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2013 Macon Ridge Research Station Pest Management and Crop Production Field Day

2013 Macon Ridge Research Station Pest Management and Crop Production Field Day published on No Comments on 2013 Macon Ridge Research Station Pest Management and Crop Production Field Day

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Cotton Leaf Spots

Cotton Leaf Spots published on 1 Comment on Cotton Leaf Spots

Cotton Leaf Spots

Trey Price, Beatrix Haggard, Josh Lofton, Boyd Padgett and Clayton Hollier

LSU AgCenter

Recently, there have been numerous reports of leaf spot in cotton. Individuals who frequent cotton fields should be monitoring for this disease. Currently, an automatic fungicide application is not recommended. The decision to use a fungicide should be made on a field-by-field basis and should take into account the severity of the disease, growth stage of the crop and yield potential. Late season (late flowering/open bolls) fungicide applications may be effective for arresting disease development, but may have limited impact on yield preservation. Fungicides have not been evaluated in LSU AgCenter tests when disease pressure was severe and cotton was just beginning to flower; therefore, yield loss data is limited. The following information will aid in identification of several leaf spots affecting cotton.

Several fungi affect foliage, petioles, stems, bracts and bolls. The two most common leaf spot diseases are Alternaria and Cercospora (see figures). This is NOT the same Cercospora that infects soybean. These leaf spots are usually found on stressed cotton (fertility or drought stress). Other less frequently occurring leaf spot diseases on Louisiana cotton are Ascochyta blight, Stemphylium leaf spot, target leaf spot and bacterial blight.

Alternaria Leaf Spot is favored by ambient temperatures of 68-86 degrees F and high relative humidity. Infection can occur early season on the cotyledons, but typically symptoms are usually evident late season. Spots begin as pale green to yellow spots on the leaves and other plant tissue (stems, petioles and bolls). Mature spots usually have concentric rings that are irregularly circular with straw-colored or reddish brown centers. During humid conditions the centers may appear sooty (these are the spores of the fungus). In some cases the centers may deteriorate and fall out giving the leaf a shot-hole appearance. The fungus overwinters in infected plant debris from the previous season. Other sources of inoculum are adjacent cotton and weeds.

Cercospora Leaf Spot is favored by the same conditions needed for Alternaria leaf spot to develop. Symptoms are similar to those caused by Alternaria. The initial symptoms are usually present late season and occur as small red lesions on the leaves. As the lesions mature, the centers are tan with a red margin and concentric rings can be present. The fungus can overwinter in infected plant debris.

In most cases Alternaria and Cercospora leaf spots are present on cotton growing in less-fertile areas of the field. Cotton growing in areas deficient in potassium or drought-stressed is at risk to these leaf spots.  Alternaria, Cercospora and Stemphylium may form a complex and may be observed within the same field. Generally, yield losses are thought to be minimal because they typically occur in areas of low production. However, under optimal conditions (susceptible variety, drought, potassium deficiency, high relative humidity), these pathogens may heavily infest cotton fields.

The risk of these diseases can be reduced by plowing under infected plant debris before planting, planting a tolerant variety if available, maintaining adequate fertility, providing adequate moisture (irrigation), and conducting any practices that maintain plant vigor. Fungicides have been used to reduce these diseases, but they are usually cost-prohibitive.

Alternaria leaf spot.
Alternaria leaf spot.
Typical foliar symptoms of Alternaria/Cercospora/Stemphylium leaf spots.
Typical foliar symptoms of Alternaria/Cercospora/Stemphylium leaf spots.
Alternaria/Stemphylium (new infections occurring on younger leaf).
Alternaria/Stemphylium (new infections occurring on younger leaf).
Alternaria/Stemphylium (typical leaf symptoms).
Alternaria/Stemphylium (typical leaf symptoms).

LSU AgCenter scientists are currently evaluating the incidence and severity of leaf spot on different varieties in Northeast Louisiana. Incidence and severity appears to vary among varieties; however, more research is needed to confirm these findings. The current evaluations of varieties are not showing visible differences of leaf spot based upon potassium rates. The evaluations of leaf spot on these varieties will continue throughout the growing season. Below are photos depicting varying variety susceptibility to Alternaria leaf spot.

