This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, firstname.lastname@example.org
Albino Striping in Grain Sorghum Leaves—Glyphosate Drift?
Herbicide drift is an issue in Texas cropping that sometimes we don’t want to talk about. I often find that producers don’t want to stir things up with neighbors and their herbicide applicators, be it land or by air, but the downside is that sometimes crops are indeed injured and yields drop. Lest anyone blame any particular crop, this is a two-way street. The sorghum producer is worried about glyphosate drift from the neighbor’s cotton field, but then cotton farmer is worried about sorghum’s possible use and mistakes in applying 2,4-D or dicamba, for which the cotton farmer’s crop can be injured. Introduce additional issues like conventional non-Roundup Ready cotton, high-value organic production (no chemical pesticides at all), and now the forthcoming dicamba and 2,4-D tolerant cottons, and drift issues can compound and become quite touchy.
In the Texas High Plains in 2014 due to some early rains and the broad distribution of Palmer ameranth species of pigweed, a lot of Roundup drift was observed onto grain sorghum. Early symptoms were often a nearly complete purple discoloration (Fig. 1) followed by various levels of tissue discoloration as some plants died (Fig. 2). Common to many of these seedlings is that secondary root growth from the base of the small crown was minimal to none (Fig. 3). These plants never recovered even with various foliar treatments with nutrients and growth regulators. The sooner they were replanted the better.
Other plants might have exhibited light stunting, but overall survival was not in question. What did eventually show up a few weeks after the apparent glyphosate drift was albino or white striping on lower leaves, usually leaves 3 to 8, depending on the field and its growth stage at the time of drift (Fig. 4, Fig. 5). Dr. Wayne Keeling, Texas A&M AgriLife Research weed scientist, Lubbock, was able to reproduce these symptoms using dilute glyphosate in a hand spray bottle.
Similar drift symptoms of glyphosate injury on grain sorghum also appeared in the South Plains region in 2015. Some fields had spotty damage (Fig. 6) whereas others received enough drift to permanently stunt or kill most plants (Fig. 7).
Through many observations, particularly in 2014, it was interesting to see how often a barrier to drift might protect grain sorghum such as the rows of sorghum that received protection from 6-7’ tall corn plants (Fig. 8.). Fencerows, weeds (24” or taller), and even terrace ridges were enough to protect several rows of grain sorghum from significant injury.
One producer has shared that the albino symptoms also can express in sorghum that was sprayed with glyphosate as a harvest aid. In this Rolling Plains example, the producer achieved a poor desiccation and kill with the glyphosate, and the plants regrew after harvest and stalks were baled. Albino symptoms were strongly evident on the regrowth (Fig. 9).
Much of the problems we have observed in the High Plains probably also occur in grain sorghum at some level in other Texas regions. Communication with neighbors before spraying—then holding people accountable if drift injury occurs—will help ensure needed safety and caution to minimize future drift injury potential.
Are there other possible factors that cause white sorghum?
Yes. Dr. Tom Isakeit, AgriLife Extension plant pathologist, College Station, notes that sorghum downy mildew is known to produce similar albino striping in leaves. There are four potential downy mildew inducing pathogens (one causes ‘crazy top’), but only Peronosclerospora sorghi in more advanced stages leads to white interveinal (between the veins) striping of the leaves (Fig. 10). This disease more likely develops under cool, humid weather and initial symptoms are a surface white powder on the leaves (mildew), but later stages of disease development lead to emerging leaves exhibiting parallel green and white stripes. The white tissue eventually becomes black (dies) and shreds.
Also, clomazone herbicide (common brand is Command) may cause some striping in rotational crops like grain sorghum if residues remain after the 9-month rotation restriction. This herbicide has been used in cotton, rice, sugarcane, soybeans, and some beans, peas and vegetables in the past, but Dr. Keeling is aware of only little if any remaining Command use in Texas.
