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Soil Sampling/Testing Recommendations for Louisiana

Soil Sampling/Testing Recommendations for Louisiana published on No Comments on Soil Sampling/Testing Recommendations for Louisiana

By Dr. Beatrix Haggard, Agronomist – Macon Ridge Research Station

Dr. Josh Lofton, Agronomist – Macon Ridge Research Station

Why should soil tests be performed?

Obtaining soil test data is an important component of any production management system. It is especially important in Louisiana due to highly variable of our soils and weather patterns, which can affect soil nutrient content. Soil tests are important for agricultural production, pastures, as well as home gardeners. Soil testing provides scientific data for available nutrients and other soil characteristics. Location throughout the landscape produces differences in, soil texture, pH, organic matter, soil depth, slope, and elevation (low spots). All of the previously mentioned differences can affect the nutrient availability for crops. Because nutrient availability can be affected by many different factors it is very important to obtain soil samples that are well representative of the area. By spending a little more on soil testing it is possible to save in the end by not over-fertilizing the entire production system.

Where should soil tests be taken in a field?

Accurate soils samples should be taken via two different methods, grid-sampling and management zone sampling.  For grid-sampling, fields should be divided into 0.5 to 10 acre sections and one soil sample should be collected per section.  Grid-sampling can provide valuable, detailed information across the field; however, this sampling method can be very costly and labor intensive.

Another sampling method that can also provide valuable information is management zone sampling.  Management zones should be determined in the production system before samples are collected from the field. These zones can be determined through multiple techniques, such as:

  • Yield maps
  • Previous farm records
  • EC (electrical conductivity)
  • Elevation differences (topography)

Yield maps would be preferred if data from multiple years existed. However, elevation and EC differences can also be used effectively (Figure 1). These management zones allow soil samples to be collected based on inherent soils properties or yield differences.

Within each grid or management zones, samples should be collected so that they are representative of the area.  Caution should be taken to not collect samples where lime or animal manures have been stored.  Additionally, samples should not be collected along fertilizer bands because these do not represent the true fertility.  To ensure this point, soils should be collected in a random manner throughout the entire sampling area.

 

Figure 1. Four management zones based on deep EC readings. Points depict a random sampling of zone 3. Image courtesy of Dennis Burns.

How deep and how many soil samples?

The depth of the sample is different based on each crops needs and should be focused on where the effective rooting depth will be located. In most instances, soil samples collected from 0-6 inches are adequate; however, for mobile nutrients and deep rooted crops grown in Louisiana’s deep alluvial soils 6-12 inches would be beneficial. Additionally, if it is thought that salts have accumulated; samples should be taken from 0-3 inches. This zone has the greatest influence on seed germination. Further, in some areas samples should only be taken where roots can penetrate. This is especially important in the Macon Ridge soils where hard layers limit deep root growth.

For grid sampling, one sample (making sure there will be enough for analysis) taken near the center of the grid.  While for management zone sampling, 15-20 samples should be obtained from each zone. Samples can be taken with a soil probe or shovel, making sure to stay within the previously mentioned depths. These samples should be mixed in a plastic bucket and placed in a quart sized sealable plastic bag. Large pieces of plant material should be removed.

When should samples be taken?

Soil samples can be taken anytime during the course of the year; however, samples taken in the fall allow for timely applications as well as time for lime to react, thereby altering the soil pH.  For mobile nutrients such as Nitrogen and Sulfur, soil samples should be taken around the same time that fertilizer will be applied. Regardless of what information is needed from the soil samples they should be taken around the same time each year.  Any residue which remains should be scraped away from the surface before samples are pulled.

For questions regarding results from the soil analysis contact your local Parish Extension Agent.

For more information contact:

Beatrix Haggard

Joshua Lofton

Desiccation of Soybean: Paraquat vs. Sodium Chlorate

Desiccation of Soybean: Paraquat vs. Sodium Chlorate published on No Comments on Desiccation of Soybean: Paraquat vs. Sodium Chlorate

Dr. Daniel Stephenson, Joey Boudreaux, and Dr. Jim Griffin

LSU AgCenter

 

Over the last month, many individuals have called about the preharvest interval of 15 days for paraquat (Gramoxone SL, Parazone, others. ) applications.  Many Louisiana soybean producers are not willing to wait 15 days after paraquat application for harvest.  As a consequence, producers are seeking an alternative for desiccation that will allow for earlier harvest.  Sodium chlorate is an option, but many have chosen to ignore this option mainly due to the excellent results obtained with paraquat.

Due to the enforcement of the paraquat 15 day preharvest interval, sodium chlorate use has increased.  A recent article written by Drs. Ronnie Levy and Jim Griffin (Soybean Harvest Aid Recommendations for 2012) provides information on use of Aim 2EC, paraquat, and sodium chlorate as harvest aids.  This article was disseminated on Friday, August 17th.

One of the main questions being asked concerns the tank-mixing of sodium chlorate and Aim 2EC.  We don’t have any data on this treatment, but we are currently investigating it.   Joey Boudreaux and Dr. Griffin published an article in Weed Technology in 2011 entitled “Application Timing of Harvest Aid Herbicides Affects Soybean Harvest and Yield” that will provide some insight on this question.  The research discussed in the article is the data from which Dr. Griffin bases the application timing of a soybean harvest aid.  Application timing of harvest aid  is discussed in the article published by Drs. Levy and Griffin.

In the Boudreaux and Griffin article,  paraquat at 0.25 lb ai/A, paraquat + Aim 2EC at 0.8 oz/A, and sodium chlorate at 6 lb/A were evaluated.  They found no differences between any of these treatments in respect to the level of dessication or rate of dessication.  That is to say that soybeans were ready for harvest at the same time regardless of whether paraquat alone, paraquat plus Aim, or sodium chlorate were applied.  This also shows that soybean desiccation with paraquat was not affected either positive or negative with the addition of Aim.

Although their research did not specifically investigate sodium chlorate tank-mixed with Aim 2EC, it did  show that sodium chlorate at 6 lb/A (1 gallon/A of a 6 lb/gallon sodium chlorate) was as effective as was  paraquat at 0.25 lb ai/A (1 pt/A of Gramoxone SL or 10.7 oz/A of a generic 3 lb/gal paraquat) for desiccation of soybean.  With sodium chlorate the label states that application should be made 7 to 10 days before anticipated harvest date.

2012 Cotton Harvest Aid Guidelines for Louisiana

2012 Cotton Harvest Aid Guidelines for Louisiana published on No Comments on 2012 Cotton Harvest Aid Guidelines for Louisiana

Dr. Donnie Miller, Professor, Northeast Research Station

Dr. Daniel Stephenson, Associate Professor, Dean Lee Research Station

Dr. John Kruse, Assistant Professor, Central and Northeast Research Station

Introduction

One of the last, but most important, steps in producing a cotton crop is harvest preparation.  Successful harvest preparation includes scheduling for defoliation and harvest operations, removal of foliage and facilitating boll opening.  Successful defoliation has many benefits including increased picker efficiency, elimination of trash in harvested seedcotton, faster drying of dew thereby increasing picking hours per day, straightening of lodged plants and reduction of boll rot incidence.

