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June 16 edition of Louisiana Rice Notes

June 16 edition of Louisiana Rice Notes published on No Comments on June 16 edition of Louisiana Rice Notes

The June 16 installment of the Louisiana Rice Notes newsletter covers the current weather influence on disease pressure, sheath blight management, SARM, grasshopper, stink bug management, and the use of gibberellic acid for the ratoon crop.

LA Rice Notes 6_Page_1

 

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Southern Corn Rust Confirmed in Louisiana

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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.

 

Foliar symptoms of southern rust.
Foliar symptoms of southern rust.
Southern rust on leaf sheath.
Southern rust on leaf sheath.
Foliar symptoms of common rust.
Foliar symptoms of common rust.

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

 

Table 11Additional 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.

scr tableAdapted 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.

Transform (Sulfoxaflor) Granted Section 18 for Use in Louisiana Cotton

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The EPA has granted a section 18 request for the use of Transform (sulfoxaflor) for 2016 Louisiana cotton production season. Please see the link below for information on conditions and restrictions outlined by the section 18 label.

Section 18 Authorization Letter for Transform in Louisiana Cotton

Figure 3 (stripe rust).

Wheat and Corn Pathology Update

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Wheat and Corn Pathology Update (4/15/2016)

Trey Price, Field Crop Pathology, Macon Ridge Research Station

Boyd Padgett, Wheat Pathology, Dean Lee Research Station

Wheat

At the time of this writing, most wheat in the state is at or past flowering with the exception of some later maturing varieties.  We have seen issues with vernalization in a few entries in variety trials throughout the state.  Simply, there was not enough cold weather to trigger reproductive development.  Fusarium head blight (scab, Figures 1 & 2) has been of utmost concern to the few wheat producers we have this year.  Conditions have been favorable for scab during flowering, and applications of Caramba or Prosaro using maximum rates and water volumes are recommended for management.  The best control we can expect is 50%, and time will tell if applications were successful or not.

 

 

Figure 1 (Fusarium head blight).
Figure 1 (Fusarium head blight).

 

Figure 2 (scabby kernels below healthy ones).
Figure 2 (scabby kernels below healthy ones).

Other concerns this season have been stripe rust (Figure 3) and leaf rust (Figure 4).  Conditions are currently favorable for both diseases; however, stripe rust activity is slowly decreasing and leaf rust activity is increasing rapidly.  Most varieties are resistant to stripe, leaf, or both rusts, and fungicide applications are usually not necessary.  In susceptible varieties, rusts are effectively and economically managed with triazole fungicide applications.

 

Figure 3 (stripe rust).
Figure 3 (stripe rust).
Figure 4 (leaf rust).
Figure 4 (leaf rust).

 

Other diseases of note have been Septoria leaf blotch (Figure 5) and bacterial streak (Figure 6).  Septoria usually remains low in the canopy and does not escalate to damaging levels; however, if infections occur on the flag leaf or flag leaf -1, a fungicide application may be warranted.  Most fungicides provide adequate control of Septoria leaf blotch.  Bacterial streak cannot be reactively managed.  Fungicides are not effective, of course, so variety selection in the fall is the primary management technique.  LSU AgCenter scientists rate wheat varieties for multiple diseases at multiple locations in the state, and the results are available online (www.lsuagcenter.com), from your county agent, or your nearest research station.  Bacterial streak and Septoria leaf blotch can be difficult to diagnose.  Older Septoria lesions will have black spots (pycnidia) within lesions, while bacterial streak will not.  Younger Septoria lesions may be indistinguishable from bacterial streak lesions; therefore, a quick diagnostic method can be used.  First, cut an affected leaf section then submerge in water.  Wait 5-10 minutes, and observe for bacterial streaming (Figure 7).  This can be accomplished on the turn row with a pocket knife and bottled water.

 

Figure 5 (Septoria leaf blotch).
Figure 5 (Septoria leaf blotch).

 

 

    

Figure 5 (Septoria leaf blotch). Figure 5 (Septoria leaf blotch). Figure 6 (bacterial streak).
Figure 6 (bacterial streak).

 

Figure 7 (bacterial streaming).
Figure 7 (bacterial streaming).


Corn

It is no secret that this has been a tough year for corn so far.  Soon after early planting, most producers received copious amounts of rainfall (particularly in NELA) over an extended period.  Many fields were replanted because of flooding.  On stands that withstood the flooding, the majority of field calls have involved corn plants that had poor nodal root development causing them to fall over (Figures 8 & 9) and stressing or breaking the mesocotyl (first true stem) in the process (Please see Dr. Dan Fromme’s post for more information on rootless corn syndrome (RCS)  http://louisianacrops.com/category/crops/corn/).  Most producers planted on the higher end of plant populations allowing tolerable losses due to RCS.