This tip was provided by:
Ronnie Schnell, Assistant Professor and State Cropping Systems Specialist, College Station, 979-845-2935, email@example.com
Yield results are in for many of the Texas A&M AgriLife Extension and AgriLife Research grain sorghum hybrid trials. Extension trials use large, replicated strips to evaluate 6-10 commercial grain sorghum hybrids on growers fields. Plots are usually 4 to 12 rows wide, up to 1500 feet in length and are planted and harvest by growers in cooperation with their local AgriLife Extension agent. Excessive spring rains result in delayed planting and undesirable growing conditions during much of the season. Extension trials in several counties in the Upper Gulf Coast region were planted in early May (4-6 weeks later than normal). This resulted in lower yields. However, good yields were obtained in other areas that were planted earlier and that avoided long periods of saturation. Full reports can be obtained from your local county Extension agent and soon will be available at: http://varietytesting.tamu.edu/grainsorghum/. When deciding which hybrids to plant next year, remember that consistent yield performance across years and locations will provide the best indication of future performance.
In addition to county Extension trials, the Texas A&M AgriLife Research Crop Testing Program has results for grain sorghum hybrid trials at three locations posted at: http://varietytesting.tamu.edu/grainsorghum/. More locations will be available soon. These trials are small replicated plots with 25-45 commercial hybrids at each location. These trials provide an opportunity to compare performance of many new hybrids to current hybrids. Again, exercise caution when evaluating results at a single location. Consistency is the key when selecting top performing hybrids.
This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, firstname.lastname@example.org
Harvest Aids in Grain Sorghum—A Review
In the June 17 and July 1, 2014 (yes, a year ago) “Sorghum Tips” Dr. Ron Schnell and I discussed harvest aids in grain sorghum as well as desiccation. You can review that information at http://texassorghum.org/sorghum-tips/page/3 A 2003 Extension publication, “Harvest Aids in Sorghum” best accessed at http://publications.tamu.edu/CORN_SORGHUM/PUB_Harvest Aids in Sorghum.pdf, also discusses glyphosate and sodium chlorate and how they work in grain sorghum. We did not note in our above 2014 “Sorghum Tips” that Diquat 2L (Aceto) or RowRunner (Rotam), but not Reglone (Syngenta) (active ingredient is diquat dibromide), are labeled for seed hybrid grain sorghum production. Diquat acts similar to paraquat but is slightly less toxic (that is relative, still ‘skull-and-crossbones!), and it is used among other things on winter canola in Oklahoma.
Sodium chlorate a desiccant choice in fields with sugarcane aphid?
This product burns the leaves and will dry the head as well as the foliage whereas glyphosate may take up to a week to work, and it may not dry the head as much. This is our concern—sugarcane aphids looking for better quality forage for feeding might move or even be forced to the head. Sodium chlorate does not kill the plant, which could be a benefit if you have lodging concerns, but the product has its own safety concerns related to fire, and any sodium chlorate product should have a fire retardant in the chemical you buy. Sorghum will grow back, however, if not harvested in timely fashion after sodium chlorate treatment. If you use this chemical in a SCA-infested setting, I would like to hear of your experience.
A Short Update on Sugarcane Aphid in the Texas High Plains
Our Extension entomologists, farmers, etc. are reporting some odd observations. In spite of continued temperatures in the low 90’s and 65-70°F at night—conditions favorable for continued SCA development, it appears that in some fields SCA numbers are decreasing, and we have received reports where farmers believe there may be less than half of SCA numbers from just a week or 10 days ago. Likewise, a few surprises arise. For example, a farmer in Yoakum Co. with several thousand acres of grain sorghum, some planted as early as late April, other acres planted in June, has not sprayed a single acre as he never saw a major issue. Though he might have hit the technical thresholds, his fields (many different hybrids) never developed excessive numbers of SCA. He didn’t spray and it appears he will be OK. I will be visiting another field in Crosby Co. Friday where a farmer has had to spray four circles for serious SCA issues, but another adjacent hybrid has far fewer SCA, and he has not sprayed it. Wow! This is interesting. I will scout the field, record SCA numbers, etc.
