application timing label requirements for the labeled products in soybean.

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Figure 1. Soybean plants where approximately 65% of the pods have turned their mature color.

In instances with excessive morningglory pressure, growers might consider co-applying Aim or Sharpen with paraquat to improve desiccation of vines. If weedy grass is problematic, co-applying paraquat and sodium chlorate can improve desiccation.

Paraquat, Aim, Sharpen, and sodium chlorate labels are very specific as to when they can be applied to soybean as a harvest aid. Soybean is essentially fully mature, at least R7.5 or later, when these herbicides can be legally applied as a desiccant.

What if a herbicide desiccant is applied earlier than labeled in soybean? Research was conducted in Louisiana to evaluate this question and indicated that harvest seed quality and yield was not affected by harvest aid application if the application was made after the plant reached physiological maturity (Boudreaux and Griffin 2011; Weed Technology vol. 25:38-43). Physiological maturity is when the seed have separated from the white membrane inside the pod and seed margins are prominently defined (Figure 2), which occurs at the growth stage 6.5 (R6.5 and approximately 50% moisture). Data indicate that maturity group IV soybean yield was reduced by 15.4% when paraquat was applied to soybean at seed moisture of 60%, which is prior to R6.5 (Figure 2). For maturity group V and VI varieties, harvest aid application prior to R6.5 or 40% seed moisture resulted in yield loss of 15.6 and 4%, respectively. Any use of a harvest aid prior to the seed reaching physiological maturity will result in a loss in yield. This research highlighted that soybean yield can be reduced if paraquat is applied prior to physiological maturity. Growers are cautioned that application of paraquat, Aim, Sharpen, or sodium chlorate that does not follow product labeling with respect to harvest aid timing to the crop is illegal. These products are labeled specifically for weed desiccation, not soybean desiccation.


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Figure 2. Soybean seed within pods showing, from left to right, youngest to oldest. The pod where the white membrane has detached with clear seed margins would be considered at R6.5 growth stage.

Plant appearance at growth stage R6.5 will vary by variety so determination should be based on the uppermost four nodes across the field and specifically whether seed have separated from the white membrane. For indeterminate type soybean varieties, when the last pods could be considered at the R6.5 reproductive stage, the plant may already be at the R7 reproductive stage with at least one mature pod (Figure 3).

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Figure 3. Soybean plants between the R6.5 to R8 reproductive growth stages.

Paraquat, Aim, Sharpen, and sodium chlorate are contact herbicides, thus good coverage is essential. Also, environmental conditions following application can greatly affect efficacy. Paraquat label states that it is rain fast in 15 to 30 minutes after application. Defol 5 label (sodium chlorate) states that applications should not be made if rainfall is anticipated within 24 hours, and as stated on the label, defoliation will be best on sunny, hot, and humid days. The longer it remains on the plant the better it will perform.

Producers must also consider the required preharvest interval (PHI) associated with each product. When using multiple products, the longest PHI must be adhered to. Labeled rates and comments are presented in Table 1 which was adapted from the 2021 Louisiana Suggested Chemical Weed Control Guide.

Redbanded Stink Bug Considerations

Across the state, redbanded stink bug (RBSB) numbers are increasing as the growing season progresses. LSU AgCenter entomologists recommend the control of threshold populations of RBSB until the soybean are out of the field. This means that the inclusion of an insecticide for the control of RBSB with a harvest aid application could be necessary (sodium chlorate cannot be tank-mixed with any insecticide). It is important to keep in mind however, 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 per acre per year 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 all label materials prior to any use of labeled product. When label restrictions prevent the inclusion of an insecticide with the harvest aid application, growers should not delay the harvest of soybean so that the seed can be removed from the field as quick as the label allows.

Table 1. Herbicides labeled for use as a desiccant in soybean.

Active Ingredient and Rate

Formulated Product and Rate

Weeds Controlled

Remarks and Precautions

carfentrazone @ 0.016-0.023 lb/A

Aim 2EC @ 1-1.5 oz/A;

Add 1% v/v COC

Better on morningglories than pigweed, sicklepod, etc.

