Red Leaf Spot
Red leaf spot is a disease that occurs on creeping bentgrass during warm and wet weather in the spring, summer, or fall. Red leaf spot is a ‘Helminthosporium’ disease, which is a complex of diseases caused by fungi that produce large, cigar-shaped spores. Symptoms of red leaf spot appear in spots or irregular patches that are red or reddish-brown. On individual plants, symptoms appear as small, red or reddish-brown leaf spots with a tan center. As the lesions expand and coalesce, the turfgrass leaves become blighted and collapse to the ground.
Host Grass Species
Month(s) with symptoms
April to October
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
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 pathogens that survive in the 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.
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 0.110” 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.
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.
Resistance Risk (2)
iprodione + thiophanate-methyl**
26/36, Dovetail, Fluid Fungicide
26GT, IPro, Iprodione Pro, Raven
Fore, 4 Flowable Mancozeb, Dithane, Mancozeb DG, Pentathlon, Protect, Wingman
mancozeb + myclobutanil**
dithiocarbamate + DMI
mancozeb + copper hydroxide**
dithiocarbamate + inorganic
azoxystrobin + propiconazole
DMI + QoI
chlorothalonil + thiophanate-methyl**
benzimidazole + nitrile
Spectro, ConSyst, Peregrine, Tee-1-Up, TM/C
chlorothalonil + propiconazole**
DMI + nitrile
chlorothalonil + propiconazole + fludioxonil**
DMI + nitrile + phenylpyrolle
Daconil, Chlorostar, Chlorothalonil, Echo, Legend, Manicure, Pegasus
Banner MAXX, Kestrel, Kestrel MEX, ProPensity, Propiconazole, Propiconazole G-Pro, Propiconazole Pro, Savvi, Spectator, Strider
3336, Fungo, Systec, T-Bird, T-Storm, Tee-Off, TM
flutolanil + thiophanate-methyl
benzimidazole + carboxamide
triadimefon + trifloxystrobin
Disarm, Disarm G
** Not for application to residential lawns.
excellent control when conditions are highly favorable for disease development
good control when disease pressure is high, or excellent control when disease pressure is moderate
good control when disease pressure is moderate, excellent control when disease pressure is low
good control when disease pressure is low
does not provide adequate control under any conditions
cannot be rated due to insufficient data
Rotating and tank-mixing not necessary, but recommended to avoid potential side effects from continuous use of same chemical class.
Rotate to different chemical class after 3-4 applications; tank-mixing not necessary.
Rotate to different chemical class after 2-3 applications; tank-mixing not necessary.
Rotate to different chemical class after 1-2 applications; tank-mixing not necessary.
Rotate to different chemical class after 1-2 applications; tank-mixing with low or moderate risk product recommended.
Rotate to different chemical class after EVERY application; tank-mix with low or moderate risk product for EVERY application.
Continual use of fungicides with similar control mechanisms (modes of action) can result in fungi that are resistant to some chemicals. Poor or ineffective disease control can be expected when this occurs. Managers can reduce the chances of this happening by mixing or alternating fungicides belonging to different chemical classes.
Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data. When more than one brand name exists for an agricultural chemical, the name of brand that first came onto the market is listed first. Otherwise, brand names are listed in alphabetical order. The order in which brand names are given is not an indication of a recommendation or criticism.
Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services does not imply endorsement by North Carolina State University or discrimination against similar products or services not mentioned. Other brand names may be labeled for use on turfgrasses. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county's Cooperative Extension agent.
© North Carolina State University. This information sheet was prepared by Lane P. Tredway, Gail G. Wilkerson, Bridget R. Lassiter, Jenifer J. Reynolds, and Gregory S. Buol. Departments of Plant Pathology and Crop Science, College of Agriculture & Life Sciences, North Carolina State University. Prepared April 4, 2011. Available on-line at www.turffiles.ncsu.edu. This publication was made possible through a grant provided by the Center for Turfgrass Environmental Research & Education (CENTERE) whose purpose is to support worthwhile projects that will benefit both the private sector and the public, and protect the environment.