Sorghum Tips

Purple Color in Grain Sorghum Seedings


Occasionally, grain sorghum seedlings growing in early cool conditions, especially if prolonged and coupled with cloudy weather, will demonstrate pronounced purpling of the leaf sheaths and leaf margins/leaf blades (see below). This may be coupled with interveinal yellow striping (chlorosis) related to iron deficiency. The purple color occurs from the accumulation of anthocyanin in the tissue and results from insufficient phosphorous uptake or from the plant’s inability to move sugars from the leaf blade (“Sorghum Growth & Development, Texas A&M AgriLife Extension, B-6137). Symptoms usually disappear when favorable temperatures return.

These conditions can occur throughout Texas whether you are planting in early March in the Coastal Bend or in early May in the High Plains. You have not done anything wrong with P nutrition for your sorghum crop.  The seedling in the left picture is at leaf stage 4 and has only recently developed sufficient roots to drive the growth and acquire P beyond what may have been available in seed reserves.

If you find a field with the purpling color and you have had cool conditions, it is advisable to re-check the field ever few days as warm weather resumes to track the return to normal colored tissue. Look for the newly emerging leaf to be green in color. As long as the plants are otherwise healthy yield potential is generally not compromised though it is possible individual plants might appear stunted.

Could this be herbicide injury?  In some cases when pre-emergent chloroacetamide herbicides (Dual, Lasso, Frontier) were applied, rain or irrigation may the chemical into the root zone. Under cool conditions the plants absorb more chemical, and some purpling may occur. Like the above scenario, the return of warm conditions and good growing conditions will diminish the symptoms and injury potential.

How does cool-induced purpling compare to conventional P deficiency?  P-deficient sorghum plants are stunted, spindly, and dark green with overtones of dark red on the leaves. The red pigment first appears on older leaves and characteristically progresses upward toward younger leaves. Interveinal (between veins) tissue is sometimes red separated by green veins. On individual leaves redness first appears on the leaf tip and margins then progresses toward the base and midrib of the leaf.


Grain Sorghum Yield Components


For any grain sorghum crop, the yield you realize across a field is a function of several factors. Of course, weather—especially rainfall—has a large impact. Your fertility program is an important key, especially for nitrogen. Whether economic thresholds of insects develop and how they may diminish your yield potential will be determined in how you control those pests.

But when a field of grain sorghum establishes, develops, and ultimately produces grain, where does the actual yield come from? Research demonstrates—as an average between irrigated, rainfed, and semi-arid dryland production—that the following yield factors in the sorghum plant itself generally establishes the contribution to grain sorghum yield:

·       Seeds per head                        63% of yield (higher in dryland)

·       Heads per acre                        30% of yield (higher for irrigated)

·       Seed size/test weight              7% of yield

Seeds per head makes a proportionally higher contribution in limited rainfall dryland, up to 70% or more.

What does this mean for a producer? Is this something your management can influence? Though irrigation, if you have it, alters your production options considerably. Naturally you use plant population to increase your yield potential. This data suggests—strongly—that seeds per head is a greater contributor to yield than heads per acre. You can indeed have too many heads per acre (whether from planting too much seed or from significant tillering, which may not be in your best interest the drier it gets), and the end result is higher heads per acre can actually limit your potential grain yield.

The bottom line, especially for dryland and limited-rainfall dryland, is that grain sorghum’s ability to compensate for yield is more in the head (seed number) than in the number of heads per field. Knowing this enables producer to manage (reduce) risk by using modest and even low seeding rates in rainfed and especially in limited rainfall dryland production. These reduced seeding rates actually favor the factor that research demonstrates has a greater impact on grain yield:  seeds per head.

Plant Height & Leaf Number – 2,4-D and Dicamba Applications


Chemical labels for the use of 2,4-D and dicamba herbicides (e.g., Banvel, Clarity) stipulate specific growth stages, either as leaf number or height of the plant, for application. Both families of growth regulator herbicides have a reputation for potential injury on grain sorghum that can damage grain yield if applications are made at the wrong time, or too much of the herbicide contacts the plant, especially if it gets down in the whorl.