Apply after crop has matured and grain has begun to dry down. More effective on annual vines. Do not apply within 3 days of harvest. Apply in 10 gal. by ground, 5 gal. by air.

saflufenacil @ 0.022-0.045 lb/A

Sharpen @ 1 - 2 oz/A;

Add 1% v/v MSO + 8.5 lb/100 gal AMS

Morningglories and other broadleaf weeds

Apply once soybean has reached physiological maturity (all pods and seeds have no green color). Indeterminate varieties: 65% brown pods, more than 70% leaf drop, 30% or less seed moisture. Determinate varieties: more than 50% leaf drop and remaining leaves are yellowing. Preharvest interval is 3 days.

paraquat @ 0.13 - 0.25 lb/A

paraquat (2 lb/gal formulation) @ 8-16 oz/A;

paraquat (3 lb/gal formulation) @ 5.4-10.7 oz/A;

Add 0.25% v/v NIS; see label

Desiccation of weeds and soybeans only

Indeterminate varieties: 65% of pods are mature or moisture content is 30% or less. Determinate varieties: 50% leaf drop and remaining leaves are yellow. Some drought stressed weeds will not be desiccated. Do not graze or harvest for hay. Apply in 20 gal. by ground or 5 gal. by air. Preharvest interval is 15 days. Immature soybeans will be injured.

sodium chlorate @ 6 lb/A

6 lb/gal formulation @ 1 gal/A;

5 lb/gal formulation @ 1.2 gal/A;

3 lb/gal formulation @ 2 gal/A

Desiccation only. Level of weed control is affected by environmental conditions.

Apply 7-10 days before harvest. Apply in 20 gal. by ground, 5 gal. by air. Check label for environmental conditions most favorable for desiccation. Apply under high temperatures and humidity.


Diagnosing In-Season Potassium Deficiency in Cotton

Rasel Parvej, LSU AgCenter Soil Fertility Specialist

Potassium (K) is the second most critical nutrient after nitrogen (N) for cotton production. Potassium deficiency can cause significant lint yield reduction with reduced fiber quality. Cotton experiences K deficiency for several reasons. One of the main reasons is cotton grown in soils with low soil-test K level and received no potassium fertilizer. Also, any biotic or abiotic stresses during the growing season such as insect damage, diseases, nematode, compaction, drought etc. that suppress cotton root growth result in reduced K uptake and increased deficiency. Although we had plenty of rain this year, the last couple of weeks we had to turn our irrigation on to minimize water stress especially during blooming period, the most critical stage to set maximum yield potential and any stress during this period will cause significant yield reduction. Figure 1 shows cotton response to K deficiency.

A bale of cotton requires about 52 lb potash (K2O) per acre with the peak accumulation occurs couple of weeks after first blooming, when cotton uptakes around 2.2 to 3.5 lb K2O per acre per day. Any shortage of K supply during this peak accumulation period will result K deficiency and yield reduction. Not all the plant parts of cotton are similarly sensitive to K deficiency. The order of sensitive to K deficiency is stems > roots > bolls > leaves. Stem is the most sensitive and leaf is the least sensitive to K deficiency. So, any K deficiency symptom in cotton leaves signify all the other plant parts are already affected. Potassium deficiency symptom first appears as yellowish-white mottling between the veins, then the center of these yellowish spots dies followed by numerous brown specks between veins, around the margins, and at the tips of leaves and eventually the whole leaf becomes reddish-brown and rusty colored. Potassium deficiency symptoms usually appear on the lower older leaves early in the growing season, but most frequently appear on the upper younger leaves of heavily fruiting cotton plants later in the growing season (Figure 2).

Cotton plants can experience K deficiency without producing any deficiency symptoms. This is called hidden K deficiency or hidden hunger. The best way to diagnose K deficiency with or without deficiency symptoms in cotton is to take tissue samples during early blooming period. For tissue sampling, at least 20 uppermost recently mature leaves without petioles from the 3rd to 5th node from the terminal (a quarter-sized main-stem leaf at the top of the plant should be counted as the 1st leaf) should be collected during the early blooming period and sent immediately to the diagnostic lab (e.g., LSU AgCenter Soil Testing and Plant Analysis Laboratory, Baton Rouge, LA) for K concentration. The critical leaf-K concentration ranges from 1.5 to 3.0% at the early bloom stage and 0.75 to 2.5% at the late bloom stage. Therefore, cotton fields with leaf K concentration lower than 1.5% K at the early blooming period should be fertilized with potassium fertilizer to rescue some yield losses and cotton, if deficient in K, is very responsive to K fertilization during blooming stage. Top-dress of 100 lb dry potash (Muriate of Potash; 0-0-60) per acre should be enough for in-season management of K deficiency. Irrigation or at least 0.25” rain followed by in-season application would result rapid K uptake and better response.

