Secondary effects of strobilurin applications may improve creeping bentgrass tolerance to high temperature stress. This research evaluated the effects of two strobilurin fungicides on the rooting of ‘Penncross’ and ‘Penn A‐1’ creeping bentgrass (Agrostis stolonifera L.) managed under two irrigation regimes during high temperature conditions in a greenhouse. The light and frequent (LF) regime irrigated to 100% evapotranspiration daily, and the deep and infrequent (DI) regime irrigated at leaf wilt to a 30 cm depth. Plants were maintained in a greenhouse that averaged a maximum daily temperature of 31°C. Fungicide treatments were pyraclostrobin (556 g a.i. ha−1), pyraclostrobin + boscalid (431 + 288 g a.i. ha−1), azoxystrobin (610 g a.i. ha−1), and a nontreated control. Azoxystrobin reduced visual root length and root biomass of Penncross plants compared to nontreated plants. Root length, root length density, and root biomass of azoxystrobin‐treated Penn A‐1 plants were also lower than nontreated plants under LF irrigation. Pyraclostrobin increased the visual root length of both cultivars under DI irrigation, and resulted in Penn A‐1 plants exhibiting increased total root length, root surface area, root length density, root volume, and root biomass compared to nontreated plants. Changes in rooting were not associated with changes in turfgrass quality for either cultivar. Additional research is needed to determine if these responses are present following applications in the field.

Dollar spot is one of the most common diseases of golf course turfgrass and numerous fungicide applications are often required to provide adequate control. Weather-based disease warning systems have been developed to more accurately time fungicide applications; however, they tend to be ineffective and are not currently in widespread use. The primary objective of this research was to develop a new weather-based disease warning system to more accurately advise fungicide applications to control dollar spot activity across a broad geographic and climactic range. The new dollar spot warning system was developed from data collected at field sites in Madison, WI and Stillwater, OK in 2008 and warning system validation sites were established in Madison, WI, Stillwater, OK, Knoxville, TN, State College, PA, Starkville, MS, and Storrs, CT between 2011 and 2016. A meta-analysis of all site-years was conducted and the most effective warning system for dollar spot development consisted of a five-day moving average of relative humidity and average daily temperature. Using this model the highest effective probability that provided dollar spot control similar to that of a calendar-based program across the numerous sites and years was 20%. Additional analysis found that the 20% spray threshold provided comparable control to the calendar-based program while reducing fungicide usage by up to 30%, though further refinement may be needed as practitioners implement this warning system in a range of environments not tested here. The weather-based dollar spot warning system presented here will likely become an important tool for implementing precision disease management strategies for future turfgrass managers, especially as financial and regulatory pressures increase the need to reduce pesticide usage on golf course turfgrass.

Poor annual bluegrass control was reported in golf course roughs following treatment with prodiamine (1120 g ai ha −1 ) and glyphosate (840 g ae ha −1 ) during hybrid bermudagrass dormancy. Research was conducted to determine if this annual bluegrass phenotype was resistant to both prodiamine and glyphosate and to determine the efficacy of herbicide mixtures for controlling this phenotype in the field. In PRE or POST dose-response experiments, 9 to 31 times more prodiamine or glyphosate was needed to control (or reduce dry biomass of) this resistant phenotype by 50% compared to an herbicide-susceptible phenotype. Moreover, glyphosate-susceptible plants accumulated 50% more shikimic acid (898 mg kg −1 ) 6 d after treatment than those resistant to glyphosate (394 mg kg −1 ). October (fall) applications of herbicide mixtures containing trifloxysulfuron, simazine, S-metolachlor, or mesotrione controlled this resistant annual bluegrass phenotype 84 to 98% in April (spring), with no differences detected among treatments. Our findings document the second instance of annual bluegrass evolving multiple resistance in a managed turfgrass system. However, several herbicide mixtures can be used to effectively manage this resistant phenotype. Nomenclature: glyphosate; mesotrione; prodiamine; simazine; S-metolachlor; trifloxysulfuron; annual bluegrass, Poa annua L.; hybrid bermudagrass, Cynodon dactylon × Cynodon transvaalensis Burtt-Davy. Key words: Turf, turfgrass, golf course, mitotic-inhibiting herbicide, EPSPS.Control limitado de Poa annua fue reportado en "roughs" de campos de golf después de tratamientos con prodiamine (1120 g ai ha −1 ) y glyphosate (840 g ae ha −1 ) durante el período de dormancia del césped bermuda híbrido. Se realizó una investigación para determinar si este fenotipo de P. annua era resistente a prodiamine y glyphosate y para determinar la eficacia de mezclas de herbicidas para controlar este fenotipo en el campo. En experimentos de respuesta a dosis con herbicidas PRE o POST, se necesitó de 9 a 31 veces más prodiamine o glyphosate para controlar (o reducir la biomasa seca) de este fenotipo resistente en 50% en comparación a un fenotipo susceptible a estos herbicidas. Además, plantas susceptibles a glyphosate acumularon 50% más ácido shikimic (898 mg kg −1 ) 6 d después del tratamiento que plantas resistentes a glyphosate (394 mg kg −1 ). Aplicaciones en Octubre (otoño) de mezclas de herbicidas que contenían trifloxysulfuron, simazine, S-metolachlor, o mesotrione controlaron este fenotipo resistente de P. annua 84 a 98% en Abril (primavera), sin detectarse diferencias entre estos tratamientos. Nuestros resultados documentan la segunda instancia de P. annua que evoluciona resistencia múltiple en un sistema manejado de céspedes. Sin embargo, varias mezclas de herbicidas pueden ser usadas para manejar efectivamente este fenotipo resistente.

