Sorghum Tips

Nitrogen Fertility Guidelines for Grain Sorghum

This tip was provided by:

Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu

Statewide

Nitrogen Fertility Guidelines for Grain Sorghum

In our four years of compiling Sorghum Tips, we should have addressed basic N requirements for grain sorghum long ago.  From the Sorghum Tips archive at http://texassorghum.org/sorghum-tips, in 2012 we did discuss 1) fully crediting 100% of your soil-test nitrate-N down to 24” and the use of Texas A&M AgriLife’s Profile Soil Sample Information Form (Nov. 7, or page 7 of archive), and 2) the full N credit you can take for any nitrate-N in your irrigation water (Dec. 4, or page 6 of archive).

But what about the straight-up, season-long N requirement for grain sorghum?

Texas A&M AgriLife’s long-time fertility goal based on soil fertility research is tied to your yield goal:

2.0 lbs. of actual N per 100 lbs. of yield goal

This is a helpful rule of thumb—for planning purposes—for your N requirement.  Therefore, if you have a 5,000 lbs./acre yield goal, then the N requirement is 100 lbs. of N per acre, e.g.:

2.0 lbs. N/cwt.  X  50 cwts. = 100 lbs. N/acre

This is not the fertilizer N requirement as there are credits you may claim against the total required N.  In Texas A&M AgriLife these recommendations include:

  • Soil nitrate-N in your surface soil sample (usually 0-6”, sometimes 0-8”).  If you have 7 ppm nitrate-N in the top 6”, that is equivalent to 14 lbs. N per acre.  (Each 6” deep layer of soil is about 2,000,000 lbs. of soil; thus for each 1 ppm nitrate-N, you have 2 lbs. of nitrate-N.)
  • Sub-soil nitrate N (if you have the data, see #1 above).  For each 6” of soil below the six-inch depth, 1 ppm nitrate-N equals 2 lbs. of nitrogen per acre, a credit against the full N requirement.  For example, you have a sub-soil test sample of 6-18” deep at 4 ppm nitrate-N, then the credit determined, calculated as two 6-inch layers, is:

2 soil layers over an acre  X  4 N (from soil test ppm)  X  2 (ppm conversion factor)  =  16 lbs. N/acre

  • If you irrigate, you could also take a credit for any nitrate-N in the irrigation water (see #2 above).
  • Are there other possible N credits?  In Texas we don’t claim any, but a farmer sending a Kansas soil sample to Kansas State’s soil test lab will answer questions for soil texture, previous crop (if legume), and soil organic matter.  Each of these will slightly alter a KSU recommendation.

The full example—

For the 5,000 lbs./A yield goal…

Fertilizer N to apply  =  N requirement  –  soil test N (0-6”)  –  subsoil test N (below 6”)

70 lbs. N/acre  =  100 lbs. N/acre  –  14 lbs. N/acre  –  16 lbs. N/acre

What this example does not address—

This is the N requirement.  It does not address timing (most N should be on by growing point differentiation about 5 weeks after planting), fertilizer placement, or N use efficiency.  I will address these in a future Sorghum Tip.  In the interim, refer to the N fertility section of your region’s USCP pocket grain sorghum production guides for Texas at http://sorghumcheckoff.com/for-farmer/production-tools/ ).

2016 Texas Grain Sorghum Weed Control & Harvest Desiccation Guide

This tip was provided by:

Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu

Statewide

2016 Texas Grain Sorghum Weed Control & Harvest Desiccation Guide

As, we have noted before in a previous Sorghum Tips, we believe your most important weed control decision for grain sorghum is always pre-plant/pre-emerge herbicide applications.  Prevent weeds in the first place, and catch the escapes or other emerging weed issues later with over-the-top herbicides.  For most growers a combination of atrazine and metolachlor (Dual) gives good control, but many growers will substitute propazine on sandy soils and in cotton rotations.  The above document has been updated by Trostle/McGinty for use in planning your herbicide program with the active ingredients (and brand commercial names) available to your grain sorghum weed control program.  View/print/download the document at http://lubbock.tamu.edu/sorghum

Is Inzen/ALS-Tolerant Grain Sorghum Available in 2016?