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Figure 1. Cotton response to K deficiency. Potassium sufficient plants on the left and deficient plants on the right. Photo was taken from research trial conducted at the LSU AgCenter – Macon Ridge Research Station, Winnsboro, LA.

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Figure 2. Potassium deficiency symptoms during mid-blooming period of cotton. Photo was taken from research trial conducted at the LSU AgCenter – Macon Ridge Research Station, Winnsboro, LA.

Fusarium Head Blight of Wheat (Scab) in Louisiana

Steve Harrison, Trey Price, and Boyd Padgett, LSU AgCenter scientists; Kelly Arceneaux, Allyson Harding, Katie Fontenot, Reddy Biradar, Myra Purvis, Dustin Ezell, Fred Collins, and Laura Lee, LSU AgCenter research associates.

Introduction

Fusarium head blight (FHB, commonly referred to as scab) is the most important disease of wheat in Louisiana and is primarily caused by Fusarium graminearum. The disease is most severe in years with rainfall and warm weather during flowering. The fungus causes shriveled and poorly filled seed that results in reduced yield and test weight. The pathogen also produces the mycotoxin, deoxynivalenol (DON), which is toxic to animals and humans and can cause grain rejection at the elevator. Scab has been a major problem in Louisiana wheat over the past several years and is a major factor in the decline of Louisiana wheat acreage. Management of FHB is difficult because there are no highly effective single management practices (varieties or fungicides) and an integrated approach is required.

Epidemiology and Symptoms

Scab management begins with an understanding of the conditions favoring infection and disease development. The fungus also infects corn and wheat fields planted to corn the previous year, are at higher risk of developing scab than those planted after other crops. Infested corn debris (also wheat straw and other hosts) can harbor the pathogen and serve as initial inoculum sources. Fungal spores produced on this debris are dispersed by rain splash or wind to nearby wheat plants. Other inoculum can be introduced into the field via windblown spores. Infection normally occurs during flowering but can occur from head emergence though early grain fill. Prolonged periods of rainfall during flowering and temperatures from 75-85 F are conducive to scab development. Symptoms usually appear 10 to 14 days after flowering as bleached sections of heads, which will be evident from the turn row (Figure 1). This symptom may be mistaken as maturing wheat later in the season. Upon closer inspection, affected fields will usually have infected heads showing the characteristic bleached appearance of sections (florets) with pinkish/salmon/light orange coloration along the glumes. This coloration is caused by millions of microscopic spores (reproductive structures) of the pathogen. Diseased heads usually have sections of healthy florets along with the diseased sections on the same head. In extreme cases, however, the entire head may be bleached out by infection. At harvest, infected seed will be shriveled, off-color, much lighter than healthy kernels, and are referred to as “tombstones” (Figure 2) or Fusarium Damaged Kernels (FDK).FDK is an important indicator of variety resistance and of grain quality and test weight.

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Figure 1. Fusarium head blight (scab) symptoms.

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Figure 2. Wheat seed infected with Fusarium head blight (scab)

DON

The advisory levels for DON are as follows:

  • One ppm DON on finished wheat products such as flour, bran, and germ, for human consumption.
  • 10 ppm DON on grains and grain by-products and 30 ppm in distillers grains, brewers grains, and gluten feeds with limits on daily intake.
  • 5 ppm DON on grains and grain by-products destined for swine with the added recommendation that these ingredients not exceed 20% of their diet.
  • 5 ppm DON on grains and grain by-products destined for all other animals with the added recommendation that these ingredients not exceed 40% of their diet.