The activity of harvest aids is very dependent on environmental factors.  Moreover, cotton defoliation is a balancing act between leaf injury that stimulates leaf drop, yet does not desiccate and stick leaves on the plant.  No one harvest aid tank mix will work in all situations.  A good understanding of the influence of defoliation timing and the relative attributes of available harvest aids can help in deciding when to terminate a crop and which harvest aids to use.

Defoliation Timing

There is always a balancing act between yield and fiber quality when defoliating cotton, but close attention to individual fields can help maintain quality while preserving yield. There are several accepted methods to time defoliation, and all methods have strengths and weaknesses.  The following is a refresher of some of the more common defoliation-timing techniques.

Percent Open Bolls

The most widely used method is based on a determination of the total percentage of bolls in a field that have opened, with 60% of bolls open being the most common recommendation for defoliant application. In many situations, unopened bolls are mature enough to resist negative impact and will open before harvest. This method, however, has limitations. Research inLouisianahas shown that, depending on fruit distribution on the plant, maximum yield can be obtained when defoliation occurs before 60% open bolls. Additionally, in cases where a large fruiting “gap” (no bolls present at fruiting sites) occurs and a large percentage of bolls are less mature and set in the uppermost region of the plant, optimum defoliation timing may occur later than 70% open.  Research evaluating optimum defoliation timing in Louisiana and other states has shown maximum yield can be achieved with application ranging from 42% to 81% open, depending on crop maturity and fruit distribution.

Nodes Above Cracked Boll (NACB)

The node above cracked boll (NACB) method, in contrast to the percent open boll method, focuses on the unopened portion of the crop. NACB is determined by locating the uppermost first-position boll that is cracked open with visible lint and counting the number of main-stem nodes to the uppermost harvestable boll. By focusing on the unopened portion, NACB takes into account potential fruiting gaps. Most recommendations call for defoliation at four NACB. Low plant population and skip-row cotton, however, are often more safely defoliated at three NACB. Lower plant population usually means a later-maturing crop, with a significant portion of yield coming from outer-position bolls and bolls set on vegetative branches.

 Accumulated Heat Units After Cutout

 Similar to NACB, a method developed in Arkansas recommends defoliation after accumulation of 850 heat units, or DD60s, after cutout. A DD60 is a measure of accumulated heat needed for growth and development using a 60o F minimum. Research from Louisiana indicates that under our environmental  conditions, the appropriate defoliation timing may be greater than 850 heat units (that is, 1050 heat units) beyond a cutout of node above white flower 4 (four main-stem nodes above uppermost first-position white flower). While this method does focus on the unopened portion of the crop and is supposed to allow enough time and DD60s for full development of all bolls, it requires making a determination of cutout. The definition of cutout is a moving target and can often be different for every field.

 

Daily DD60 =  (Daily High + Daily Low) ÷ 2 – 60       ex. 95 + 74 = 169 ÷ 2 = 84.5 – 60 = 24.5 DD60’s

Visual Inspection

Whatever method is employed, growers should also visually inspect unopened bolls for maturity. A boll is considered mature if it is difficult to slice in cross-section with a knife and seeds have begun to form a tan/brown or black seed coat. Once a dark seed coat has formed, defoliation will not affect yield of those bolls adversely. Cotton bolls need 40 to 60 days to mature, depending on temperature. Bolls set later in the season will take longer to mature and may never be harvestable. Growers should walk their fields before defoliation and examine only those bolls that can reasonably be expected to mature.

Research in Louisiana has shown that, on average, cotton is harvested from a 12-14 node range on the plant.  This fact can serve as a tool to simplify identifying the last harvestable boll as well as timing defoliation.  To use the 12-node rule, identify the lowest first position boll that is expected to be harvested.  Count up 12 nodes on the plant.  The boll present at that position is likely to contribute to yield.  Under some circumstance, a boll on the 14th node from the bottom could be considered harvestable.  Bolls produced above that position on the plant are unlikely to contribute to yield and waiting on them to mature places heavier bolls at the bottom of the plant at risk to unnecessary weather-related losses.  Once the last harvestable boll has been identified, use the visual inspection technique to determine when it is mature and ready for defoliation.

Harvest Scheduling

Harvest capacity also should be a consideration in relation to defoliation timing. In general, defoliating only the amount of acreage that can be harvested within the 12-day period following treatment greatly reduces exposure of lint to weathering loss and possible grade discounts. Additionally, a delayed harvest may require regrowth to be controlled more aggressively using higher rates of regrowth-inhibiting products. In severe cases, an additional application of desiccant may be required to remove regrowth.

Defoliation may not always be warranted because cotton that is completely cutout will drop some of its leaves naturally. If cotton is harvested with care, defoliation may not be needed to eliminate leaf trash and prevent excess staining. Before proceeding with this option, growers are strongly urged to harvest an adequate sample to evaluate effects on ginning efficiency. Limited research inLouisianahas suggested that as little as 20% green leaf (mature and juvenile) on the plant can significantly affect final grade and loan value when a single lint cleaning operation is used. Therefore, growers are urged to proceed with caution when deciding to eliminate defoliation.

Defoliation of Late-Maturing Varieties

Full-season varieties tend to initiate fruiting on higher nodes and cutout earlier compared with earlier varieties.  The implication for defoliation timing is that these varieties are more likely to continue to produce small, green bolls in the top of the plant.  The value of waiting on these bolls is questionable, especially considering the relative lack of “stormproofness” of these varieties.  The temptation, however, will be to wait on those bolls at the top of the plant to mature.  In many cases, these varieties may need to be picked with some green bolls at the top of the plant, but this can be done without reducing overall yield.

Table of Expected Activity of Various Harvest   Aids

Material

Estimated minimum   temperature

Expected activity

Mature leaves

Juvenile growth

Regrowth prevention

Boll opening

Def 6/Folex 6 EC

60oF

Excellent

Fair

Poor

None

Thidiazuron

65oF

Excellent

Excellent

Excellent

None

Ginstar EC

60oF

Excellent

Excellent

Excellent

None

Aim EC

55oF

Good-Excellent

Excellent

Poor

None

ET

55oF

Good-Excellent

Excellent

Poor

None

Resource

55oF

Good-Excellent

Excellent

Poor

None

Blizzard

55oF

Good-Excellent

Excellent

Poor

None

Ethephon

60oF

Fair

Poor

Poor

Excellent

Finish 6 Pro

60oF

Excellent

Poor

Fair

Excellent

FirstPick

60oF

Good/Excellent

Poor

Poor-Fair

Excellent

Glyphosate

55oF

Fair

Fair

Excellent

None

Sodium Chlorate

55oF

Fair

Fair

Poor

None

Paraquat

55oF

Desiccation

Excellent

Poor

Fair

Spray Coverage

Thorough canopy coverage is essential for acceptable results with all harvest aids.  Carrier volume and nozzle selection are the most important factors in obtaining adequate spray coverage.  Research in Louisiana and Tennessee has indicated that defoliant activity increases as carrier volume increases.  Carrier volumes less than 10 GPA are not recommended, and 15 GPA is suggested.  Lower carrier volumes increase the likelihood of needing a second application.  While higher carrier volumes are inconvenient, water remains the cheapest thing that you can put in the tank.