 

 

 Figure 8 (plant death as a result of RCS).
Figure 8 (plant death as a result of RCS).

 

Figure 9 (normal vs. poor nodal root development).
Figure 9 (normal vs. poor nodal root development).

 

Interestingly, damping off (Rhizoctonia solani) was commonly observed in RCS situations where fields had been planted for at least one month (V3-V4).  Over time, seed treatment efficacy declined, plants were stressed (particularly at the mesocotyl), and the pathogen took advantage of optimal environmental conditions.  Classic damping off lesions were observed on the upper sections of mesocotyl (Figures 10 & 11), and the pathogen was subsequently isolated in the laboratory.

 

 

 Figure 10 (damping off).
Figure 10 (damping off).

 

 Figure 10 (damping off).
Figure 10 (damping off).

 

Since we have a significant number of corn acres that will be relatively late, foliar diseases, southern rust (Figures 12 & 13) in particular, will likely be a concern this year.  Southern rust (SR) can be devastating if it develops early (tasseling or before) and conditions (warm, wet) are favorable for development.  Scouting is key to managing this disease.  Typically SR will develop low in the canopy and progress upward.  Fungicides are effective on SR (Table 1).  If the disease is present at or before tasseling, fungicide applications are warranted.  Depending on disease severity and prevailing environmental conditions, applications could occasionally be warranted between tasseling and milk stage.  Applications are rarely warranted after this stage, because the crop will usually “out-run” disease progression.  Keep in mind that tasseling is the most vulnerable stage to foliar diseases.  As plants mature, more defoliation can be tolerated as time goes by.

 

Figure 12 (southern rust on upper surface of leaf).
Figure 12 (southern rust on upper surface of leaf).

 

 Figure 13 (southern rust on leaf sheath).
Figure 13 (southern rust on leaf sheath).

Northern corn leaf blight (NCLB) is an annual problem in Louisiana.  In fact, we can probably drop the “northern” at this point.  Scouting also is key to managing this disease.  Similar to SR, if NCLB develops during late vegetative stages or near tasseling, a fungicide application may be advisable.  Once the disease initiates, it will continue to progress for the remainder of the season.  Hot and dry weather may slow NLCB progression somewhat, but with most of our acreage irrigated, temperature and moisture requirements for the pathogen are satisfied until black layer.  Specific fungicide efficacy data on NCLB remains elusive; however, pooling of nationwide data indicates that fungicides are effective on NCLB (Table 1).  Similar to SR, the further the crop is past tasseling, more defoliation can be tolerated.

For more information please do not hesitate to contact your local county agent, specialist, or nearest research station.  Please visit our websites (www.lsuagcenter.com and www.louisianacrops.com) for the latest in field crop pathology.

 

 

 

 

 

Table 1.  Fungicide Efficacy for Control of Corn Diseases—April 2016

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.

 

Soybean Insecticide Seed Treatment Decisions

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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.

Photo 1.  A view of a field heavily-infected with FHB.

Conditions Favorable for Fusarium Head Blight (scab) in Wheat Again This Year

Conditions Favorable for Fusarium Head Blight (scab) in Wheat Again This Year published on No Comments on Conditions Favorable for Fusarium Head Blight (scab) in Wheat Again This Year

Trey Price, Field Crop Pathology, Macon Ridge Research Station;

Boyd Padgett, Central Region Director, Dean Lee Research and Extension Center

Last year Louisiana wheat was devastated by Fusarium head blight (scab) because of warm and wet weather conditions during flowering.  Weather conditions are currently favorable for wheat scab development statewide.  Most of the wheat in the state is at or very near flowering, which is the most susceptible stage to scab infections.  Wheat in southernmost production regions is already showing early signs of scab infection.

The disease is mainly caused by the fungus, Fusarium graminearum, which also causes ear, stalk, and root rots in corn. Symptoms of the disease will first appear 10 to 14 days after flowering as bleached heads which will be noticeable from the turn row (Photo 1).  This symptom is often mistaken with the appearance of maturing wheat.  Upon closer inspection, affected wheat heads will usually have infected kernels showing the characteristic bleached appearance with pinkish/salmon/light orange coloration along the glumes (Photo 2).  This coloration is millions of microscopic spores (reproductive structures) of the fungal pathogen.  There are usually healthy kernels along with the diseased kernels on the same head (Photo 3).  In extreme cases, however, the entire head may be infected.  At harvest, affected seed will be shriveled, off color, and much lighter than healthy kernels and are referred to as “tombstones” (Photo 4).

