Sorghum Preemergence Weed Control
Brent Bean, Director of Agronomy, USCP
HP/MAFG March 2023
Although grass in emerged sorghum can be a major problem, the new igrowth®, Double Team™ and Inzen™ sorghum technologies provide good options for grass control. However, the list of herbicides for control of broadleaf weeds once sorghum has emerged is small and their effectiveness has been lessened due to the development of resistant weeds. For this reason, it is imperative that a good pre emergent program is implemented in sorghum.
There are seven active ingredients that are primarily used that fall under four mode-of-action categories. These are:
|PS II inhibitor (Group 5)||atrazine|
|Fatty Acid inhibitor (Group 15)||s-metolachlor and metolachlor|
|HPPD inhibitor (Group 27)||mesotrione|
|PPO inhibitor (Group 14)||saflufenacil|
|ALS Inhibitor (Group 15)||Imazamox – use in igrowth® sorghum ONLY|
The use of at least two active ingredients is critical for successful preemergence control in sorghum with today’s tough weeds. A popular mix is atrazine plus one of the Group 15 herbicides listed in the table. Two popular premixes used are Bicep II Magnum (atrazine + s-metolachlor) and Fultime NXT (atrazine + acetochlor). For growers wanting to limit the amount of atrazine being used, Fultime NXT might be a better choice since at a 1X rate this treatment has significantly less atrazine in it compared to Bicep II Magnum.
A popular non-atrazine treatment is the use of Verdict + Outlook. Verdict contains saflufenacil and dimethenamid. Some additional dimethenamid (Outlook) is usually added to increase the longevity of residual control while boosting the control of grass. This is an especially good choice on sandy soils.
Mesotrione use has become a more popular herbicide to use in sorghum the last few years, with several premixes with other herbicides now being sold. Mesotrione is often applied in a two way mix with atrazine or s-metolachlor, and often, as a three way mix of all three active ingredients. In herbicide comparison studies, treatments that include mesotrione are typically the most consistent in giving good broadleaf weed control, especially of Palmer amaranth. However, it is important to note that mesotrione cannot be used on sandy soils or unacceptable crop injury will occur. Check the herbicide label for soil type prior to use.
The final and newest active ingredient that is used for preemergence in sorghum is imazamox and is sold as ImiFlex by UPL. This can ONLY be used with igrowth® sorghum. ImiFlex is primarily used for grass control but does have broadleaf activity. Always apply ImiFlex with one of the Group 15 herbicides.