The use of drift-reduction nozzles has become widespread in recent years.  These nozzles are excellent at controlling drift and placement of any spray solution.  However, as droplet sizes become larger, thorough coverage of leaf surfaces within the canopy can decrease.  Research inLouisianaandTennesseehas shown decreased defoliant activity with some drift-reducing nozzles when used at low operating pressures and/or low carrier volumes.  Flat-fan and hollow cone nozzles provide excellent spray coverage of harvest aids and are recommended for most applications.  Always operate calibrated sprayers within the nozzle manufacturer’s guidelines for operating pressure and carrier volume to obtain maximum canopy coverage and minimal off-target movement.

 Rotational Crops Restrictions

When double-cropping wheat following cotton, some consideration should be given to label restrictions of harvest aids for rotational crops.  The following table summarizes harvest aid label restrictions for planting wheat following cotton.

Label Restrictions for Planting Small Grains   Following Application as a Harvest Aid in Cotton

Material

Recrop interval following   application for planting small grains

Def 6/Folex 6 EC

None

Thidiazuron

14 days

Ginstar EC

1 month

Aim EC

None

ET

None

Blizzard

None

Resource

30 days

Ethephon

30 days

FirstPick

30 days

Finish 6 Pro

30 days

Glyphosate

None

Sodium Chlorate

None

Paraquat

None

 Harvest Aid Materials

            The following is a list of the majority of products available for use as harvest aids (other products with the same active ingredient may be available).  No one harvest aid or tank mix combination may be appropriate for every situation or field.  The selection of a harvest aid is often made based on prior experience and price.  When selecting a harvest aid program, consider environmental and crop conditions, yield potential, and value of the crop in the field.  All materials listed have strengths and weaknesses and perform better in certain environments.  Always refer to the label for use directions, precautions, notes, appropriate rates, adjuvant use, pre harvest intervals, and tank mixes allowed.

 

Harvest Aids for    Cotton

 

Product

 

Active

Ingredient

 

Labeled Rate of Product per Application per Acre

Acres Treated by 1 Gallon or Pound Product

 

Remarks

Aim EC

 

carfentrazone-ethyl

 

0.25 – 1.6 oz

80 – 512

Can provide desiccation of morning   glories and other broadleaf weeds.  Use   an adjuvant according to label directions.    Maximum of 3.2 oz per season. Rainfall within 6 to 8 hrs after   application may reduce efficacy.  Leaf   desiccation potential may increase with higher rates under high temperature.  Low rate application ranging from 0.25 to   0.5 oz per acre is labeled as a Managed Maturity Application at 15% open boll   being optimum.
FirstPick

 

ethephon + synergist

 

3 – 3.5 qt alone

1.5 – 2 qt tank-mix

1.1 – 1.3

2 – 2.67

Effective   defoliation when applied alone to very mature cotton.  Most consistent defoliation and regrowth   inhibition observed with tank mixes.    Maximum of 3.5 qts per season.
Finish 6 Pro ethephon + cyclanilide

1.3 – 2.67 pt

3 – 6

Rainfall within 6 hrs after application   may reduce efficacy.
Several brands

 

glyphosate

 

    For non-Roundup Ready cotton only.  Use labeled rates for weed control.
ET

 

pyraflufen-ethyl

 

1.5 – 2.75 oz 47 – 85

 

Can provide desiccation of morning   glories and other broadleaf weeds.  Use   an adjuvant according to label directions.

Maximum   of 5.5 oz per season.  Rainfall within   1 hr after application may reduce efficacy.    Leaf desiccation potential may increase with higher rates under high   temperatures.

Resource

 

flumiclorac pentyl-ester

 

6 – 8 oz

 

21 – 32

 

Apply   with 1 – 2 pt COC or methylated seed oil.    Maximum of 14 oz per season.    Rainfall within 1 hr of application may reduce efficacy.
Blizzard

 

fluthiacet-methyl

 

0.5 – 0.6 oz

 

256 – 213

 

Use an adjuvant according to label   directions.  Maximum of 1.25 oz per season.    Rainfall within 1 hr after application may reduce efficacy.

 

DroppSC

FreefallSC

 

thidiazuron

 

1.6 – 6.4 oz

1.6 – 6.4 oz

 

40 – 80

40 – 80

 

Thidiazuron is temperature sensitive;   either avoid or use higher rates in cooler conditions.  Rainfall within 24 hrs after application   may reduce efficacy.

 

Ginstar EC

 

thidiazuron + diuron

 

6.4 – 16 oz

 

10 – 40

 

Higher rates and tankmixes with other   products and adjuvants can increase likelihood of desiccation under high   temperatures.  More active than thidiazuron   alone under cooler conditions.  Maximum   of 16 oz per season.  Rainfall within   12 hrs after application may reduce efficacy.
Def 6

Folex 6 EC

tribufos

 

1.3 – 1.5 pt

 

5.3 – 6.1

 

Maximum   of 1.5 pt per season.  Rainfall within   1 hr after application may reduce efficacy.
Several brands

 

ethephon 1.3 – 2.67 pt 3 – 6.1 Maximum   of 2 lb per season (2.67 pt of a 6 lb formulated material).  Rainfall within 6 hr after application may   reduce efficacy.
Gramoxone Inteon paraquat

 

See   label   See label for specific application   timings.  Maximum of 2 pt per   season.  Rainfall within 15 min of   application may reduce efficacy.  Can   provide desiccation of weeds.

 

Several   brands sodium chlorate

 

See label

 

  Can   provide desiccation of weeds.

Defoliation Decision Guide

This guide can be used in determining the appropriate harvest aid or harvest aid combination for particular situations. Use the key to identify the group of suggested materials that best fit a specific situation. Some of the products are sold under a variety of trade names; refer to the descriptions of specific materials for alternate brand names. The following should be used only as a guide in determining materials, combinations and rates. Cotton response to these and other harvest aid options always depends on environmental conditions, sometimes requiring rates higher or lower on the labeled range than those suggested here. For some combinations, an adjuvant may be required or suggested on the label. Always read and follow label instructions.

