© 2013 Plant Management Network.
Fungicide Management of Brown Patch of Tall Turf-type Fescue in the Residential Landscape in Oklahoma
Damon L. Smith, Department of Plant Pathology, University of Wisconsin, Madison, WI, 53706; and Nathan R. Walker, Department of Entomology and Plant Pathology; Oklahoma State University, Stillwater, OK 74078
Smith, D. L., and Walker, N. R. 2013. Fungicide management of brown patch of tall turf-type fescue in the residential landscape in Oklahoma. Online. Plant Health Progress doi:10.1094/PHP-2013-1022-01-RS.
In the transition zone of the USA, cool-season grasses such as tall fescue are often planted in shaded areas, where warm-season grasses are less adapted. The most damaging disease of tall fescue is brown patch, caused by Rhizoctonia solani. Fungicide applications and cultural practices are often used to manage brown patch in this region. A three-year study was implemented in Oklahoma to evaluate ready-to-use fungicides available to residential lawn owners and compare these to several common commercial fungicide formulations used by professional lawn care applicators. A selection of fungicides representing products commonly available to the residential market and commercial standards were applied to small plots of tall fescue or tall fescue/Kentucky bluegrass mixtures from 2008 to 2010. All products tested, with the exception of azoxystrobin, provided limited or inconsistent control of brown patch and resulted in lower turfgrass quality in all years. Further examination of carrier type (granular vs. liquid) and timing (preventive vs. curative) did not result in strong differences in the level of brown patch control or overall quality. These studies suggest that control of brown patch in tall fescue in the transition zone should focus on integrated disease management principals and not only on applications of fungicides directed at the residential market.
In transition zone locations such as Oklahoma, many warm-seasons grasses do not grow well in shaded landscapes due to limited light, and cool-season grasses such as tall fescue [Schedonorus phoenix (Scop.) Holub. syn. Festuca arundinacea], mixtures of tall fescue and perennial ryegrass (Lolium perenne L.), Kentucky bluegrass (Poa pratensis L.), or a combination of all three grasses, are commonly grown (13). Typically, these stands grow well in spring and fall months when heat stress does not limit plant growth. During the summer months, stands of tall fescue in residential areas are not only stressed by heat and low light levels but also competition from trees, reduced air movement, and disease. During summer months, taller mowing heights (3 inches) are recommended to reduce the effect of heat stress on plants (13,17). Yet, stands of tall fescue may still experience a decline in plant density and appearance that can be caused by many factors including diseases caused by fungi or Oomycetes.
In the southern US transition zone, the most common and destructive disease of tall fescue is brown patch caused by Rhizoctonia solani AG 2-2 IIIB (Kuhn) (17). In stands of cool-season grasses, brown patch can appear as light-brown, circular or irregular patches. Under moist conditions, tufts of white mycelium develop on affected leaves and will often spread from one leaf to another. Leaf lesions caused by brown patch are straw-colored and have a dark-brown margin between healthy green tissue and dead tissue. Rhizoctonia solani is a soil-inhabiting fungus that can survive unfavorable weather or the absence of a host by forming survival structures such as bulbils or sclerotia (17). Brown patch is favored by night temperatures of >16°C and either high humidity or 10 h or more of leaf wetness (4,5). When conditions are favorable, brown patch epidemics can kill large portions of a turfgrass stand resulting in reduced quality and weed encroachment (8).
Brown patch has been reported to be more severe on tall fescue grown in shade because it may induce morphological and physiological changes in the plants (20). In addition, shade increases the leaf wetness duration resulting in an increase in brown patch severity. Modern varieties of tall fescue often have greater leaf densities, much reduced leaf widths, and are planted at greater plant densities. Giesler et al. (9) found that tall fescue canopy density influenced the severity of brown patch and stands that had greater leaf blade densities typically had more severe disease. Blade proximity and micro-environmental conditions were responsible for the increased severity of brown patch observed in the denser stands (10). Residential stands of tall fescue often receive excessive rates of nitrogen fertilizer at inappropriate times to promote a desirable dark green appearance. Burpee showed that increasing rates of nitrogen fertilizer resulted in an increase in severity of brown patch (3).
Integrating management strategies to control turfgrass diseases are more successful than applying a single management approach. Current integrated management of brown patch relies on reducing the period during which plants are exposed to free moisture or high humidity. For example, preventing excessive irrigation and encouraging good water drainage reduces leaf wetness and humidity in the microenvironment, thereby potentially reducing the severity of brown patch. Additional integrated approaches include applying recommended rates and properly timed applications of nitrogen fertilizer, using cool-season turfgrasses with disease resistance, adjusting mowing height to reduce plant stress, and using preventive fungicide applications.
