Due to complex interactions between social and ecological systems, herbicide resistance has classic features of a “wicked problem”. Herbicide-resistant (HR) Poa annua poses a risk to sustainably managing U.S. turfgrass systems, but there is scant knowledge to guide its management. Six focus groups were conducted throughout the United States to gain understanding of socio-economic barriers to adopting herbicide-resistance management practices. Professionals from major turfgrass sectors (golf courses, sports fields, lawn care, and seed/sod production) were recruited as focus-group participants. Discussions emphasized challenges of the weed management of turfgrass systems as compared to agronomic crops. This included greater time constraints for managing weeds and more limited chemical control options. Lack of understanding about the proper use of compounds with different modes of action was identified as a threat to sustainable weed management. There were significant regional differences in perceptions of the existence, geographic scope, and social and ecological causes of HR in managing Poa annua. Effective resistance management will require tailoring chemical and non-chemical practices to the specific conditions of different turfgrass sectors and regions. Some participants thought it would be helpful to have multi-year resistance management programs that are both sector- and species-specific.

The ability of Poa annua L. to adapt to most turfgrass environments extends to its ability to develop resistance to commonly used herbicides. Herbicide resistant P. annua is of almost epidemic proportions. The loss of once viable chemical‐based treatments pushes practitioners towards more expensive, and often less effective, control strategies. This management guide focuses on integrated weed management (IWM) practices for P. annua control and herbicide resistance—what it is and how to overcome it. Also discussed are resistance mechanisms and documentation of common occurrences of field‐level resistance within much of the United States. Finally, a summary of some of the social and economic constraints that practitioners face in the implementation of IWM strategies for P. annua is discussed.

Poa annua L. (annual bluegrass) is a common weed in turfgrass and has been confirmed resistant to twelve different herbicide sites of action, with various combinations of multiple‐herbicide resistance having been identified. In an effort to quantify the extent of herbicide resistant P. annua, the ResistPoa Project (resistpoa.org) surveyed 1349 P. annua populations for resistance to nine sites of action and one plant growth retardant. Herein we report results from sequencing of known target site mutations found in EPSPS, ALS, psbA, and 𝛼‐tubulin genes. Populations were sequenced using either capillary or amplicon sequencing (AmpSeq), depending on the complexity of the gene, and were analyzed for target‐site resistance. After additional resistance screening, a total of 389 suspected resistant populations were sequenced—131 for ALS, 83 for EPSPS, 93 for psbA, and 82 for 𝛼‐tubulin. From the resistant populations, 64 displayed resistance to multiple sites of action. After sequencing, it was determined that target‐site resistance was the common form of resistance for all sites of action outside of psbA with 65.6% of ALS populations, 73.5% of EPSPS, 39.8% of psbA, 91.5% of 𝛼‐tubulin having presented a target‐site mutation.This article is protected by copyright. All rights reserved