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Key Takeaways

  • Establishing a brown patch resistant turf-type tall fescue cultivar is the most effective nonchemical management strategy for reducing disease.
  • Contrary to previous thoughts, nitrogen applications in the summer do not need to be avoided over concerns of increasing the risk of brown patch in tall fescue.
  • Consecutive years of overseeding with brown patch resistant tall fescue will significantly reduce disease and lessen the need for a complete renovation.
  • Establishing a brown patch resistant cultivar effectively reduces the frequency and/or rate of fungicide applications.


     

Throughout the transition zone and northern regions of the United States, turf-type tall fescue is an increasingly popular choice for golf course rough (Shaddox et al., 2023). Increased use of tall fescue compared to other cool-season species, like Kentucky bluegrass, is due to its lower fertility and irrigation requirements and higher tolerance to heat, drought and insect damage. Currently, “turf-type” tall fescues are bred and selected for darker green color, increased tiller density, rhizome production and improved disease resistance, making them more desirable than older tall fescue cultivars like ‘Kentucky-31’.

While tall fescue has many strengths, brown patch (Rhizoctonia spp.) is a major disease concern and can severely damage the turf during summer. Deciding whether to manage this disease using cultural or chemical strategies, or a combination of both, depends on the need to reduce pesticide inputs, labor availability and the golf course’s budget. In this article, we will look at how brown patch develops, nonchemical management strategies and options for chemical control.

Brown Patch Development and Symptoms

Specific brown patch symptoms are dependent on weather conditions, turfgrass species and mowing height. Certain weather conditions must be present for a plant pathogen to infect and cause disease symptoms. Environmental conditions favorable for brown patch infection include daily minimum and maximum air temperatures of approximately 68 F and 86 F, respectively, with relative humidity greater than 90% during the night, and leaf wetness duration over 10 hours (Fidanza et al., 1996). Other favorable conditions include shade, poor soil drainage and irrigation applied late in the day, which increases the duration of leaf wetness.

For turf maintained at lower mowing heights (less than 1 inch), initial brown patch symptoms appear as dark, purple-green patches in an irregular shape that fades to lighter brown with a dark purple “smoke ring” remaining on the outer edge of the patch. Patches can range in size from approximately 2 inches to 3 feet (Tredway et al., 2023). Turf maintained at mowing heights greater than 1 inch, like golf course rough, can show symptoms of coalesced patches or infection on individual plants resulting in a diffuse pattern. Symptoms on individual leaves begin as small tan lesions with chocolate brown-reddish margins, and over time can expand over a large portion of the leaf blade. Delays in regrowth from the crown or complete plant death allows for opportunistic weed species like crabgrass and annual bluegrass to establish. In areas where shoot density declines due to brown patch, regular seeding may be required to maintain acceptable visual quality and playing conditions.

Cultural Management Practices and Current Research

Nonchemical strategies for reducing brown patch are centered around implementing favorable cultural management practices throughout the growing season. These may include adjusting nitrogen fertilization schedules, exploring ways to modify environmental conditions during key infection periods, and identifying commercially available tall fescue cultivars with improved brown patch resistance. Properly employed, combinations of these strategies can limit disease damage and maintain acceptable turfgrass quality throughout the growing season. Here’s a closer look at some cultural practices that can reduce the occurrence and/or severity of brown patch on golf course tall fescue.

Nitrogen Fertility

Nitrogen is an essential nutrient for plants, and the application of nitrogen-containing fertilizers throughout the growing season helps maintain consistent green color, shoot density, growth, vigor, wear tolerance and persistence during environmental stresses. In the Midwest, recommended annual nitrogen application rates range between approximately 2.0 to 3.5 pounds per 1,000 square feet for tall fescue golf course rough. Specific nitrogen sources depend on the time of year, but general recommendations are to use slow-release fertilizers during the spring and summer, and combinations of slow-release and soluble nitrogen sources in early to late fall.

Depending on the specific Rhizoctonia pathogen, nitrogen can either reduce or intensify disease severity. The relationship between nitrogen and brown patch is complex. The rule of thumb has historically been that brown patch severity increases when turf is fertilized with higher nitrogen rates throughout the growing season (Burpee, 1995; Fidanza & Dernoeden, 1996; Watkins & Wit, 1993). However, a recent study conducted at N.C. State University in Raleigh, North Carolina, evaluated various nitrogen rates and scheduling program effects on brown patch severity (Butler et al., 2019). Results of this study found that increased nitrogen rates, up to 6 pounds per 1,000 square feet per year, using urea (46-0-0) did not impact brown patch severity on ‘Coronado’ tall fescue mowed at 3.5 inches.

