Research Profile: Grassy Weed Control in Grain Sorghum

Overview: Grain sorghum is being considered as an alternative grain crop for ethanol and feed, particularly in geographic areas that are more susceptible to dry soil conditions or whereby it is difficult to cultivate land early in the spring. Achieving good control of grassy weeds has been identified by producers as a significant management challenge that must be addressed in order for the crop to be economically sustainable. 

Technical Background: Prowl and Dual II Magnum have been identified as two potential herbicides for management of grassy weeds in grain sorghum. A registration submission under the Minor Use Program of the Pest Management Regulatory Agency (PMRA) is being investigated. Historically, crop injury with both products has been a concern, especially when applied preemergent and then followed by excessive precipitation. The proposed use guidelines would dictate that both Prowl and Dual II Magnum be applied post-emergent to the grain sorghum crop but before any grassy weeds have emerged, as both products do not control emerged annual grasses. Furthermore, Dual II Magnum would be applied at a reduced rate for suppression only of grassy weeds. 

Research Objectives:

• To evaluate grassy weed control with Prowl and with a reduced rate of Dual II Magnum at various application timings.
• To identify the most effective application timings for each herbicide program.
• To explore opportunities for improved grassy weed control in grain sorghum.

Key Learnings from 2007 Trials:

• In the absence of adequate rainfall, the reduced rate of Dual II Magnum provided poor weed control regardless of application timing.
• Prowl applied at the 2-3 leaf stage of grain sorghum provided adequate grassy weed control (Figure 1).
• Prowl applied at the 4-5 leaf stage of grain sorghum provided poor grassy weed control (Figure 2).
• A pre-plant application of glyphosate to remove any emerged grassy weeds, followed by an application of Prowl at the 2-3 leaf stage of grain sorghum provided the best level of grassy weed control (Figure 3).

Future Research:

• Evaluate other potential grassy weed herbicides.
• Evaluate seed applied herbicide safeners.

Contributors:

Dr. François Tardif and Peter Smith (University of Guelph)

Figure 1. Prowl applied at the 2-3 leaf stage of grain sorghum

Figure 2. Prowl applied at the 4-5 leaf stage of grain sorghum

Figure 3. Pre-lant application of glyphosate followed by an application of Prowl at the 2-3 leaf stage of grain sorghum

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