Genetic resistance to brown patch in tall fescue has been identified but is limited with very few varieties offering acceptable disease control (5). Many resistant cultivars are not desirable as turfgrasses due to excessive leaf width (11). In tall fescue, single-gene resistance to brown patch has not been observed, instead host-plant resistance to this disease is quantitatively inherited and is stable over multiple environments (1,2). However, cultivars with excellent genetic resistance to brown patch and also having fine leaf texture may not be adapted to all regions or commercially available. Therefore, the dependence on fungicide applications is important for the management of brown patch of tall fescue.
Successful management of brown patch in residential lawns has unique challenges. Often owners of residential lawns will select or establish a tall fescue cultivar that is not well adapted to a particular region. When quality or health issues with the stand are observed, homeowners often increase nitrogen fertilizer rates or increase irrigation volume and frequency in an attempt to improve appearances, but ultimately encourage brown patch and abiotic stress. When mismanagement issues are corrected, fungicide applications may still be required to reduce the severity of brown patch.
Several different groups of fungicides based on the Fungicide Resistance Action Committee (FRAC) including multisite contact fungicides (FRAC class M), fungal mitosis (FRAC class 1) and cell wall division (FRAC class 19) disrupters, sterol demethylation (FRAC class 3), quinone outside (FRAC class 11), or succinate dehydrogenase (FRAC class 7) inhibiting fungicides are registered for brown patch management for turfgrasses (12). However, not all of these fungicides are labeled for use on residential lawns. Most fungicides promoted to residential lawn owners are demethylation inhibitors. This class of fungicides has activity on a wide spectrum of plant pathogenic fungi. However, these fungicides have variable activity against R. solani. The FRAC class 11 and 7 compounds are considered to have excellent efficacy on R. solani (12). However, the FRAC class 11 and 7 compounds are not widely available as residential formulations.
Fungicides are often specially formulated for residential consumers for use in residential landscapes and differ from those used by commercial applicators. The common difference is that fungicide formulations marketed to residential consumers typically include either ready-to-use liquid or granular formulated fungicides versus concentrated liquid formulations typically applied by commercial applicators in the form of a low carrier volume spray. Many residential-type fungicides are formulated for subsequent dilution in water at the time of use and applied with a sprayer; however, these sprayers are often of insufficient size to treat the entire turfgrass stand. A water hose-end applicator can be used in place of a low volume sprayer; however, these devices deliver large quantities of water that may encourage brown patch development. Granular fungicides address some of the common issues with water-delivered fungicides but generally have poor distribution in the stand versus fungicides that are sprayed (12). Another common problem with residential lawn owners applying pesticides is the lack of proper calibration of equipment. Occasionally, homeowners will contract with commercial applicators to perform fungicide applications, which often results in greater cost of managing brown patch. Therefore, many homeowners will attempt to control brown patch themselves using ready-to-use, over-the-counter fungicides. The objectives of this study were to evaluate ready-to-use fungicides (liquid or granular carrier) available for application to residential lawns and compare these to commercial fungicide formulations used by professional lawn care applicators. In addition, the effects of fungicide application timing (before brown patch symptoms were observed vs. after brown patch symptoms were observed) for brown patch management was also investigated. Portions of the work have been previously documented (18,19)
Field Studies Evaluating Fungicide Effectiveness for Control of Brown Patch of Tall Fescue Turfgrass
Field studies were conducted from 2008 to 2010 at the Oklahoma State University Turfgrass Research Center in Stillwater, OK. In 2008, plots were established on a Norge loam soil. The turfgrass sward was a mature mixture of tall fescue cvs Rembrandt, Picasso, Masterpiece, and Kentucky bluegrass cv Ryce. In 2009 and 2010 plots were established in a mature stand of tall fescue cv Rebel IV that was planted to an Easpur loam soil. All plots were 0.91 m (3.0 ft) wide and 2.44 m (8.0 ft) long with 0.60-m (2.0-ft) alleys between plots. Plots used in 2008 received much longer morning shade, due to the presence of a large planting of trees on the east side of the plots, while those in 2009 and 2010 received longer late day shade due to the presence of a large tree planting on the west side of the plots. The experimental design was a randomized complete block with five replications in 2008 and four replications in 2009 and 2010. Mowing height was 7.5 cm (3.0 inches) and irrigation was applied as needed to maintain an environment favorable for the disease. Recommended turfgrass management practices were followed throughout the growing season (13).
