How to Manage Pests
UC Pest Management Guidelines
Pathogen: Bipolaris sorokiniana
(Reviewed 9/09, updated 9/09, pesticides updated 12/16)
In this Guideline:
DESCRIPTION OF THE DISEASE
Leaf spot occurs on leaf blades, sheaths, and stems as circular to elongated purplish or brown spots with brown colored centers and purplish to dark brown borders. Spots may be found on turfgrass leaves throughout the site, indicating spread by windborne spores. Crown and roots are frequently affected with a dark brown rot. Plants with crown infections are weakened and may die in hot, windy weather, resulting in a thinning out of the turf in scattered areas.
Bentgrasses, bluegrasses, fescues, and ryegrasses are susceptible to leaf spot. The fungus survives in infected grass plants or grass debris and may be seedborne. Spores are airborne.
CONDITIONS FAVORING DISEASE
The disease is favored by warm temperatures (70° to 90°F), high humidity, extended leaf wetness, and closely cropped turfgrass. It is more severe under high nitrogen fertilization.
Follow good management practices to prevent the development of leaf spot. Fungicides are usually not warranted.
Reduce shade and improve soil aeration and water drainage. Avoid dry spots, overfertilizing with nitrogen, and maintain as high a cutting height as possible. Avoid prolonged leaf wetness by irrigating in pre-dawn, or early morning hours. If possible, increase air movement.
Leaf spot usually is not serious enough in California to warrant the use of fungicides although they may be used in areas where leaf spot is severe.
UC IPM Pest Management Guidelines: Turfgrass
A. Downer, UC Cooperative Extension, Ventura County
Acknowledgment for contributions to Diseases:F. Wong, Plant Pathology, UC Riverside
J. Hartin, UC Cooperative Extension, San Bernardino County
M. E. Grebus, Plant Pathology, UC Riverside