Contrasting genetic structure between Magnaporthe grisea populations associated with the golf course turfgrasses Lolium perenne (perennial ryegrass) and Pennisetum clandestinum (kikuyugrass).

Gray leaf spot (GLS) disease of perennial ryegrass (Lolium perenne) and kikuyugrass (Pennisetum clandestinum) in golf courses in California was first noted in 2001 and 2003, respectively, and within 5 years had become well established. The causal agent of the disease is the fungus Magnaporthe grisea, which is known to consist primarily of clonal lineages that are highly host specific. Therefore, our objective was to investigate host specificity and population dynamics among isolates associated primarily from perennial ryegrass and kikuyugrass since the disease emerged at similar times in California.

Two Mutations in β-Tubulin 2 Gene Associated with Thiophanate-Methyl Resistance in Colletotrichum cereale Isolates from Creeping Bentgrass in Mississippi and Alabama.

Turfgrass anthracnose, caused by Colletotrichum cereale (≡C. graminicola), has become a common disease of creeping bentgrass putting greens during the summer in Mississippi and Alabama over the last 15 years. Thiophanate-methyl is a single-site mode-of-action fungicide applied to control C.

Geographic Distribution and rDNA-ITS Region Sequence Diversity of Waitea circinata var. circinata Isolated from Annual Bluegrass in the United States.

Waitea circinata var. circinata is the causal agent of brown ring patch, an emergent disease of turfgrass in the United States. Forty-two isolates from annual bluegrass were obtained from California, Connecticut, Idaho, Illinois, Massachusetts, New York, Ohio, Oregon, and Rhode Island.

Phylogenetic Relationships of Xylella fastidiosa Strains Isolated from Landscape Ornamentals in Southern California.

ABSTRACT Xylella fastidiosa is an insect-borne, xylem-limited pathogenic bacterium that has been associated with a rise in incidence of diseased landscape ornamentals in southern California. The objective of this study was to genetically characterize strains isolated from ornamental hosts to understand their distribution and identity. Strains of X.

Detection and Characterization of Benzimidazole Resistance in California Populations of Colletotrichum cereale.

Colletotrichum cereale is the causal agent of turfgrass anthracnose, which has become a serious problem on annual bluegrass (Poa annua) and creeping bentgrass (Agrostis palustris) golf course putting greens. Thiophanate-methyl is a benzimidazole (methyl benzimidazole carbamate [MBC]) fungicide used for the management of anthracnose. In this study, we examined 481 isolates from 10 California populations to determine the presence and frequency of MBC resistance.

Sensitivity Distributions of California Populations of Colletotrichum cereale to the DMI Fungicides Propiconazole, Myclobutanil, Tebuconazole, and Triadimefon.

The baseline sensitivity of a California population of Colletotrichum cereale (turfgrass anthracnose) to the sterol demethylation inhibitor (DMI) fungicide propiconazole was determined using an in vitro assay with known reproducibility. The 50% effective dose (ED) values for propiconazole for a nonexposed, baseline population ranged from 0.025 to 0.

Occurrence and Distribution of QoI-Resistant Isolates of Colletotrichum cereale from Annual Bluegrass in California.

Turfgrass anthracnose, caused by Colletotrichum cereale (ex. Colletotrichum graminicola), is an important disease of turf used on golf course putting greens. Recent management of the disease has become increasingly difficult, partly due to the possible development of practical resistance to the QoI fungicides.

Discovery and Characterization of Waitea circinata var. circinata Affecting Annual Bluegrass from the Western United States.

Waitea circinata var. circinata was identified as the causal agent of a new disease of annual bluegrass (Poa annua) in the United States. This pathogen is also known to cause brown ring patch on creeping bentgrass (Agrostis stolonifera) in Japan, but it had not been reported on any turf species outside of Japan.

Sensitivity to Azoxystrobin Among Isolates of Uncinula necator: Baseline Distribution and Relationship to Myclobutanil Sensitivity.

Two hundred fifty-six single-conidial chain isolates of Uncinula necator were assayed for their sensitivity to azoxystrobin and myclobutanil. These isolates were collected from two sites in New York in 1999: an "organic" vineyard where no synthetic fungicides have been used (baseline population) and a commercial vineyard having a history of compromised powdery mildew control with myclobutanil (demethylation inhibitor [DMI]-resistant population). Mean coefficients of variance for a leaf disk assay used to test fungicide sensitivities were 31% for azoxystrobin and 41% for myclobutanil.

Comparative Physical Modes of Action of Azoxystrobin, Mancozeb, and Metalaxyl Against Plasmopara viticola (Grapevine Downy Mildew).

The physical modes of action of azoxystrobin, mancozeb, and metalaxyl were evaluated on grapevine seedlings using Plasmopara viticola as a model pathogen. The protectant, postinfection, postsymptom, translaminar, and vapor activities of azoxystrobin were evaluated at a rate of 250 μg/ml. Azoxystrobin provided 100% disease control when applied 1 to 5 days before inoculation.

Distribution of Baseline Sensitivities to Azoxystrobin Among Isolates of Plasmopara viticola.

An excised leaf disc assay was developed for determining the sensitivity of isolates of Plasmopara viticola (causal agent of grapevine downy mildew) to the strobilurin fungicide azoxystrobin. Five repeated assays with the same five single-sporangiophore isolates showed that the technique yielded reproducible results; that is, coefficients of variation ranged from 4.0 to 20% (mean 12%) for effective doses for 50% control (ED values) based on disease incidence and from 4.