Applications in Sorghum Forages
When nitrates and prussic acid accumulate in forage, the feed may not be safe for livestock consumption. This Extension document—available for view, print, or download at https://agrilifebookstore.org/ (then use the search box) —highlights the symptoms of nitrate and prussic acid poisoning.
Prussic acid (cyanide) occurs primarily when a strong frost hits sorghum family forages or grain sorghum. It can also occur in fresh growth on drought-stressed forages. Cattle normally need to be off the forage at least 1 week after a frost or freeze, and properly cured hay should be OK. Testing for prussic acid is tricky because handling the forage can lead to decomposition of the prussic acid. If you need a prussic acid test decide first which lab you are going to use and call them ahead of collection for their instructions.
Nitrate accumulation in sorghum and sorghum hays is most likely in rainfed conditions when either significant N applications have been made or the crop is drought stressed but still accumulating N. Nitrate is likely accumulated in the base of the stalk, so simple measures to use this forage include raising the cutting height 3-4”. Drought stressed grain sorghum in the High Plains that may be used for hay should consider testing the forage for nitrate accumulation in 2012.
Numerous producers in all regions of Texas are already considering increasing their grain sorghum acreage in 2013. Cotton price prospects for 2013 do not appear strong and grains do. Aflatoxin concerns have backed some growers off of corn in Central and South Texas. Producers are already checking seed supplies of favorite sorghum hybrids for next year.
A pitfall to avoid, however, for grain sorghum production is going too far into the too-common low-input mentality for grain sorghum production. For too many producers, this in fact approaches a no-input mentality. Or at least minimal inputs. This applies foremost to nitrogen (N) fertilizer, but can affect P fertilizer, the willingness to spray for insects like headworms or stink bug when economic thresholds suggest you should, etc. Yes, grain sorghum production at the yields we expect on an acre is less than for corn. But we know that if inputs are cut significantly below crop requirements then you receive mediocre and even poor results. And then the tendency is to blame the crop for underperformance.
I attended the recent national grain sorghum conference at Kansas State University. Colleagues with KSU as well as Oklahoma State Univ. spoke highly of grain sorghum’s role in Great Plains farming, that sorghum has a fit in many production systems that is more appropriate than corn. But they noted producers must ensure inputs are managed appropriately to maintain good profitable yields else reduced inputs restrict yield potential and lead to disappointment.
When can I stop irrigating grain sorghum?
Irrigation cut-out will most likely occur prior to hard dough stage. The sorghum seed will proceed through grain development from watery ripe to milky ripe to mealy ripe (the seed when squeezed no longer squirts, but oozes a gel-like or mealy material) then begins to firm at soft dough on to hard dough. As a rule of thumb, if good soil moisture is still available to the plant (at least 2 inches) then terminate irrigation as sorghum moves past soft dough. It is not reliable to base irrigation termination on grain color as different hybrids do not change color in the same fashion. A final irrigation may be applied during hard dough only if soil moisture storage is completely depleted or drought conditions are severe enough to hinder stalk quality at harvest.
When examining the head for seed maturation be sure to check many heads and check the whole head. Some difference in maturity will be observed on each head as seeds at the tip could be up to 7 days older (and more mature) than seeds at the bottom of the head, and primary tillers may also be several days later than the main head.
As a general rule of thumb, if you have doubts about whether to irrigate one more time prior to hard dough then do so, especially when grain prices are high.
Plant population in grain sorghum is a key to fitting your production potential to field conditions. But seeding rate does not equal plants per acre, and just because you set an air-vacuum planter to a target seed drop doesn’t ensure you are close to that number of seeds let alone plants.
Whether you have an existing crop in West Texas or have already harvested in South Texas (but your stubble is still standing), estimate actual plants per acre. Record this number in your field notes. Use the equation below and repeat it at least 3 times in a typical field area. Calculate a separate average for a thin area of the field, but watch it at harvest time to see if your yield is actually different (you may expect lower yield, but that is not always the case). Use all measurements in feet (including how wide the row is).
(43,560 sq. ft./acre) X (Plants in count area) = Plants per acre
(Length of count area) X (Row width) X (# of rows)
For example, if you measure two 30-inch rows 25 feet long and count 110 plants, then:
(43,560 sq. ft. per acre) X (110 plants) = 38,332 plants per acre
(25) X (2.5) X (2)
Round to the nearest 1,000, i.e., 38,000, then average this with at least 3 other points. You may have difficulty distinguishing tillers from the main stem, but count only individual plants (ignore small plants that will not contribute to grain yield). This method is easiest if counted 30 to 45 days after planting.
Some producers are familiar with counting plants in a fixed distance per single row, then multiplying by 1,000 to determine plants per acre. For a specific row spacing, use the length provided below (e.g., 1/1000th of an acre) then multiply by 1,000 to estimate plants per acre.