The prospect of over-the-top grass control in grain sorghum has been teasing us for several years.  Five years ago we thought it would be here by 2014 or perhaps 2015 at the latest.  We are indeed closer to this sorghum’s availability, but only one limited opportunity exists for 2016.  First, this ALS-tolerant system has been named “Inzen” by Dupont, and eventually the active ingredient nicosulfuron (currently as Accent, soon as Zest) will be labeled for over-the-top application.

Currently, Pioneer does not have any hybrids that are available for growers, but Dupont licensed the technology to Advanta US, which has one hybrid (medium maturity) in their Alta Seed brand that is available on a limited basis for 2016 (one 50 lb. bag, maximum of 20 planted acres) if you are willing to partner with Advanta/Alta in a demonstration.  This will involve a stewardship agreement which governs what you can do with the grain (currently only for livestock feed or ethanol—it cannot go in to the commercial grain market yet), and, for now anyway, what you can rotate to next year (not sorghum).

If you are interested in this limited opportunity with Alta seed contact an Alta dealer.  You may be especially interested if you have a portion of a field where grasses are a special problem.  If any TGSA members try the technology this summer, please let your county ag. agent, myself & Dr. Ron Schnell know so we can learn from your observations.

2016 Sugarcane Aphid Watch–South and Central Texas

This tip was provided by:

Robert Bowling, (361) 265-9201, Robert.bowling@ag.tamu.edu, Assistant Professor, Extension Entomology, Corpus Christi
IPM Extension agents Stephen Biles (Port Lavaca), Danielle Sekula-Ortiz (Weslaco) and Kate Harrell (Wharton)

South and Central 

2016 Sugarcane Aphid Watch 

Another season is upon us as farmers have begun seeding sorghum in the Lower Rio Grande Valley and Coastal Bend of Texas. Sorghum has emerged in the Valley and in some areas around Corpus Christi. Warm and dry conditions have made possible the early start to the season, especially when compared with the 2015 cropping year. How might these conditions influence sugarcane aphid infestations in sorghum?

Sugarcane aphid reproduction is favored by hot and dry conditions. Currently, sugarcane aphids have already been observed overwintering on Johnsongrass as far north as Hill County (Waxahachie).  Numerous cast skins in aphid colonies have been observed around Corpus Christi up to Austin County suggesting that sugarcane aphids are maturing and producing offspring. It is possible they will start moving to sorghum early this season.  What is the path forward to protect the crop from sugarcane aphid injury in 2016?

Our full first-of-the-season report on SCA for South & Central Texas is online at http://ccag.tamu.edu/sorghum-insect-pests/  Several additional SCA resources are also there including the Scout Card for use in field ID of SCA and the all-important Quick Aphid Checker to rapidly estimate the number of aphids per leaf.

Here are some additional points from our full write-up:

  • Know the aphid.  Use a magnifying lens for ID.  If honeydew is observed, look at the underside of the leaf above.  If the sugarcane aphid is found on Johnsongrass or volunteer sorghum start scouting sorghum shortly after plants have emerged.
  • Start scouting sorghum early! If the planting seed was treated with an insecticide seed treatment (which AgriLife generally recommends; the cost is spread out over many acres), the crop should be protected for 30 to 45 days.
  • Several grain sorghum hybrids have been identified as ‘tolerant’ to sugarcane aphid.  Be aware, however, that tolerance does not equate to immunity and all sorghum fields should be scouted for sugarcane aphid.  Ask your preferred seed company for their best tolerant material.
  • In-season insecticide options for managing sugarcane aphid are limited.  Sivanto (Bayer) is currently the most effective product labeled on sorghum and is safe to beneficial insects.
  • Carrier total volume of water applied to the field is important!  Complete coverage of all foliage is critical for maximum performance of an insecticide targeting the aphid.  Do not apply less than 10 gallons of final volume of spray solution per acre if treating with a ground rig and no less than 5 gallons per acre if applying by air (even if the product is labeled for 3 gal/acre or less).
  • DON’T BE COMPLACENT!  Last year in South/Central Texas was cool and wet.  SCA’s growth was slow thus insect predators to maintained sugarcane aphid populations at a low level.