 

Expected daytime high temperature above 80 degrees F

Regrowth potential is high

Boll opening is needed

Will attempt a once-over defoliation program……………… SEE GROUP 1

Will be a two-step program……………………………………………… SEE GROUP 2

Boll opening is not needed

Will attempt a once-over defoliation program……………… SEE GROUP 3

Will be a two-step program……………………………………………… SEE GROUP 4

Regrowth potential is low

Boll opening is needed

Will attempt a once-over defoliation program……………… SEE GROUP 5

Will be a two-step program……………………………………………… SEE GROUP 6

Boll opening is not needed

Will attempt a once-over defoliation program……………… SEE GROUP 7

Will be a two-step program……………………………………………… SEE GROUP 8

 

Expected daytime high temperature lower than 80 degrees F

Boll opening is needed

Will attempt a once-over defoliation program……………………………. SEE GROUP 9

Will be a two-step program……………………………………………………………. SEE GROUP 10

Boll opening is not needed

Will attempt a once-over defoliation program……………………………. SEE GROUP 11

Will be a two-step program……………………………………………………………. SEE GROUP 12

Suggested Harvest Aids and Combinations

 

GROUP 1 – High temperatures; boll opening; regrowth control; once-over

thidiazuron 2.4 – 3.2 oz + ethephon 1.3 pt

thidiazuron 1.6 – 2.4 oz + Def 6/Folex 6 EC 1.3 pt + ethephon 1.3 pt

thidiazuron 1.6 oz + Aim 1.0 oz*/ET 1.5 oz*  +  ethephon 1.3 pt

thidiazuron 1.6 oz + Finish 6 Pro 1.3 pt

thidiazuron 1.6 oz + FirstPick 2.0 qt

**Glyphosate 1 lb ai + ethephon 1.3 pt or Finish 6 Pro1.3 pt or FirstPick 2.0 qt

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

**For control of grasses and pigweeds only in non-RR cotton. Weed control may take 14 days.

 

GROUP 2 – High temperatures; boll opening; regrowth control; two-step programs

thidiazuron 2.4 oz + ethephon 1.3 pt followed by Def 6/Folex 6 EC 1.3 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials)

thidiazuron 1.6 oz + Finish 6 Pro 1.3 pt followed Def 6/Folex 6 EC 1.3 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials) or Aim 1.0 oz*/ET 1.5-2 oz*

thdiazuron 1.6 oz + FirstPick 2.0 qt followed by Def 6/Folex 6 EC 1.3 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials) or Aim 1.0 oz*/ET 1.5 oz*

Aim 1.0 oz*/ET 1.5 oz* + ethephon 1.3 pt or Finish 6 Pro 1.3 pt or FirstPick 2.0 qt followed by Aim 1.0 oz*/ET 1.5 oz*

Def 6/Folex 6 EC 1.3 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials)  + ethephon 1.3 pt or Finish 6 Pro 1.3 pt followed by Aim 1.0 oz*/ET 1.5 oz*

Finish 6 Pro 1.3 – 2.0 pt followed by Aim 1.0 oz*/ET 1.5 oz*

FirstPick 3.0 – 3.5 qt followed by Aim 1.0 oz*/ET 1.5 oz*

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

GROUP 3 – High temperatures; regrowth control; once over

thidiazuron 2.4 – 3.2 oz (for well-cutout cotton only)

thidiazuron 1.6 – 2.4 oz + Def 6/Folex 6 EC 1.3 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials)

thidiazuron 1.6 – 2.4 oz + Aim 1.0 oz*/ET 1.5 oz*

Ginstar EC 6.4 – 8 oz (potential for desiccation increases with rate and temperature)

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

GROUP 4 – High temperatures; regrowth control; two-step programs

thidiazuron 1.6 – 2.4 oz followed by Def 6/Folex 6 EC 1.3 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials) or Aim 1.0 oz*/ET 1.5 oz*

Def 6/Folex 6 EC 1.3 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials) followed by Aim 1.0 oz*/ET 1.5 oz*

Aim 1.0 oz followed by Aim 1.0 oz*/ET 1.5 oz*

Ginstar EC 6.4 oz followed by Aim 1.0 oz*/ET 1.5 oz*

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

GROUP 5 – High temperatures; low regrowth potential; boll opening; once-over

thidiazuron 1.6 oz + Def 6/Folex 6 EC 1.3 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials) + ethephon 1.3 pt

thidiazuron 1.6 oz + Finish 6 Pro 1.3 pt

thidiazuron 1.6 oz + FirstPick 2.0 qt

Def 6/Folex 6 EC 1.3 – 1.5 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials) + ethephon 21 oz

Finish 6 Pro 2.0 pt

Finish 6 Pro 1.3 pt + Def 6/Folex 6 EC 1.3 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials) or Aim 1.0 oz*/ET 1.5 oz*

FirstPick 2.0 qt + Def 6/Folex 6 EC 1.3 pt (lower rates have provided good defoliation and reduced potential for desiccation in research trials) or Aim 1.0 oz*/ET 1.5 oz*

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

GROUP 6 – High temperatures; low regrowth potential; boll opening; two-step programs

Def 6/Folex 6 EC 1.3 pt + ethephon 1.3 pt followed by Def 6/Folex 6 EC 1.3 pt or Aim 1.0 oz*/ET 1.5 oz*

thidiazuron 1.6 oz + ethephon 1.3 pt followed Def 6/Folex 6 EC 1.3 pt or Aim 1.0 oz*/ET 1.5 oz*

Finish 6 Pro 1.3 – 1.5 pt followed by Def 6/Folex 6 EC 1.3 pt or Aim 1.0 oz*/ET 1.5 oz*

FirstPick 2.0 qt followed by Def 6/Folex 6 EC 1.3 pt or Aim 1.0 oz*/ET 1.5 oz*

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

GROUP 7 – High temperatures; low regrowth potential; once over

thidiazuron 1.6 oz + Def 6/Folex 6 EC 1.3 – 1.5 pt or Aim 1.0 oz*/ET 1.5 oz*

Def 6/Folex 6 EC 1.5 – 2.0 pt

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

GROUP 8 – High temperatures; low regrowth potential; two-step programs

Def 6/Folex 6 EC 1.3 pt followed by Def 6/Folex 6 EC 1.3 pt or Aim 1.0 oz*/ET 1.5 oz*

Aim 1.0 oz followed by Aim 1.0 oz*/ET 1.5 oz*

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

GROUP 9 – Lower temperatures; boll opening; once over

Def 6/Folex 6 EC 1.3 – 1.5 pt + ethephon 1.5 pt or Finish 6 Pro 1.3 – 1.5 pt

Finish 6 Pro 1.5 – 2.0 pt

Finish 6 Pro 1.3 – 1.5 pt + Aim 1.0 oz*/ET 1.5 oz*

FirstPick 2.0 qt + Def 6/Folex 6 EC 1.3 pt

FirstPick 2.0 qt + Aim 1.0 oz*/ET 1.5 oz*

Ginstar EC 6.4 – 9 oz + ethephon 1.3 pt

Ginstar EC 6.4 oz + Finish 6 Pro 1.3 pt

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

GROUP 10 – Lower temperatures; boll opening; two-step programs

Def 6/Folex 6 EC 1.3 – 1.5 pt + ethephon 1.5 pt followed by Aim 1.0 oz*/ET 1.5 oz*

