Ascochyta (leaf blight of turfgrass)

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Dothideomycetes
Subclass	Pleosporomycetidae
Order	Pleosporales
Family	Didymellaceae

Scientific Name

Ascochyta

Common Name

Ascochyta fungi

Author: Lee Miller, University of Missouri

Reviewed by:Name, Organization

Pathogen

Ascochyta blight of turfgrass has been associated with a number of Ascochyta spp., which are dothidiomycetes. Pycnidia are 70 – 200 μm in diameter and yellow brown, rust brown, or brick red. They are more common in groups and are more dominant on the upper leaf surface. Pycnidial wall is stromatic with many layers of cells. The outer most layer of the pycnidial wall is rust sepia colored with the inner layers hyaline. Conidia are hyaline to pale yellow colored, uni-septate, and fusoid.

Symptoms and Signs

Ascochyta spp. rarely infect the crown of the turfgrass plant and cause permanent damage. The disease is most commonly observed and conspicuous on Poa pratensis L. (Kentucky bluegrass). A uniform or localized blighting results in a bleached, chlorotic stand symptom that is loosely aggregated in the landscape. Individual leaves die back from the tip when infected. The leaf lesions are circular or elliptical, usually white or brown in color, and may develop red or thin off-brown borders.

Ecology and Spread

Ascochyta survives as mycelium and pycnidia in debris. The pycnidia release conidia during wet periods, which are transferred to uninfected leaves through splashing or mechanical dispersion. The pathogen enters through cut leaf tips caused by mowing and grows toward the leaf base. Leaf wetness events such as periods of high humidity, heavy dew events and frequent irrigation favor disease occurrence and spread. Frequent mowing, particularly during leaf wetness periods can encourage disease spread.

Geographic Distribution

Ascochyta blight is a common occurrence on grasses in many parts of the world, including the United States, Great Britain, Europe, Russia, Mexico and South America.

Management

Although conspicuous, Ascochyta blight is generally not a severe disease that causes permanent damage. For this reason, fungicides are rarely recommended for control. Cultural practices such as mowing, irrigation, and fertilizing can be important factors in managing disease outbreaks.

Cultural Control

(Only focus on turfgrass) Mowing – Maintain grass recommended height for species is a cultural practice that tends to help the spread of Ascochyta blight. Mowing a grass species at the recommended height is important along with maintaining sharp clean mowing blades when trying to avoid spread. Irrigating early to knock off the dew and irrigating deeply and infrequently (without causing stress) can help control this disease. Also, maintaining adequate amounts of nitrogen without excessive fertilizer application has shown to be helpful.

Host Resistance

Cultivar resistance is not available.

Diagnostic procedures

If pycnidia are present in the leaf blotches, they can be removed with a needle, mounted under a cover slip in water, and crushed by applying light pressure. This will allow the spores to be observed, which are fusoid, uni-septate, and two-celled.

Acknowledgments

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30818 as part of "Diagnostic Image Series Development for Supporting IPM in the North Central Region" (USDA-NIFA-RIPM-003349)