Next Sorghum Tip (late Mrach):  Guidelines for sugarcane aphid in the Texas High Plains, where thresholds are lower, even just the Presence of SCA in the field (in contrast to a set number of SCA per leaf for South & Central Texas).

Part II: An Important Component of Weed Control that Doesn’t Involve Chemicals, Equipment, or even Weeds. II. Your Custom Applicator

This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu

Statewide

An Important Component of Weed Control that Doesn’t Involve Chemicals, Equipment, or even Weeds.  II. Your Custom Applicator

Clear Communication is Important

In the last Sorghum Tip I discussed ensuring that your employees are clear on what needs to be done, that you cross-check with them on application practices, and even provide the means for your permanent employees to obtain their own pesticide applicator license and the training that goes with it.

Here are some key tips for working with your custom applicator:

Be clear with any commercial applicator you hire and ensure they understand what is needed and they are following label guidelines.  Confirm the rate of chemical you need applied.  Are their additives needed like AMS or crop oil?  If so, make sure.  I especially encourage farmers hiring custom application work to know what the label calls for as a minimum of carrier volume, whether by air or ground rig.  Expect—require—that your applicator use the minimum labeled rate for water per acre.  This is important for coverage; make sure you get what you are paying for.

Some labels unfortunately state a too-low carrier volume rate.  Here are two examples that reflect different reasons why carrier volume is too low and should be increased:

  • Dupont’s Prevathon, which better enables sorghum growers to attack worms in the whorl is labeled in Texas for 2 gallons per acre for aerial application.  Even Dupont staff in Texas disagree with this.  It needs to be at least 3 gallons per acre, and probably more for optimal coverage.  Unfortunately, since this is the labeled rate your custom applicator may balk without you paying more if you want 5 gallons per acre.  This is a dilemma, but if you are serious about achieving good insect control then carrier volume must be considered.  A poor application may require a second application.
  • Transform for sugarcane aphid.  If this insecticide becomes labeled again for use, Texas A&M AgriLife entomologists are in wide agreement that coverage is critical.  The labeled rate for aerial application for Transform is 3 gallons per acre, but our entomologist agree this is a situation with SCA that you need to apply 5 gallons by air (or 15 or more gallons/acre by ground vs.; 5-10 gpa is labeled).  So this is somewhat different situation than above in that SCA presents a special situation.  Also, there is wide agreement among AgriLife entomologists that different additives are merited (DowAgro agrees), but this information is not on the label, so you would need to relay this to your applicator to ensure they can follow best recommended practices.

Ready On-line Access to Chemical Labels for Agricultural Production
Herbicides, insecticides, seed treatments, fungicides, etc.  All in one place.  Chemical Data Management Systems maintains current full and Section labels at http://www.cdms.net (click on Label Database, then type in the name of the chemical in the search box).  For additional use of this website, including instructions on how to search for chemicals by active ingredient (often a generic), consult the AgriLife Extension guide for using CDMS’ website at http://lubbock.tamu.edu/files/2015/05/2015-Texas-Grain-Sorghum-Weed-Control-Guide-A.pdf

An Important Component of Weed Control that Doesn’t Involve Chemicals, Equipment, or even Weeds

This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu

Statewide

An Important Component of Weed Control that Doesn’t Involve Chemicals, Equipment, or even Weeds. I. Your Employees

I believe applicator awareness is often overlooked in weed control.  Communication and the needed instruction between a farmer and their own employees can make the difference in a serious mistake that damages a current crop or affects a planned crop rotation next year, or perhaps amounts to 85% weed control instead of the near 100% that you otherwise would expect.

Here are some tips as you work with your on-farm weed control team…

  • First, simply emphasize safety at all times.  On the farm I grew up on, I will admit that didn’t always happen.  I will admit that as a teenager I did some things that were stupid.
  • Confirm and cross-check with your staff which chemicals and any additives are being used.
  • Eliminate potential confusion about amount of chemical added to tanks, proper land speed, and issues involving calibration.
  • Ride the rig with your staff as much as is needed to ensure they are properly trained.
  • Communicate how important it is to fix plugged nozzles immediately (stop right there in the field!) and address other equipment issues; or in some cases that tank and system cleanout is conducted properly.
  • Teach your staff to stop and CALL YOU if something doesn’t look right.  Imagine one of your staff spraying dicamba on 16” tall grain sorghum with a hooded sprayer.  But the ground is rough and at the speed you are calibrated for the hoods are banging into the ground.  Instead of calling you, your employee raises the hoods 6” and sprays the field.  Now you have the risk that some crop loss may occur due to unacceptable contact of dicamba with the sorghum and potential blasted heads which don’t fill very well.

