Blast disease (gray leaf spot) of perennial ryegrass (Lolium perenne L.), caused by Pyricularia grisea (Cooke) Sacc., in golf course fairways in Pennsylvania, was first reported in 1991 (1). The disease was primarily confined to the southeastern region of the state. In August and September 1998, severe outbreaks of blast disease occurred in perennial ryegrass fairways in numerous golf courses in the same region in Pennsylvania. Additionally, in 1998, the disease was diagnosed in ryegrass fairways for the first time in the western region of the state, where serious disease outbreaks occurred. The disease develops on leaf blades as small, watersoaked lesions that become necrotic spots. The spots expand rapidly, and develop into gray, grayish-brown, or light brown, circular spots with purple to dark brown borders often surrounded by a yellow halo on the leaf blades. As the disease progresses, the circular necrotic spots coalesce, become irregular in shape, and cause partial (tip blight) or complete blighting of the leaf blades. The blighted blades may often appear twisted. Turfgrass loss due to the disease was over 90% in several golf courses. During the 1998 epidemics, a survey was conducted in the affected regions, which included three golf courses in western Pennsylvania and 15 golf courses in southeastern Pennsylvania. P. grisea was consistently isolated from the symptomatic ryegrass leaf blades of turf samples (12 to 28 samples per location) collected from the blighted fairways. Of the 122 isolates of P. grisea collected from the 18 golf courses, seven isolates (two from western Pennsylvania and five from southeastern Pennsylvania) were selected for pathogenicity assays. Five Pennfine perennial ryegrass plants were grown in each Cone-Tainer (4 mm in diameter) that was filled to 1 cm below the rim with granular calcine clay medium (Turface MVP; Allied Industrial Material, Buffalo Grove, IL). Three weeks after seeding, grasses were fertilized with water-soluble 20-20-20 fertilizer (1.3 g per liter of water) once a week to field capacity of the growing medium. Treatments (the isolates) were arranged as a randomized complete block with four replications (a Cone-Tainer per replication). Six-week-old ryegrass plants were atomized with an aqueous suspension of P. grisea conidia (approximately 8 × 104 conidia per ml of sterilized, distilled water) until the leaves were completely wet. Individual Cone-Tainers were placed in clear polyethylene bags, enclosed, and were placed in an incubator that was maintained at continuous 28°C and 12-h-day fluorescent light (72 μE s-1 m-2). Three days after inoculation, water-soaked lesions (<2 mm in diameter) developed on leaves of the ryegrass inoculated with each isolate of P. grisea. No lesions developed on leaves of the control plants. Seven days after inoculation, the polyethylene bags were removed, and disease incidence (percent infected leaves) was assessed. P. grisea was isolated from the necrotic lesions or the blighted leaf blades of every plant inoculated with the fungus. This is the first report of blast disease outbreak in golf course fairways in western Pennsylvania. The impact of blast disease epidemics on golf courses in the northeastern United States in 1998 was significant, and caused serious concern to turf managers. The survey indicates that blast disease of perennial ryegrass may be emerging as a new problem for the turfgrass industry in the northeastern United States. Reference: (1) P. J. Landschoot and B. F. Hoyland. Plant Dis. 76:1280, 1992.

The effects of N source, fall fertilization, and preventive fungicides were evaluated in bermudagrass [Cynodon dactylon (L.) Pers.] artificially inoculated with Ophiosphaerella korrae and O. herpotricha, the most common spring dead spot (SDS) pathogens in the United States. The source of N applied to bermudagrass from May to August 2006–2008 had a significant effect on SDS symptoms appearing in the spring of 2007–2009. Ammonium sulfate [(NH4)2SO4] provided excellent suppression of O. herpotricha but had no effect on O. korrae, which was suppressed instead by calcium nitrate (CaNO3). More research is needed to determine the underlying mechanisms responsible for suppression of SDS with N sources and the potential role of Mn and Ca in development of the disease. Fall applications of K, S, gypsum, or dolomitic lime had no influence on SDS development. Preventive applications of propiconazole, propiconazole + azoxystrobin, tebuconazole, or fenarimol provided effective control of O. herpotricha but failed to provide significant suppression of O. korrae. The differential response of SDS pathogens to fertilization practices and preventive fungicide applications highlight the importance of pathogen identification in development of integrated management programs.