During 2020 and 2021, researchers at Purdue University in West Lafeyette, Indiana, and at N.C. State evaluated brown patch severity in turf-type tall fescue when fertilized with various nitrogen rates and sources. Nitrogen was applied monthly between April and July using three rates totaling 1.25, 2.5 and 5.0 pounds of nitrogen per 1,000 square feet per year and three sources (urea, polymer-coated urea and composted turkey litter). Regardless of location or year, brown patch severity did not increase as nitrogen rates increased. Additionally, differences in brown patch among the nitrogen sources were not found at N.C. State. The only time nitrogen source affected disease was during 2021 at Purdue, with the polymer-coated urea increasing seasonal brown patch by 18% – measured using area under the disease progress curve (AUDPC). Although the high nitrogen rate did not increase brown patch in this study, increased gray leaf spot in North Carolina and Pythium foliar blight in Indiana was observed in turf receiving the higher nitrogen rate.

"Regardless of location or year, brown patch severity did not increase as nitrogen rates increased."

Based on this research, fertility plans should follow best management practices in the specific geographic region where the golf course is located to maintain healthy tall fescue turf. Contrary to conventional wisdom, completely avoiding summer nitrogen is not warranted simply due to concerns of increasing the occurrence of brown patch. If environmental conditions favoring disease have passed, a one-time application of water-soluble nitrogen – i.e., urea at 0.5 pounds of nitrogen per 1,000 square feet – could help improve recovery of areas that have been affected by brown patch.

Mowing Height

There is a relationship between the occurrence of brown patch and mowing height, but the exact nature of this interaction remains unclear. This is of significant interest to golf course superintendents who often need to balance the health of their tall fescue turf with playability, and often manage an intermediate cut of rough at a much lower height than the primary rough. Higher mowing heights could reduce air movement in the turf canopy, increasing humidity and leaf wetness resulting in conditions favoring pathogen infection.

In 1995, a study conducted in Georgia evaluated brown patch severity using multiple cultivars and mowing heights (1.5, 2.5 and 3.5 inches) over two growing seasons (Burpee, 1995). During the first year of evaluation, the lower mowing height reduced brown patch, while in the second year the lower height had the greatest brown patch. In a study conducted in Virginia, mowing at 2.4 inches reduced brown patch severity during select times of the year compared to mowing at 4 inches, but bermudagrass encroachment was greater at the lower mowing height (Cutulle et al., 2014). Although improved turf-type tall fescue cultivars have been shown to tolerate lower mowing heights (as low as 0.5 inch) than older cultivars like ‘Kentucky 31’, the current recommendation for mowing turf-type tall fescue is to maintain a height between 2.0 and 3.5 inches. Mowing in this range appears not only best for brown patch management, but also helps reduce other abiotic and biotic stresses, such as weed pressure, drought stress and insect feeding.

Irrigation and Leaf Wetness

During the summer months when conditions increase disease pressure, supplemental irrigation should be applied deeply to maintain turf health during periods of low rainfall. Evening watering will extend canopy wetness and favor disease development; therefore, irrigation should be applied early in the morning during periods of high disease pressure. Other conditions that extend leaf wetness and promote brown patch include shade, poor soil drainage and reduced air movement.

Dew removal is a common practice for golf course putting greens and fairways to prepare surfaces for play and a potential disease reduction strategy that can be used on tall fescue rough as well. Various mechanical dew displacement methods like early morning mowing, dragging, whipping, rolling or light irrigation are commonly practiced by superintendents (Tredway et al., 2023). While dew displacement methods on high-value, close-cut turfgrass areas are common, this strategy is not generally practical for rough or other turfgrass areas mowed higher than 1.5 inches. Additional research at N.C. State and Purdue evaluated applications of chemical dew mitigation using surfactants to reduce dew formation on leaf blades on higher-cut turf (Powlen, 2023). Preliminary research found that this practice has potential to reduce brown patch, but the amount of dew reduction was product specific and dependent on application frequency. Further work is needed to determine the practicality of this management approach.