Asking confirmation questions of your staff—there is a right way to do this…

A good way to double-check with your staff that proper chemicals and amount are being prepared for application is to ask what has been done.  But how you ask will give you a more accurate indication of proper procedure and more likely identify if mistakes have been made.

Here is an example where you instruct your son/daughter or other employee to add a given amount, 2.0 gallons, of dicamba to a 300-gallon tank or spraying grain sorghum.  Now you want to ask if they did it right.

  • This is not a good question to ask:  “Did you add 2.0 gallons of Banvel to the tank?”  Why is this not a good question to ask?—because the employee can answer ‘Yes’ without revealing if they might have made a mistake.  Maybe they did make a mistake.  They added 2 jugs of Banvel (2.5 gallons each) to the tank.  An employee might realize they made a mistake and be afraid to admit it (even though the long-term consequences—severely damaged sorghum—are worse; but they might not know this could be a problem, or they will only be working for you through the summer then quit and go back to school, etc.).  This question may not have revealed the error.
  • Instead ask this question:  “What chemical and how much did you add to the tank?”  Now this is a question they can’t answer ‘Yes’.  They have to tell you something.  They will either guess (still might be right, but not likely), or they don’t know, or they will tell you the wrong thing.  Now you have a good chance of knowing if a mistake has been made.  If the sorghum field hasn’t been sprayed yet, you can avert a potential disaster.

Investing time and training in your employee that handles spray duties, and rewarding them…

For your family member (even a teenager) or permanent staff that helps spray your crops:

  • Have them study and train on your timeclock for their own pesticide applicator’s license.
  • Arrange for them to take the test.
  • When they pass it give them one-time bonus ($250?) or an annual supplement.  This tells your employee he or she has increased value as part of your team and that you value their new skills.  Increased training and sense of value on the part of your employee might avert a crucial mistake that could cost tens of thousands of dollars.
  • Have your newly licensed applicator help you maintain your records for TDA.

In my next Sorghum Tip I will discuss some pointers for interacting with your custom applicator.

Ready On-line Access to Chemical Labels for Agricultural Production

Herbicides, insecticides, seed treatments, fungicides, etc.  All in one place.  Chemical Data Management Systems maintains current full and Section labels at http://www.cdms.net (click on Label Database, then type in the name of the chemical in the search box).  For additional use of this website, including instructions on how to search for chemicals by active ingredient (often a generic), consult the AgriLife Extension guide for using CDMS’ website at http://lubbock.tamu.edu/files/2015/05/2015-Texas-Grain-Sorghum-Weed-Control-Guide-A.pdf

 

Evaluating if Grain Sorghum Hybrids with Seed Company Designation of Tolerance/Resistance to Sugarcane Aphid Are Right for You in 2016

This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu

Ron Schnell, State Cropping Systems Specialist, College Station,  (979) 845-2935, ronschnell@tamu.edu

Statewide 

Evaluating if Grain Sorghum Hybrids with Seed Company Designation of Tolerance/Resistance to Sugarcane Aphid Are Right for You in 2016

(Trostle)

In our last Sorghum Tip we published a list of 19 hybrids that companies have designated as what they believe are there most likely tolerant/resistant hybrids to sugarcane aphid.  Since then, as a Texas A&M AgriLife Extension staffer, I recognize that we in AgriLife don’t have enough information (or any in several cases) to publish about these hybrids’ tolerance/resistance and SCA.  Thus as a needed Disclaimer on the AgriLife December Sorghum Tip, though AgriLife staff have contributed to information (hybrid trial data, aphid and damage ratings, field observations) to the information Dr. Bean, USCP compiled, we in AgriLife have not verified the company information as well as other sources ourselves, and we have no AgriLife data of any kind on about half of these hybrids.