2,4-D (amine or ester formulations):  Apply when grain sorghum is 6-15” tall (some labels say 5-15”), but if sorghum is 8” or taller, use drop nozzles to minimize chemical application to the plants.

Dicamba:  Apply in the “spike” stage (meaning all sorghum emerged) but before 15” tall (and especially at 3-5 leaf stage—when determining the leaf stage, count the rounded-tip coleoptile leaf as leaf 1, and all subsequent leaves that have a collar, meaning the leaf is fully expanded). Use drops for grain sorghum ≥ 8” tall.

It is difficult sometimes to equate leaf stage and sorghum plant height. Leaf stage is more defined. The main consideration is that the growing point by about leaf stage 6 to 7 is now at the soil line and beginning to move up the stalk. In my experience, I equate leaf stage with about 8” tall. That growing point is very sensitive to these growth regulator herbicide applications! In fact, one former Kansas State University agronomist colleague told the Sorghum U attendees in January that 2,4-D is an inexpensive way to hurt your grain sorghum.

Summary Tips

  • Be sure to follow label directions.
  • Because of the sensitivity of grain sorghum to 2,4-D and dicamba applications, re-read the section of your label on the timing and growth stage for using these herbicide applications.
  • If you are having doubts about whether you should still spray either of these herbicide families in grain sorghum, I suggest you don’t do it. This injury potential IS very real.
  • If someone else is making spray applications for you, but you are close to the label restriction when to apply, ensure that your applicator doesn’t “get to it later” or “wait until next week,” and be willing to tell them it is too late and stop the planned application.
  • If you believe you should not use either of these chemicals—growth stage too advanced, or you are simply risk-averse with these chemicals—consult your chemical dealer or Texas A&M AgriLife weed specialist for alternatives.

Grain Sorghum Growth & Development


Sorghum growth and development was first detailed in an easy-to-read document from Kansas State University’s Dr. Richard Vanderlip about 1980. Dr. Vanderlip was the first person I ever worked for other than my Dad on the family farm. I was a student worker in his research group. We were each given a copy of “How a Sorghum Plant Develops,” and we were expected to read it several times. This classical document remains a standard for grain sorghum,

In 2001, Texas A&M AgriLife staff working with Dr. Vanderlip updated the 1980 document by incorporating some additional research along with explanation suited more to Texas than the Central High Plains.  “Sorghum Growth and Development” (publication B-6137) was published in 2003.  You can view, download, or print this document at (type the publication number in the search box).

The latter document includes more discussion on heat unit accumulation and explains how this drives grain sorghum growth. The Kansas State sorghum document places more emphasis on the nutrient accumulation of N, P, and K in the plant during the cropping season. For example, about 70% of the total nitrogen, or N, that grain sorghum needs is already in the plant at flowering; this is one reason why later N fertilizer applications have reduced impact on grain yield.

Each edition offers some unique points about how sorghum growth is a reflection of its environment.  I re-read one or the other of these documents every three or four years as a refresher, especially since I have likely learned something new about grain sorghum. I encourage you to take a look at the documents to better understand your grain sorghum crop and how you may improve your management.

Pre-Emerge Weed Control in Grain Sorghum


In our Sorghum Tip last week on Huskie herbicide, I noted overall improved weed control this Bayer herbicide offers, particularly when paired with atrazine. The advent of Huskie for Texas sorghum, however, should not overshadow the fact that a farmer’s weed control decisions about pre-plant and especially sorghum pre-emergent weed control are far more important than the options Huskie offers. In fact, pre-emerge (or PRE) weed control is the most important weed control decision a farmer will make in grain sorghum production in Texas.

