Josh Lofton- Cropping System Specialist
Tom Royer- Extension entomologist/IPM coordinator
Full-season sorghum across the state is reaching maturity, while late-season and double-crop sorghum are at various stages of early reproductive growth. In the last several weeks, insect pressure has been a major issue throughout the state. Therefore, growers will be left with several management decisions in the next several weeks.
Harvest management for sorghum:
Sorghum harvest aids or desiccants have been periodically used in sorghum throughout Oklahoma. Several reasons exist for growers to use these practices; however, two primary reasons include drying down the vegetative portion of the sorghum plant or managing late-season weeds present in field. Most years in the southern Great Plains, as with this one, there is very little need to rapidly dry-down the primary sorghum stem and first tillers. Higher temperatures, higher winds, and lower humidity will often result in the plant drying at a similar rate to the grain. Since desiccants have little impact on dry-down of the grain, this can result in rapid stem dry-down potentially leading to lodging issues. However, later tillers could still be maturing and take much longer to finish grain and dry-down. Growers have to decide if it is worth waiting for these later tillers prior to harvest. Often, the presence of wildlife and the risk of lodging will result in growers harvesting closer to when the main stem matures. Growers can use desiccants to rapidly dry-down these later tillers, which terminates the tillers. Some grain in these may be harvestable, depending on how close the grain was to black-layer.
The second reason for using desiccants is to help manage late-season weeds in the sorghum crop. Grassy weeds, especially Johnsongrass, are the primary weeds of concern. Currently, few in-season options are available to help control grasses in sorghum. The problem with Johnsongrass is that resources developed can be stored over winter in rhizomes for the successive year’s plants. Using late-season desiccation treatments can limit the transfer of these resources to the storage portions Johnsongrass. Further information regarding using harvest aids in grain sorghum can be found in PSS-2183 (Using Harvest Aids in Grain Sorghum Production | Oklahoma State University (okstate.edu)).
Sorghum pests emerging:
In recent weeks discussion has focused on armyworms and their impact not only on lawns but crops. While these can still be a major issue on crops, especially those that are still vegetative. Most of the impact will be in those crops planted late, without a large amount of vegetative growth. While these are still a major concern, other pests are around. Stinkbugs have been present in sorghum for several years, but they are not normally at high populations, or are not widespread enough to cause major issues. However, we experienced an increased number of calls regarding stinkbugs this year. The particle stinkbug of interest is rice stinkbug. The question becomes, “When do growers need to think about treating for stinkbugs in sorghum?” The best fit for Oklahoma sorghum growers for a treatment threshold for rice stinkbug is to sample 30 emerged heads, and treat when the average number is 0.5 to 1 stinkbug per head. Research based damage thresholds numbers are per acre, not numbers per plant. Therefore, the 0.5 per head threshold is for higher plant populations, and the 1 per head is for lower plant populations. A number of products are available for control of panicle feeding bugs in sorghum.