Ladybugs like about all of us have never seen!…
I was in a field northeast of Lubbock on August 27 where aphids commonly ranged from 200 to 2,000 per leaf. I saw as many as 38 lady beetle adults on a single leaf, as many as four lady beetle larvae and 12 or more adults within a single head. This field had few winged adults. On Monday, August 31, the farmer called to say that with a light 0.2” shower over the weekend and all these beneficials, it appeared that SCA numbers were greatly less. Another interesting situation. He was preparing to spray either Transform or Sivanto, but now will not. This is one reason why we are fortunate these two insecticides are not damaging to beneficials.
Still making insecticide sprays for sugarcane aphid?—Silicone additives
Bayer and DowAgro both now recommend a silicone based adjuvant/surfactant to improve coverage. Examples of a few commercial names include ‘Airforce’ and ‘Syl-tac’.
This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, email@example.com
Threshold is Lowered for Triggering Sugarcane Aphid Sprays
The following was published Friday, August 14, by Dr. Pat Porter, Extension entomologist, Lubbock. The full story is on the main page at http://txscan.blogspot.com/ (scroll down for August 14).
“Now that we have had a few weeks of experience with field-scale sugarcane aphid control in the southern High Plains, it appears we need to move to a more conservative treatment threshold than the one currently in use. What we are finding in commercial fields and our insecticide trial is that our insecticides do not seem to be working quite as well as they do in more southern locations with higher humidity and less intense sunlight. Whether our environment affects the insects, plants and/or insecticides differently is unknown, and what we are seeing could be a combination of all three factors – or two or one or none, we just don’t know. Insecticide coverage issues may also be in play. We could be experiencing insecticide interception by excessive honeydew such that some of the insecticide never gets to the leaf surface. We also do not know the importance of reduction in coverage and canopy penetration attributable to aerial application rather than ground application with higher volumes of water. Additionally, we also have reports of narrow row fields (less than 36 inches) having reduced insecticide efficacy, and this of course is a coverage issue.
The preceding paragraph is basically to say that we are not sure what is causing reduced control. We want to make it absolutely clear that there is no reason to think this is a resistance issue. However, with regard to application timing the prudent thing to do is to initiate insecticide applications sooner, before the aphids reach 50-125 aphids per leaf. For that reason we are recommending the action thresholds in use in Mississippi.”
** ** **
Consult the above URL for the full report. Thresholds have been changed from 50-125 average aphids per plant to a percent infested plants (20% or 30% depending on growth stage). Furthermore, some additives may be considered to potentially enhance insecticide effectiveness. I have also heard reports of suggestions to increase insecticide rates (now possibly 1.5 oz/A for Transform, up from 1.0; and 5.0 oz./A for Sivanto, up from 4.0). Do not overlook the importance of coverage—which requires higher gallonage, closer spraying to the target (airplanes flying too high?), etc. –Calvin Trostle
High Plains & Rolling Plains
High Plains growers are getting their first ‘real’ taste of sugarcane aphid (SCA). It isn’t sweet. It is ironic that High Plains growers might have more issues in 2015 than did most Central & South Texas growers where SCA had to deal with a lot of cool, rainy weather, which seems to suppress the aphid, allow beneficials to keep it in check, etc. Dr. Ron Schnell (College Station) and Dr. Josh McGinty (Corpus Christi), others report that at most 10%, maybe 15% of acres in their areas were sprayed for SCA.
Where will we be in the High Plains? Especially since SCA was first reported here up to two months sooner than 2014.
As of August 5 a few thousand acres in the High Plains have been sprayed for SCA. I am not sure that all of these were the right acres. Indications, including comments from regional IPM agents, are that some acres were sprayed below threshold (misinformation, lack of proper scouting, poor recommendations from private scouts?), and some acres need spraying but haven’t been. Premature spraying is not a good idea as 1) you perhaps use some of your allotted insecticides sprays (especially Transform, which you can only spray twice), and 2) it is possible that you actually might not reach threshold.
