Even with prices lower than anyone would like, Southwest farmers have good reasons to plant grain sorghum this year — but they will need to watch input costs closely and guard against losing yield to weed and insect pests.
Texas A&M AgriLife Extension and Research Agronomist Jourdan Bell at Amarillo offered some production guidelines at the Red River Crops Conference at Childress, Texas.
“Why should you grow grain sorghum?” she asked. “It offers good yield potential, with limited water; it has an extremely efficient root system; and it’s a good rotation crop, providing valuable residue for the next enterprise.” Plus, she says, cotton farmers often see a yield increase when they plant cotton behind grain sorghum. Other advantages include an opportunity to clean up troublesome weeds with less expensive herbicides.
“But sorghum prices are low,” Bell notes, “so input costs will be a factor.” Low seed costs will help some, and she says farmers should consider seed per acre instead of pounds of seed per acre. “And make sure to pencil in costs for controlling sugar cane aphids. Some farmers have backed away from grain sorghum because of this pest, but it can be successfully managed.”
Weed control is another production cost, but an important management practice, she says. “Know the weed species in the field, and prioritize control strategies. Know the field history and the weed seed bank. Control as many weeds as possible prior to planting.”
Efficient and effective weed control starts early, Bell says. “With burndown treatments, target small weeds — mustards and weeds like prickly lettuce are easier to control at the rosette stage.”
Application rate and timing also matter. “Weeds in drought stress are harder to control, as are larger weeds.” She recommends targeting weeds before they reach 4 inches tall.
Coverage is critical; she advises applying herbicides with at least 10 gallons of water per acre with ground spray equipment. “Water is the cheapest component in the sprayer, so use enough. Applying 2 gallons over an acre doesn’t put out much product. Also, select the appropriate nozzles (flat fan), and consider a herbicide program that fits your tillage system.
“Make the application in front of the strip-tillage operation, or a couple of days later, to avoid the weed being covered up by soil at the time of application.” Additives (surfactants, UAN, etc.) may be needed.
Some herbicides may have plant-back restrictions, if wheat or cotton will be the next rotation crop. “Check the label for plant back restrictions.”
Bell recommends burndown, preplant, and residual materials, as needed, for effective weed management, and notes that herbicide products and programs vary in effectiveness and cost, so producers should shop around to determine the best fit for the weeds present and the cost of the product and application. However, pre-emergent herbicides are critical. “It’s important for long-term management that we start clean. Starting clean is important this season, as well as reducing the weed seed bank for future seasons.”
A GOOD FOUNDATION
Bell says atrazine is a good foundation herbicide in sorghum programs. It is a cost effective pre-emergent product. But it has limitations: atrazine-resistant weeds and crop rotation considerations (cotton and wheat), and it can be inconsistent, especially on large weeds. But it enhances the activities of other products, especially providing some residual activity against annual grasses. “It’s important that producers watch the rates on sandy and loam soils, as well as consider their cotton rotations.”
Lumax is commonly used as a preplant material in corn, but it’s also labeled for grain sorghum. There may be some plant-back issues, if sprayed too close to planting. Target weeds include kochia, pigweed, marestail, lambsquarter, and witchgrass. “Lumax consists of three different chemistries with three different modes of action,” she says.
Lumax requires rainfall or irrigation to activate, should not be used on sandy or loam soils, and is labeled for use up to 21 days before planting. It should not be applied to emerged grain sorghum. Cost would be about $41 per acre, so it may not be cost-effective for some sorghum growers, but it could be targeted to fields with known herbicide-resistant kochia.
Warrant is labeled for preplant and post- applications, prior to 11 inches, for select grasses and
broadleaf weeds. Seed must be safened for preplant application. Target weeds include johnsongrass, possibly Texas panicum, volunteer wheat, purslane, and pigweed. Cost is about $13 per acre for the chemical.
Grasses are often a concern in grain sorghum. Other pre-emergent options with some grass activity include Dual II Magnum, Cinch, Parallel, Outlook, Micro‐Tech, and Milo-Pro. These require Concep III treated seed.
Pre-emergent herbicides with broadleaf weed activity include Bicep II Magnum, Cinch ATZ, Guardsman Max, Bullet, Lariat, Lumax, and Verdict. These also require Concep III treated seed.
Verdict, applied as a pre-emergent with Outlook and atrazine, would cost about $31.73 per acre. A postemergent treatment with Facet, Outlook, and MSO would cost about $44 per acre.
Facet provides a good burndown on hard-to-control weeds, but it significantly increases the cost of the tank mix. It is labeled for grain sorghum in Arkansas, Louisiana, Mississippi, and Texas as a pre-emergent material targeting annual grasses and some broadleaf weeds, such as kochia and bindweed.