Def 6/Folex 6 EC 1.3 pt + Finish 6 Pro 1.3 pt followed by Aim 1.0 oz*/ET 1.5 oz*

Def 6/Folex 6 EC 1.3 pt + FirstPick 2.0 qt followed by Aim 1.0 oz*/ET 1.5 oz*

Finish 6 Pro 1.3 – 1.5 pt followed by Aim 1.0 oz*/ET 1.5 oz*

Finish 6 Pro 1.3 pt followed by Finish 6 Pro 1.0 pt

FirstPick 3.0 – 3.5 qt followed by Aim 1.0 oz*/ET 1.5 oz*

Ginstar EC 6.4 oz + ethephon 1.3 pt followed by Aim 1.0 oz*/ET 1.5 oz*

Aim 1.0 oz + ethephon 1.5 pt followed by Aim 1.0 oz*/ET 1.5 oz*

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

GROUP 11 – Lower temperatures; once over

Def 6/Folex 6 EC 1.5 – 2.0 pt

Finish 6 Pro 1.3 – 1.5 pt + Def 6/Folex 6 EC 1.0 pt or Aim 1.0 oz*/ET 1.5 oz*

Finish 6 Pro 1.5 – 2.0 pt

FirstPick 2.0 – 3.0 qt + Aim 1.0 oz*/ET 1.5 oz*

Ginstar EC 6-10 oz

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

GROUP 12 – Lower temperatures; two-step

Def 6/Folex 6 EC 1.5 pt followed by Def 6/Folex 6 EC 1.5 pt or Aim 1.0 oz*/ET 1.5 oz*

Aim 1.0 oz/ET 1.5 oz followed by Aim 1.0 oz*/ET 1.5 oz*

Finish 6 Pro 1.5 pt followed by Aim 1.0 oz*/ET 1.5 oz*

PirstPick 2.0 qt followed by Aim 1.0 oz*/ET 1.5 oz*

Ginstar EC 6 oz followed by Ginstar EC 6 oz

Ginstar EC 6 – 9 oz followed by Aim 1.0 oz*/ET 1.5 oz*

Sodium chlorate followed by sodium chlorate

*Addition of Aim or ET at recommended rates will desiccate most broadleaf weed species.  Blizzard and Resource at labeled rates have resulted in similar levels of cotton defoliation.

 

Visit our Web site:

www.lsuagcenter.com

Louisiana State University Agricultural Center, William B. Richardson, Chancellor

Louisiana Agricultural Experiment Station, John S. Russin, Vice Chancellor and Director

LouisianaCooperative Extension Service, Paul D. Coreil, Vice Chancellor and Director

Pub.  3194                   (online only)    8/12

Issued in furtherance of Cooperative Extension work, Acts of Congress of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. The Louisiana Cooperative Extension Service provides equal opportunities in programs and employment.

End-of-Season Corn Harvest Checklist

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by Dr. John Kruse, Cotton and Feedgrains Specialist and Dr. Josh Lofton, Macon Ridge Research Station Agronomist

Irrigated corn on silt loam soil exhibiting potassium deficiency due to compaction. The limited root zone restricted potassium uptake.

The Louisiana corn crop developed more rapidly than normal this year, and more than a few producers will be ready to harvest this crop in the month of July. With the harvest comes a well-deserved feeling of completion and a sense that after months of intense labor and difficult management issues, it is time to rest – or at least move on to the next crop! However, before you leave the corn crop behind, there are a few issues to attend to that will put the next crop in a better position to succeed.

Final watering: A critical decision that must be made is how much more to water and when to discontinue irrigation.  Corn continues to need water until it reaches “black layer. If irrigation is terminated prematurely without adequate rainfall you could see yield losses up to 25%.  To estimate how many more irrigation events are needed you need to have knowledge of your soil as well as your crop’s maturity.  If you break a cob that has begun to dent and look at the top side you should see the milk line.  This line is the dividing line between a very bright yellow starch layer toward the top and a more opaque yellow toward the bottom.  It takes 20 days for that milk layer to progress from the top to the bottom of the kernel.  Therefore, you can estimate the number of days you have left until black layer.  With the recent trends of hot temperatures, high winds, and lowered humidity with very little rainfall, it is going to be vital to continue irrigation until we reach the critical black layer growth stage.

Residue management: Corn produces a tremendous amount of biomass during the growing season, and a grower only harvests the grain, leaving a substantial amount of residue that needs to be managed properly. As a rule of thumb, the amount of residue produced by a corn crop is roughly equal to the amount of grain harvested, by weight. Therefore, a 200 bushel corn crop would produce about 11,200 pounds of residue per acre. LSU AgCenter staff received several calls this year about residue that spring rains washed into lower areas of fields, literally burying young corn plants and reducing plant stands.  Instead of cutting corn stalks off at ground level after harvest, consider leaving knee-high stalks in place for the fall. The roots will do a better job holding soil in place over the winter, and by spring the stalks will be rotten enough that planting equipment will push the soft stalks over.

Fall fertilization: If you have not soil tested in three years, you really need a soil test. Modern crop cultivars with higher yield potential are pulling more nutrients – particularly phosphorus and potassium – out of the soil than in years past. We can no longer count on smokestack output to supply sulfur, and more and more fields are turning up sulfur deficient. Additionally, corn requires zinc in order to optimize yields, and if your soils are high in pH or naturally zinc deficient (less than 1.5 ppm soil test Zn), your yields suffered this year. Finally, most of our modern nitrogen fertilizers (UAN, urea, ammonium sulfate, etc.) create soil acidity as they transform from ammonium to nitrate in the soil. A low soil pH can prevent a crop from utilizing nutrients to their full extent. Lime is an investment in your future, and should be applied in the fall so that it can be incorporated and then dissolve with the winter rains. The only way to know if you need lime, and how much, is to take a soil test. If you have a soil best described as a loam (not too sandy and not too clayey), and the pH is between 6.0 and 6.9, then a fall application of phosphorus and potassium may make sense from a management perspective. However, if the soil is too sandy or has a low cation exchange capacity (CEC), some applied potassium could be lost over the winter. A clayey soil tends to tie up phosphorus, as does a soil with a too-low or too-high pH. In these cases, a spring application of P and K is better utilized by the next crop. Also, fall applied fertilizer is there to feed winter

weeds. Collecting a good representative sample is vital. In a corn production system for most nutrients, soil sampling can be carried out any time following harvest, but make sure there is adequate time for processing and analysis prior to desired application period. This is true for P, K, and micronutrient analysis.  However, for N and S analysis, soil samples taken in the fall will not give a clear indication of N and S levels in early spring at planting.  These samples should be collected shortly before desired applications.  All soil samples should not be taken soon after nutrient or lime applications.  Soil samples should be taken across each field in at least 20 randomly collected locations. These should be taken at least to the depth of the tillage layer (and potentially lower for deep rooted crops such as cotton) for cultivated fields and at least 6 inches for no-till fields.  After the collection, the samples should be allowed to air dry for all nutrients except N and S which need to be placed in a drying oven or refrigerator soon after collection.  A routine soil analysis at the LSU AgCenter soil testing and plant analysis laboratory ($10 for each sample under 10 or $8 for each sample over 10) should be adequate in most instances; however, if you would like additional analysis contact your extension agent or specialist to discuss.  Once a soil test report has been received, pay close attention to those nutrients in the low and very low range.  This indicates that supplemental fertilizer will be needed to sustain the corn crop for the coming production cycle.  Those values that are indicated as optimum, suggest that nutrient levels in the soil are within the accepted range for optimum production.  Soil test values that are high to very high, indicate nutrient concentrations are higher than the crop will take up.  While these high to very high levels are typically not harmful for crop production, caution should be taken with continued applications due to: 1) limited economic return for additional fertilizers and 2) dangers of toxicity, especially for micronutrients.