Dr. Wayne Keeling, Texas A&M AgriLife Research weed scientist in Lubbock, notes that although Huskie is a great asset to Texas sorghum farmers, our priority effort should be focused on effective PRE weed control. Our goal? — Prevent weeds in the first place, especially during sorghum emergence and early growth. Then post-emergent (POST) weed control (Huskie, dicamba, Ally, Permit, 2,4-D, etc.) can focus on controlling escapes as needed. Furthermore, if PRE weed control is good, producers may be able to delay needed POST control by 1-3 weeks to provide a longer window of either direct control of existing weeds or extending residual control further into the growing season.

Also, because Huskie herbicide largely relies on atrazine to enhance weed control, there is a concern, especially on more coarse soil types like sandy loam to reduce total atrazine rates especially if rotating to cotton the next year. PRE control can be accomplished with other chemicals, including mixes with reduced rates of atrazine, so that your field ‘loading rate’ of atrazine does not create rotation issues (especially cotton next year) when you pair atrazine with Huskie.

Below are several PRE options. Talk to your chemical supplier or company representative to further refine your PRE management strategy, especially if you anticipate needing mid-season or POST weed control options. (*) requires safened seed (e.g., Concep III, Screen) for chloroacetamide herbicides.

  • Propazine (Milo-Pro) as Pre-plant or PRE (no incorporation except in rare cases)
  • Individually, s-metolachlor* (Dual Magnum, etc.), alachlor* (Micro-Tech, Intrro), or acetochlor* (Warrant)
  • s-metolachlor* or alachlor* in combination with reduced rates of atrazine (e.g., Bicep II Magnum, Cinch ATZ, Bullet, Lariat, etc.), which should still allow suggested POST atrazine rates when paired with Huskie
  • Dimethenamid* (Outlook), possibly mixed with atrazine (Guardsman Max)
  • Saflufenacil (Sharpen), possible mixed with dimethenamid* or reduced atrazine rates; Verdict* is a saflufenacil/dimethenamid pre-mix.

For a recent summary of grain sorghum weed control options in Texas, consult “Quick Guide for Weed Control in Texas Grain Sorghum—2013”, Notes for saflufenacil (PRE) and trifluralin & diuron (POST) as well as harvest aids will be added this spring.

Huskie Herbicide: Major Addition for Weed Control in Texas Grain Sorghum – 2013 Update


In our very first TGSA Sorghum Tip last year we highlighted to producers the opportunity to use Huskie herbicide in grain sorghum (see here). Since the end of the 2012 cropping season, numerous producers have commented they were well satisfied with Huskie’s control. Here is a sampling of common comments from producers as well as the Huskie manufacturer, Bayer Crop Science.

  • Low to modest Huskie injury on grain sorghum was acceptable. A quick flashing, or burn, of the leaves was not uncommon, but injury levels were modest, and the grain sorghum quickly grew out of the injury with no apparent lasting effect on grain sorghum.
  • Producers were largely well satisfied with overall weed control. This included Palmer ameranth, other pigweed species, morningglory, Russian thistle.
  • Good control of glyphosate-resistant Palmer ameranth is a primary attribute of Huskie. This allows producers to more safely use herbicidal modes of action when they rotate grain sorghum.
  • Were there any problems or dissatisfaction with Huskie? In the High Plains there were but a few producers that were not pleased, but the common thread among their comments were:  a) dryland (especially in a major drought year), b) weeds were hardened off, and/or c) the sorghum itself was not doing well and not actively growing in some cases.

What to expect in the future for Huskie in Texas grain sorghum?

Bayer suggests that for optimum weed control, use:

1 pint of Huskie  +  1 pint of atrazine  +  1 lb. of ammonium sulfate (AMS) per acre

This rate of atrazine might be a concern for farmers on sandy loam to loamy sand soils; however, Texas AgriLife as well as Bayer staff has not observed any apparent issues with atrazine as long as the applicator follows the labeled rate.

Rotation to cotton on the Huskie label remains at 18 months or field bio-assay. Texas A&M AgriLife and Bayer staff have not yet observed any significant rotation issues to cotton.

There is consideration of expanding the Huskie label for applications up to flag leaf emergence.  Though this might be appealing to producers, we should only view this as a potential rescue treatment. Waiting until nearly flag leaf emergence means that pigweed and other problem weeds will be larger, thus harder to kill. Weed control will more likely be incomplete.