Alternaria leaf spot symptoms on "Variety A".
Alternaria leaf spot symptoms on “Variety A”.
Alternaria leaf spot symptoms on "Variety B".
Alternaria leaf spot symptoms on “Variety B”.

ULV Malathion

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I have been receiving more calls about ULV malathion and its use on cotton. Outlined below are the rules regarding the use of ULV malathion and application intervals outlined by the LDAF.

Courtesy of Bobby Simoneaux:

An ultra-low volume (ULV) malathion and a ULV pyrethroid insecticide (tank mixed) may be applied to control plant bugs in cotton only between sunrise on May 15 through sunrise on September 15 of each year, subject to the following.

1.     Applications shall be made at no less than seven day intervals at an application rate not to exceed the individual pesticide product labels and with no other dilutions or tank mixes.

2.     Each application shall be reported, in writing and within 24 hours of the application, to the appropriate Boll Weevil Eradication Program district office by the farmer, agricultural consultant or owner/operator.

3.     The report shall include the names and addresses of the farmer, agricultural consultant (if appropriate), owner/operator and applicator; the applicator’s number issued by the department; the field name or number; the number of acres treated; the name and EPA registration number of the pesticide product; and the application date and time.

If you have any questions or concerns, please contact the LDAF, Sebe Brown or Dr. David Kerns for more information.

Bobby Simoneaux:  225-925-3763

Sebe Brown     Cell: 318-498-1283       Office: 318-435-2903

Dr. David Kerns    Cell: 318-439-4844     Office: 318-435-2157

Cotton Replant Decisions

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David Kerns LSU AgCenter Entomologist and Interim Cotton Specialist

Cool damp weather has greatly hindered Louisiana cotton emergence and stand establishment.  Some cotton has been languishing in the soil for 10 days with only 20% or so emerged.  Many growers are beginning to wonder if they should replant.  However, I would stress patience and give the crop 14 days and then make that replant decision. There are no hard and fast rules for making the right replant decision and circumstances are going to vary from field to field.  When assessing whether to replant we need to consider plant stand density, stand uniformity, potential death of surviving plants, and the cost associated with replanting.

On 38-40 inch rows we optimally would like to have 25,000 to 50,000 plants per acre or 2-4 plants per foot; but if fairly uniformly spaced, we should be able to tolerate as few as 1.5 plants per foot and still not see a huge hit on yield, although maturity will be delayed.  As mentioned stand uniformity is an important replant decision as well.  Some skips can be tolerated as long as adjacent rows have healthy stands, but in areas were stand is inadequate across several or more rows, yield will be impacted.

Another complicating factor is the health of the surviving plants. Under the conditions where we see poor plant emergence (cool and damp), seedling disease and wireworm damage are much more prevalent and lethal.  It’s a good idea to pull up a few surviving plants and examine the roots for disease.  Unhealthy roots will have black water soaked or collapsed areas.  Consider these plants as having a high probability of dying.  Additionally, I suggest cutting into the stem’s vascular tissue lengthwise and looking for discoloration for further evidence of probably infection and death.  Also take note of how the cotyledons look.  Do they look healthy? Do they have holes from wireworm feeding? And do you see wireworms in the root area when digging up plants? Answering yes to any of these is indicative that further stand loss may occur.

Replanting costs money in seed, labor, diesel, etc.  Fortunately the major cotton seed suppliers all have replants or “shared risk” programs.  These programs generally cover the technology fees for the Bt and herbicide traits, but do not fully cover the cost of the non-traited genetics.  Although there is a move towards an industry-wide standard, there are differences in the programs.  If you decide you need to replant, you should contact the seed dealer from whom you purchased the seed.  In turn they will contact the seed company representative and they will verify the need for the replant.

For more information or if you have questions or concerns contact David Kerns or Sebe Brown.

Dr. David Kerns   Cell: 318-439-4844    Office: 318-435-2157

Sebe Brown   Cell: 318-498-1283   Office: 318-435-2903

Storm Expectations for the Louisiana Cotton Crop

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By John Kruse, Ph.D.

