By Jason Kelley, Wheat and Feed Grains Agronomist, and Gus Lorenz, Nick Bateman and Glenn Studebaker, Extension Entomologists
Arkansas grain sorghum acreage has varied dramatically over the last few years due to grain prices and more recently due to the threat of sugarcane aphid. In 2017, Arkansas producers planted only approximately 9,000 acres. However with the recent increase in grain sorghum prices into what some producers would call a profitable level, more producers are considering growing grain sorghum again in 2018. Successful sugarcane aphid management is critical for our producers to grow profitable grain sorghum. Below are sugarcane aphid management practices to consider.
We strongly recommend that to successfully grow grain sorghum that you: 1) plant early to avoid sugarcane aphid infestations as much as possible; 2) plant only hybrids that have some level of tolerance/ resistance to sugarcane aphid; 3) use a neonicotinoid seed treatment to protect from early season infestations; 4) scout at least once per week for developing populations of sugarcane aphid and adhere to the established threshold. An insecticide application is recommended once a preliminary action threshold of 25% of plants are infested with 50 or more sugarcane aphids per leaf is reached.
Planting Date: Planting date is a critical component to successful grain sorghum production. Grain sorghum is not nearly as cold tolerant as corn, but relatively early planting is needed to maximize yields and reduce impacts of insects later in the season, including midge, head worms, and sugarcane aphids. In general, there is a 4-6 week window when yields are likely to be maximized, generally during the month of April to early May. Planting date studies at Marianna, Arkansas (east-Central) showed that April planting maximized yields every year during a 6-year planting date study. Planting in May can still give good yields, but insect pressure will likely increase with May plantings, increasing expenses and reducing overall profitability. In the past few years, the fields that were hardest hit by sugarcane aphids were nearly always later planted fields. Early planting is a critical management practice to reduce the impact of sugarcane aphid as well as other insects such as midge and the headworm complex.
Sugarcane Aphid Tolerant Grain Sorghum Hybrids:
Grain sorghum hybrids differ tremendously in their tolerance to sugarcane aphids. In the past years we have seen that growing a tolerant hybrid has made the difference between having a crop and having a total loss if aphids are not adequately controlled. Screening of sugarcane aphid tolerant hybrids over the last few years has shown large differences in yield and aphid numbers on plants between hybrids when aphids were not controlled in late plantings. Some hybrids evaluated that were supposed to be sugarcane aphid tolerant did not show what we considered adequate tolerance. Other hybrids may have exhibited good tolerance, but were generally not agronomically adapted to our area (ie, too early of maturity, poor disease resistance, poor agronomic traits). From our work in 2015-2017, the table below represents grain sorghum hybrids that had moderate to good tolerance to sugarcane aphid, overall adequate agronomic traits, and respectable yield potential under Arkansas conditions, and are commercially available in 2018. If planting is delayed into May, planting a sugarcane aphid tolerant hybrid is highly recommended.
Insecticide Seed Treatments: Regardless of whether or not you choose to use an aphid tolerant hybrid listed above, we strongly recommend the use of an insecticide seed treatment. Poncho, NipSit, Cruiser or Gaucho are your choices. Some grain sorghum seed companies will automatically apply a seed insecticide, but others you will have to specify that you want one. Using a seed insecticide has been a recommended practice as we generally see improved stands and early-season growth and ultimately improved yields. We don’t see a lot of differences between these seed treatments and they all do a good job providing protection for below-ground insect pests and a few above ground pests like chinch bugs. When sugarcane aphids arrive early in the growing season, seed insecticides have shown to provide 30-40 days of protection or more. Research on seed treatments indicate they have value regardless of whether we have sugarcane aphid, so make sure you get your seed treated!
Additional sources of Grain Sorghum information:
Arkansas Grain Sorghum Production Handbook, MP 297: http://www.uaex.edu/publications/pdf/mp297/MP297.pdf
Arkansas Grain Sorghum Quick Fact Sheet: https://www.uaex.edu/farm-ranch/crops-commercial-horticulture/grain-sorghum/2018%20Arkansas%20Grain%20Sorghum%20Quick%20Facts.pdf
Arkansas Grain Sorghum Hybrid Testing Results: www.ArkansasVarietyTesting.com
Sugarcane Aphid, a New Pest of Grain Sorghum in Arkansas: http://www.uaex.edu/publications/FSA-7087.pdf