This guidance has been prepared by the Division of Plant and Dairy Food Safety in the Center for Food Safety and Applied Nutrition and the Office of Surveillance and Compliance in the Center for Veterinary Medicine at the Food and Drug Administration (FDA). Additional information on DON can be found at: Guidance for Industry and FDA: Advisory Levels for Deoxynivalenol (DON) in Finished Wheat Products for Human Consumption and Grains and Grain By-Products used for Animal Feed

Management

The best FHB management strategy is a combination of a resistant or moderately resistant variety coupled with a timely fungicide application if the scab forecast model indicates a significant risk of scab development. The scab risk forecast can be found at: http://www.wheatscab.psu.edu/It is important to have a management plan in place before planting. Each year LSU AgCenter scientists evaluate scab severity in variety trials, and in inoculated, misted nurseries at several locations. This information along with yield data can be used to help a grower choose varieties with moderate levels of FHB resistance along with good yield and agronomic characteristics. That data can be accessed at: http://www.wheat.lsu.edu/data.shtml.

Other management practices that may aid in management include: crop rotation with non-host crops, tillage, mowing/shredding, or staggered planting/varietal maturity. At harvest, combine fan speed may be increased to blow out infected seed, which is lighter than healthy seed. This practice can lower DON, and increase test weight of harvested grain. Additionally, seed cleaning equipment may help remove affected seed but may not be cost effective. These cultural practices alone will not completely manage FHB. If possible, plant moderately resistant, locally adapted varieties, avoid following corn, and start with a clean seedbed if possible.

Apply a suppressive fungicide in a timely manner. Triazole fungicides are suppressive on FHB, and some are more effective than others (Table 1). Generally, applications of Prosaro, Proline, or Caramba at flowering will reduce scab severity and DON while preserving yield. More recently, an SDHI/triazole premix marketed as Miravis Ace, has been shown to be competitive with the best triazoles.

Table 1. Fungicide Efficacy for Control of Fusarium head scab

Class

Fungicides(s) Active Ingredient

Product

Rate (fl. oz)

Head Scab1

Harvest Restriction

Strobilurin

Picoxystrobin 22.5%

Aproach SC

6.0 – 12.0

NL

Feekes 10.5

Strobilurin

Pyraclostrobin 23.6%

Headline SC

6.0 - 9.0

NL

Feekes 10.5

Triazole

Metconazole 8.6%

Caramba 0.75 SL

10.0 - 17.0

G

30 days

Triazole

Tebuconazole 38.7%

Folicur 3.6 F5

4.0

F

30 days

Triazole

Prothioconazole 41%

Proline 480 SC

5.0 - 5.7

G

30 days

Triazole

Prothioconazole19%

Tebuconazole 19%

Prosaro 421 SC

6.5 - 8.2

G

30 days

Triazole

Propiconazole 41.8%

Tilt 3.6 EC2

4.0

P

Feekes 10.5.4

Mixed

Tebuconazole 22.6%

Trifloxystrobin 22.6%

Absolute Maxx SC

5.0

NL

35 days

Mixed

Cyproconazole 7.17%

Picoxystrobin 17.94%

Aproach Prima SC

3.4 - 6.8

NR

45 days

Mixed

Prothioconazole 16.0%

Trifloxystrobin 13.7%

Delaro 325 SC

8.0

NL

Feekes 10.5

35 days

Mixed

Pydiflumentofen 13.7%

Propiconazole 11.4%

Miravis Ace SE

13.7

G3

Feekes 10.5.4

Mixed

Fluapyroxad 2.8%

Pyraclostrobin 18.7%

Propiconazole 11.7%

Nexicor EC

7.0 - 13.0

NL

Feekes 10.5

Mixed

Fluoxastrobin 14.8%

Flutriafol 19.3%

Preemptor SC

4.0 - 6.0

NL

Feekes 10.5 and

40 days

Mixed

Fluxapyroxad 14.3%

Pyraclostrobin 28.6%

Priaxor

4.0 - 8.0

NL

Feekes 10.5

Mixed

Propiconazole 11.7% Azoxystrobin 13.5%

Quilt Xcel 2.2 SE2

10.5 - 14.0

NL

Feekes 10.5.4

Mixed

Prothioconazole 10.8%

Trifloxystrobin 32.3%

Stratego YLD

4.0

NL

Feekes 10.5

35 days

Mixed

Benzovindiflupyr 2.9%

Propiconazole 11.9% Azoxystrobin 10.5%

Trivapro SE

9.4 - 13.7

NL

Feekes 10.5.4

14 days

1Application of products containing strobilurin fungicides may result in elevated levels of the mycotoxin Deoxynivalenol (DON) in grain damaged by head scab.