Watch for an upcoming Texas A&M AgriLife survey of 2012 Huskie users to share their experience with this herbicide. This will likely merit an additional mid-season Huskie sorghum tip.

Narrow Row Grain Sorghum – Increase the Seeding Rate?: Probably Not


A frequent question across Texas is whether a grain sorghum producer should increase the seeding rate if moving to narrower row spacing. Most Texas grain sorghum is planted on 30-, 36-, 38-, or 40-inch rows.  In general, Texas A&M AgriLife recommends that you do NOT increase the per-acre seeding rate when moving to narrower rows for several reasons:

  • Many producers are actually already dropping as much if not more seed than they probably need for good production.
  • If moving to a narrower spacing, let the additional space around the individual plant be the means of compensating for slightly higher yield potential. Grain sorghum does indeed compensate, and if there is more space around an individual plant, the plant will likely tiller more in response to the environment.
  • Maintaining the same per-acre seeding rate is easier if you are using an air-vacuum planter that meters the seed and also has the same or similar equipment to achieve good placement of the seed.
  • What about drilling grain sorghum seed?—In this case producers must be careful.  We like the idea of spreading your plants out, however, most drills were not made to drop such small amounts of seed, 5 lbs. down to as little as 2 lbs., per acre. Drills measure volume of seed, not seed number. You probably can’t get most drills shut down enough, especially if they are older and worn some. If you are drilling, expect to tape or close off at least 1 of 3 drops and perhaps 1 of 2 drops. Drills do not place seed as well as planters, hence reduced seedling establishment may be expected, especially if not irrigated. Due to reduced optimum seed placement, I will allow an increase in per-acre seed drop by 10% – in other words, not much!—if you are drilling. If seedbed conditions are truly rough, then perhaps 20% increase in per acre seeding rate; however, if you get a good rain, and it all comes up, you are immediately over-populated. (If field conditions are truly rough, then use the planter anyway for managing the best seed placement you can get.)
  • Moving to narrow row spacings means you forego the opportunity to conduct mechanical cultivation for weed control. Thus you have a question of narrow row spacing for weed suppression vs. retaining the ability if needed to cultivate. Since grain sorghum has few aerial over-the-top weed control options, if you anticipate weedy issues, you may prefer to not close the door on cultivation if it becomes necessary.

Grain Sorghum Seed Size


Seed size in grain sorghum ranges from about 12,000 to 16,000 seeds per pound. Grain sorghum in general will sometimes have slightly smaller seed size (18,000 seeds per pound). Usually seed companies will select what they believe is their best seed to bag for your planting and so this tends to be the larger seed. Planting seed size for hybrid seed most commonly runs about 13,500 to 15,000 seeds per pound. For planting seed I am most likely to assume 14,000 seeds per pound if I don’t know the specific number.

Seed size should not really affect a farmer’s decision on which seed to select. Good germination is much more important. Seed and subsequent seedling vigor is not necessarily higher with larger seed size though as a grower we would likely feel more confident in a larger seed. No correlation has been demonstrated between seed size and eventual yield. In dry conditions, larger seed needs to imbibe more moisture to germinate, but this is not normally an issue for grain sorghum. It can be with larger seeded crops like soybean or sunflower.

The one caveat about large grain sorghum seed is that at 13,000 seeds per lb. versus smaller seed at 15,000 seeds per lb., is the larger seed has 13% less seed in a bag so it will not plant as far (essentially costs about 13% more to plant) when using an air-vacuum planter. If you have an older planter that uses plates, your pounds-per-acre seeding rate will stay the same but the seed drop will decrease. Because many Texas producers plant more than enough seed, I would not worry about the slight reduction in seeding rate. Plate planters should be calibrated to ensure they are delivering the desired amount of seed regardless of seed size.