Field research was conducted in 2010 and 2011 to investigate the efficacy of herbicides for dallisgrass control when applied at various growing (GDD) or cooling degree day (CDD) –based application timings. Herbicide treatments included fluazifop-p-butyl (fluazifop; 105 g ai ha−1), mesotrione (280 g ai ha−1), tembotrione (92 g ai ha−1), topramezone (37 g ai ha−1), and tank mixtures of fluazifop plus mesotrione, tembotrione, or topramezone. Herbicide treatments were applied at either 75, 175, 375, 775 GDD, or 5 CDD. Treated plots were subjected to three tall fescue interseeding regimes: no seeding, seeding in spring, or seeding in fall (0, 353, and 353 kg pure live seed ha−1, respectively). In 2010, dallisgrass control from fluazifop applied at 75, 375, and 775 GDD was poor (< 50%) by 52 wk after treatment (WAT); in 2011, control from fluazifop application at these timings was higher (62 to 72%). When applied at 175 GDD or 5 CDD in 2010 and 2011, dallisgrass control from fluazifop ranged from 79 to 93% at 52 WAT. The addition of mesotrione, tembotrione, or topramezone to fluazifop did not affect dallisgrass control at any application timing, and control provided by these herbicides alone was low (< 65%). Interseeding tall fescue in the fall improved dallisgrass control from herbicides applied at 75 GDD in 2010 and 175, 375, and 775 GDD at 52 WAT in both years. Results suggest that timing of fluazifop applications at 175 GDD and 5 CDD enhances dallisgrass control.

Poa annua L. is a common component of turfgrass systems both as a weed and a desirable species. Since first classified by Carl von Linné in 1753, nearly 50 taxa of P. annua have been described, with delineations made on the basis of plant morphology and not life cycle. Yet, peer‐reviewed turfgrass literature has recognized only two of these taxa over the past 50 yr, P. annua L. var. annua and P. annua var. reptans, categorizing var. annua ecotypes as upright growing annuals and var. reptans ecotypes as laterally growing perennials. Herein we provide a comprehensive review of peer‐reviewed literature to highlight that these associations between life cycle and plant morphology are flawed given that morphology is plastic and strongly influenced by environment. We conclude by exploring knowledge gaps regarding P. annua perennation that, if addressed through research, would help turfgrass managers better understand the biology of the ecotypes they aim to eradicate or maintain.

No abstract

Anthracnose basal rot (ABR) is a serious disease of turfgrasses that is caused by the pathogen Colletotrichum graminicola. The relationships of isolates causing ABR on turfgrasses to those causing disease on important crop hosts (maize, sorghum) remain unresolved. Genetic variation among isolates from annual bluegrass, creeping bentgrass, maize, and sorghum was evaluated based on host origin and geographic origin. Isozymes were used to estimate the genetic variation of the isolates. Five enzyme systems comprising 16 alleles from 5 loci were used. Allele frequencies, genetic distance, and linkage disequilibrium values were calculated for isolates based on both host and geographic origin. Isolates from creeping bentgrass and annual bluegrass were the most closely related based on Nei's genetic distance, while isolates from maize and sorghum were the most distantly related, consistent with their known species-level relationship. Isolates from annual bluegrass and creeping bentgrass had different genetic distances to isolates from both maize and sorghum. Annual bluegrass isolates from different geographic regions had the smallest genetic distance values observed in this study, indicating a very close relationship regardless of geographic origin. Based on these data, it appears that host origin, not geographic origin, plays a more important role in the genetic diversity of these fungi.

Dollar spot (Sclerotinia homoeocarpa F.T. Bennett) causes one of the most important diseases faced by golf course superintendents throughout the USA. Fungicides are effective, but fungicide resistance and regulation have restricted their use. Site‐specific application allows more judicious use of fungicides, but the spatial heterogeneity of dollar spot incidence has been unknown. An intensive study was designed to determine the spatial distribution of dollar spot incidence using geostatistical analysis. Dollar spot foci were manually counted every 2 to 3 d in 200 quadrats in 2000, and in 888 quadrats in 2001 and 2002. Variograms showed spatial aggregation of dollar spot foci on a small scale, and remained stable throughout the growing season despite increasing disease incidence. The range parameter of the variograms was stable within a season, with values ranging between 2.5 and 9.5, 1.3 and 1.9, and 1.2 and 2.2 m in 2000, 2001, and 2002, respectively. Kriged maps of dollar spot incidence also show a stable pattern of spatial aggregation remains throughout the growing season. The locations of dollar spot clusters changed between seasons, but the variograms from each season were similar, further suggesting stability of the spatial structure. It appears that limited secondary dispersal of S. homoeocarpa occurs during epidemics, as evidenced by the stable variograms observed throughout the three growing seasons. The underlying factors involved in the observed stability are unknown.