I urge all—producers, scouts, chemical dealers—in your area: be aware of SCA. There does appear to be some misinformation regarding SCA in the High Plains. All High Plains and Rolling Plains fields should be scouted at least weekly to identify the Presence of SCA. Here are two cases that highlight what can happen or what some producers might have in mind (nonchalance?):
- Producer on Lynn-Dawson border: He knew SCA was in the area (Presence), but since he planted a so-called ‘tolerant’ hybrid in early (mid-May) in the cropping season (a good strategy), he wasn’t too worried about things, or at least hadn’t gotten to follow-up on a couple of his own fields that he found some aphids about July 13. He did not check fields again until Wednesday, July 29, in late bloom (16-day gap), and the SCA’s were so bad that he actually wondered if he could save his field (he can). He sprayed 1,100 acres, all at or above threshold (50-125 aphids per leaf). This grower has other fields about 10 miles to the west that are a different purported tolerant hybrid, and though he hasn’t yet seen aphids there, he sure needs to check at least once per week, then go to two 2X/week once the initial presence is confirmed. What if you were this farmer’s neighbor and you have grain sorghum?—Do you need to spray? No, scout first!
- August 3 I made a field visit to a producer at Wilson, Lynn Co., to assess another issue in grain sorghum. I asked the farmer if he was checking any for SCA on his grain sorghum. “Some.” He knows a few farmers are spraying, he has heard it is worse in one company’s hybrids (I don’t think so; no one brand is more susceptible than others—all hybrids, even those designated as ‘tolerant’ are still susceptible to SCA, e.g. the first grower above). After we finished, I looked at two of his fields, and a neighbor’s across the road. SCA on about 10% of plants. Needs to be scouted every 3-4 days.
Kerry Siders, Hockley/Cochran/Parmer Co. IPM agent, firstname.lastname@example.org, (806) 894-3150, is in the midst of ten Extension meetings on SCA. Kerry noted August 4th that fields are highly variable with SCA, and he has yet to report a field in his service area that has reached the threshold for spaying. But a few of his growers have been told by scouts they have SCA (threshold or not) and told to “spray it all.” Whoa! That was bad advice. Kerry told his producer to ask the scout for the field SCA counts to verify what levels of SCA were in the field. Also, Kerry advised that you CAN NOT adequately evaluate SCA on field edges—you will have to walk the field. In one case he walked several hundred feet into the field, found a major hot spot with several plants with 1,000 or more SCA per leaf, but then in all directions from this hot spot couldn’t find ANY more SCA! Just as we would not want to spray a field at threshold SCA (or worse) late; likewise, we do not want to spray a field early. Field results will be variable. Hot weather fires off SCA, but cloudy, cool days like Saturday, August 1, in the South Plains can suppresses SCA growth according to Siders. Siders did note, however, that SCA is with us to the end of the season in the High Plains. Growers that planted early, knowing that SCA might be an issue, are probably glad they did so (this is similar to how we would manage for sorghum midge, by the way).
A special note for the Texas Panhandle — Common current aphids are not SCA: Several SCA reports from the east and northeast Texas Panhandle proved to be not SCA but yellow sugarcane aphid (these are distinctly different). Yellow sugarcane aphids can be a damaging pest, but it is managed differently than SCA. For information on this insect review the Texas grain sorghum insect and pest guide (Extension publication E-1220) online here.
Sugarcane Aphid Resources—Summary & Key Documents, including “Scout Card”
This is a summary of key documents that entail numerous aspects of sugarcane aphid (SCA) biology, scouting, control options, etc. The documents listed below are found across four AgriLife websites so this will bring these to one location for your convenience.*Click the colored title to be directed to the website.
1) Sugarcane Aphid Management Guide, e.g. “The Sugarcane Aphid: A New Pest of Grain and Forage Sorghum” (April 25, 2015). Comprehensive guide to SCA in Texas grain sorghum.