LSU AgCenter

As Isaac passes through the heart of Louisiana, we can expect that the winds and torrential rains from the storm may cause some or even extensive injury to the cotton crop. The high, sustained wind speeds in particular will leave the leaves wrinkled and injured – something akin to what we cause when we apply tribufos. The plant will respond to stress with increased ethylene production and the whole process will likely result in some natural defoliation in the days after the storm passes through. Some cotton fields will be physically flattened or pushed over, but we hope that many of the plants will eventually stand back up. However, defoliation strategies may require aerial applications instead of ground rigs to prevent mechanical damage. One common misconception is that the crop damage results from all the salt water that the storm dumped on the crop. In truth, rain from the storm started out as ocean water evapotranspiration – in effect purifying the salts from it. No doubt the coast will be affected by salt water that is blown in by the storm surge, but once the storm is inland by a few miles, the deluge from above is fresh water. The best defoliation strategy at this point is to wait out the storm and let the leaves on the plant protect the cotton from the winds as best it can. Inspect the crop after the storm and make the appropriate plans. Even with some natural defoliation caused by the storm, defoliation strategies should take into account the current temperatures and crop condition, rather than trying to guess rate changes based on already defoliated leaves. We hope your cotton avoids serious injury from the storm, and are here to assist you.

John Kruse

Cotton and Feedgrain Specialist

LSU AgCenter

318-229-8180

JKruse@agcenter.lsu.edu

Cotton Insecticide Formulation, Rate and Pre-harvest Intervals

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Cotton Insecticide Formulation, Rate and PHI
Cotton Insecticide Formulation, Rate and PHI

Beware, generics were not included in the above list, rates and formulations may be different. 

(**) Curacron 8E: Do not apply Curacron 8E within 14 days of harvest when application is made in a water carrier or within 30 days of harvest when application is made in an oil carrier. 

If you have any questions or concerns please contact:

Sebe Brown   Cell: 318-498-1283   Office: 318-435-2903

Dr. David Kerns  Cell: 318-439-4844    Office: 318-435-2157

 

ULV Malathion

ULV Malathion published on No Comments on ULV Malathion

I have been receiving more calls about ULV malathion and its use on cotton. Outlined below are the rules regarding the use of ULV malathion and application intervals outlined by the LDAF.

Courtesy of Bobby Simoneaux:

An ultra-low volume (ULV) malathion and a ULV pyrethroid insecticide (tank mixed) may be applied to control plant bugs in cotton only between sunrise on May 15 through sunrise on September 15 of each year, subject to the following.

1.     Applications shall be made at no less than seven day intervals at an application rate not to exceed the individual pesticide product labels and with no other dilutions or tank mixes.

2.     Each application shall be reported, in writing and within 24 hours of the application, to the appropriate Boll Weevil Eradication Program district office by the farmer, agricultural consultant or owner/operator.

3.     The report shall include the names and addresses of the farmer, agricultural consultant (if appropriate), owner/operator and applicator; the applicator’s number issued by the department; the field name or number; the number of acres treated; the name and EPA registration number of the pesticide product; and the application date and time.

If you have any questions or concerns, please contact the LDAF, Sebe Brown or Dr. David Kerns for more information.

Bobby Simoneaux:  225-925-3763

Sebe Brown     Cell: 318-498-1283       Office: 318-435-2903

Dr. David Kerns    Cell: 318-439-4844     Office: 318-435-2157

Leaf Spot on Cotton Revisited

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Boyd Padgett, LSU AgCenter

Recently, I have received reports of leaf spot in cotton fields located in several areas of the state. After examining some plants, I confirmed the leaf spot to be caused by Alternaria. Another common leaf spotter is Cercospora. These leaf spots are usually present every year, and it is usually on cotton that is stressed, usually due to a nutrient deficiency (usually potassium). However, last year these diseases were present in fields where cotton WAS NOT STRESSED and had high yield potential. Individuals who frequent cotton fields should be monitoring for this disease. Currently, an automatic fungicide application is not recommended. The decision to use a fungicide should be made on a field by field basis and should take into account the severity of the disease, growth stage of the crop, and yield potential. The following information will aid in identification of several leaf spots affecting cotton.