Fungicides were applied preventively before symptoms of brown patch (starting 3 July 2008, 26 June 2009, and 11 June 2010) or curatively after 5% of the stand had distinct straw-colored patches of grass indicative of brown patch caused by R. solani (starting 21 July 2008, 24 July 2009, and 25 June 2010). Application intervals varied according to product used and the year of study. Fungicides registered and available for residential use were compared to the commercial fungicides and a non-treated control. Liquid carrier fungicides were applied with a CO2-pressurized wheeled sprayer equipped with TX8008 flat fan nozzles and calibrated to deliver 814 liters/ha (2 gal/1000 ft²). Granular carrier fungicides were pre-weighed and broadcast by hand. The experimental areas had either natural or previously inoculated infestations of R. solani. To provide more uniform disease the areas were inoculated each year after the first preventive treatments were applied by broadcasting wheat grain (approximately 300 gm) colonized with an isolate of R. solani AG2-2 IIIB. Disease severity or the visual estimation of percent of plot area with symptoms of brown patch was rated weekly during the brown patch epidemics. Turfgrass quality was rated on a scale of 1-9 where: 1 = no turf present; 5 = unacceptable turfgrass; 6 = acceptable turf; 9 = dense, dark color, thick stand of turfgrass ratings were also taken weekly.
Disease severity data were subjected to the area under the disease progress curve (AUDPC) transformation to account for season-long ratings (16). Due to weather and disease severity differences between studies in each year, all analyses were performed separately for each season. Standardized AUDPC was also calculated for each year by dividing the AUDPC for each plot by the epidemic duration within each year (6). Standardized area under the disease progress curves (STAUDPC) were subjected to an analysis of variance using the mixed procedure (PROC MIXED) and the RANDOM statement of the SAS statistical system (v 9.3, SAS Institute Inc., Cary, NC). Separation of least-squares means (α = 0.05) was performed using a freely available macro (14). Turfgrass quality data were analyzed using non-parametric techniques because of the ordinal nature of the rating scale (15). First, overall turfgrass quality for each plot was determined by calculating the average of weekly ratings for each plot. Overall turfgrass quality data were ranked from lowest to highest using the RANK procedure (PROC RANK) of SAS. The rank transformed data were analyzed using the ANOVAF option of the mixed procedure (PROC MIXED) and the ANOVA-type test statistic was used to test the null hypothesis that fungicide treatments had no effect on turfgrass quality. Estimated relative effects and confidence intervals were calculated by invoking the ld_ci.sas macro freely available from E. Brunner (University of Göttingen, Germany) as described by Shah and Madden (15). Single-degree-of-freedom contrast statements (P = 0.05) were also generated using the least-squares means of STAUDPC and quality ranks for only the plots that received azoxystrobin (Heritage G and Heritage 50WG) in 2009 and 2010. Contrast statements were used to test the effects of preventative vs. curative treatments and liquid vs. granular carrier.
Weather conditions varied for each year with 2008 having weather conditions that were initially cool with low humidity and limited precipitation followed by hot and very humid conditions with above-average rainfall. In 2009, weather conditions were unseasonably cool and wet and generally were not favorable for disease. In 2010, weather conditions were again wet and cool but then transitioned to unseasonably hot and dry, which persisted for the remainder of the study. For all years, there was a significant fungicide treatment effect on the progression of brown patch epidemics (Table 1). In 2008 and 2009, disease severity in non-treated check plots was similar to many of the fungicide treated plots (Figs. 1 and 2). In both years, severity was significantly greater in plots preventively treated with propiconazole (Fertilome Liquid Systemic Fungicide) at 0.94 kg a.i./ha than the non-treated control. The application rate of propiconazole used for this product targeted for the homeowner market was the same as the highest labeled application rate for Banner MAXX (Syngenta Professional Products, Greensboro, NC), another propiconazole formulation available to professional turfgrass managers. Similarly plots preventively treated with myclobutanil (Spectracide Immunox Lawn Disease Control) at 0.65 kg a.i./ha had a higher brown patch severity compared to non-treated plots in 2009.
Table 1. Mean squares (MS) and F values from analyses of variance for the random effect of replicate (Rep) and the fixed effect of treatment on the progress of brown patch epidemics on tall fescue or bluegrass/tall fescue mixtures during three seasonsy.
y Analysis of variance performed on data transformed
using the area under the disease progress curve, standardized within each year
by the epidemic length. z
zF values: ** = significance at the P ≤ 0.01 level.
