Soil & Crop Sciences
Non Technical Summary
Problem and BackgroundKnown popularly as the 'Green Industry' or the 'Environmental Horticulture Industry', turf is a >$100 billion specialty crop industry in the US with about 50 million acres of managed turf operations nationwide (Haydu et al. 2006; SRI 2012). Turfgrass is the most widely grown irrigated crop in the US (Milesi et al. 2005). Turf is also among the most economically important specialty crops, with significant contributions to local economies and employment generation across the nation. Golf courses, athletic/sports fields, sod production operations, and residential lawns are the four major sectors of the US turf industry.Annual bluegrass (Poa annua L.), known commonly as Poa, is the most troublesome weed in managed turf systems throughout the US, revealed recently by a nationwide survey conducted by the Weed Science Society of America (Van Wychen 2016). This weed has grown to epidemic proportions in different turf systems, causing severe economic losses to the US turf industry. Annual bluegrass has high levels of genetic diversity and exhibits rapid adaptation to climatic gradients and management interventions. Annual bluegrass has a distinctly light-green color with white flower heads, and its presence is not tolerated in managed turf systems because of its severe negative impact on turf quality.Existing annual bluegrass management programs rely heavily on herbicides in all four major turf sectors. According to the International Survey of Herbicide Resistant Weeds, annual bluegrass ranks third among all herbicide-resistant weed species globally, with resistance to at least 9 different herbicide sites of action (Heap 2018). This includes resistance to all major herbicides used in turf systems such as photosystem II-, acetolactate synthase (ALS)- and mitosis-inhibiting herbicides. Additionally, annual bluegrass resistance to glyphosate has been reported (Brosnan et al. 2012; McElroy et al. 2013). Evolution of multiple herbicide resistance in this species is a serious issue as this trend has been quickly removing important herbicide options from the turf manager's toolbox.There is a critical need for developing sound best management practices (BMPs) based on a better understanding of the ecology and biology of annual bluegrass, current levels of herbicide resistance, and the nature and characteristics of resistance evolution and spread in this species. Limited information is available on the longevity of annual bluegrass seed in the soil. A thorough knowledge of seedling emergence patterns and environmental drivers governing emergence is yet to be developed, but will directly inform appropriate management timing. Such information can be linked with weather forecasts to provide seedling emergence advisories. Moreover, a thorough understanding of phenological development as influenced by environmental variables, and knowledge of demographic parameters such as fecundity will be beneficial.An important lesson from herbicide resistance management in agronomic crops is that developing and implementing BMPs that do not consider human and social dimensions of herbicide resistance are ineffective. A robust integration of human and social dimensions with the biophysical aspects of herbicide resistance is critical in innovating effective weed management approaches (Ervin and Jussaume 2014; Ervin and Frisvold 2016). The herbicide resistance epidemic in annual bluegrass in managed turf systems has likely resulted from the interaction of biophysical and social (behavioral) systems. A turf manager's decision to rely on a narrow spectrum of herbicides for weed control may be influenced by socio-economic factors, such as relative prices and personal values. Thus, to develop effective annual bluegrass resistance management, we must understand and address the various socio-economic and biophysical factors that serve as barriers to BMP adoption.Project objectives and supporting hypotheses1) Conduct surveys and document the extent of annual bluegrass susceptibility/resistance to key turf herbicides and develop methods for rapid resistance detection [Hypothesis: annual bluegrass resistance is prevalent in managed turf systems], 2) Establish physiological and molecular mechanisms of resistance prevalent in annual bluegrass across a regional scale [Hypothesis: there is a significant presence of non-target site resistance in annual bluegrass populations], 3) Generate information to fill critical knowledge gaps on the biology and ecology of annual bluegrass [Hypothesis: annual bluegrass exhibits prolonged seed persistence in soil with extended emergence periodicity], 4) Evaluate and optimize innovative weed management options for integration [Hypothesis: novel management practices can be optimized to provide detrimental impact on weed growth and seed production], 5) Survey turfgrass managers to identify socio-economic and other barriers to the adoption of herbicide resistance BMPs [Hypothesis: a thorough socio-economic investigation will help identify factors influencing weed management decision making by turfgrass practitioners], 6) Develop a user-friendly bio-economic decision-support tool for facilitating the implementation of BMPs [Hypothesis: decision-support tools will allow for easy visualization of the impact of various management options on long-term economics, weed population size and risk of resistance over short-term