There are several fungi that affect foliage, petioles, stems, bracts, and bolls. The two most common leaf spot diseases are Alternaria and Cercospora (see figures). This is NOT the same Cercospora that infects soybean. These leaf spots are usually found on stressed cotton (fertility or drought stress), as well as, in non-stressed cotton. Other less frequently occurring leaf spotters on Louisiana cotton are Ascochyta blight and bacterial blight.

Alternaria Leaf Spot is favored by ambient temperatures of 68 to 86o F and high relative humidity. Infection can occur early season on the cotyledons, but typically symptoms are usually evident late season. Spots begin as pale green spots on the leaves and other plant tissue (stems, petioles, and bolls). Mature spots usually have concentric rings that are irregularly circular with straw or reddish brown centers. During humid conditions the centers may appear sooty (these are the spores of the fungus). In some cases the centers may deteriorate and fall out giving the leaf a shot-hole appearance. The fungus overwinters in infected plant debris from the previous season. Other sources of inoculum are adjacent cotton and weeds.

Cercospora Leaf Spot is favored by the same conditions needed for Alternaria leaf spot to develop. Symptoms are similar to those caused by Alternaria. The initial symptoms are usually present late season, and occur as small red lesions on the leaves. As the lesions mature the centers are tan with a red margin and concentric rings can be present. The fungus can overwinter in infected plant debris.

In most cases Alternaria and Cercospora leaf spots are present on cotton growing in poor areas of the field. Cotton growing in areas in the field that are deficient in potassium or drought-stressed is at risk to these leaf spots. Yield losses are thought to be minimal because they typically occur in areas of low production.

 

Alternaria leaf spot
Cercospora Leaf Spot

The risk of these fungi can be reduced by plowing under infected plant debris before planting, maintaining adequate fertility, provide adequate moisture (irrigation), and any practices that maintain plant vigor. Fungicides have been used to reduce these diseases, but they are usually cost-prohibitive.

Spider mite injury to cotton leaf

Spider Mite Control Options

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Dr. David Kerns and I have been receiving more phone calls regarding spider mites in cotton.  Mite problems are exacerbated by hot, dry weather and applications of broad-spectrum insecticides for early season pests.

Do not wait for spider mite treatments in cotton if populations are found scattered throughout the field or if mites are moving in from field borders. When making applications, correct nozzles and high water volumes are essential for adequate coverage and application rates should reflect mite severity.

Miticide application rates should be adjusted for population severity with higher rates used for more severe infestations. Some control options available for spider mite control include Oberon, Portal, Abamectin, Athena and Zeal. Below is a brief description of each product and recommended use.

Oberon, a slower acting miticide, may to take 5-7 days before mortality is observed in the field.

Spider mite injury to cotton leaf
Spider mite injury to cotton leaf: Photo by David Kerns

Portal has given satisfactory results when applied at 16-20 oz/acre, lower rates in large cotton may not give complete control. Portal is a contact miticide but one should still allow 5-7 days to assess effectiveness.

Abamectin has been widely used for mite control across the Northeast region with multiple applications required for control of severe infestations. However, producers and consultants should consider rotating chemistries on fields that have had numerous abamectin applications for resistance management and if efficacy has decreased.

If mixed populations of bollworms and mites are in a field, Athena a premix of bifenthrin and abamectin, is another available control option.  Ten ounces of Athena is equivalent to 3.8 ounces of bifenthrin 2E and 7.5 ounces of abamectin. For effective bollworm control, Athena should be supplemented with more bifenthrin and ½ lb of acephate should be added to increase efficacy on any tarnished plant bugs and pyrethroid tolerant worms.

Zeal is one of our most effective options for controlling spider mites in cotton. Because we are limited to 1 application of Zeal per season, we usually prefer to save our Zeal shot for more troublesome mite problems.

If you have any questions or concerns, do not hesitate to contact Sebe Brown or Dr. David Kerns for more information.

Sebe Brown     Cell: 318-498-1283       Office: 318-435-2903

Dr. David Kerns    Cell: 318-439-4844     Office: 318-435-2157

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