RED LEAF SPOT

red leaf spot plant symptoms	Characteristic	Description
	Host Grass Species	creeping bentgrass
	Month(s) with symptoms	April to October
	Stand Symptoms	spots, patches (4 to 12 inches)
	Foliar Symptoms - Location/Shape	oval leaf spots
	Foliar Symptoms - Color	small, red or reddish-brown leaf spots with a tan center
	Root/Crown Symptoms	none
	Fungal Signs	none

 

Note: Still not sure if this is the right disease? The Turfgrass Disease Identification program may be helpful. Or consult the experts at the Turf Diagnostics Lab. Check the TurfFiles glossary for definitions of unfamiliar terms.

FACTORS AFFECTING DISEASE DEVELOPMENT

Red leaf spot is one of several Helminthosporium diseases which survive in thatch during periods that are unfavorable for disease development. The red leaf spot pathogen is most active during warm, wet weather in the late spring, summer, or early fall.

Red leaf spot is most severe on turf that is growing slowly due to adverse weather conditions or improper management practices. Shaded areas with little or no air movement result in weak turf and extended periods of leaf wetness that favor disease development and plant infection. Deficient or excessive nitrogen, excessive thatch, extended periods of leaf wetness, drought stress, and low mowing heights are factors that encourage the development of Helminthosporium diseases.

Certain cultivars of turfgrasses are very susceptible to injury from Helminthosporium diseases while many of the newly released cultivars have exhibited good resistance.

CULTURAL CONTROL

Use turfgrass cultivars with resistance to this disease when available. Use of resistant cultivars is one of the best means of prevention. Select cultivars based on regional trials and University recommendations. Use blends and mixtures of cool-season grasses whenever possible.

Fertilize to meet the nutritional needs of the turf but avoid over-stimulation and the development of lush, succulent growth. Do not apply more than one pound of nitrogen per 1000 ft² in a single application. Creeping bentgrass should be mowed at heights between 0.1” and 0.125” during fall, winter, and spring and between 0.125” and 0.15” during summer. Keep the mower blades sharp to prevent open wounds through which the fungus can enter.

Reduce extended periods of leaf wetness with deep and infrequent irrigation, wetting the entire root zone then re-applying when the root zone becomes dry. Do not irrigate just before or after sunrise and remove dew in the morning to shorten leaf wetness periods. Remove unwanted vegetation that impedes air movement and prune trees to increase light penetration. Regular aerification and topdressing is needed to reduce thatch accumulations and minimize pathogen survival.

CHEMICAL CONTROL

Red leaf spot can be controlled on a preventative or curative basis. Where the disease has been a persistent problem, apply an effective fungicide every 14 to 21 days when conditions are favorable for infection. Once the symptoms of read leaf spot appear, tank-mixtures of contact and systemic fungicides are recommended for curative control.