returns], 7) Develop and deliver an extension program for sustainable management of annual bluegrass [Hypothesis: robust outreach programs that utilize advanced tools will be effective in promoting BMP adoption], and 8) Provide educational opportunities to train the next generation of research and extension scientists and turfgrass practitioners [Hypothesis: involving undergraduate researchers, graduate students, and postdoctoral scholars in research and extension activities will provide adequate training in preparing them for tackling similar issues in future].Stakeholder involvementThe team recognizes the vital need for engaging stakeholders in defining the problem and integrating their experiential knowledge into BMP strategies. This project has been developed based on critical research and extension needs identified by various stakeholders in the managed turf industry. These include: regional and national turf industry organizations, turfgrass sod producer groups, golf course superintendents, athletic turf managers, and scientists-at-large, including representatives from the global Herbicide Resistance Action Committee (HRAC) and the Weed Science Society of America (WSSA). A stakeholder advisory panel has been formed involving key personnel from the above sectors. A detailed stakeholder engagement plan has been developed to ensure sustained engagement of stakeholders throughout the project development, implementation, and evaluation phases.Broader impacts of this proposalThe products and deliverables of this proposal are expected to have a tremendous impact on the broader turfgrass industry across the nation, including the states and regions not directly represented in the proposal. The socio-economic issues affecting weed management decision-making and adoption of BMPs are comparable in those areas. Most of the non-chemical tactics to be optimized and the BMPs to be formulated can be applied more broadly for the management of other turf weeds as well. Thus, the solutions to be developed in this project will benefit herbicide resistance management in turf weeds nationwide. Additionally, the proposed outreach activities will develop a fundamental understanding among the broader stakeholders of pesticide resistance evolution in any biological organism and promote sustainable IPM practices for the management of all turf pests (weeds, diseases, insects, and nematodes).
Animal Health Component
Research Effort Categories
Goals / Objectives
The short-term goal of the project is to develop knowledge and tools to facilitate the development, dissemination and adoption of BMPs for tackling annual bluegrass herbicide resistance in managed turf systems, through a coordinated, multi-institutional and inter-disciplinary approach. The long-term goal of the project is to improve the economic profitability as well as environmental and social sustainability or resilience of managed turf systems through implementation of sound weed management practices.
Field activities of this project will be conducted in 13 different states across the nation: TX, MS, AL, GA, SC, FL, TN, NC, VA, OR, IN, NJ, and PA, representing different plant hardiness zones relevant to warm-season as well as cool-season turfgrass systems. The socioeconomic specialists (Drs. Ervin and Frisvold) are located in OR and AZ, respectively. The project locations were chosen carefully such that the activities carried out yield the largest and most wide-reaching impact. Field surveys will be carried out to collect annual bluegrass samples for subsequent resistance evaluations. To achieve a representative sampling across the study locations, the area will be divided into five zones spanning across different states, based on the USDA plant hardiness map. Susceptibility/resistance evaluations will be conducted under greenhouse conditions; a consistent environmental condition of 30/25 C day/night temperature and 14 hr photoperiod will be followed. Evaluations will be conducted for the most commonly used ALS- (trifloxysulfuron and foramsulfuron), EPSPS- (glyphosate), PSII- (atrazine, simazine, and amicarbazone), and mitosis- (prodiamine and pronamide) inhibiting herbicides.To assess the potential for herbicide-resistant annual bluegrass to spread from seed production fields, we will test annual bluegrass seed from seed cleaners (weed seed removed from the lots after harvest, but before seed lot testing) and seed lots tested prior to retail distributions (i.e. certified seed lot). Rapid diagnostic assays will be developed for annual bluegrass resistance to the ALS-, EPSPS- PS II- and mitosis-inhibitor herbicides commonly used in turf systems. Two different approaches (agar culture as well as leaf-tissue incubation) that have been currently investigated by Co-PD Brosnan and Co-PD McCarty will be further improved in this project.Target-site (TSR) as well as non-target-site (NTSR) mechanisms of resistance will be tested using established methods. In annual bluegrass, TSR is known to occur for ALS-, PSII- and mitotic-inhibiting-herbicides. SNP target-site mutations will be identified in the samples using cDNA and allele specific primers to separate target-site genes from homeologous genes. NTSR can be endowed by reduced absorption, translocation and/or enhanced metabolic detoxification by the R individuals. Experiments will be conducted to elucidate NTSR mechanisms for ALS- and PSII-inhibitor herbicides as well as