Grain Sorghum Seed Costs & 2013 Supply


No kidding, seed is in short supply for 2013 due to reduced hybrid seed production in both 2011 and 2012. An increased in expected acres will further shorten supplies. This has created the highest grain sorghum seed cost we have ever seen.

Action Tips for Grain Sorghum Seed:

  • If you anticipate needing grain sorghum seed in 2013 I urge you to check with your preferred seed dealer now.  Supply is declining and prices are subject to change (they won’t be going down!). The longer you wait, the less selection you will have.
  • Be cautious about moving to a maturity of grain sorghum seed that is not appropriate for your production system. In Central & South Texas if all you can find is early maturity hybrids, then call another dealer. In the High Plains, don’t book a medium-long or long season hybrid for dryland just because that’s all you can get.
  • Evaluate your seeding rate.  For grain sorghum seeding rate targets in your area, consult the three different United Sorghum Checkoff Program grain sorghum pocket guides that cover Texas here. {These include editions for South & Central Texas, West Texas (South Plains, Concho Valley, Rolling Plains), and the High Plains (Texas Panhandle)}. Many producers in Texas still plant more seed than they need, sometimes at the expense of grain yield. I would rather pick a preferred hybrid and reduce the seeding rate by 20% to stretch a limited supply of seed than go with something I am not familiar with or is less appropriate.

Here is a sampling of grain sorghum seed prices from four seed companies with Texas sales.  This represents both regional and national brands. Prices are the same across Texas.

  • Company #1:  Concep III treated seed only (allows use of Dual Magnum herbicide), $109/bag. Gaucho or CruiserMaxx treated, about $159/bag.  Three of six primary hybrids sold out, 1 is thin, 2 with modest supply. Discount 6% if paid by 12/31, 4% discount if paid Jan. – Feb.
  •  Company #2:  $100 to $135/bag, depending on hybrid.  Add $18/bag for Concep III.  Gaucho treatment about $13-15/bag. Other premium comprehensive seed treatments somewhat higher than Gaucho. Seed supply is extremely short, and some hybrids are sold out. No pre-pay discounts as seed supplies are too short.
  • Company #3:  All hybrids are $172-184/bag which have Concep III and CruiserMaxx.  They don’t sell grain sorghum seed any other way. All medium maturity hybrids sold out (at least in High Plains), but some supplies left of medium-early and medium-long.  7% cash discount if paid by Jan. 18, and quantity discounts available.
  • Company #4:  $102/bag for older lines, $110/bag for newer lines, all Concep III treated. Up to $64/bag for Poncho treatment. Seed supplies low and company will re-allocate remaining seed stocks in early January. Call about discounts.

“Free” Nitrogen for Grain Sorghum (Irrigated) #2 – Nitrate N in Irrigation Water


In my previous tip I noted the value of existing subsoil (below 6”) nitrate that is readily available to grain sorghum and other crops, which should be fully credited to grain sorghum N requirements nor soil nitrate between 6” and 24” deep.  Now for irrigated crop producers, let’s consider the amount of nitrate-N (also expressed as nitrate-nitrogen or NO3-N) that potentially exists in irrigation water.  This N—like soil N—should be fully credited to crop production with only a minor exception or two.

For reference read the three-page Extension publication “Nitrates in Irrigation Water:  An Asset for Crop Production” (Texas A&M AgriLife Extension Service, E-619, type ‘nitrate’ in the search box at  This recent 2012 document explains the justification for valuing nitrate in irrigation water, which by reducing fertilizer N requirements, can save producers input costs.  Most Texas irrigation waters contain 3 to 10 parts per million (ppm) nitrate-N, but some waters are over 20 ppm.

In general, for each 1 ppm of nitrate-N in your irrigation water you are adding 0.23 lbs. of N per acre.  A producer who irrigates 12” and has 6 ppm nitrate-N in the water is applying about 14 lbs. of N per acre.  For a 6,000 lbs./A yield goal, this level of long-term N concentration is about 12% of your total crop requirement.  The cost of N fertilizer, were you to buy it, would currently be about $9/acre for this example, and that does not include application costs.

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