Fungicides are typically used in grain sorghum to control foliar disease when the potential for yield loss is significant. However, some suggest fungicides should be used to improve “plant health”, regardless of disease presence. This preemptive application is thought to improve physiological function of the plant, improve stress tolerance and standability of crop. The actual benefits of these applications are uncertain.
Texas A&M AgriLife has conducted several on-farm trials over multiple years on the Upper Gulf Coast of Texas to evaluate fungicide use in grain sorghum. Trials include several strobilurin type fungicides. Headline (6 oz/ac), Topguard (14 oz/ac), Quadris (6 oz/ac), Quilt (14 oz/ac) and Quilt Xcel (10.5 oz/ac) were applied in early bloom stages and compared to untreated checks. Plant health measurements included SPAD readings (leaf greenness), leaf temperature, and lodging along with yield, grain moisture, and test weight. Disease was present at most test locations but at very low levels of severity. None of the tested products produced measurable differences in plant health or yield. Lack of yield response certainly limits justification for application of the fungicides, given disease presence and severity was low.
Similarly, trials at the University of Nebraska evaluated the effects of several strobilurin fungicides, including Headline (6 oz/ac), Quadris (6 oz/ac), Quilt (14 oz/ac) and Quilt Xcel (10.5 oz/ac) applied at early flowering. The fungicide applications did reduce the incidence of disease (leaf spot and bacterial leaf stripe) compared to untreated checks, although severity levels were very low overall. They also showed that the fungicide treatments improved plant greenness or stay green. However, the fungicide treatments did not increase yield or test weight compared to untreated checks and did not affect moisture at harvest. In the end, the plants looked better but did not yield better.
Bottom line. Only apply fungicides when disease is present and has crossed established agronomic and economic thresholds. Strobilurin fungicides are very effective in controlling labeled diseases. Fungicides applied to improve plant health may result in a “better looking” crop. However, the applications are not justified if disease is not present and significant yield losses are not eminent.
If you have questions about grain sorghum and plant health, consult our Texas A&M AgriLife plant pathologists working in grain sorghum: Dr. Gary Odvody, Corpus Christi; Dr. Tom Isakeit, College Station; Dr. Ron French, Amarillo.
This tip was submitted by Dr. Ronnie Schnell, Ph.D., email@example.com (Cropping Systems Specialist, Texas A&M AgriLife Extension – College Station) and by Dr. Dan Fromme, Ph.D., firstname.lastname@example.org (Extension Agronomist, Texas A&M AgriLife Extension – Corpus Christi)
Iron deficiency related to caliche soils and outcroppings in West Texas (usually pH ≥ 7.9) or frequent alkali spots in fields (Coastal Bend, South Texas). This is a particular concern for sorghum. Chalky soils that appear whitish across the field should probably never have grain sorghum, and it is prohibitively expensive to correct it. Many fields, however, simply experience some degree of iron deficiency, the classical condition of interveinal chlorosis where the veins of the younger leaves remain green and the leaves are yellow between the veins (Figure 1). In the worst of cases, the leaves are almost completely bleached out and the plants do not grow.
Iron deficiency can also be induced temporarily due to water-logged conditions and possibly fast growth in young sorghum (root system not well established yet) or a possible response to herbicide (replant situation where residual is present or a subsequent post-emerge application). In modest cases where iron deficiency occurs, as the root volume expands iron deficiency diminishes. On the other hand, strong cases of iron deficiency in grain sorghum may merit treatment at as early as 10 to14 days after emergence.
Fig. 1. A) Iron deficiency in chalky soil where some leaves are almost completely bleached out and others show the striping of interveinal chlorosis (Fluid Fertilizer Foundation). B) Iron deficiency in older plants exacerbated by wet soil (J. Powell).
Iron deficiency compared to N deficiency. Iron deficiency is normally expressed mostly on newest leaves, and iron is immobile within the plant. When iron becomes available again, newly emerging leaves will again be dark green. Older chlorotic leaves will not green up unless they receive a direct foliar feed. In contrast, N is mobile in the plant, and will move to the youngest leaves from older plant tissues (which may express N deficiency) and shows no striping symptoms.
