By Sorghum Checkoff Agronomy Director Brent Bean, Ph.D.

EPA approved the use of IMIFLEX for in Advanta’s igrowth sorghum in late 2020. The Sorghum Checkoff is certainly excited about having a new sorghum herbicide.

IMIFLEX will be sold by UPL. The active ingredient is imazamox, which some growers will be familiar with as Raptor in soybeans or Beyond in Clearfield wheat and Clearfield sunflowers. Another herbicide in this same class, although it is a different herbicide, is Pursuit.

For more information on igrowth sorghum and IMIFLEX see the following link:

What to expect from IMIFLEX

Most of what we know about the active ingredient in IMIFLEX comes from its use in soybeans and a couple other crops. It has both PRE and POST activity. It was used as a POST herbicide in soybeans, but the product does have surprisingly good PRE activity for use in sorghum. How it is applied will likely depend on the particular weed species.

Although IMIFLEX is not a sulfonylurea herbicide, it is in the ALS mode-of-action group. As such, do not expect it to control weeds or grasses that have resistance to sulfonylurea herbicides.

Below are comments based on trial results in 2020 and discussions with weed scientists who have experience with IMIFLEX:

First, IMIFLEX should be used in a system with other herbicides. In most cases, this is not a standalone product, if there is such a product anymore. For POST control, grass and broadleaf weed size will matter. Control will be much better on small grass and broadleaves. Similar to other herbicides, delaying application past optimum application timing will result in significant decrease in control.

Grass Control

Control of green foxtail and crabgrass has been good when IMIFLEX was applied PRE or POST. PRE control was at least as good as group 15 herbicides (Dual, Outlook, Warrant). The recommendation, if applied PRE, is to apply with one of the group 15 herbicides. Alternatively, apply a group 15 herbicide PRE and then follow with IMIFLEX early POST.

Texas panicum (Colorado grass) has been a historically difficult grass to control. Again, as a PRE application, control appears similar to group 15 herbicides. Since the label only allows for one application of IMIFLEX during the growing season, for this grass it may be best to apply a group 15 PRE and then apply IMIFLEX early POST to control escapes. This eliminates the variable of timely rain to activate the IMIFLEX if applied PRE.

For other grasses I have simply not seen enough data to be comfortable making a recommendation. Tough grasses like witchgrass, tumble windmill grass and sandbur may prove more difficult to control. If applying IMIFLEX POST to these grasses, make the application to small grass, less than 3 inches in height. I should also mention that none of these grasses are currently listed on the IMIFLEX label.

Broadleaf Weed Control

Most of the data I have seen has been on Palmer amaranth and even that has been limited. IMIFLEX will provide a different mode of action that should help in a weed control system with other herbicides. PRE results with IMIFLEX alone have been in the 60 to 75 percent range, approximately 50 days after application. Adding a group 15 herbicide increased control to 80 to 93 percent, depending on location. Results with IMIFLEX alone when applied POST have been mixed, but it is very important that Palmer amaranth be small at the time of POST application.

Crop Rotation and Integrated Weed Management

An important benefit of IMIFLEX is that while it has good soil activity, crop rotation should not be an issue with any major crops. Check the label for more details. In addition, adding a new class of herbicide into cropping systems that include sorghum will provide an advantage in weed resistance management programs.

As with all new crop protection products, check the label for the list of weeds and grasses, application timing, tank mix and crop rotation restrictions. Similar to other products, we will learn a lot about IMIFLEX and how to best use this technology after a year of commercial use.

Please contact Sorghum Checkoff Agronomy Director, Brent Bean, Ph.D. with any questions.