Verdict, another pre-emergent product on the market for broadleaf weeds and annual grasses, contains two chemistries with two different modes of action. “Verdict needs to be activated with at least one-half inch of rain or irrigation before sorghum emergence,” Bell says. “Chemigation is also permitted, which provides farmers flexibility at application time.” Verdict costs about $24 per acre, applied alone. “But it controls a large number of weeds.” Restrictions include sandy soils with low organic matter.
Dicamba products (Banvel and Clarity), tank-mixed with glyphosate, are effective as a preplant burndown, but have a 15-day prior to planting restriction. Sharpen is a good burndown material, and is useful as a preplant and pre-emergence product. “Short term residual activity is significant,” Bell notes, “and adding Verdict extends the residual effect. For post activity, use with MSO and AMS or UAN.”
Outlook, with an estimated cost of $16.25 per acre, works to control grassy weeds, sedges, and annual broadleaf weeds, applied pre-emergence or early post. “Warrant is a preplant and post- material, but grain sorghum seed must be safened for preplant applications. Targets include johnsongrass and Texas panicum, but it only targets the germinating seedling — it will not touch existing stands. Cost is about $14 per acre.”
Huskie, a relatively new product in grain sorghum, was originally labeled for wheat. It costs about $15 per acre. “With kochia, it will not work alone,” Bell says. “Starane Ultra would be a good addition for approximately $5 more per acre.” Tank-mixing Huskie with Banvel can also be an option to improve broadleaf control.
She warns that if a producer uses Starane NXT, it should be applied between the 4- and 7-leaf stage of sorghum. After 8 leaves, drop nozzles are recommended, and no application after the flag leaf. “Additionally, some foliar leaf damage may result at high humidity with Starane NXT because we are heating up the tank-mix with bromoxynil. Also, do not include atrazine with a Huskie and Starane NXT combo — it’s too hot.”
Huskie may cause injury to a following cotton crop, Bell cautions. “In clay loam, studies have shown no injury, but in sandy soils injury has been identified with high rates, 32 ounces.”
Some grain sorghum producers may want to consider ALS herbicide-resistant hybrids (Inzen). “We are seeing research come to fruition. This will give farmers an in-season ability to control grasses in grain sorghum. Zest is the only herbicide currently labeled for application only on ALS-tolerant hybrids. Producers may plant ALS-tolerant sorghum behind failed cotton on Staple ground. However, we still don’t know the yield potential for the ALS hybrids, but we hope to see yield data in 2017.”
Even with the best herbicides available and the best of intentions, producers sometimes see herbicide failures, Bell says. Those failures can’t always be attributed to herbicide problems or to resistant weeds. Failures may result from:
- The herbicide does not get activated.
- Crop residue is too thick and ties up the herbicide.
- Too much rain leaches the herbicide out of the soil or dilutes the material.
- The rate is not high enough for the soil type.
Crop injury also occurs. Causes may include:
- Rain moves herbicide to the top of the soil.
- Cool conditions slow emergence, allowing more herbicide to be absorbed by the seedling.
- Rate is too high for the soil type.
After the weed control program is initiated and the crop is off to a decent start, a relatively new pest can wipe it out, if not managed, Bell says. The sugarcane aphid can negate all the other management practices producers have carried out — and it can cause significant damage quickly. When the pest shows up, she says, producers have to be ready to act quickly.
“Proper identification is critical. You may need a magnifying glass to be certain, and aphids are often misidentified. They are pale yellow to sometimes white, with black-tipped feet and antennae. But the key to identifying the damaging sugarcane aphid is the two black cornicles on the rear end. That’s the bad one.”
Sugarcane aphid populations can explode quickly. “All sugarcane aphids are female, and they are all born pregnant, producing five or six aphids a day. We have to treat quickly when populations reach threshold — if we wait and see, we risk losing yield.
“Sugarcane aphid populations start on lower leaves. The first identifying factor may be honeydew secreted on lower leaves.” It is important for producers to consult their Extension entomologist if they need help identifying the sugarcane aphid and making application decisions.
“However, the first line of defense for any producer is to plant a hybrid with known tolerance.” Sorghum hybrids that have shown tolerance to sugarcane aphid include Pioneer 83P17 and 83P56; DeKalb 37097 and Pulsar; Sorghum Partners SP 7715, SP 78M30, and SP 73B12; Richardson RS260E, Sprint W FG, Jowar 1, and Swift; Alta AG1201, AG1301, and AG1203; Mycogen, 627 and 1G688; B&H Genetics BF 4100 and BH 3400; Warner Seed W-844-E and W-7051; and Golden Acres 3960B. An updated list for 2017 is expected anytime.
“Grain sorghum is more than a catch crop,” Bell says, and even though it does have some advantages as a lower input option, best management practices are necessary to make decent yields. “Don’t lose your yield potential and profit to weeds and sugarcane aphids.”