Figure 1. Low nitrogen levels (such as that on left) consistently had lower brown patch levels than high nitrogen levels (on right) if no fungicide was applied.
Tall fescue (Festuca arundinacea Schreb.) is widely used in Kansas and much of the Midwest as it is fast to germinate and grow in and demonstrates good heat tolerance and drought avoidance (4). Tall fescue generally performs well in spring and fall but can be impacted significantly by brown patch (Rhizoctonia solani Kuhn) in midsummer. Several factors can impact brown patch on tall fescue, including seeding rates, nitrogen application rates, rainfall or irrigation and fungicide applications.
Some research done on the effect of N sources applied to grasses other than tall fescue has shown an impact on disease. For example, in South Carolina, the use of urea rather than ammonium sulfate resulted in less impact of Rhizoctonia leaf and sheath spot (Rhizoctonia zeae) on bermudagrass (2).
When N from urea was evaluated in North Carolina at 0 to 6 pounds per 1,000 square feet (0 to 294 kilograms per hectare) per year over two years, the high level (6 pounds per 1,000 square feet) resulted in significantly higher levels of brown patch in one year than tall fescue receiving N at 0, 1, 2 or 3 pounds per 1,000 square feet (0, 49, 98 or 147 kilograms per hectare) per year (1).
Little information is available on the impact that different sources of N can have on brown patch in tall fescue. In Maryland (3) and Nebraska (6), N sources had only minor impacts on brown patch in swards of perennial ryegrass. Frequent rainfall or irrigation can enhance brown patch outbreaks in tall fescue. In particular, irrigation in the evening can stimulate brown patch, because it tends to become intensive when water results in a wet canopy for over 10 hours in tall fescue swards (4).
In Oklahoma, the use of azoxystrobin on tall fescue was significantly better for suppression of brown patch in tall fescue than several homeowner-based fungicide applications (5). Our objectives were to evaluate the impact of brown patch and quality on tall fescue based upon: 1) several N sources applied at low or high annual rates, and 2) application or no application of a fungicide receiving all N sources and rates.
Table 1. Monthly average weather conditions in Olathe, Kan., from June through August 2023.
Materials and methods
This experiment was arranged on a blend of tall fescue that was seeded in 2019 at the Olathe Horticulture Research and Extension Center in Olathe, Kan. Soil type was a silty clay loam (pH 6.9). The cultivar blend included Corbett (25.14%), Falcon IV (24.97%), Rendition RX (24.95%) and Covenant II (24.42%). The design was a split-plot with fungicide treatment versus no fungicide treatment as the whole plot, and N sources and annual application rates as the sub-plots. Whole plots were replicated four times and measured 28 feet × 10 feet (8.5 meters × 3 meters), and individual sub-plots measured 5 feet × 7 feet (1.5 meters × 2.1 meters) and were arranged randomly within each of the whole plots. This experiment was conducted in 2022 and 2023, but the focus here will be on the more significant results that occurred in 2023. Weather conditions differed among months in 2023. Monthly high and low temperatures, rainfall and humidity are shown in Table 1.
Fungicide-treated areas of whole plots received azoxystrobin (Heritage G, Syngenta, Greensboro, N.C.) applied at 0.32 ounce per 1,000 square feet (0.98 kilogram per hectare) at 40 pounds per square inch and 87 gallons per acre (813.79 liters per hectare) using a hand-held sprayer on half of the fertilizer treated plots as part of the split-plot design. The other half did not receive fungicide treatment. Dates of azoxystrobin application were June 7 and July 14, 2023.
Fertilizers shown in Table 2 were applied on plots receiving low rates of N (1.5 pounds per 1,000 square feet/73.24 kilograms per hectare in September 2022) or high rates (1.5 pounds per 1,000 square feet in September 2022; 1 pound per 1,000 square feet in November 2022 and April and May 2023, for a total of 4.5 pounds per 1,000 square feet/219.71 kilograms per hectare per year), or non-treated (no fertilizer applied). Specific fertilizers evaluated were urea (46% nitrogen-0% phosphorus-0% potassium); humic-coated urea (HCU; 44-0-0; 2% humic coating by weight); and a combination of fast and slow-release [50:50 blend of 46-0-0 urea and 43-0-0 poly-coated sulfur-coated urea (4% sulfur coating)]. Specific dates of fertilizer treatments were as follows: Sept. 12 and Nov. 4, 2022; April 12 and May 26, 2023. In addition, N from the slow-release product was applied at 2.25 pounds per 1,000 square feet (109.85 kilograms per hectare) in September 2022 and April 2023 (Duration 43-0-0, poly-coated slow release).