Compaction: Today’s modern equipment exerts a heavy footprint on agricultural soils. Compaction layers led to several calls this year in which corn appeared to be potash deficient. It turned out that the rows on either side of the tractor tires were so compacted, the crop developed a shallow root system and when that shallow layer was fully exploited by the crop (by V5), there was no more potash available for it. Many producers are reporting that running a deep vertical shank down the row in the fall is breaking the plow pan and allowing winter rains to penetrate the soil more deeply and build greater moisture reserves for the following crop season. Roots are able to grow deeper into the soil profile and extract that moisture as well as nutrients.

Fall weed control: A late July or early August corn harvest leaves 6 or 7 months of fallow ground on which  weeds can grow and mature. Weed scientists in the LSU AgCenter have been warning that winter weed management is becoming more problematic as Italian ryegrass and other weeds are displaying herbicide resistance. Henbit appears to be growing longer into the late spring and becoming a more robust competitor to spring-planted crops. Identify your fall and winter weeds and come up with a proactive program to control them that includes at least one fall application in addition to a spring burndown. For details on your specific situation, contact your County Agent or Dr. Daniel Stephenson.

Cover crops: While more Louisiana-based research needs to be conducted to quantify the benefits, much is already known about the advantages of winter crops. The plants hold soil all winter (drastically reducing erosion), allow for better winter-rain infiltration, suppress winter weeds, and build soil organic matter. Soils with higher organic matter have a much greater capacity to hold soil moisture during the summer, and have higher nutrient holding capacity.

The corn harvest for this year will be upon us, wrapping up a successful year. But it is also the beginning of a successful crop next year, if a producer is pro-active and starts his plan right away.

 

 

 

Sampling Methods for Tarnished Plant Bug in Cotton

Sampling Methods for Tarnished Plant Bug in Cotton published on No Comments on Sampling Methods for Tarnished Plant Bug in Cotton

by Sebe Brown and Dr. David Kerns, LSU AgCenter Entomologists, and Dr. John Kruse, Cotton and Feedgrains Specialist

With most of the cotton in Louisiana at or reaching bloom, producers and consultants have options when sampling for tarnished plant bugs.  Sweep net, drop cloth and visual inspections are sampling methods that help aid in application decision making. However, each method has its advantages and disadvantages.  Drop cloths and sweep nets are not intended for all types of insects. Sweep nets work best for sampling adults while drop cloths for immature insects, and visual inspection is subject to variability from person to person and is not standardized.

Drop cloth sampling has typically been regarded as the best way of accurately measuring the amount of tarnished plant bugs present in a field.  A typical drop cloth is 2.5 X 3 ft in area and black in color.  However, pest managers and consultants are often reluctant to use drop cloths because of effort and timed required for sampling.  Drop cloth efficiency is dictated by crop size, weather conditions and row spacing.  Dr. Roger Leonard, in the link below, demonstrates how to effectively use a drop cloth.

http://www.lsuagcenter.com/en/crops_livestock/crops/Cotton/Insects/Explaining-the-proper-use-of-a-shake-sheet.htm

Sweep net sampling employs the use of a canvas net fitted to a standardized 15 inch metal hoop attached to a handle. Sweep net sampling allows the user to scout large areas with increased efficiency and mobility. However, due to the sweep nets limited sampling area, sweeps may miss insects in the lower portion of the plant canopy.  Dr. Roger Leonard, in the link below, demonstrates how to effectively use a sweep net.

http://www.lsuagcenter.com/en/crops_livestock/crops/soybeans/Insects/Using-a-Sweep-Net-for-Insect-Scouting.htm

Visual inspections base recommendations on perceived damage and fruit retention by cotton plants.  However, these visual methods are not standardized and considerable variability exists between individuals. Also, accurate thresholds have not been established for visual damage and often rely on experience rather than research.

With corn beginning to dry down across Louisiana and tarnished plant bugs migrating into fields, utilizing sweep nets for continued scouting would a prudent choice for detecting adults. It is not uncommon to find tarnished plants bugs above threshold near corn, but 20 or 30 rows into the field have numbers drop off. In these situations, strip treatments may be an economical way for producers to save money and control migrating adults.

 

For more information concerning insect pest management, contact your local LSU AgCenter parish agent, LSU AgCenter specialist, or Louisiana independent agricultural consultant.

 

Soybeans Off to a Good Start

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by Dr. Ronnie Levy, Soybean Specialist

 

Dr. Ronnie Levy in soybean field on June 26, 2012

Soybean planting got an early start this year with most acres planted mid-April through the first part of May.  The picture taken June 26th shows one of the soybean varieties in the Official Variety Test at Dean Lee Research and Extension Center in Alexandria.  While most areas were planted early, we are still planting soybeans behind wheat and crawfish ponds.  There is talk of planting soybeans after early corn harvest in other states.  Louisiana was projected to plant a little over a million acres of soybeans in 2012.    As strong exports and demand for soybeans continue, soybean acres continued to increase throughout the planting season.  The total acres planted will be limited by dry conditions is some areas and prevented in others, but overall planting could be as high as 1.25 million soybean acres.

Insect and disease control are always a concern in Louisiana.  Due to numerous insects and diseases that attack soybeans, proper timing of insecticides and fungicides is a must.  Scout fields weekly and treat when thresholds are reached. After treating, check results and retreat as needed.  Soybean seed quality at harvest is a result of proper timing of insecticides and fungicides.  Insects and diseases can reduce photosynthate production, cause pod abortion, and/or plant death.  While environmental conditions at harvest affect quality, insect feeding on pods can compromise the integrity of the pods providing sites for disease and moisture to attack the developing seed.

For more information, contact me at my New Cell Number:  318-542-8857 or your local County Agent Office.

 

Bacterial panicle blight in rice

Bacterial Panicle Blight in Rice

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Bacterial panicle blight in rice
Bacterial panicle blight in rice

 

With the amount of rice flowering for the past couple of weeks I was expecting to get more calls about the disease shown at right.  There are several things to look at in the photograph that help us identify the disease.  The base of the some of the pedicels (where that part of the plant joins the spikelet) are discolored.  Note its discoloration compared to others that are green. Also take a look at the band of slightly darker area of some of the spikelets in comparison to those that are completely straw colored.  Third diagnostic aids are the green panicle branches.  What cannot be seen in the photograph is the absence of grain in the affected spikelets.

 

The disease is bacterial panicle blight.  It is associated with high night time temperatures during flowering.  Just as a reminder, no matter how much fungicide is used it will not control this disease.  Fungicides control fungi NOT bacteria.  We have nothing to control bacterial panicle blight yet.  The only thing we can recommend is to plant a variety that is resistant or moderately susceptible or plant early to avoid flowering when night time temperatures have risen.