Row Spacing Length of row for plant count
20” 26’ 2”
30” 17’ 5”
36” 14’ 6”
38” 13’ 9”
40” 13’ 1”
We all know that crop rotation has its place in cropping of any type, but factors like commodity prices, crop insurance, the equipment you have, and even your landlord will influence cropping and rotations. Sorghum, like corn, no—more than corn—affords a residue producing crop on your land with a fibrous root system that is well distributed in at least the top 2 feet of your soil. When sorghum is a part of your rotation, you generate residues, which depending in Texas you farm, these residues are a key component to reducing erosion from water and wind, catching and keeping more of the rainfall you receive, etc. Texas AgriLife encourages producers to consider means to retain significant residues on the soil surface. Give your precious soil resource a blanket! This is a challenge for many producers, and I encourage you to learn about different types of coulters, trash whippers, and residue managers that fit on your planter so you can preserve the surface stubble as long as possible. Ask neighbors who farm a lot of sorghum how they approach this and watch for fields that retain a lot of stubble and learn the pros and cons to see if doing so fits your farming.
Likewise, turning grain sorghum under with any form of tillage does not increase soil organic matter from the surface residues. Instead you are more likely to disturb and destabilize existing soil organic matter. Soil organic matter increases from grain sorghum will come from the root system, and the longer you can leave it alone, the less tillage you use, the more likely grain sorghum can increase soil organic matter. It is not easy and sometimes not even practical to try to deliberately increase soil organic matter (a long, slow process), but leaving the roots in place is the most effective means of doing so.
So consider your 2012 grain sorghum—whether you have already harvested in South Texas or your crop is only 3 weeks old in the High Plains—and think about how to use this resource to enhance your soil quality and potential productivity for 2013 and beyond.
Sodium chlorate and glyphosate are labeled for pre-harvest use in grain sorghum. The former is a burn down chemical that acts as a defoliant, whereas glyphosate (technically labeled for weed control) kills the plant which aids in drydown. For seed milo growers, diquat dibromide is also labeled. Although limited Texas AgriLife research has not demonstrated yield differences among treated and untreated grain sorghum, the ability to manage and potentially accelerate harvest can have significant advantages in Texas, especially when humid conditions slow drydown. Furthermore, combine operators have often noted that the uniform condition of the crop at harvest makes use of these harvest aids a plus. The primary physiological criteria for application include seed moisture below 30% AND physiological maturity, which is best determined by identifying black layer in the seed (Figure 1).
For a summary of grain sorghum harvest aid uses in grain sorghum, whether this may be an appropriate management tool in your farming, as well as links to Texas AgriLife guidelines, consult Nueces Co. ag. agent Jeff Stapper’s blog at http://cbagbriefs.blogspot.com/2012/06/preparing-grain-sorghum-for-harvest.html.
Figure 1 (below). Sorghum kernels in various stages of maturity harvested from the same head from the most mature (1) to the least mature (5). The black layer is first readily visible in (3) and becomes more distinguishable as the seed loses moisture. Do not confuse black layer, which develops where the seed is attached to the plant (bottom end when in the head), with the black dot on the opposite end of the seed.
Staple Herbicide Use in Texas Cotton Restricts Rotation to Grain Sorghum
Staple (or Staple LX), a.i. pyrithiobac sodium, is an occasional herbicide used in Texas cotton. Texas producers of any crop are encouraged to rotate their weed control herbicides to slow the potential for development of herbicide-resistant weeds (use pre-plant herbicides, do not rely on the same chemistry year after year, etc.). Staple is one pre-emerge and post-emerge option, but the label states “do not rotate to grain sorghum in the year following a Staple (LX) application.”
According to Dr. Paul Bauman, Texas AgriLife weed specialist, College Station, Staple is used some along the Texas Gulf Coast for pigweed control, and Staple offers some help for Roundup resistant waterhemp control. In the High Plains Staple is a herbicide of choice for morningglory control and likewise is an option for control of newly documented Roundup resistant Palmer amaranth (pigweed). However, Staple use precludes any consideration of grain sorghum the following year. Dr. Pete Dotray, Texas AgriLife, Lubbock notes ‘the injury potential on grain sorghum the next year is real,’ let alone trying to plant sorghum in the year when hailout of cotton occurs.
Texas High Plains
Hailout/Replant/Late Plant Guide is Now Available
The 11thth annual edition of Texas AgriLife Extension Service’ “Alternative Crop Options after Failed Cotton and Late-Season Crop Planting for the Texas South Plains” has been updated for 2012. The guide is a “first things” approach to what you need for assessing hail damage and stands in current crops, and what your replant options are. Grain sorghum is a key replant consideration in most cotton hailout/replant decisions due to inexpensive establishment costs, income potential, and generating valuable surface residues in a cotton rotation. Herbicides, as noted above, can limit sorghum as an option. Tips for planting dates, seeding rates, herbicides already applied, etc. are noted throughout the document, which is available at http://lubbock.tamu.edu.