Data collected were visual brown patch coverage, turf quality and normalized difference vegetation index (NDVI). Brown patch coverage was most predominant in summer 2023 and was rated visually on a scale of 0% to 100%. Turf quality was rated on a 1-to-9 scale, where 6 = acceptable quality (density, uniformity, texture, color) and 9 = optimum quality. Data for NDVI were recorded in August 2023 using Field Scout CM 1000 NDVI Meter (Spectrum Technologies, Aurora, Ill.).
Prior to the experiment, the tall fescue area received 1 pound N per acre from urea each September from 2019 to 2021. Mowing was conducted once weekly using a rotary mower at a height of 3 inches (7.62 centimeters). Irrigation was applied to prevent stress, and often when conditions were enhanced for brown patch, additional irrigation levels were applied. For example, during some weeks when rainfall had not occurred, irrigation was sometimes applied up to 2 inches (5.08 centimeters) per week to encourage brown patch. The preemergence herbicide prodiamine (Barricade 4FL, Syngenta, Greensboro, N.C.) was applied in April of 2022 and 2023 at 0.6 pound per acre (29.29 kilograms per hectare) to reduce arrival of annual grasses.
Data were subjected to analysis of variance using proc glimmix procedure in SAS 9.4. Whole plot errors were assigned as random effects for split-plot analysis. Treatment means were separated using Tukey-Kramer test at α ≤ 0.05.
Table 2. Fungicide × fertilizer interaction on brown patch, turf quality and NDVI on tall fescue in 2023.
Results
Highest levels of brown patch on tall fescue occurred in mid-summer 2023; over 6 inches (15.24 centimeters) of rainfall occurred in July in Olathe, which also enhanced the disease (Table 1). Results in 2023 clearly show the impact of nitrogen rates and sources on tall fescue brown patch (Table 2). A significant fertilizer level × N source interaction occurred for brown patch. In whole plots not receiving fungicide, high levels of N sources all resulted in higher levels of brown patch compared to those receiving no fertilizer. In addition, tall fescue receiving high levels of HCU were significantly higher in brown patch than those receiving high levels of urea on all dates in 2023 (up to 5% higher on July 14, 18.5% higher on July 21, and 35.3% higher on Aug. 10). Brown patch in HCU-treated plots was not significantly different than other N sources on July 14 but was 17.5% higher than slow-release N on July 21, 25.1% higher than the combination of fast- and slow-release N, and 18.1% higher than slow-release N on Aug. 10. It is possible that HCU was releasing more N to tall fescue in the summer, possibly due to heavy rainfall that occurred, but more research would be required to determine that. There were no significant differences among brown patch levels receiving different N levels or sources when treated with azoxystrobin.
Clearly, high levels of N among all sources provide the highest tall fescue quality when azoxystrobin was applied, and there were no differences among N sources. High levels of N applied without azoxystrobin resulted in high levels of brown patch (Figure 1). That said, there may be some consideration of specific N sources to use if no fungicide will be applied. Nitrogen sources had little effect on brown patch in perennial ryegrass in previous research. In Maryland, two locations were evaluated, and brown patch was affected on perennial ryegrass in one of three years at one of the two locations (3). A few N sources resulted in less brown patch than non-treated turf, including those receiving ammonium sulfate, Sustane (5-2-4 organic fertilizer) and Ringer Lawn Restore (10-0-6 organic fertilizer). In Nebraska, urea and sulfur-coated urea caused higher levels of brown patch compared to one another at different times, so N sources were not consistent on perennial ryegrass (6). In addition, lower brown patch severity occurred in perennial ryegrass receiving N at 8 pounds per 1,000 square feet (390.59 kilograms per hectare) per year compared to 2 or 4 pounds per 1,000 square feet (98 or 195.3 kilograms per hectare) per year in Nebraska. In Kansas research, higher N was more impactful on brown patch in tall fescue. That said, future research should consider additional N sources for reduction of brown patch on tall fescue if no fungicide will be applied.
