Flumioxazin: A pre-emergence herbicide option for warm-season turfgrasses

Annual bluegrass (Poa annua) is widely regarded as one of the most troublesome golf course weeds. There are many factors that make annual bluegrass a difficult-to-control weed. Pertinent to herbicidal control, the weed has a long germination period that can outlast the control period of many pre-emergent herbicides. Many times this long germination period requires multiple pre-emergence applications, follow-up post-emergent applications, or both to achieve complete control. Annual bluegrass can also exist as a short-lived perennial, limiting the usefulness of pre-emergent herbicides. Lastly, the weed has developed resistance to many herbicides use pre- and post-emergence, further complicating herbicidal control.

SureGuard is a new herbicide for the turfgrass market that offers a solution to some of these problems. Flumioxazin, the active ingredient in SureGuard, inhibits the protoporphyrinogen oxidase (PPO) enzyme in susceptible plants which eventually leads to the desiccation of the plant. This mode-of-action has both pre- and post-emergence activity. Pre-emergence control results from soil application where the herbicide is predominantly absorbed by the roots. Post-emergence control results primarily from foliar contact, which causes rapid desiccation and necrosis with negligible translocation.

This mode-of-action is similar to oxadiazon (Ronstar). Managers familiar with Ronstar Flo will note that it should not be applied to actively growing turfgrass because it can lead to foliar necrosis. The same is true with flumioxazin. However, since both herbicides have limited translocatation within the plant, established grasses can recover. Therefore, application of both SureGuard and Ronstar Flo is restricted to dormant periods.

Flumioxazin may be an alternative to other herbicides currently available in Bermudagrass (Cynodon sp.) for annual bluegrass control. Having both pre- and post-emergent activity, it may be possible to apply flumioxazin after annual bluegrass germination has begun. That is, the post-emergent activity would control plants already emerged while the pre-emergent activity could control weeds not yet germinated. Post-emergent applications may control perennial biotypes of annual bluegrass and provide residual control. Additionally, there are no reports of annual bluegrass resistant to flumioxazin or other PPO-inhibitors, which could benefit managers with herbicide-resistant populations. Despite these beneficial aspects of flumioxazin, applications on Bermudagrass and other warm-season turfgrasses are limited to periods of dormancy which could limit application timings that are safe for use.