glyphosate. Following initial resistance screening, a subset of R populations (sampled as in TSR studies) spanning the study region will be selected to investigate any differences in absorption (foliar as well as root), translocation and metabolism.Several experiments will be conducted to further our understanding of the ecology and biology of annual bluegrass. Annual bluegrass seedbank persistence will be evaluated using a classical seed bag burial experiment in each of the five target zones. Annual bluegrass seedling emergence will be monitored in the four turfgrass systems in each of the five hardiness zones across a two-year period. In each hardiness zone, 2 distant sites will be identified for each turfgrass system (as above) (thus, a total of 20 site-years per system across the country). Further, a common-garden study will be conducted across seven locations, to evaluate growth cycle, time taken for different developmental stages as influenced by the environment, as well as specific traits that might be favoring adaptation. In each garden, annual bluegrass originated from 10 different locations (2 distinct sites in each of the five zones) will be compared.Experiments will also be conducted to evaluate and optimize innovative options for annual bluegrass control. These include non-synthetic compounds, fraze mowing, grass species and variety selection, mowing regime and grass-clipping removal, and irrigation and nutrient management. The non-synthetic compound evaluations will include Fiesta®, Thaxtomin-A®, Civitas®, X-Poa®, corn gluten meal (fall preemergence), concentrated acetic acid (40%), baking soda, hydrated lime, and a high rate each of zinc and ferrous sulphate, applied at three different growth stages (5-7 cm tall seedlings, peak tillering/vegetative growth stage, and early flowering stage), on four turfgrass species important to each location. Fraze mowing studies will be conducted in already established turf facilities in two locations, Knoxville, TN and Milton, FL, over a two-year period. Treatments will include a factorial combination of two different turfgrass species suitable for fraze mowing (bermudagrass and zoysiagrass), three mowing timings (May, June, and July), and three mowing depths (0, 1.5, and 3 cm).Laboratory (Clemson and Purdue), greenhouse (Clemson) and field experiments (all locations) will be conducted to understand the importance of turfgrass species and variety selection as a cultural tactic for annual bluegrass management. Laboratory assays will be conducted in Petri dishes to determine potential allelopathic activity of three popular varieties each of four warm-season turfgrass species (bermudagrass, centipedegrass, zoysiagrass, and St. Augustinegrass) and four cool-season turfgrass species (Kentucky bluegrass, perennial ryegrass, tall fescue, and strong creeping red fescue) on annual bluegrass seed germination and seedling growth. Field experiments will be conducted in the participating states to study the impact of mowing regime (height and frequency) and grass-clipping removal (thereby reducing seed addition to the soil seedbank) on annual bluegrass population size over a three-year period. A separate field experiment similar to that of the mowing/grass-clipping removal study will be conducted at the participating locations over a two-year period to evaluate the impact of irrigation and fertilization on annual bluegrass. Treatments will include a factorial combination of two irrigation regimes (field capacity versus gravitational), two sources of nitrogen (standard and a slow-release formulation), three rates of N (0.5, 1, 2X for each species), and three rates of P (0.5, 1, 2X for each species).A socio-economic analysis will be conducted to identify major barriers that are impeding best management practice (BMP) adoption by turf practitioners. Five analytical steps are planned: 1) conduct focus groups, 2) develop a list of turf managers, 3) develop a survey instrument, 4) implement the survey in a mixed mode fashion, and 5) perform univariate and multivariate analysis of the survey dataset. Economic studies will be conducted to collect data and build dynamic programming models to measure the long-term returns to resistance management. These models will be used to estimate the net present value of costs of annual bluegrass control under proactive resistance management strategies compared to reactive strategies that do not manage to delay resistance. Additionally, a user-friendly, web-based annual bluegrass management decision support tool will be developed and implemented. This tool will allow the user select and evaluate a combination of different weed management options for their impact on resistance risk. A herbicide site of action and management diversity calculator will indicate the long-term sustainability of the management programs tested.A strong outreach and education plan is in place. The Extension and outreach responsibilities of this project will focus on information transfer as well as implementation of BMP tactics by turfgrass managers that will reduce the risk of herbicide resistance while simultaneously improving weed control outcomes. The proposed educational plan includes incorporating direct classroom teaching in turfgrass management and weed science courses taught by the team members in various institutions, as well as training undergraduate researchers, graduate students, and postdoctoral scientists.