Host (Cultivar) Resistance

Among all cultural strategies, host resistance is frequently suggested as one of the most effective nonchemical methods to reduce disease. To determine resistance to diseases like brown patch, varieties in breeding programs are compared in national field trials, such as the National Turfgrass Evaluation Program (NTEP). Research conducted in the 1990s found that tall fescue cultivars with wide leaf texture, open canopies and faster growth rate like ‘Kentucky 31’ had greater brown patch resistance than finer-textured cultivars on the market at that time. It was postulated that the disease-resistant cultivar could outgrow the disease and/or the longer distance between the leaf blades reduced hyphal growth (Green et al., 1999; Giesler et al. 1996).

Multiple greenhouse and field studies were recently conducted at Purdue to determine the overall range in brown patch resistance among contemporary, commercially available tall fescue cultivars and evaluate if characteristics such as growth rate and density influenced disease. Fifteen cultivars were evaluated in a greenhouse study to determine if morphological characteristics – i.e., growth rate, sheath length, leaf blade width or sheath width – were correlated with brown patch resistance (Powlen et al., 2024). Cultivars were inoculated with Rhizoctonia solani and placed in a high-humidity chamber to induce disease. Results of this study found that a resistant tall fescue cultivar reduced brown patch symptoms by 45%. Additionally, cultivars with narrow leaf blades and reduced growth rate were not correlated with increased disease.

Five tall fescue cultivars with a range of host resistance were identified in the humidity chamber study and were then seeded as field study plots in the fall of 2020 at Purdue to evaluate resistance under field conditions. After two growing seasons (2021 and 2022), the same resistant cultivar from the chamber trial, ‘Raptor III’, reduced seasonal brown patch in the field by 61% across both years compared to the most-susceptible cultivar, ‘Kingdom’. This research confirmed that fine-textured, high-density cultivars need not be avoided due to concerns of increased brown patch.

Overseeding Resistant Cultivars

Planting a resistant tall fescue cultivar is an effective strategy to reduce brown patch. However, complete renovation of golf course rough to a resistant cultivar is costly and challenging. A two-year field study was conducted at Purdue to evaluate renovation and seeding strategies to reduce brown patch severity in an existing turf-type tall fescue lawn by overseeding a resistant cultivar at two seeding rates, 6 or 12 pounds of pure live seed per 1,000 square feet. Three overseeding strategies were also evaluated: reducing the mowing height from 3 inches to 1 inch (scalping) and collecting clippings; scalping and vertical mowing; and scalping, vertical mowing and complete renovation with a nonselective herbicide.

The brown patch resistant cultivar reduced seasonal brown patch by 42% and 56% in year one and two, respectively. Seeding rate did not affect visual quality or brown patch severity. In year one, complete renovation practices reduced seasonal brown patch by 37% compared to the other two overseeding strategies; however, differences among renovation practices in year two were generally not observed. Results from this study reinforce the value of resistant cultivars and demonstrates that a complete renovation may not be necessary to establish resistant cultivars in golf course rough.

"Results from this study reinforce the value of resistant cultivars and demonstrates that a complete renovation may not be necessary to establish resistant cultivars in golf course rough."

Chemical Control

Fungicide applications are an effective brown patch control strategy. Preventative applications are recommended if a golf course’s threshold for damage is low, especially when the forecast environmental conditions favor disease development. Preventative fungicide applications should be made when night temperatures exceed 60 F for three consecutive nights. Fungicide classes that are effective for preventative control of brown patch include carboxamides, benzimidazoles, carbamates, dicarboximides, DMI, QoI (strobilurins) and nitriles (Clarke et al., 2019). To date, fungicide resistance issues with brown patch have yet to be documented.

Interaction of Cultivar Resistance and Fungicide Applications

Planting resistant tall fescue cultivars can reduce brown patch compared to susceptible cultivars. The question remains however, can a resistant cultivar effectively reduce disease to a level comparable with a traditional fungicide program. In 2023, a preliminary field study was conducted at Purdue to evaluate brown patch severity as affected by cultivar selection, fungicide application frequency, and fungicide formulation. Resistant (‘Raptor III’) and susceptible (‘Kingdom’) cultivars were seeded in the fall of 2020. Fungicide treatments included either one or three applications and were initiated on June 2, 2023, with additional fungicide applications applied every 28 days for treatments receiving three applications. A liquid and granular formulation of azoxystrobin – Heritage TL (2 fluid ounces per 1,000 square feet) and Heritage G (4 pounds per 1,000 square feet) – were selected for the fungicide treatments. Preliminary results found that without fungicide treatment, a resistant cultivar reduced seasonal brown patch by 82% compared to a susceptible cultivar as measured by the AUDPC. Additionally, the resistant cultivar without a fungicide application reduced brown patch by 47% compared to the susceptible cultivar treated with fungicide. Based on these preliminary results, the answer to our question is yes – a resistant tall fescue cultivar can reduce brown patch to a level comparable to what you get with multiple fungicide applications on a susceptible cultivar.