Turf quality differences occurred more in non-fungicide-treated whole plots than those treated with azoxystrobin (Table 2). The only treatment that had acceptable quality was urea at a low level on Aug. 10, 2023. In fungicide-treated whole plots, nonfertilized tall fescue was below acceptable quality in all months. The low level of the slow/fast fertilizer combination was lower than acceptable on July 14, 2023, and low level of urea was lower than acceptable on July 21, 2023, in plots receiving fungicide treatment. All low- and high-level N treatments among sources had superior quality through the summer when treated with fungicide.
On Aug. 10, 2023, the only treatments that were higher than non-treated tall fescue for NDVI were non-fungicide-treated whole plots with urea at a low level and the slow-/fast-release N combination application at a low level (Table 2). Highest NDVI in fungicide-treated tall fescue on the same date was slow-release fertilizer (high rate), and those statistically equal were urea (high level), HCU (high level) and slow-/fast-release combination (high level).
Summary
Tall fescue was most susceptible to brown patch in midsummer, when temperatures and humidity were high, and rainfall was significant. Tall fescue receiving high levels of N (4.5 pounds per 1,000 square feet per year) was most susceptible to brown patch, and there were slight differences among N sources. To ensure high-quality tall fescue, high N levels are recommended in combination with preventive fungicide applications.
The research says
- Higher nitrogen application rates (4.5 pounds nitrogen per 1,000 square feet per year) resulted in significantly more brown patch on tall fescue than that receiving lower rates (1.5 pounds nitrogen per 1,000 square feet per year).
- Nitrogen sources that contained 50% or more slow-release nitrogen were comparable to the percentage of brown patch on tall fescue that received quick-release nitrogen (urea). Humic-coated urea at a high rate had higher brown patch levels than urea applied at a high rate.
- Highest tall fescue quality occurred with all nitrogen sources applied at a high rate when preventive fungicide applications were made during the summer.
Literature cited
- Butler, L.E., G.H. Galle and J.P. Kerns. 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(1):1-6 (https://doi.org/10.2134/cftm2019.03.0018).
- Dant, L.A., S.B. Martin, J.P. Kerns and L.B. McCarty. 2020. Nitrogen source impacts Rhizoctonia leaf and sheath spot severity in ultradwarf bermudagrass. International Turfgrass Research Journal 14(1):940-950 (https://doi.org/10.1002/its2.15).
- Fidanza, M.A., and P.H. Dernoeden. 1996. Influence of mowing height, nitrogen source, and iprodione on brown patch severity in perennial ryegrass. Crop Science 36(6):1620-1630 (https://doi.org/10.2135/cropsci1996.0011183X003600060035x).
- Fry, J., and B. Huang. 2004. Applied Turfgrass Science and Physiology. Wiley and Sons, Hoboken, N.J.
- Smith, D.L., and N.R. Walker. 2013. Fungicide management of brown patch on tall turf-type fescue in the residential landscape in Oklahoma. Plant Health Progress 14(1) (https://doi.org/10.1094/PHP-2013-1022-01-RS).
- Watkins, J.E., R.E. Gaussoin, K.W. Frank and L.A. Wit. 2001. Brown patch severity and perennial ryegrass quality as influenced by nitrogen rate and source and cultivar. International Turfgrass Society Research Journal 9:723-728.
Jack D. Fry is a professor and commercial turf Extension specialist in the Department of Horticulture and Natural Resources at Eastern Kansas Research and Extension Centers, Kansas State University, Olathe; Manoj Chhetri is an assistant teaching professor of turfgrass science in the Department of Plant Science at Penn State University, University Park, Pa.; and Ben Pease is a turfgrass agronomist for The Andersons Inc., Maumee, Ohio.