By Jason Kelley, Wheat and Feed Grains Extension Agronomist, and Gus Lorenz, Nick Seiter, and Glenn Studebaker, Extension Entomologists
Arkansas grain sorghum acreage increased dramatically in 2015 with 440,000 acres harvested, compared to only about 40,000 acres in 2010. Increased interest in grain sorghum was partially driven by very positive basis levels at local grain markets. Currently producers are looking at receiving a $1.00-1.50/bu less in 2016 than 2015. With lower grain prices it is more important than ever to scrutinize inputs and maximize yields without increasing input costs. Below are some early-season management tips and considerations to help increase yields and profitability level of grain sorghum in 2016.
Herbicide Carryover Potential: One of the most important items to consider is what residual herbicides were applied to the field last year. In the fight against glyphosate tolerant pigweeds, overlapping residual herbicides seems to be one of the solutions. However some of these herbicides can carryover and injure grain sorghum the following year. Herbicides containing fomesafen (Flexstar, Reflex, etc) have a 10 month plant back interval for grain sorghum. We have seen injury when grain sorghum is planted sooner than 10 months. Other herbicides such as Classic and Newpath (Clearfield rice) could also be a problem.
Consult the MP519 – Row Crop Herbicide Plant Back Interval Publication at:
http://www.uaex.edu/publications/pdf/MP519.pdf to review herbicide plant back intervals.
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 2015, very early planted grain sorghum (late March or early April) struggled with cool wet weather and yielded less than grain sorghum planted in late April. Early planting is needed, but grain sorghum will not handle cold wet weather. Current soil temperatures and extended weather forecast is not conducive for planting grain sorghum for the next 7 days.
Hybrid Selection: Grain sorghum hybrid selection is important. There are several companies that have grain sorghum hybrids that have been tested multiple years and have performed well in the Mid-South. Hybrids with two-year average yields from the Arkansas Grain Sorghum Hybrid testing program are listed below:
Sugarcane Aphid Tolerant Grain Sorghum Hybrids:
Sugarcane aphid has quickly become one of the leading pests of grain sorghum in Arkansas since its arrival in 2014. Recently there has been considerable discussion about grain sorghum hybrids that are tolerant to sugarcane aphid. In 2015, a vast amount of work was done in Arkansas evaluating sugarcane aphid tolerant hybrids compared to our standard hybrids we have been growing. Large differences in yield and aphid numbers on plants were found 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 consider 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, 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 2016. Yields from these tolerant hybrids may be similar to some of the top yielding hybrids listed in the table above, but will likely not exceed them when aphids are properly controlled. Our current recommendation is to continue to plant our standard hybrids listed above in early plantings because they likely have the greatest yield potential when aphids are properly controlled. If planting is delayed into May, switching to or planting some sugarcane aphid tolerant hybrids may be a good consideration.
Seed Treatments: There are several seed treatments to consider. Concep treated seed is a must. This seed safener allows s-metolachlor (Dual) to be applied with minimal risk of injury. Without the Concep seed treatment, significant injury will likely occur with preemergence applications of s-metolachlor. Nearly all seed sold in the Mid-South is Concep treated, but NOT ALL, so double check before you plant.
Insecticide Seed Treatments: Regardless of whether or not you choose to use a aphid tolerant hybrid listed above we strongly recommend the use of an insecticide seed treatment. Poncho, NipSit, Cruiser or Gaucho are your choices. We don’t see a lot of differences between these seed treatments they all do a good job providing protection for below-ground insect pests and a few above ground pests like chinch bugs. What’s important about it this year is that with sugarcane aphid we have no idea when they will hit.
The past two seasons they have come in very late on our crop but if they have more favorable conditions, like warmer and drier, they could hit grain sorghum early. So these seed insecticide treatments could provide needed protection if the aphids do hit early. Research on these seed treatments indicate they have value regardless of whether we have sugarcane aphid, so make sure you get your seed treated!
Plant Population: Plant population is an important item to consider. In general for irrigated fields we recommend 75,000 plants/acre (final stand), which would be a planting rate of about 90,000 seeds/acre. This would roughly be 6-7 lbs of seed/acre (depending on seed size). For non-irrigated fields, a final plant population of 60,000 plants/acre is recommended (75,000 seeds/acre, approximately 5 lbs of seed/acre). In plant population work that we have done under irrigated conditions, increasing populations greater than 75,000 plants/acre did not result in any greater yield and increased the risk of late season lodging. In non-irrigated fields, high plant populations tend to run out of water at the critical heading stage, resulting in lower yields.
Grain sorghum has a tremendous ability to compensate for thin stands. In 2015 plant population trials, uniform stands as low as 35,000 plants/acre did not yield more than higher populations. Given grain sorghums ability to tiller and compensate for thins stands, it is generally more desirable to keep a perceived thin stand of early planted grain sorghum than to replant later in the season, provided plant stands are uniform.
Early-Season Weed Control: Starting off weed free is critical, so an adequate burndown program or tillage is needed. Immediately after planting, a preemergence application of s-metolachlor herbicide should be applied for weed control. There are no “good” grass control options once grass has emerged in grain sorghum, although atrazine or facet can control very small grass. It is very important to apply s-metolachlor immediately after planting to avoid grass problems. I generally do not recommend atrazine immediately after planting, especially if planting very early. Cold wet soil is stressful enough on small grain sorghum and adding atrazine to that scenario can make it tougher.
Early-Season Nitrogen Management: Nitrogen management should be performed similar to corn with small amount applied before or at planting (up to 1/3 of total N) and then side-dress the remainder nitrogen once the plant gets to the 5-6 leaf stage. At about the 6-leaf stage, the plant will be entering a rapid growth stage and the plant will need to have the nitrogen available at that time for optimal yields. Total nitrogen will vary on whether the crop will be irrigated, soil type, and yield potential, but generally ranges from 110 units of total nitrogen/acre for non-irrigated silt loam/sandy loam fields to 160 units total nitrogen/acre for the highest yields on irrigated silt loam/sandy loam soils.
Of course there is more to growing grain sorghum than what I have listed above, but early season blunders unfortunately last the whole season. Getting the crop off to a good start is a critical first step for high yielding and profitable grain sorghum.
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: http://www.uaex.edu/farm-ranch/crops-commercial-horticulture/grain-sorghum/2015%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
Please contact me by email at firstname.lastname@example.org, if you have questions or comments regarding this newsletter. This article and other timely articles on Arkansas crops can be found at: www.arkansascrops.com