Oklahoma sorghum growers facing decisions about their crop

Friday, May 26, 2017

This spring has presented a number of challenges to agricultural producers throughout Oklahoma, and sorghum growers have been no exception.

“Most crops have struggled at some point this spring,” said Josh Lofton, Oklahoma State University Cooperative Extension cropping systems specialist. “To date the Oklahoma sorghum crop this year can be fit into three categories, with some growers dealing with all three.”

First are those growers who were able to plant their crop in a timely manner, had good soil and weather conditions, and the crop is currently growing well.

“While we would like to see this on most acres, the majority of Oklahoma’s sorghum crop has fallen into the other two categories,” Lofton said. “Either growers have not been able to get into their fields and still have sorghum in bags waiting to be planted or they were able to plant but have marginal stands.”

For growers who have yet to plant, the question has become whether or not to continue with grain sorghum planting. While most growers have to work through financial considerations relative to their individual operations, growers still have the potential to establish fields and be productive.

Historically, OSU’s Division of Agricultural Sciences and Natural Resources has advised growers at this stage hold off planting until late-season in order to minimize the negative effects of the traditionally challenging environmental conditions of late June and early July.

“Unfortunately, sugarcane aphids have made the success of a late-season crop more dependent on insecticide applications,” Lofton said. “If growers are willing to budget two insecticide applications and be proactive on scouting and applications, this remains a potential option.”

Other growers who have stands in the field are facing questions about whether to maintain their stands or terminate and replant. There are a number of management considerations growers need to address before making a final decision.

As a general rule, if growers have between 18,000 to 20,000 active plants per acre, adequate yields still can be achieved without additional seeds planted, especially this late in the season and provided the plants are presenting consistently even stands across the field.

“If stands are spotty or skipping, growers can decide to plant certain areas of the field while maintaining others,” Lofton said. “If growers have less than 18,000 active plants per acre and growers decide that replanting must occur, there are instances where growers can get away with over-seeding the crop over the current stands as opposed to completely terminating and completely replanting.”

OSU recommends growers who choose to over-seed look at planting around half of the initial seeding rate.

The validity of this critical 18,000 plant population to maintain a crop depends on several factors:
● Stand distribution is a critical component. An even stand can maintain high enough canopy coverage to cover the soil surface in order to help maintain soil moisture and help compete against weeds.
● Equally important is the type of hybrid that was planted. Hybrids that have lower tillering potential would require higher populations to achieve adequate yields.

“Without these tillers there just might not be enough heads per acre in order to maintain yields,” Lofton said. “Hybrids with better tillering potential can sustain these lower populations while still maintaining adequate yields.”

When growers have achieved stands, both weed control and fertility issues start to emerge. If growers have made a large application on fertilizer preplant, especially nitrogen, then the weather patterns Oklahoma has experienced through May likely means a good portion of the application may already have been denitrified or leached deep into the soil profile.

“Growers will need to be proactive with side-dress applications,” said Josh Bushong, OSU Cooperative Extension area agronomist for the state’s Northwest District. “To trigger these, a grower’s best option is to make sure to have N-rich strips throughout their fields. If not, growers need to look for overly pale, stunted sorghum and be timely with an application.”

Of course, nitrogen fertilizer is not the only thing influenced by the moisture in these fields; high levels of moisture can decrease the efficacy of many preplant herbicide programs. Thus, sorghum growers may need to make subsequent herbicide applications.

“This becomes critical as some chemicals need to be applied prior to the sorghum plant reaching 12 inches in height,” Bushong said.

Then there is the “boogeyman” of recent years: sugarcane aphid numbers are growing and moving north through Texas. MyField website numbers as of May 25 indicate the shift from populations solely in the Gulf Coast to several populations moving into south-central Texas.

“While there is little need for Oklahoma producers to be concerned at this point, growers do need to be aware of the aphid population movement,” Lofton said. “For growers who have been active with their scouting management plans and timely with insecticide applications in recent years, most should have experienced minimal impact of the pest on overall yields. For growers who have not been as diligent, challenges may well occur.”

Currently the OSU recommendation for applications is an average of 100 aphids per leaf blade. To scout for aphids, growers need to identify four to five locations that are representative of the field and collect five to six plants at each location.

“For each plant, growers need to look at the underside of the lowest most fully green leaf and the highest most fully developed leaf,” Bushong said. “If the plant is at flag leaf or later in reproductive stages, growers should scout the leaf under the flag leaf.”

While counting aphids in-field on leaves can be a challenge, the 100-aphids-per-leaf rule of thumb visually will be approximately the size of a quarter to half dollar. As populations tend to congregate on the leaves, growers also should look for multiple smaller populations.

Oklahoma produced more than 21 million bushels of sorghum in 2015, according to USDA National Agricultural Statistics Service data.