Managing Diseases in Louisiana Corn

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by Boyd Padgett, Ph.D. and Clayton Hollier, Ph.D.

I have received numerous calls from producers, consultants, and agents reporting diseases in corn. These reports are earlier compared to previous years, and disease management strategies will change based on this fact. The diseases most prevalent are southern rust,  common rust, and northern corn leaf blight. The LSU AgCenter DOES NOT recommend an automatic fungicide application to corn. HOWEVER, when disease epidemics are progressing in young corn (tassel or earlier) a fungicide will be needed to slow epidemics and protect yield and quality.

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. When it is determined an application is needed, a premix fungicide will offer wide spectrum activity (examples are: Headline AMP, Stratego YLD, Quilt, and Quilt Xcel). Follow label instructions for application timings, rates, etc. In most cases, a single application at tassel is justified when disease is present and active. The decision to apply a fungicide should be made on a field by field basis. The remainder of this newsletter will address disease identification and management considerations.

Diseases can be found in Louisiana corn fields every year, but their impact on grain quality and yield is dependent on several variables. Therefore, the decision to apply a fungicide should be based on a solid understanding of disease initiation and development. Diseases commonly found in Louisiana corn include common and southern rusts, smut, and northern corn leaf blight. Other diseases that occur less frequently are ear and stalk rots, gray leaf spot, and southern corn leaf blight. While these diseases rarely develop to statewide damaging levels in most years, disease incidence and severity in individual fields may warrant a fungicide application. However, before applying a fungicide, several factors need to be considered. These include: disease identification, environmental conditions favoring disease development, and the relationship between disease severity and yield loss.

Identification and Development

Common Rust

Common rust usually can be found every year in Louisiana (figure 1). This disease is caused by the fungus Puccinia sorghi. In some fields signs of this disease can be present early in the growing season. Common rust is usually the first disease present in Louisiana corn, but subsides when temperatures exceed 77oF. Initial infections occur from wind-blown spores from corn-producing areas in tropical and sub-tropical regions of the world. This disease usually does not cause yield loss in Louisiana corn.

Conditions favoring development:

Temperature: 60-77oF

Moisture period: 6 hours of leaf wetness or high relative humidity

Symptoms

This disease can be found in fields prior to tasseling.  Sporulation on the leaf surface can occur within 7 days after infection. Pustules are elongated, ragged looking and occur on the upper and lower leaf surfaces. Spores with pustules are cinnamon-brown in color. In some cases, pustules occur in bands because of infections that occurred while the leaf was in the whorl.

Southern Rust

Southern rust, caused by the fungus Puccinia polysora, is also present in Louisiana corn (figure 2). Similar to common rust, initial infections are caused by wind-blown spores. This is a warmer-season rust compared to common rust and usually occurs late season and does not have adequate time to impact yield. However, this rust is very aggressive and if disease epidemics initiate early (prior to or at tasseling), yields could be reduced.

Conditions favoring development

Temperature: 80-90oF

Moisture: High relative humidity or abundant rainfall

Symptoms

Southern rust produces small circular to oval pustules and contain orange to light brown spores. The spores are lighter in color when compared to spores associated with common rust. Pustule size is usually smaller and less ragged looking than those produced by the common rust pathogen. Pustules are more abundant on the upper leaf surface and can also be found on the leaf sheath when disease is severe.

Northern Corn Leaf Blight

Northern corn leaf blight is caused by the fungus Exserohilum turcicum (figures 3&4). This disease was present at damaging levels in some fields during the 2010 growing season. The disease can be found in Louisiana corn fields during mid-season (tasseling/flowering) and, in some cases, can cause yield loss. The fungus can survive on infected corn debris left on the soil surface from the previous growing season. Therefore, the risk to this disease increases in fields where reduced-tillage practices are used and corn is planted continuously. Corn debris from the previous season provides inoculum for disease initiation and establishment. Spores produced on this debris are disseminated by wind and rain splash infecting the current crop. Subsequent infection results from spores produced within lesions on the current crop. There are several races of this pathogen. Therefore, the effectiveness of genetic resistance may vary depending on the races present in a particular field.

Conditions favoring development

Temperature: 60-90oF

Moisture: 6-18 hours

Symptoms

Lesions of Northern corn leaf blight usually begin in the lower canopy and progress upward. Lesions begin as small elliptical or spindle shaped lesions. Mature lesions can be six inches in length and about ½ to 1 inch wide. The lesions are grayish green in color.

Less Common Disease and Abnormalities

Gray Leaf Spot

Gray leaf spot is caused by the fungus Cercospora zeae-maydis. The fungus can overwinter on infected corn debris from the previous season. Therefore, risk to disease is increased when corn is continuously cropped and  reduced tillage allows debris to overwinter.

Conditions favoring development

Temperature: 70-85oF

Moisture: Repeated moisture over 11 or more hours OR high relative humidity

(95% or more)

Symptoms

Initial lesions are rectangular, small, necrotic, with yellow halos. As lesions mature, they expand and turn gray where the fungus may sporulate on the underside of the leaf.

Smut

This disease is caused by the fungus Ustilago madis and is generally not thought to impact yield. This disease is usually present at very low levels in every corn field, and is most severe when actively growing tissue of young corn is wounded. The fungus overwinters on infected corn debris from the previous growing season or in the soil (for many years). The fungus is NOT seedborne, as is the case with some smuts in other crops.

Symptoms

Symptoms can occur on foliage and ears and are very evident. Individual kernels enlarge and are silvery gray in color. Diseased kernels can be cut in half to reveal black sooty spores.

Purple leaf sheath

Each year this abnormality can be found in some corn fields within the state. THIS IS NOT A DISEASE.  While fungi and bacteria are associated with this condition, this is not harmful to the plant. The purple discoloration on the stalk and leaf sheath results from colonized (fungi and bacteria) pollen that is lodged between the sheath and stalk.

Risk and Management

Risk to disease is influenced by several factors including:  genetic resistance, tillage practices, planting date, and environmental conditions. Plant debris left on the soil surface (no-till or reduced-tillage production systems) harbors disease pathogens which increase the risk to disease. Later planted corn can also heighten risk to southern rust and possibly common rust. A favorable environment will always increase risk; therefore, it is important to know what conditions favor disease development.

The first line of defense for managing corn diseases should be selecting a disease-resistant variety. When resistance is not available, a fungicide may be needed. However, when disease is not present a fungicide is not necessary. Another factor to consider is when disease epidemics initiate relative to crop growth stage. The potential for yield loss is high when disease develops prior to tasseling and conditions remain favorable for development during the growing season. When disease initiates after tasseling, the potential for disease loss decreases. Therefore, a fungicide may not be needed even in the presence of disease.

The relationship of yield and defoliation can be found in table 1 adapted from the National Crop Insurance Service ‘Corn Loss Instruction’.

Fig. 2. Southern rust. Spores orange.Fig. 3. Northern corn leaf blight.Fig. 4. Northern corn leaf blight.
Fig. 1. Common rust. Spores brick red.

