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Roundup brand agricultural herbicides (Roundup PowerMAX Roundup PowerMAX® II, and Roundup WeatherMAX® are registered for pre-harvest use to kill weeds and terminate grain sorghum plants. Benefits of a pre-harvest application can include earlier harvest timing, reduced grain moisture at harvest, increased harvest efficiency due to less green matter, late-season weed control, and reduced late-season water uptake, which can result in more soil moisture available for the next crop.
When—Apply a Roundup brand agricultural herbicide when grain sorghum is at 30% moisture or less. Physiological maturity occurs when a “black layer65533;? forms at the base of grain berries. Tiller heads may mature later than primary heads.
Rate—Apply 22 to 32 fl oz/acre. Do not apply more than 44 fl oz/acre. By ground application equipment at 5 to 10 gal/acre, and by aerial application at 3 to 5 gal/acre.13;10;Add ammonium sulfate (AMS) at 8.5 to 17 lbs per 100 gal of spray solution.
Restrictions—Allow a minimum of 7 days between application and harvest of grain sorghum.
Roundup brand agricultural herbicides should not be used pre-harvest on sorghum grown for seed as a reduction in germination or vigor may occur. After an application of a Roundup brand agricultural herbicide, sorghum should not be harvested for a minimum of 7 days and it may take from 2 to 3 weeks for the herbicide to completely kill the sorghum plant. Making a pre-harvest application too early may reduce grain quality and yield potential.
When applying a Roundup brand agricultural herbicide pre-harvest, if grain sorghum is drought-stressed, diseased, or lush due to irrigation, it is recommended to increase the application towards the higher end of the labeled herbicide rate and add a full rate of AMS (17 lbs/100 gal of spray solution).
Grain sorghum plants infected with charcoal rot will have stalk degradation, and should not receive a pre-harvest application of a Roundup brand agricultural herbicide. Plants infected with charcoal rot are more likely to lodge after application, reducing harvest efficiency, grain quality, and yield potential.
Regehr, D. 1998. Weed control. Kansas State University. Grain Sorghum Production Handbook. C-687. http://www.bookstore.ksre.ksu.edu/. Trostle, C. and Bean, B. 2014. Quick guide for weed control and harvest desiccation in Texas grain sorghum. Texas A&M AgriLife Extension. http://lubbock.tamu.edu/. Schnell, R. 2014. Grain sorghum harvest aids. http://www.texassorghum.org. Web sources verified 06/02/17. 170604201711