Ethofumesate is a widely used herbicide for control of annual bluegrass (Poa annua) in perennial ryegrass (Lolium perenne) fairways on golf courses in the United States. Effect of timing of ethofumesate application on development of gray leaf spot was evaluated on perennial ryegrass turf treated with six classes of fungicide. Two applications of ethofumesate (2.28 kg a.i./ha) were made to perennial ryegrass turf maintained at a 2-cm height, at 4-week intervals, each fall (October and November 1999 and 2000) or spring (April and May 2000 and 2001). In addition, turf was treated with the fungicides, azoxystrobin, chlorothalonil, flutolanil, iprodione, propiconazole, or thiophanate-methyl at the label rates at 14-day intervals. There were significant effects (P ≤ 0.05) of ethofumesate application timing and fungicide regime on gray leaf spot development. There also were significant interactions between the ethofumesate application timing and fungicide. Severity of gray leaf spot was significantly greater in turf plots treated with ethofumesate in spring compared to turf treated in fall or nontreated control plots treated with fungicides, flutolanil, iprodione, and propiconazole that were relatively less effective in control of gray leaf spot. There was no significant difference in disease severity in turf treated with ethofumesate in fall or to turf not treated with herbicide regardless of the fungicide used. Results of this study indicate that spring application of ethofumesate contributes to development of gray leaf spot epidemics, and the application timing interacts with the classes of fungicides. This study suggests that ethofumesate should be applied only in fall for control of P. annua, particularly in golf courses with a chronic gray leaf spot problem, as part of an integrated management of gray leaf spot in perennial ryegrass fairways.

Pythium root dysfunction (PRD), caused by Pythium volutum, has been observed on golf course putting greens established with creeping bentgrass in the southeastern United States since 2002. To evaluate preventative strategies for management of this disease, a 3-year field experiment was conducted in Pinehurst, NC on a ‘G-2’ creeping bentgrass putting green. Fungicide treatments were applied twice in the fall (September and October) and three times in the spring (March, April, and May) in each of the 3 years. Applications of pyraclostrobin provided superior preventative control compared with the other fungicides tested. Azoxystrobin and cyazofamid provided moderate control of PRD in two of three seasons. Experiments were conducted to determine whether the disease suppression provided by pyraclostrobin was due to fungicidal activity or physiological effects on the host. In vitro sensitivity to pyraclostrobin, azoxystrobin, fluoxastrobin, cyazofamid, mefenoxam, propamocarb, and fluopicolide was determined for 11 P. volutum isolates and 1 P. aphanidermatum isolate. Isolates of P. volutum were most sensitive to pyraclostrobin (50% effective concentration [EC50] value = 0.005), cyazofamid (EC50 = 0.004), and fluoxastrobin (EC50= 0.010), followed by azoxystrobin (EC50 = 0.052), and mefenoxam (EC50 = 0.139). P. volutum isolates were not sensitive to fluopicolide or propamocarb. Applications of pyraclostrobin did not increase the foliar growth rate or visual quality of creeping bentgrass in growth-chamber experiments. This work demonstrates that fall and spring applications of pyraclostrobin, azoxystrobin, and cyazofamid suppress the expression of PRD symptoms during summer and that field efficacy is related to the sensitivity of P. volutum to these fungicides.

Fairy ring species induce symptoms on putting greens mostly indirectly, by modifying the soil physical or chemical properties. Therefore, preventive rather than curative fungicide applications may be more effective in managing fairy ring. Two field experiments were conducted on a creeping bentgrass research green to evaluate fairy ring control from preventive fungicide applications. A 3-year study investigated the optimal rate and soil temperature-based timing of a preventive application of triadimefon and tebuconazole. A 2-year study evaluated the impact of irrigation timing and fungicide + surfactant tank mixtures on the efficacy of preventive applications of triadimefon and triticonazole. Fungicide-treated plots in both studies exhibited less fairy ring severity than untreated plots. Data suggest that a 5-day average soil temperature range of 13 to 16°C may be suitable for initiating preventive applications. Symptoms occurred earlier in plots treated with a surfactant tank mix than in those treated with fungicide alone. Irrigation timing had no effect on fungicide performance. The sensitivity of 16 isolates representing major fairy ring species to flutolanil, propiconazole, tebuconazole, triadimefon, and triticonazole was determined with a mycelial growth assay. No significant differences in fungicide sensitivity were detected among species. Isolates had significantly higher 50% effective concentration values for triadimefon than for the other fungicides tested.