Summary

Although brown patch can be a concern for turf-type tall fescue during the summer months, this grass species has many advantages compared to other cool-season rough options. Tall fescue’s drought and heat tolerance, lower irrigation and fertility needs, insect tolerance and the good visual quality of modern, commercially available cultivars make it a good choice for low-input rough.

Selecting resistant cultivars will significantly reduce brown patch throughout the growing season and contrary to previous thoughts, fine-textured cultivars with slower growth rates do not need to be avoided for fear of increased brown patch. Consecutive years of overseeding is an effective approach to introduce resistant cultivars into existing turf, and under high disease pressure, reduced fungicide applications can be achieved by establishing these cultivars. Other practices such as early morning irrigation, improving drainage and air movement, and applying low to moderate nitrogen rates during the summer months using slow-release fertilizer sources can help reduce environmental conditions favoring disease and promote a dense, healthy turf. Together, these management strategies can help golf course superintendents effectively manage brown patch in tall fescue.

About the Authors

Jada Powlen, Ph.D., is a Lead Research Scholar in the Department of Horticulture and Landscape Architecture at Purdue University in West Lafayette, Indiana.

Mike Fidanza, Ph.D., is a Professor of Plant and Soil Sciences at the Pennsylvania State University, Berks Campus in Reading, Pennsylvania.

Jim Kerns, Ph.D., is a Professor & Extension Specialist of Turfgrass Pathology in the Department of Entomology and Plant Pathology at North Carolina State University in Raleigh, North Carolina

Cale Bigelow, Ph.D., is a Professor of Turfgrass Science and Ecology in the Department of Horticulture and Landscape Architecture at Purdue University in West Lafayette, Indiana.  

References

Burpee, L. L. (1995). Interactions among mowing height, nitrogen fertility, and cultivar affect the severity of Rhizoctonia blight of tall fescue. Plant Disease, 79, 721-726.

Butler, E. L., Galle, G. H., & Kerns, J. P. (2019). Influence of nitrogen rate and timing, fungicide application method, and simulated rainfall after fungicide application on brown patch severity in tall fescue. Crop, Forage and Turfgrass Management, 5, 190018. https://doi.org/10.2134/cftm2019.03.0018

Clarke, B. B., Vincelli, P., Koch, P., & Munshaw, G. (2019). Chemical control of turfgrass diseases 2020. Lexington, Kentucky: Cooperative Extension Service, College of Agriculture, Food and Environment, University of Kentucky. Revised Edition. http://www2.ca.uky.edu/agcomm/pubs/PPA/PPA1/PPA1.pdf  

Cutulle, M., Derr, J., McCall, D., Nichols, A., & Horvath, B. (2014). Effect of mowing height and fertility on bermudagrass (Cynodon dactylon) encroachment and brown patch severity in tall fescue. Weed Technology, 28, 225-232. https://doi.org/10.1614/WT-D-13- 00121.1

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Fidanza, M. A., Dernoeden, P. H., & Grybauskas, A. P. (1996). Development and field validation of a brown patch warning model for perennial ryegrass turf. Phytopathology, 86, 385-390.

Giesler, L. J., Yuen, G. Y., & Horst, G. L. (1996a). Tall fescue canopy density effects on brown patch disease. Plant Disease, 80, 384-388.

Green, II, D. E., Burpee, L. L., & Stevenson, K. L. (1999a). Components of resistance to Rhizoctonia solani associated with two tall fescue cultivars. Plant Disease, 83, 834-838.  

Powlen, J. S. (2023). An integrated cultural management approach for brown patch disease suppression in tall fescue lawns (Doctoral dissertation). Purdue University, Purdue University Research Repository. https://doi.org/10.25394/PGS.22677676.v1

Powlen, J. S., Fidanza, M. A., Kerns, J. P., Hoagland, L. A., & Bigelow, C. A. (2024). Turf-type tall fescue brown patch resistance as influenced by morphological characteristics. Plant Health Progress, 1-8. https://doi.org/10.1094/PHP-10-23-0082-RS.

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