As an alternative I have written an article with the above title that discusses how you the producer may evaluate whether one of the 19 grain sorghum hybrids noted above is right for you.  Read the full edition at http://lubbock.tamu.edu (posted title is “Grain Sorghum Hybrid Selection and Sugarcane Aphid 2016).

As a sampling of the document’s advice, here are five questions you can ask your grain sorghum seed dealer:

1)    “What hybrid(s) do you have with a proven SCA resistance gene in its parentage?”

2)    “If you do, does that genetic background transfer actual hybrid resistance to SCA in the field?”

3)    “What field evidence do you have for this hybrid’s substantial tolerance/resistance? Seedling tests?  Field observations?  Field insect counts?  Yield data?”

4)    “Is at least some of your field data from independent or external sources?” (If so, who?)

5)    “How does the yield of your current SCA tolerant/resistant hybrid(s) compare to your company’s best grain sorghum hybrids?” (Agronomically, you want to understand the grain yield potential of good grain sorghum hybrids even if susceptible to SCA vs. tolerant/resistant hybrids.  If there are significant yield differences be sure to ask/understand if those differences may be due to likely lower-yielding shorter maturity in a hybrid.)

The list of 19 sorghum hybrids noted above that have stronger claims about SCA tolerance/resistance will be maintained by United Sorghum Checkoff Program, http://sorghumcheckoff.com/pest-management/, and it may change with additions and deletions.

Texas A&M AgriLife Grain Sorghum Yield Data & Sugarcane Aphid Tolerance/Resistance

(Schnell)

Planting resistant or tolerant hybrids will be vital for long-term management of sugarcane aphid in sorghum.  As noted previously, USCP has provided a list of grain sorghum hybrids that are believed to have some level of tolerance to sugarcane aphids.  However, identifying well-adapted hybrids with consistent yield performance in your region will remain the most important criteria for hybrid selection.  You should not sacrifice significant yield potential to plant resistant or tolerant hybrids.  There is no guarantee significant pest pressure will materialize and no guarantee that treatment for sugarcane aphid will be avoided.

The Soil & Crop Sciences Department’s Crop Testing Program collects information on grain sorghum hybrid performance from more than a dozen locations across Texas each year.  Results can be found at: http://varietytesting.tamu.edu/grainsorghum/.  In addition, hybrids identified as having unspecified levels of tolerance to sugarcane aphids will be summarized along with several susceptible public checks. These results will be available at the website above by the end of the week of January 18th.  Again, consistent yield performance will be the most important criteria when selecting hybrids.  Hybrids that perform well across multiple locations (regional summaries) and years (2- & 3-year summaries) should be strongly considered.  Make sure to select a hybrid that has a maturity rating appropriate for your environment. Several early to medium-early hybrids listed in the USCP report may be appropriate in certain situations (dryland and later plantings in west or south Texas).

Which Grain Sorghum Hybrids have Significant Apparent Tolerance/Resistance to Sugarcane Aphid?

This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu

Statewide 

Which Grain Sorghum Hybrids have Significant Apparent Tolerance/Resistance to Sugarcane Aphid?

Dr. Brent Bean, agronomist, United Sorghum Checkoff Program (and formerly Texas A&M AgriLife Extension agronomist, Amarillo), has compiled an initial list of grain sorghum hybrids that appear to have significant tolerance/resistance to sugarcane aphid (SCA).  Some other hybrids may have a lesser degree of tolerance, but those are not listed.  Dr. Bean has visited across the Sorghum Belt with companies, state university staff, farmers, etc. to arrive at this list as of Dec. 17, 2015.  Producers should consult the USCP website, www.sorghumcheckoff.com, for possible updates beginning in early January.

Before I say anything else about how to use this list or how it was derived, know this: All commercial grain sorghum hybrids, including these listed below, have at least some level of susceptibility (and most are highly susceptible) to sugarcane aphid.  All hybrids must be scouted, and at this time the same treatment thresholds apply to these hybrids as any other.  No commercial hybrid is immune to SCA.  Some Texas farmers made the mistake of assuming too much about the early purported tolerant hybrids in 2015, and they failed to treat SCA in timely fashion, or even scout their fields regularly if at all.
*Please note the following list is in alphabetical order by company and the order is not associated with believed tolerance levels.