Disease severity was greatest in 2010. Plots treated preventively with a water dispersible granule formulation of azoxystrobin (Heritage 50WG) at 0.33 kg a.i./ha had less disease than the non-treated plots and all other treatments, with the exception of plots preventively treated with a granular formulation of azoxystrobin (Heritage 0.31G) at 0.30 kg a.i./ha (Fig. 3). In 2010, plots treated curatively with propiconazole (Fertilome Liquid Systemic Fungicide) and myclobutanil (Spectracide Immunox Lawn Disease Control) had the greatest brown patch severity. However, brown patch severity in these plots was not greater than the non-treated plots.
Mean turfgrass quality evaluations were significantly different among treatments in 2008 (P < 0.01). Plots treated preventively or curatively with azoxystrobin (Heritage 50WG) had a higher mean turfgrass quality than all other treatments (Table 2). Mean turfgrass quality in all other treatments was similar to the non-treated check. No significant differences in mean quality were observed among treatments in 2009 (P = 0.21; Table 3) or 2010 (P = 0.16; Table 4).
Turfgrass STAUDPC and mean season-long quality were examined further to answer the null hypotheses that there were no differences between preventive and curative applications and between liquid and granular formulations for products containing azoxystrobin (Heritage G and Heritage 50WG) in 2009 and 2010. Only in 2010 was there a significant difference in liquid vs. granular carrier (Table 5). During the 2010 growing season there was significantly higher disease severity in plots treated with azoxystrobin on a granular carrier vs. azoxystrobin applied as a liquid. While not significantly different, mean quality was higher in plots that received azoxystrobin as a liquid compared to azoxystrobin applied in granular form.
Table 5. Single-degree-of-freedom contrasts testing effects of application timing and fungicide carrier type for products containing azoxystrobin (Heritage G and Heritage 50WG) on control of brown patch of tall fescue in 2009 and 2010
v Area under the disease progress curve divided by the duration of the brown patch epidemic each season.
w Mean ranks of mean season-long quality for treatments in each season.
x Standard error of estimated differences.
y F values: * = significance at the P ≤ 0.05 level; ns = not significant at the P ≤ 0.05 level.
z Preventative = fungicide applied before symptom appearance; Curative = fungicide applied after symptom appearance
The integrated management of lawn diseases includes the use of cultural, physical, and chemical management strategies. In this study the primary objectives were to evaluate the differences in fungicides available for residential lawns and to determine if carrier type (liquid or granular) and application timing influenced the control of brown patch of tall fescue. Based on these studies, the fungicide products widely available for residential use did not provide significant disease control over not treating with a fungicide. Only azoxystrobin (a FRAC class 11 active ingredient) in formulations not readily available to homeowners provided consistent control of brown patch relative to non-treated turf. In both 2008 and 2009 preventive applications of propiconazole, resulted in higher brown patch severity than not treating. Greater brown patch severity on tall fescue treated with Cycloheximide-thiram or Triphenyltin hydroxide fungicides has been previously reported (7). It was suggested that fungicide resistance was the cause for the increased brown patch severity. However, in those studies propiconazole did not increase brown patch and provided adequate control. For the R. solani used in these studies, no in vitro fungicide resistance was detected (data not shown). The reason for this disease response in this study is not clear. Homeowners should be advised that application of consumer-grade formulations of fungicides containing propiconazole for control brown patch may increase disease. In addition, the carrier type (liquid or granular) had a marginal effect on level of brown patch in tall fescue. Furthermore, treating preventively did not offer a significant advantage over treating curatively.
Considering the results, recommendations for residential lawns for control of brown patch in tall fescue in the transition zone should focus on integrated disease management principals and less on fungicide use. Homeowners should reduce or remove the conditions that promote brown patch. If brown patch occurs, reseeding of tall fescue stands with a grass species or mixtures of grass species better adapted to a particular region should be advised over applying a consumer-grade fungicide product. If a fungicide program is desired, homeowners should be urged to use a certified lawn applicator with the capability of applying a product containing the active ingredient azoxystrobin. Finally, turfgrass breeders should focus on developing improved tall fescue cultivars with high levels of brown patch resistance and desirable agronomic qualities that are adapted to a particular region.
Published with the approval of the Director, Oklahoma Agricultural Experiment Station, Stillwater, OK. This project was supported in part the Oklahoma Agricultural Experiment Station projects 2420 and 2667. The authors thank K. J. Black for technical assistance with this study. The mention of trade names or commercial products in this publication does not imply recommendation by Oklahoma State University or The University of Wisconsin.
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