2Multiple generic products containing the same active ingredients also may be labeled in some states.

3Based on application timing at the beginning of anthesis (Feekes 10.5.1).

DO NOT APPLY a QoI (strobilurin) fungicide after flag leaf emergence. These fungicides can increase DON.

Timing is critical. There is a very short window during flowering to make an effective fungicide application for FHB control (Tables 2, 3). The biggest problem is that ideal conditions (wet weather) for FHB infection are not conducive to making fungicide applications by ground. Head coverage also is critical. Sprayers should be calibrated to deliver maximum water volume (minimum 15 GPA by ground, 5 GPA by air) and optimal droplet size (300 to 350 microns). For ground sprayers, nozzles angled at 30° to the horizontal will maximize head coverage. Some research has shown that dual nozzles angled in opposite directions will also increase head coverage.

Table 2. Fungicide timing evaluation at Macon Ridge, 2020

Treatment (fl oz/a)

Growth

Stage at

Application

Scab
0-9

Yield
bu/a

Non-treated

--

7.8

21.0

Prosaro (6.5)

Flowering

3.3

43.8

Caramba (13.5)

Flowering

3.0

41.7

Miravis Ace (13.7)

Flowering

3.3

49.4

Miravis Ace (13.7)

Heading

3.0

40.2

Miravis Ace (13.7)

6 DA Flowering1

6.8

35.2

LSD P=0.1

0.8

3.6

1Six days after flowering.

Table 3. Fungicide timing evaluation at Macon Ridge, 2021

Treatment (fl oz/a)

Growth

Stage at

Application1

Scab
% Severity

Non-treated

--

31.6

Prosaro (6.5)

Flowering (FLW)

20.1

Caramba (13.5)

Flowering

21.3

Miravis Ace (13.7)

Flowering

11.8

Miravis Ace (13.7)

Heading

19.1

LSD P=0.1

1.0

1Applied at flowering followed by an application six days later.

It is common to see several years of scab epidemics followed by a year with little to no disease. In Louisiana, scab epidemics have occurred in 5 of the last 6 seasons. There are disease forecasting tools that predict the likelihood of a scab epidemic based on weather pattern, variety susceptibility, and crop growth stage. The ScabSmart (www.wheatscab.psu.edu ) risk assessment tool that is based on temperature and relative humidity is available online and has regional commentary that will help determine scab risk at your given location. This is the only practical way to determine the need to spray since scab symptoms may not show up for a week or more after infection occurs. For more information, please see the following resources:

www.scabsmart.org

www.scabusa.org

http://www.wheat.lsu.edu/data.shtml

Varietal Resistance to Fusarium Head Blight Disease

A very high priority is placed on development of FHB resistant wheat varieties by the SunGrains breeders (http://www.sungrains.lsu.edu/), particularly the LSU AgCenter wheat breeding program. The goal is to develop high-yielding FHB-resistant wheat varieties adapted to the unique environment of the Gulf Coast region and to present information to growers to help them deal effectively with FHB. To accomplish this, misted nurseries inoculated with scabby corn are grown at Alexandria, Baton Rouge, and Winnsboro to characterize FHB reaction of LSU breeding lines and entries in the state variety trials and regional nurseries. Molecular markers and genomic selection methods are also used to enable ‘stacking’ of several FHB resistance genes in the same variety. This is important because there are no single genes that provide a high level of resistance, but genes can be stacked in a variety to provide a higher level of resistance.

When evaluating FHB ratings keep in mind that scab is greatly influenced by rainfall and temperature during heading. When comparing FHB, FDK, and DON of varieties in the yield trials, it is important to compare varieties that head within a few days of each other. Very early or late-heading varieties may escape disease by virtue of flowering at a time when weather was not conducive for infection. The use of misted and inoculated nurseries (Figure 3) ensures heavy disease pressure during flowering and avoids confounding of genetic resistance with maturity differences. Determination of genetic resistance should be based on several locations and years when scab was present. AgCenter researchers collaborate with other scientists across the nation as a part of the U.S. Wheat and Barley Scab Initiative(https://scabusa.org/), and this is an excellent source of information on scab. Efforts from this multi-state initiative are directed toward developing and identifying varieties and management practices that minimize the impact of this disease on growers. In addition, new and existing fungicides are evaluated for their ability to reduce infection and spread of scab.