Photo 1. A view of a field heavily-infected with FHB.
Photo 1. A view of a field heavily-infected with FHB.
Photo 2. Closer view of a head infected with FHB. Note the salmon-colored fungal growth near the center.
Photo 2. Closer view of a head infected with FHB. Note the salmon-colored fungal growth near the center.
Photo 3. Wheat heads with FHB-affected and healthy kernels.
Photo 3. Wheat heads with FHB-affected and healthy kernels.
Photo 4. Diseased kernels (left) vs. relatively healthy kernels (right).
Photo 4. Diseased kernels (left) vs. relatively healthy kernels (right).

The pathogen over summers on corn, wheat, small grain residue, and other grasses.  With that in mind, there are some cultural practices that may aid in management:  crop rotation, tillage, mowing/shredding, or staggered planting/varietal maturity.  At harvest, combine fan speed may be increased to remove infected seed, which is lighter than healthy seed.  Additionally, seed cleaning equipment may help remove affected seed but may not be cost effective.  These cultural practices alone will not completely manage FHB.  An integrated approach is required to lessen the impact of FHB.

Triazole fungicides may be somewhat effective on FHB.  Some earlier research indicated that tebuconazole (Folicur and generics) may reduce incidence and severity of FHB.  Later research has shown that Prosaro (prothioconazole + tebuconazole), Proline (prothioconazole), and Caramba (metconazole) are most efficacious on FHB.  THESE APPLICATIONS WERE MADE UNDER IDEAL CONDITIONS WITH IDEAL TIMINGS AND THE MAXIMUM CONTROL WAS AROUND 50%.  AVERAGE CONTROL WAS ABOUT 40%.

Timing is critical.  We have a very short window during flowering to make an effective application for FHB.  The biggest problem is that ideal conditions (wet weather) for FHB infection are not ideal for making fungicide applications.  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.

It is common to see 2-3 years of epidemics of FHB followed by years with little to no disease.  Judging by the amount of scab we saw last year and current weather conditions, the probability is high for another severe epidemic.  An online (www.wheatscab.psu.edu) risk assessment tool that is based on temperature and relative humidity is available online, which has regional commentary that will help you to determine your risk at a given location.

For more information, please see the following resources:

www.scabsmart.org

www.scabusa.org

http://www.mississippi-crops.com/2015/04/24/wheat-disease-update-april-24-2015/

LA Rice Notes 2016_3_Page_1

Louisiana Rice Field Notes #3

Louisiana Rice Field Notes #3 published on No Comments on Louisiana Rice Field Notes #3

The third edition of the Louisiana Rice Notes newsletter is now available.  This edition covers planting progress, cold damage to rice seedlings, selecting the correct sulfur and zinc fertilizer for rice, Louisiana rice seeding methods poll results, and a little crawfish trivia.  Just click the link below.

LA Rice Notes 2016_3

Figure 2. Corn plant with nodal root development (left) and a corn plant without nodal development (right). Plant taken from a field in Rapides Parish, Louisiana. March 23, 2016.

Rootless Corn Phenomenon Appearing in Louisiana Corn Fields

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Rootless corn has appeared in many fields during the early part of the 2016 growing season in Louisiana. Most are all of the nodal roots are missing in corn that is at the V1 to V2 stage. Existing nodal roots may be stubby and not anchored to the soil. Without an adequate root system, affected plants may be lodged, wilted, stunted, or even die (Figures 1 and 2).

Rootless corn phenomenon is currently attributed to the excessive amounts of rainfall which has eroded the soil near the plant base and/or the strong winds we have experienced breaking the upper roots and hindered the establishment of a strong root system.

Also, many fields currently have a hard packed soil surface from heavy rainfall which has hindered the establishments of the nodal root system penetrating into the soil. Other situations where rootless corn syndrome can occur are under hot and dry conditions on the soil surface, planting too shallow, compacted soils, and loose or cloddy soils.

These symptoms are unlike any associated with herbicide or insect feeding injury. Several sets of roots may not have formed below-ground, the crown may appear to be at or above the surface.

The important thing to remember is that roots will not develop in dry soil. They will not grow toward moisture. Plants can recover if rainfall is received which will soften the soil surface and promote nodal root development. Also, row cultivation may encourage root development if moist soil is thrown around the bases of the plant.

Figure 1. Example of rootless corn plant in the field. Rapides Parish, Louisiana. March 23, 2016.
Figure 1. Example of rootless corn plant in the field. Rapides Parish, Louisiana. March 23, 2016.
Figure 2. Corn plant with nodal root development (left) and a corn plant without nodal development (right). Plant taken from a field in Rapides Parish, Louisiana. March 23, 2016.
Figure 2. Corn plant with nodal root development (left) and a corn plant without nodal development (right). Plant taken from a field in Rapides Parish, Louisiana. March 23, 2016.

 

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