Most soil tests will flag Fe < 4 ppm as deficient. Currently, there are no economical sources of soil-applied Fe available. Therefore, the only options for correcting Fe deficiencies are to apply foliar Fe sprays in-season or to apply manure for long-term correction. If iron chlorosis has been observed during previous years in a field, iron fertilizer materials may be applied preemptively to the foliage through multiple sprayings early in the season. Table 1 gives suggested foliar treatments to correct iron as well as zinc deficiencies.
Table 1. Suggested sources, rates, and timing of iron foliar sprays.
|Deficiency||Product*||Product/100 gals water||Product/Acre||Timing|
|Iron||Iron sulfate (20% Fe)||20 lbs (2.5% solution)||1 lb. then 2-3 lbs.||10-14 days after emergency – 5 gals/A over crop row. Follow w/ additional applications @ 10-14 day intervals @ 10-15 gals/A|
|Iron chelate (10% Fe)||8 lbs. (1%)||0.4-0.5 lbs||Same as above|
*Include a surfactant or other wetting agent. Product composition may vary. Select similar products or adjust mixing ratios to achieve comparable rates of nutrient application.
Source: Updated information based on research results and recommendations through the Texas AgriLife Extension Service Soil, Water and Forage Testing Laboratory.
For further information about iron consult ‘Correcting Iron Deficiencies in Grain Sorghum’ L-5155, from Texas AgriLife Extension (http://agrilifebookstore.org, or contact your local county Extension office).
“Do you regularly see grain sorghum suffer from heat stress, even if moisture is adequate? If so, about how hot is too hot and at what stage of growth is grain sorghum most susceptible?”
There are two critical times in sorghum growth and development which are particularly sensitive to heat: 1) about 30-35 days after planting, when sorghum’s growing point switches from vegetative to reproductive and thus begins the process of determining the number of potential spikelets and seeds per spikelet in each head, and 2) at flowering when pollen is sensitive during formation when hot conditions can reduce viability. Grain sorghum’s upper temperature when heat units are calculated is 100°F. This implies that additional heat does not meaningfully contribute to growth and development (or could in fact be detrimental). Grain sorghum handles these temperatures better than most other crops, but that doesn’t mean it isn’t stressed. Low soil moisture and low humidity make this potential stress worse.
Occasionally we see what is called ‘sun scald’ on leaves resulting from heat stress (see Figure 1), and this can occur in irrigated grain sorghum as well. An entire leaf may occasionally die but usually just part of a leaf. I do not believe we have ever seen significant yield reduction due to sun scald alone, but heat of course can stress a crop. In the record-breaking heat of 2011 some sorghum was damaged due to heat stress, even in irrigated fields. Seed set was less than normal due to damage to pollen (reducing viability) and stigmas (less receptivity). Night-time low temperatures that remain near 80 F can compound this problem.
It is that time of year when in the Rolling Plains, Concho Valley, and High Plains in West Texas when hail and wind risks on grain sorghum, cotton, and other crops are high. For producers in this region, an annual guide to crop damage assessment, replanting decisions, and late planting decisions covers many crops. Grain sorghum is a crop of choice for planting after hailed out cropping due to relatively inexpensive production costs, ready markets, and a range of hybrid maturies that can be planted into early July.
As the updated 2013 edition is finalized, you may review the 2012 guide (agronomics essentially the same; prices, contractors, etc. will change) which includes many of the ‘First Things’ that are involved in planting after hail damage, replanting to grain sorghum, or planting a few weeks from now. You may review the document at http://lubbock.tamu.edu/files/2012/06/8cHailout-Replant-LatePlant-Guide-TX-S-Plains-Trostle-2012-TOC.pdf.
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.
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.
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.
- 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.
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, http://www.ksre.ksu.edu/bookstore/pubs/s3.pdf
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 http://agrilifebookstore.org (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.
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”, http://lubbock.tamu.edu/programs/crops/sorghum/. Notes for saflufenacil (PRE) and trifluralin & diuron (POST) as well as harvest aids will be added this spring.
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.