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Figure 3. A nursery for misting and inoculating wheat with Fusarium head blight.

The complete wheat performance report and data tables can be found at the wheat and oat variety trials website or http://www.wheat.lsu.edu/data.shtml.Table 4 gives a Fusarium reaction type and FHB traits data based on at least two years of data in the misted FHB nurseries. FHBIndex is a numerical rating of FHB resistance calculated based on percent of the test mean of each variety for FHB, FDK, and DON.A lower FHBI indicates greater scab resistance. Misted nursery data is a worst-case scenario for scab and is useful to separate variety reaction. Normal yield plots and grower fields are very unlikely to experience this magnitude of disease pressure.

Table 4.Fusarium Headblight Misted Nursery Data from Alexandria and Winnsboro for Normal Wheat Variety Trials.

HarrisonTable 4pdf

Varieties are classified as Resistant (R), Moderately Resistant (MR), Moderately Susceptible (MS), Susceptible (S) or Very Susceptible (VS) based on the FHB Index for two or three years. There are big differences in FHB reaction of the varieties. If possible, growers should choose a MR or R variety that has good grain yield and agronomic characteristics. There are ten varieties tested across north Louisiana across two years that are classified as resistant or moderately resistant to scab (Table 4) and another seven varieties classified as intermediate in scab reaction. Two-year FHB Index ranged from 4.3 to 19.6 with an average of 10.1 and a range of 4.3 to 19.6.The varieties classified as R or MR had DON concentrations of six percent or less.

Nine of the varieties classified as R or MR had above average yield (Table 5) and seven of these nine had excellent stripe rust resistance, demonstrating that it is possible to choose high-yielding varieties with good scab and stripe rust resistance. An additional seven varieties have an intermediate reaction to scab. Scab reaction should be an important consideration when choosing varieties for production in Louisiana.

Table 5. Fusarium reaction and agronomic performance of released varieties in the normal maturity trial across north Louisiana for two years.

HarrisonTable 5pdf

Acknowledgements

  • The authors appreciate and acknowledge support for this research provided by the Louisiana Soybean and Grain Research and Promotion Board.

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This research is also supported by the U.S. Department of Agriculture, under Agreement

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No. 59-0206-8-206 and No 59—2-6-137. This is a cooperative project with the U.S. Wheat & Barley Scab Initiative.

  • DON analysis was conducted by the USDA Mycotoxin Diagnostic Laboratory in the Department of Plant Pathology Department at the University of Minnesota under the direction of Dr. Yanhong Dong.

Harvest Aid Use in Grain Sorghum

Matt Foster, LSU AgCenter Grain Sorghum Specialist

The use of a harvest aid in grain sorghum is a common management practice in Louisiana. Even though grain sorghum harvest is possible without using a harvest aid, considering the pros and cons will help you make the most out of your sorghum harvest. Unlike corn, sorghum is a perennial crop and won’t naturally dry down after physiological maturity. The use of a harvest aid will desiccate the green sorghum plant along with any weeds that may be present. Key benefits of using a harvest aid include:

  • More efficient combining
  • Dry down of the late-emerging, non-productive suckers or tillers
  • Earlier harvest that can minimize weather-related damage and help meet pricing or delivery deadlines

Be aware that harvest aids do not speed up the maturity process of the grain. If a harvest aid is applied too early (before physiological maturity), grain yield and test weight can be negatively impacted. Approximately 25% of seed weight is filled during the last 10-14 days prior to physiological maturity. Therefore, it is very important to scout the whole sorghum field and properly identify mature kernels before applying a harvest aid. Grain sorghum matures from the top of the head and progresses downward (Figure 1), so scouting should focus on the bottom of the head for grain maturity. Sorghum seed change color and accumulate hard starch similar to maturing corn kernels. If you observe a substantial amount of green seed rather than red or brown mature seed, the field needs more time to mature. Mature seed will contain approximately 25-30% moisture and will be hard to penetrate when pinching the bottom of the kernel between your fingernails.

