Bushy wallflower and flixweed resistant to ALS-inhibiting herbicides (such as Finesse, Glean, Ally, Express, Affinity, Amber, Olympus or PowerFlex) have been confirmed in central Kansas in recent years. This class of herbicides has been around for many years and has historically provided excellent control of mustard species in general.

A complete failure to control one of the mustard species with an ALS-inhibiting herbicide is probably a pretty good indication that an ALS-resistant population has developed.

ALS-resistant bushy wallflower was first confirmed in Marion County in 2005 and, based on field reports, seems to be fairly common in Marion, Dickinson and Saline counties, but also could be present elsewhere. It was highly resistant to all ALS-inhibiting herbicides evaluated.

ALS-resistant flixweed was first confirmed from Saline County in 2007. ALS resistant flixweed still seems to be confined to that general area. Some ALS-inhibiting herbicides still had some activity on the resistant biotype, but history tells us that if we switched to another ALS herbicide, it wouldn't be long until we had resistance to those products as well.

ALS-resistant mustard populations likely developed in continuous wheat fields where Glean or Finesse was applied routinely in combination with a topdress fertilizer application and in the absence of a tank-mix partner such as 2,4-D or MCPA.

Fortunately, the ALS-resistant mustards still can be controlled with a timely application of 2,4-D, MCPA or the new herbicide Huskie. These products can be tank-mixed with ALS herbicides or used as an alternative to ALS herbicides. MCPA and Huskie can be applied safely to wheat in the fall through spring after the wheat has two leaves. However, 2,4-D should not be applied until wheat is fully tillered, which generally does not occur until sometime in spring.

These herbicides are active primarily through foliar uptake and have limited soil activity, so ideally they should be applied to plants with viable foliage and when temperatures are 50 degrees or higher to achieve optimum performance. If applying MCPA or 2,4-D with topdress nitrogen fertilizer, the ester formulation needs to be used as amine formulations are not compatible with liquid N fertilizers.

Starane or dicamba products generally do not provide very good mustard control, so these would not be very good choices to help control ALS-resistant mustards.

Another problem with ALS-resistance has been cheatgrass with resistance to Olympus, Olympus Flex, PowerFlex, Maverick and Beyond herbicides -- first confirmed in Cowley and Saline counties in 2007. Since then, we've had other reports and confirmed several additional cases of ALS-resistant cheatgrass through the central part of the state. The occurrence of ALS-resistant cheatgrass is likely to become more common over time as farmers continue to use these herbicide products, especially in continuous wheat and repeated applications of this group of herbicides.

If producers are having consistently poor control of cheatgrass with the labeled ALS herbicides, they need to consider alternative methods of control. Crop rotation to summer crops is still the best way to manage a cheatgrass problem. Burning the fields after harvest and moldboard plowing also can be effective for cheatgrass control, but might be inconsistent and are undesirable for soil and water conservation considerations.

Even though our area of the state has not been impacted yet with the ALS-resistant mustards and cheatgrass, it might only be a matter of time, especially if you are growing continuous wheat and always are using an ALS herbicide alone. Crop rotation is always the cheapest and most effective approach, especially in the case of cheat grasses and jointed goat grass in wheat. Switching to a herbicide with a different mode of action or using another herbicide in combination with an ALS would be a good management practice for the ALS-resistant mustards.

* Information provided by Dallas Peterson, weed management specialist, dpeterso@ksu.edu.

Stacy Campbell is Ellis County agricultural agent with Kansas State Research and Extension.