Texas High Plains
Dryland Seeding Rates
This is the most cussed and discussed and explained grain sorghum topic in my 13+ years as Extension agronomist in the Texas High Plains. Historically, many producers planted too much seed for ever present drought potential. When deep soil moisture is good (not 2012!), Extension recommends a maximum seeding rate of ~32,000 seeds/Acre, but we will readily drop that for drier conditions. If deep soil moisture is minimal consider ~26,000 seeds/Acre, and even lower if you are dusting in a later crop in very dry conditions. At these lower seeding rates and the subsequent stands you still retain surprising yield potential if conditions improve, but on the other hand, you have a better shot at harvesting a crop—we want a grain crop rather than a hay crop—with low plant populations in spite of dry conditions.
Texas Coastal Bend
Damaged Sorghum Heads
On May 21, Nueces Co. AgriLife Ag. Extension agent, Jeff Stapper noted some area fields showed blanking and undeveloped sections on the head, particularly at the tip (examples below). Along with Dr. Dan Fromme, extension agronomist from Corpus Christi, they concluded that this malady, already evident at heading, was likely related to stress in the sorghum plant. Grain sorghum breeder Dr. Gary Peterson, Texas AgriLife Research in Lubbock, concurs noting the symptom is consistent with heat stress during panicle (head) formation while the developing heads are still wrapped up in the stalk surrounded by leaf sheaths. This indeed requires hot conditions to cause damage down in the plant. No fields reported excessive damage. If 20% of field heads lost 20% of grain potential (and the head compensates some) this is a 4% loss, so though the damage may looks bothersome, the overall loss was still minimal.
Whether you are scouting for stink bugs in maturing grain sorghum on the Texas coast, assessing early season insects further north, or debating purchase of insecticide-treated seed in the Texas High Plains, then Texas AgriLife offers a valuable insect control source. “Managing Insect and Mite Pests of Texas Sorghum,” B-1220 (2007) has 30 color pictures and the guide systematically describes identification, insect activity, field thresholds, and suggested control measures including insecticides for 29 species of insect pests in Texas sorghum. You may view, print, or download the document for free from http://agrilifebookstore.org (type “sorghum” in the search box), or you can purchase your own color print copy.
For extension assistance with insect issues in grain sorghum, contact Texas AgriLife Extension insect personnel including integrated pest management agents, or Extension specialists through your county Extension office, or the Texas A&M Department of entomology – http://insects.tamu.edu.
One-Stop Online Access to All Chemical Labels
Do you need easy access to chemical labels for planning purposes, wish to ‘shop’ for herbicide specifics or for names of generics vs. brand name chemicals? Texas AgriLife staff rely on http://www.cdms.net to readily obtain label information from their computer. Access is free. To use Chemical Data Management Systems’ database, log in to the website then: 1) click ‘Services’, then ‘Labels/MSDS’, 2) enter the desired product name in the search box (keep the name simple, for example ‘Dual’ rather than ‘Dual Magnum’ to ensure you return all labels for Dual products), 3) select the label of your choice, 4) choose the main label or any supplemental labels you might need.
You may also search for chemicals based on active ingredient, target crop, or other criteria: 1) click ‘Services’ then on the left choose ‘Other Search Options’, 2) register with CDMS (free), 3) enter the common name (e.g. s-metolachlor, the a.i. in Dual), product type (herbicide, insecticide, etc.), and ‘crop/site’ which is your target crop (e.g. sorghum), and ‘Texas’ at the bottom. You will then receive a summary of active ingredients, possibly in combination (there are several for s-metolachlor)—make your choice, click ‘Next’ then choose the particular sorghum crop (e.g., grain sorghum, sorghum/sudan, etc.), then you receive the final results—labels comparable to Dual (nine in this example).
Irrigated Grain Sorghum Seeding Rate Suggestions
Grain sorghum hybrid typically range from about 13,000 to 16,000 seeds per lb., and this differential is a major reason why we do not recommend basing seeding rate on lbs. per acre, especially when you are likely to have an air vacuum planter.
For limited irrigation sorghum: (6″-8”; typical of many producers in the South Plains & Texas Panhandle) With low soil profile moisture conditions—and there is essentially no profile moisture in most areas in 2012 unless you have pre-watered—target 40,000-45,000 seeds/A, but if soil moisture is good, consider 50,000-55,000 seeds/A.
For full irrigation sorghum: (12″-16”) Target 68,000-80,000 seeds/A if soil profile moisture is good, but reduce for dry soil. Cap seeding rates at 80,000 seeds/A in just about any high irrigation scenario, though by late June/early July consider up to 90,000-100,000 seeds/A for non-tillering hybrids or when the development of tillers may cause difficulty with lack of uniform maturity across the field which causes problems at harvest time. High Plains producers report they regularly achieve 10,000 lbs/A grain sorghum with seed drops of 55,000-60,000 seeds per acre. “I have learned that is all I need,” notes one Bailey Co. grower.