Physiological maturity in grain sorghum is reached when a “black layer” is visible at the base of the kernel following individual detachment from their outer glume (Figure 2). Once the black layer is formed, water and nutrient uptake from the green plant is halted. Therefore, applying a harvest aid after physiological maturity has little to no effect on grain moisture or drying rate. Environmental conditions are the main factor influencing grain drying rate.

Keep in mind that harvest aid application may accelerate plant degradation and promote stalk lodging (especially if plants are stressed). Therefore, it is recommended to apply harvest aids to only the fields that can be harvested within 14 days of application.

Harvest aid options include carfentrazone, glyphosate, and sodium chlorate. For complete information concerning these products, please consult the 2021 Louisiana Suggested Chemical Weed Control Guide and the product labels.

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Figure 1. Grain sorghum head with green immature seed at the bottom (left) and red/brown mature seed at the top (right). LSU AgCenter photo by Matt Foster.

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Figure 2. Grain sorghum seed maturity comparison. (Source: 2015 KSU Sorghum Growth and Development).

Nematology Update for Louisiana – August 2021

Tristan Watson, LSU AgCenter Nematologist

Plant-parasitic nematodes are semi-microscopic roundworms that cause considerable root damage to fiber and grain crops grown in Louisiana. During the 2020 growing season, 101 soybean fields and 43 cotton fields were randomly selected throughout the state and sampled for nematodes. The reniform nematode (Rotylenchulus reniformis) was detected in 55% of soybean fields and 41% of cotton fields, whereas the southern root-knot nematode (Meloidogyne incognita) was detected in 16% of soybean fields and 23% of cotton fields. For both nematode species, population densities were often above the damage thresholds for soybean and cotton, suggesting significant yield loss likely occurred on these crops. The invasive guava root-knot nematode (Meloidogyne enterolobii) was not detected in any soybean or cotton field; however, growers should be vigilant to monitor fields that have recently been rotated with sweetpotato for symptoms, as contaminated sweetpotato storage roots imported from out-of-state are a primary means of entry into Louisiana for this new pest.

Now is the time to scout fields for nematode damage so that a management plan can be developed for next year’s crop. The southern root-knot nematode causes characteristic root galling (i.e., root knots; Figure 1a), not to be mistaken for the loosely adhering nitrogen-fixing nodules common on soybean and other legume crops. Infested fields typically show irregular patches of stunted crop growth (Figure 1b), with significant root galling observed on plants uprooted from the center of the patch. The reniform nematode doesn’t produce root symptoms that can be easily diagnosed in the field (Figure 2a); however, heavily infested fields often show symptoms similar to that of nutrient deficiency, including premature yellowing of leaves and stunting of growth (Figure 2b).

Management strategies are available for both of these important nematode species. Several nematicides are registered for use on soybean and cotton. Please refer to the 2021 Louisiana Plant Disease Management Guide for a list of available products and suggested application rates (link below). Root-knot and reniform nematode resistant soybean and cotton varieties are also commercially available to growers and are currently under evaluation by LSU AgCenter researchers.

We encourage all growers to utilize LSU AgCenter’s Nematode Advisory Service. Growers are invited to submit soil and root samples collected from any symptomatic commercial fields during the 2021 growing season to the Nematode Advisory Service for free nematode diagnostics. Below is a link to the LSU AgCenter Nematode Advisory Service root-knot nematode survey form and a guide on how to sample your field for nematodes. This service will help you identify if nematodes are a problem in your field and assist you with developing an appropriate management strategy.

Root-Knot Nematode Survey Form: https://www.lsuagcenter.com/profiles/coverstreet/articles/page1510779228352

How to Sample for Nematodes: https://www.lsuagcenter.com/portals/our_offices/departments/plant-pathology-crop-physiology/nematode-advisory-service/how-to-submit-a-sample

2021 Louisiana Plant Disease Management Guide: https://www.lsuagcenter.com/portals/communications/publications/management_guides/plant_disease_guide


Fig 1_Tristan_LA Crops Augustpng

Figure 1 – Uprooted soybean roots displaying extensive root galling due to root-knot nematode (Meloidogyne incognita) parasitism (A), and field-level symptoms of root-knot nematode damage showing a characteristic irregular patch of stunted growth (B). Photo credit: C. Overstreet.