Screen Shot 2015-12-18 at 2.10.02 PM

Understand the Potential Caveats of this Initial List of SCA-Resistant/Tolerant Hybrids

  • Much of the above information is derived only from seedling tests conducted in a controlled setting in a growth chamber or greenhouse.  Real life conditions in your field are not a guarantee that the hybrid will demonstrate the same level of tolerance/resistance.
  • Several of the above hybrids also have documented favorable reactions to SCA in field conditions, and additionally, there may be numerous reports from producers, Extension staff, field scouts, and crop consultants noting an individual hybrid performed well relative to other neighboring hybrids, etc.  Dr. Bean notes that in most cases these hybrids have exhibited the ability to withstand higher infestation populations of SCA while retaining their yield potential, or SCA has been shown to increase in number much slower than in susceptible hybrids.
  • You may hear a producer or other agriculturalist disagree with a hybrid being included on the above list.  Know that these hybrids probably can’t tolerate/resist heavy SCA infestations on their own.  For example, Dekalb DKS 37-07 has numerous documented and anecdotal observations of reduced SCA activity (not sprayed as soon, sprayed once instead of twice relative to other hybrids, not sprayed at all), but an elevator manager told me Dec. 16 that he thought that 37-07 had the same level of problems as any susceptible hybrid.
  • Visit with the seed company about the hybrids you are interested in.  Ask them what evidence they have for the hybrid’s tolerance/resistance.  Seedling tests?  Field observations?  Field data?  Do they have new information on any other hybrids?
  • Regardless of a hybrid’s tolerance/resistance to SCA it is still critical to chose a hybrid based on its local adaptability and other favorable characteristics.

In our next Sorghum Tip in January we will provide a link to a summary of yield data comparisons for the above hybrids vs. trial averages from the Texas A&M AgriLife Crop Testing Program’s sorghum hybrid performance tests.  (Most of the individual trial reports are already posted at http://varietytesting.tamu.edu/sorghum )

Texas Plant Disease Diagnostic Lab (TPPDL) vs. Direct Assessment by Sorghum Disease Experts
In our last Sorghum Tip we noted the services of TPPDL.  Dr. Isakeit noted that this service lab is in part oriented toward horticultural assessments.  You may wish to call your regional Texas AgriLife disease specialist (contact info. in previous Tip) to inquire if you might submit samples directly to Drs. Isakeit (College Station), Odvody (Corpus Christi), or French (Amarillo).

Texas Plant Disease Diagnostic Lab (TPPDL)

This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu

Statewide 

Texas Plant Disease Diagnostic Lab (TPPDL)
A service of Texas A&M University’s Department of Plant Pathology

In the previous Sorghum Tip we discussed where producers, agronomists, and others can access not only pictures of various sorghum diseases but also an understanding of the biology of common diseases in grain sorghum and possible management strategies.

But sometimes pictures just won’t do.  Or you need an accurate diagnosis.

Enter TPPDL!  This Plant Path lab and its clientele services may be accessed through http://plantclinic.tamu.edu/  With the exception of sorghum ergot sample analysis for seed, all sorghum samples in need of diagnostics may be submitted by filling out form AG-1178 then submitting the sample to Texas A&M.  Cost is $35 per sample (out-of-state samples pay a surcharge).  Instructions are on page 2 of the form.

TPDDL

 

Texas A&M AgriLife Plant Pathologists for Grain Sorghum

Three primary staff for AgriLife are experts on grain sorghum diseases among their primary duties.  These are:

These pathologists can help you with any field, hybrid, or management issues you may be facing with regard to grain sorghum and plant health.

Pictures of Grain Sorghum Diseases–Resources

This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu

Statewide 

Pictures of Grain Sorghum Diseases–Resources

In the previous Sorghum Tip we discussed some unusual foliar disease symptoms (zonate leaf spot) in grain sorghum that were more prominent in much of Texas this year.  If there is a field question I often rely on published pictures to understand what I might be looking at in grain sorghum for possible diseases (the same goes for nutrient deficiencies and herbicide injury symptoms).  Where are resources for grain sorghum?