Table 1. Estimated % corn grain yield loss due to defoliation at various growth stages.

 

% Defoliation

Growth Stage

10

20

30

40

50

60

70

80

90

100

Tassel

3

7

13

21

31

42

55

68

83

100

Silked

3

7

12

20

29

39

51

65

80

97

Silks Brown

2

6

11

18

27

36

47

60

74

90

Pre-Blister

2

5

10

16

24

32

43

54

66

81

Blister

2

5

10

16

22

30

39

50

60

73

Early Milk

2

4

8

14

20

28

36

45

55

66

Milk

1

3

7

12

18

24

32

41

49

59

Late Milk

1

3

6

10

15

21

28

35

42

50

Soft Dough

1

2

4

8

12

17

23

29

35

41

Early Dent

0

1

2

5

9

13

18

23

27

32

Dent

0

0

2

4

7

10

14

17

20

23

Late Dent

0

0

1

3

5

7

9

11

13

15

Nearly Mature

0

0

0

0

1

3

5

6

7

8

Adapted from the National Crop Insurance Service’s ‘Corn Loss Instruction’ to represent the leaf collar growth staging method. Included in the Mississippi State University, Grain Crops Update June 4, 2010, Erick Larson.

 

Proper Irrigation is Critical to Corn Success

Proper Irrigation is Critical to Corn Success published on 1 Comment on Proper Irrigation is Critical to Corn Success
Many corn fields in Louisiana need irrigation as plant growth rapidly escalates.

by John S. Kruse, Ph.D.

Louisiana corn producers were blessed for the most part with good soil moisture during the optimal planting window. While the drought of the previous two years is still fresh in everyone’s mind, the late winter and early spring rainfall that moistened the soil profile and refilled many bayous and irrigation reservoirs is most appreciated. However, as temperatures rise and the winds blow steadily, many producers are finding their soil moisture is moving from abundant to scarce rapidly. Early planted corn in particular, is rapidly reaching a critical phase of development and should not be left without adequate water. It may be hard to fathom, but corn planted in late February is approaching tassel. This phase of development is critical to the crop’s success and adequate water is vital. Note in Table 1 that as corn matures beyond 12 leaves, water consumption increases to over 2 inches of water per week. Two inches of rain/irrigation water is equivalent to 54,305 gallons of water per acre. Be sure to know the output capacity of your irrigation wells and how many acres it must cover, then schedule accordingly.

When to get started:

If your fields still have adequate moisture due to timely rainfall, you do not have to water based on crop stage alone. In fact, watering young corn in particular, that already has adequate soil moisture, may promote an unnecessarily shallow root system. Growers and consultants may wish to consider implementing a watering budget to help guide irrigation decisions. The University of Arkansas has a program called the Irrigation Scheduler that is based on soil texture and average pan evaporation rates, and may prove useful . You can find it at:

(http://www.aragriculture.org/computer_programs/irrigation_scheduling/default.asp

Dr. Dewey Lee, Feedgrain Specialist for the University of Georgia, published a corn water use table that is applicable to Louisiana (Table 1), and growers and consultants can use it to predict water use for their crop. The only requirement is to know either the planting date (so you can use the “Days After Planting” Column) or the current growth stage of your corn crop (so you can use the “Growth Stage” Column). This table will provide a good basis of understanding on how much water corn consumes as it develops. Key items to note when thinking about irrigation are how quickly water use increases as the crop matures, how critical adequate water is during tasseling, and how much an adequate water supply is still important right up to “black layer” or physiological maturity.

Table 1. Estimated Water Use of Corn in Georgia (115-119 day maturity) CREDIT: Dr. Dewey Lee, University of Georgia

Growth Stage 

Days After

Planting

Inches Per Day

Inches Per Week Equivalent

Emergence and primary root developing

0-7

8-12

.03

.05

.21

.35

Two leaves expanded and nodal roots forming.

13-17

18-22

.07

.09

.49

.63

Four to six leaves expanding. Growing point near surface.Other leaves and roots developing.

23-27

28-32

33-36

.12

.14

.17

.84

.98

1.19

Six to eight leaves.Tassel developing. Growing point above ground.

37-41

42-45

.19

.21

1.33

1.48

Ten to twelve leaves expanded. Bottom 2-3 leaves lost. Stalks growing rapidly. Ear shoots developing. Potential kernel row number determined.

46-50

51-54

.23

.25

1.61

1.75

Twelve to sixteen leaves. Kernels per row and size of ear determined. Tassel not visible but about full size. Top two ear shoots developing rapidly.

55-59

60-64

.27

.29

1.89

2.03

Tassel emerging, ear shoots elongating.

65-69

.31

2.17

Pollination and silks emerging.

70-74

75-79

.32

.33

2.24

2.31

Blister stage.

80-84

.33

2.31

Milk stage, rapid starch accumulation.

85-89

.34

2.38

Early dough stage, kernels rapidly increasing in weight.

90-94

.34

2.38

Dough stage.

95-99

.33

2.31

Early dent.

100-104

.30

2.10

Dent.

105-109

.27

1.89

Beginning black layer.

110-114

.24

1.68

Black layer (physiological maturity).

115-119

.21

1.48

Brittle Snap Reported in Louisiana Corn Following Storms

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by John S. Kruse, Ph.D.

We have recently received reports of corn plants snapped off or crimped and laid over. The injury is most often associated with violent storms producing winds, but not always. “Brittle snap” or “Green snap” is much more widespread in the Midwest and High Plains where high winds can cause substantial damage, but occurs in Louisiana from time to time, particularly during periods of active weather. The damage usually occurs below the point on the stalk where the ear sets, is very visible, and generally results in total yield loss for that plant once the stalk has broken or severely crimped and fallen over. There are several factors that can contribute to brittle snap, including wind speed and direction, growing conditions, and hybrid type.

High wind speed, particularly when it hits perpendicular to the corn rows, is the main factor causing brittle snap. Injury may be more likely to occur during wind downbursts from a storm cloud, creating areas or pockets of damage in a field. If the winds hit during cooler periods of the day when transpiration is reduced and the plant is more turgid, the injury may be more widespread.

Growing conditions can be a factor as well. Warm weather, adequate soil moisture, and high soil nitrogen levels allow for rapid vertical stalk growth from roughly V5 to V18. Rapid cell elongation is occurring – thinning the cell walls – leaving the stalk vulnerable to snap. Inadequate potassium in relation to the amount of nitrogen available may exacerbate thin cell wall issues.

Corn seed producers recognize there are differences between hybrids as to their susceptibility to brittle snap. Some companies take the time to rate and report brittle stalk ratings, and it is worth taking these ratings into account when making seed buying decisions. Thin, rapidly growing stalks, high ear placement, and inherently thin cell wall structure in some hybrids make them more vulnerable to brittle snap than others. It may be that a few hybrids are susceptible enough that equipment (such as a boom) running through the field could knock over the plants, so producers should be aware if this is occurring and consider a different hybrid in the future.

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