2) Sugarcane Aphid Newsletter, e.g. Crop Management Newsletter 23:6, (July 1, 2015). A good Dawson-Lynn summary from Tommy Doederlein on expectations with the earlier arrival of SCA in the South Plains (initial confirmation late June 2015 relative to 2014 (identified about 2 months sooner this year).
3) Sugarcane Aphid Scouting School PowerPoint, (early 2015?). Summary of tips including specifics regarding labeled SCA insecticides Transform and Sivanto.
4) Recognizing the Sugarcane Aphid, (February 27, 2015). How to distinguish SCA from greenbug, corn leaf aphid, and especially the yellow sugarcane aphid (a different pest, which is currently prevalent in Texas Panhandle grain sorghum, late July 2015). You will need a good magnifying glass (and your reading glasses if you use them) to simplify aphid identification.
5) Sugarcane Aphid Field Scout Card, (April 2015). You can use this in the field to guide scouting, estimate SCA infestations and aphid numbers, etc. (approximate numbers without actually counting to comparable reference pictures).
6) Insecticide Selection for Sorghum at Risk to Sugarcane Aphid Infestations, (April 2015). The labeled and common pyrethroid insecticides for other common grain sorghum insects reduce beneficial insect populations thus enhancing potential increases in SCA. Options are discussed.
Updated News and Blog Post Notifications
High Pains growers, it is not too late to sign up on the right side of the page at http://txscan.blogspot.com/ to receive regular SCA news and blog update notifications to your e-mail.
Upcoming Texas A&M AgriLife Extension SCA Meetings in the High Plains
Friday, August 7
Brownfield – Terry County Extension Office – 8:30 am
Monday, August 10
Morton – Cochran County Activity Room, Cochran Co. Extension Office – 8:30 am
This tip was provided by:
Jourdan Bell, AgriLife Extension Agronomist, Amarillo, 806-677-5600, email@example.com
Managed Deficit Irrigation Scheduling in Grain Sorghum to Enhance Yield
The ample rainfall during the 2015 cropping season has allowed many Texas High Plains producers to significantly reduce their number of irrigations, but in an average year, irrigation is necessary to minimize production risks. However, on the Texas High Plains, well capacities are declining and producers have to make critical decisions on how to manage limited water resources to optimize production. In grain sorghum production, irrigation is commonly applied at a fraction of the crop water requirement throughout the season (deficit irrigation). However, in a three-year study on a clay loam soil at Bushland, our research found that concentrating irrigation during critical growth stages (managed deficit irrigation) maximized yield. Using a managed deficit irrigation strategy, yield was maximized by increasing the number of seeds per panicle in two of three years. Grain sorghum yield is a function of the number of seeds per head (63%), number of heads per acre (30%), and seed size (7%). While peak water use occurs around boot, irrigation targeting the critical growth period between growing point differentiation and half-bloom is the critical period to increase yield with this strategy because seeds per head make a proportionally higher contribution to yield. Growing point differentiation occurs approximately 30 days past emergence when there are seven to ten leaf collars visible. At growing point differentiation, the number of seeds per head is being determined. Half-bloom occurs when 50% of the plants are blooming.
With a managed deficit irrigation strategy, two early season irrigation events prior to growing point differentiation were eliminated in comparison to a deficit rate at 50% of the crop water demand. From growing point differentiation through half-bloom, irrigation was approximately 75% of the crop water demand, and from half-bloom through reproductive maturity, irrigation was applied at a deficit rate. While management was intensified, the cumulative seasonal irrigation was comparable between the deficit and managed deficit strategies.