The dated (1985) but still relevant Texas A&M Sorghum Diseases Atlas at http://amarillo.tamu.edu/files/2010/11/SorghumDiseases.pdf is still useful though of course the pictures are grainy (other crop diseases and a few updates for grain sorghum, some with a High Plains emphasis, may be accessed at http://sickcrops.tamu.edu).  A newer publication from Texas A&M Plant Pathology is not currently on the web (only the print descriptions of plant diseases, for sorghum see http://plantdiseasehandbook.tamu.edu/food-crops/cereal-crops/grain-sorghum/; we are looking at getting this publication back on the Web via extra-A&M links).

Kansas State recently published S125 “Diagnosing Sorghum Production Problems in Kansas” (2014) which also has its own series of pictures and descriptions of common sorghum diseases, http://www.bookstore.ksre.ksu.edu/pubs/S125.pdf

A Comprehensive Guide for Grain Sorghum Diseases and other Maladies

Compendium of sorghum disease

“Compendium of Sorghum Diseases (2nd Edition)”, 2000 is published by the American Pathological Society, and it is available for purchase by clicking here. Texas A&M AgriLife’s Dr. Odvody is a co-author.  I often carry my copy with me in the truck during the summer.  It has over 130 descriptions and photos of symptoms of numerous of sorghum diseases, plant nutrient deficiency symptoms, herbicide injury symptoms, and environmental injury.  If you work with sorghum a lot, I recommend you get a copy.

Zonate Leaf Spot in Grain Sorghum—2015 Observations

This tip was provided by:
Dr. Gary Odvody, Plant Pathologist, Texas A&M AgriLife Research, Corpus Christi, 361-265-9201, godvody@ag.tamu.edu  (compiled by Calvin Trostle)

Coastal Bend

Zonate Leaf Spot in Grain Sorghum—2015 Observations

Zonate leaf spot (ZLS) produces unusual leaf disease symptoms on grain sorghum. You may not notice it at low levels but if incidence is pronounced this fungal disease produces unique and strongly expressed leaf symptoms (Fig. 1). Zonate leaf spot (Gloeocercospora sorghi) was common on grain sorghum in the Texas Coastal Bend in 2015 due to season long wet conditions through about July 1 when rains abruptly ended.  Under conditions conducive to zonate leaf spot, the disease often develops as multiple lesions per leaf which coalesce to eventually kill the leaf tip and most of the entire leaf (Fig. 1, 2).

Fig. 1.  Zonate leaf spot damaging grain sorghum foliage, Texas Coastal Bend, 2015.  (Gary Odvody)

Fig. 1. Zonate leaf spot damaging grain sorghum foliage, Texas Coastal Bend, 2015. (Gary Odvody)

Fig. 2.  Top:  Multiple zonate lesions that have coalesced to kill most of the leaf blade, especially from mid-leaf to the tip.  Bottom:  Earlier leaf margin pattern of lesion development which may eventually coalesce across the leaf blade.  (Gary Odvody).

Fig. 2. Top Leaf: Multiple zonate lesions that have coalesced to kill most of the leaf blade, especially from mid-leaf to the tip. Bottom Leaf: Earlier leaf margin pattern of lesion development which may eventually coalesce across the leaf blade. (Gary Odvody).

As grain sorghum plants mature, leaves lose much of their resistance to pathogens so this disease can cause lots of foliar damage under disease-conducive conditions from mid to late season. However, ZLS typically does not cause economic loss of grain yield in Texas. Loss of leaves due to ZLS might affect forage yields in sorghum family forages although actual forage losses have not been documented. Under the multiple planting dates of 2015, sorghum maturing after July 1 in the lower coastal bend of Texas had progressively lower zonate leaf spot as drier, hotter conditions began to prevail.

Today’s grain sorghum hybrids and zonate leaf spot: Plant pathologists and sorghum breeders collaborate to eliminate sorghum lines and hybrids that are highly susceptible to foliar diseases including ZLS. This disease is present across South Texas in most years but generally at levels much lower than observed in 2015.  The disease usually becomes most noticeable late in the season when the potential effect on yield is minimal.  Except for avoiding highly susceptible hybrids there are no practical or necessary management strategies for ZLS on Texas sorghum.

For further information on this disease and additional photographs contact Dr. Odvody.

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