Fig 2_Tristan_Augustpng

Figure 2 – Microscopic examination of reniform nematode (Rotylenchulus reniformis) actively parasitizing a soybean root (A), and field-level symptoms of reniform nematode showing premature yellowing of soybean leaves and stunted growth similar to that of nutrient deficiency (B). Photo credit: C. Overstreet.

Weed Management in Winter Wheat

Daniel Stephenson, LSU AgCenter Extension Weed Scientist

Winter wheat prices could encourage an increase in acres in Louisiana this coming fall and weed management is critical for maximizing yield. Strategies for a sound weed control program in wheat is very similar to cotton and soybean: plant into a clean seedbed, use residual herbicides, and target small, less than 3-inch, weeds.

The best weed control and wheat yields are achieved when weeds are managed in the fall. Prior to planting, fields should receive a herbicide application to control all existing vegetation. This can be accomplished with glyphosate or paraquat, but tillage is another option. Ryegrass, annual bluegrass, little barley, canarygrass, vetch, henbit, and other grass and broadleaf weeds can be troublesome in Louisiana winter wheat.

Ryegrass and other grass weed management requires two herbicide applications. The first should be applied in the fall and the second in January or February. Below is a series of bullet points describing ryegrass and other grass control options.

  • Anthem Flex or Zidua will provide residual control. Both must be applied as a delayed-PRE following 80% wheat emergence. They can provide residual control/suppression of ryegrass, annual bluegrass, little barley, canarygrass, and may other grass and small-seeded broadleaf weeds. Neither Anthem Flex or Zidua will provide foliar control of any weed, so fields must be clean when wheat is planted.
  • Finesse applied preplant or PRE at 0.5 oz/A will control or suppress ryegrass and many other grass and broadleaf weeds.
    • If soybean will be planting following wheat harvest:
      • 4 month rotation interval for BOLT soybean
      • 6 month rotation interval for STS soybean
      • 18 month rotation interval to corn, cotton, grain sorghum, rice, and soybean
      • ALS-resistant ryegrass or other weed species will not be controlled.
  • Metribuzin must be applied at the 2- to 3-leaf wheat stage before ryegrass emerges. Wheat tolerance to metribuzin varies by variety.
  • PowerFlex HL can be applied POST when wheat reaches the 3-leaf growth stage to jointing. PowerFlex HL application in the fall will provide control/suppression of annual bluegrass. However, it will not control ALS-resistant weeds. Rotation interval to soybean is 5 months.
  • Osprey can be applied POST from emergence up to jointing. One of Osprey’s strengths is annual bluegrass control. Osprey will not control ALS-resistant weeds. Rotation interval to soybean is 3 months. Osprey Xtra is another product labeled for use, but the LSU AgCenter has not evaluated the utility of this product.
  • Axial XL should be applied in January/February as the second application in a two-pass program for ryegrass management. Suspected ACCase-resistant Italian ryegrass has been a concern in Louisiana. Axial XL will not control little barley or annual bluegrass. Also, no broadleaf weed control is possible with Axial XL.

Vetch, henbit, and other broadleaf winter weeds are also a concern in wheat. Severe infestations often require two applications like the ryegrass management options shown earlier.

  • PowerFlex HL or Harmony Extra both provide control of troublesome broadleaf weeds.2,4-D is also another option, but cannot be applied until wheat has completed tillering. PowerFlex HL in the fall following by Harmony Extra in January/February is an overall good program for broadleaf weeds in wheat.

Louisiana producers have the tools available for a good weed management program in winter wheat. As will all crops, timing is essential. Target weeds prior to emergence with residual herbicides and weeds less than 3-inches tall with POST herbicides. And as always, read the herbicide label before doing anything. This article did not discuss adjuvants and many other aspects of the labels, so please read them. Below is the link to the Small Grains section of the 2021 Louisiana Suggest Chemical Weed Control Guide.

https://www.lsuagcenter.com/~/media/system/d/9/c/6/d9c65025862a52032feaf01c7f510f5a/21j_smallgrains%20kppdf.pdf

If you have questions, please contact your local parish agent. You can reach me at 318-308-7225 or dstephenson@agcenter.lsu.edu.Thanks and have a great day.

8/12/2021 3:56:46 PM
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