By reducing the early season irrigation events with a managed deficit irrigation strategy, early season evaporative losses from the soil surface prior to canopy closure were minimized. And while deficit irrigation was a fraction of full irrigation (100% crop water demand), the same irrigation depth was applied but at different intervals in the Bushland study. In doing so, evaporative losses of irrigation intervals less than one inch were also minimized. While this complicates irrigation scheduling, it was a more valid approach than applying frequent irrigations of one-half inch or less. Grain yield and seeds per head were greatest in all years under full irrigation; however, these components were significantly greater under the managed deficit irrigation than the deficit irrigation in two of the three years. Under normal precipitation and in-season temperatures (2010), the effect of irrigating at the critical growth stages was not significant because the crop was not stressed during the period of growing point differentiation. However, under extreme drought and heat stress of 2011 and 2012, yield and seeds per head were significantly greater. This research and the associated management implications provide a valid management strategy to optimize irrigated grain sorghum yield.
While this strategy is valid on fine textured soils, it needs to be evaluated on a coarse textured soil with nominal soil moisture storage capacity. Additionally, this strategy requires a greater well capacity than would be required by a traditional deficit strategy if irrigation a large area. However, it is ideal in a split pivot scenario and allows the producer flexibility in irrigating secondary crops.
This tip was provided by: Ronnie Schnell, Ph.D., Cropping Systems Specialist, College Station, (979) 845-2935, firstname.lastname@example.org
Grain Sorghum Recovery from Saturated Conditions
Central and North-Central Texas
Repeated rain events during May resulted in soils being saturated, or even flooded, for extended periods of time for many sorghum fields across Texas. Rains have continued through June for many areas as well. At that time, many wondered what the impact would be on grain yield, if any? Predictions of final yield are difficult to produce for such an unusual situation but are important when deciding how much to invest to protect the crop from late season weeds and insect pests. Figure 1 shows grain sorghum in north central Texas on June 12, after two weeks of dry weather. This crop showed severe stunting and yellowing the previous week after over a month of repeated rain events and saturated conditions. This field received between 15 and 20 inches of rain during the month of May alone. However, new leaves had emerged from the whorl with good size and color by June 12.
With signs of recovery during early June, actual yield potential was still uncertain. Revisiting this field on June 30 revealed that significant recovery had occurred and substantial yield potential was available (Figure 2). An additional 6-8 inches of rainfall distributed throughout June with sunshine likely helped this crop recover, which had a shallow and damaged root system from May rains. Now it is obvious that there is yield worth protecting as this crop continues through grain fill stages.
Several issues have been reported throughout the region, including stinkbugs, midge, head worms and sugarcane aphids. Uniformity of crops within fields will create challenges for management of these pests (Figure 3). Sugarcane aphids are present, but numbers are generally below economic thresholds (http://txscan.blogspot.com/). It is uncertain what aphid populations will do later in the season. Therefore, it is important to treat pest problems that are present, such as stinkbugs or midge, when economic thresholds are reached (https://insects.tamu.edu/extension/apps/sorghumricestinkbug/index.php). Scouting will be important, making sure to check all areas of the field that are in various stages of development and to estimate the proportion of each field in contrasting stages of development.
As reported in the newsletter above, please click here to view more information on the sugarcane aphid in the High Plains.
As Dr. Ronnie Schnell noted in the previous Sorghum Tip, Central Texas flooding conditions and saturated soils are cause for concern on sorghum growth and development. Texas High Plains grain sorghum that was planted early (late April and early May) has seen unprecedented rainfall as well though saturated and flooding conditions are less likely. Either case can lead to a lot of foliar and growth & development symptoms. It is difficult to know what we are looking at as some symptoms may appear similar.
For example, the traditional “interveinal chlorosis” that is associated with iron deficiency, and which grain sorghum is much more susceptible to than most crops, is normally green veins in the leaves with yellow in between. But this is not the only nutrient that may cause such a symptom. Zinc and sulfur can cause symptoms that might be confused with iron deficiency (yellowing, less pronounced striping in the leaves). Add in the general yellowing that can occur from nitrogen deficiency, and you have a difficult time deciding what is occurring. Tissue testing can be conducted, but sometimes the “normal” ranges in the leaves, for example, may not give you an accurate indication. And what standard leaf ppm is being used as a reference? These reference levels are not all the same.
