NET BLOTCH

net blotch leaf spots	Characteristic	Description
	Host Grass Species	tall fescue
	Month(s) with symptoms	March to June, Sept to November
	Stand Symptoms	irregular distribution across turf stand
	Foliar Symptoms - Location/Shape	angular leaf spot or oval leaf spot
	Foliar Symptoms - Color	yellow, brown
	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

Net blotch is one of several Helminthosporium diseases which survive in thatch during periods that are unfavorable for disease development. These fungi are most active during periods of cool (60 to 65°F) and wet weather, but some are able to cause disease whenever temperatures are above freezing.

Net blotch 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. When planting cool-season turfs, use blends and mixtures of multiple species and/or varieties 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 1,000 square feet in a single application. Tall fescue should be mowed to a height of 3 to 3.5 inches. Keep the mower blades sharp to prevent open wounds through which the fungus can enter.

Reduce extended periods of leaf wetness by watering deeply but infrequently to wet the entire root zone. Do not irrigate just before or after sunrise, and ensure good surface and soil drainage. Remove unwanted vegetation that impedes air movement and prune trees to allow for light penetration. Power rake or dethatch to remove excessive thatch and reduce the potential for pathogen survival.

CHEMICAL CONTROL

Net blotch can be controlled on a preventative or curative basis. Applications should be made in the early stages of disease development for best results. Susceptible turfgrasses should be monitored regularly for disease development during cool and wet weather conditions.