Though this publication is dated and the pictures are old, I find this 1980s Australian resource “Nutritional Disorders of Grain Sorghum” to be as thorough as any in the description of nutrient deficiency and toxicity symptoms. See http://ageconsearch.umn.edu/bitstream/118045/2/2.pdf
Waiting 7-10 Days…
When soils are flooded, temperatures are cold, or you have had a hail, sometimes 7 to 10 days is all it takes to “tell the story” of a grain sorghum crop or other crop turning around. Examples in Central & South Texas, the Texas South Plains, etc. currently reveal what draining and drying soil, warmer temperatures, and sunshine can do for a crop. Much of the Texas sorghum crop has a limited root system due to either flooding, as Dr. Schnell noted, or simply not needed to root deeply for moisture. But as drier, aerating conditions in the soil return, root volume will begin to expand. This often fixes a lot of foliar leaf symptoms—watch for new leaves appearing in the whorl and recently emerged leaves to return to near normal green coloration. This is a good sign.
Sorghum and Brace Roots—Key to Standability
The above picture, courtesy of Tate Newsom in Terry Co., shows grain sorghum that has leaned over from a strong wind. I would not call this lodged sorghum (which often involves stalk breakage). This sorghum is planted flat, and is at a stage of growth where the brace roots are just starting to emerge from the base of the stalk. Given time, these roots will anchor the stalk and stand the plant up. Where grain sorghum can struggle in this type of situation is 1) the sorghum is planted on top of a bed (that does not fit the type of plant and the root system of grain sorghum, but it works OK for taproot crops like cotton); you can’t very well throw soil with cultivation ‘uphill’ to cover the brace roots, and hard rains can wash soil away from brace roots entering the soil; b) soils are hot and dry, and thus roots don’t as easily enter the soil. If you still use cultivation for weed control, when you throw soil around the base of the sorghum plant, the brace roots are then already in the soil when they emerge. This is a win-win for grain sorghum and the producer, and you may have buried a few small weeds in the process.
Fading Weed Control from Pre-Plant/Pre-Emerge Herbicides
We are receiving numerous reports that “weeds are coming” where excessive rainfall has occurred and early atrazine (or propazine, particularly on sandier soils in a cotton rotation) appear to have shortened weed control. Be ready to promptly address in-season weed control needs. Many producers are well past the window for using 2,4-D or dicamba. See the earlier June edition of Sorghum Tips for additional in-season options. Could you possibly consider additional atrazine if sorghum is still 12” tall or less? This might be a consideration, but how readily you would decide to add more might depend on your crop rotation goals. Talk to your chemical dealer, company rep, or our AgriLife weed scientists if you need options. AND… scout your fields for weeds. They grow faster than our kids! Do your best to not let them get away, remembering the smaller weed size is easier to control. I assert that if you ever find yourself asking/doubting “Should I go ahead and apply my weed control?…” based on the size of your weeds, you should probably go ahead and apply.
This tip was provided by:
Ronnie Schnell, Extension Agronomist, College Station, 979-845-2935, email@example.com
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, firstname.lastname@example.org
North, Central & Coast
Impact of Flooding or Saturated Conditions on Sorghum
Recent rain events have resulted in flooding or significant ponding of water in many sorghum fields across Texas. While low-lying areas may be flooded, other areas of fields may be saturated for extended periods of time. How long can sorghum survive under saturated or flooded conditions? What impact will these conditions have on grain yield, if any?
Oxygen is required by plants for respiration, including above ground (shoots) and below ground (roots) plant tissue. Respiration is the process where plants metabolize sugars, producing energy needed for growth and development. Soil contains about 50% pore space that is occupied by air and water. Flooding increases the proportion of pore space occupied by water and reduces exchange of air between the soil and atmosphere. Deep ponding has the same effect on above ground tissue. Oxygen does not easily move through water so saturated or flooded conditions will limit oxygen availability to plant tissue, especially roots. This can have detrimental affects on plants.
The growth stage of the crop will influence the plant’s ability to withstand flooded conditions. Younger plants are more susceptible to damage or death by flooding, especially when the growing point is at or below the soil surface. Younger plants (growing point) are easily submerged compared to older, taller plants. Higher temperatures will exacerbate the effects of flooding. Young plants may survive for up to 48 in oxygen limited environments under cool conditions but may not survive 24 hours under warm conditions (>77°F). For this reason, yield loss is typically greater when young plants (< 6 leaves) are exposed to saturated or flooding conditions. Stand loss at early growth stages is a major factor in yield loss. Similar to freeze and hail damage, look for new growth several days after conditions improve to determine surviving plant populations.
Extended periods of flooding or saturation will affect plants of all ages. Root tissue can die and new growth will be stunted or delayed under saturated conditions. Flowering can be delayed for affected plants. Reduction in root volume will reduce the capacity for uptake of water and nutrients during later growth stages. Flooding can induce nutrient deficiency symptoms. Nitrogen will be remobilized from older (lower leaves) to younger (upper leaves) resulting in yellowing of lower leaves. Purpling of leaf tissue is possible due to accumulation of carbohydrates in the shoot tissue under flooded conditions, a symptom usually associated with phosphorus deficiency. In addition, denitrification and leaching of nitrate can result in loss of nitrogen from soil and potentially reduce yield. Damaged root systems and associated stress can increase the potential for various plant diseases, including root and stalk rot diseases. The degree of flooding will ultimately determine the potential for yield loss.
A brief period of flooding will likely have minimal impact on grain yield, especially for older plants. Repeated or long-term saturation/flooding will increase the potential for yield loss due to a variety of complications.
2015 Texas Grain Sorghum Weed Control & Harvest Desiccation Guide
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.
This sorghum tip was provided by:
Dr. Ed Bynum
Texas A&M AgriLife Extension Entomology, Amarillo
Sorghum midge, Stenodiplosis sorghicola, is a devastating pest of flowering grain sorghum but also coexists on Johnsongrass. This little fly, about the size of a gnat, is orange-red in color and has a unique biology. The midge lives less than 1 day but during that time a female can lay approximately 50 eggs. She will deposit only one egg in one of the flowering spikelets. The next day another brood of adults emerges from nearby Johnsongrass or other previously infested sorghum fields to deposit eggs in new flowering spikelets. So, depending on an individual flowering head it may be vulnerable to egg lay for 7 to 9 days and individual fields for 2 to 3 weeks.
Each of egg infested spikelet will have a midge larvae hatch in it in 2 to 3 days. The larva consumes the newly fertilized ovary resulting in the spikelet not developing a kernel. Depending on the number of sorghum midge present during the flowering period a portion of destroyed spikelets may be scattered among normal kernels or a majority of spikelets may not develop kernels. Insecticides are ineffective at controlling midge larvae once spikelets are infested.
Scouting fields during the flowering period is critical to knowing if insecticide applications are needed to kill adults before they have a chance to lay eggs. The residue from an insecticide application should provide midge suppression for 1 to 2 days after treatment. If adults are still found 3 to 5 days after the first application, immediately apply a second application.
The time to check flowering fields for midge is when temperatures are around 85o F. This could be mid-morning in some areas or afternoon in other areas. Adjusting the time to scout based on the temperature is important because midge are not active during lower temperatures.
Currently, midge activity is relatively low in the Lower Rio Grande Valley, according to Dr. Raul Villanueva, Extension Entomologist. Dr. Robert Bowling, Extension Entomologist, Corpus Christi, reports grain sorghum fields were late planted due to rains and are at least 2 weeks from flowering. Late planted fields in the Blacklands and north Texas regions may also be vulnerable to midge when fields begin to flower, notes Dr. Allen Knutson, Extension Entomologist, Dallas. Rains across the other areas of the state may have delayed grain sorghum planting and could influence midge infestations later in the growing season.
More detailed information about the sorghum midge can be accessed here.