Tall fescue is the most widely planted turfgrass species in North Carolina, currently being managed on over 1 million acres in the state. This grass is preferred throughout the piedmont and mountain-valley regions due to its low maintenance requirements, tolerance to drought, and year-round green color. New turf-type varieties of tall fescue produce a dense, fine-textured stand that rivals the aesthetic quality of any other turfgrass species. However, tall fescue has one major weakness, and that is its susceptibility to brown patch, caused by the fungus Rhizoctonia solani. This disease causes significant damage to tall fescue landscapes nearly every year in North Carolina.
As the name implies, brown patch appears as roughly circular patches that are brown, tan, or yellow in color, ranging from 6" to several feet in diameter (Figure 1). The affected leaves typically remain upright, and lesions are evident on the leaves which are tan in color and irregular in shape with a dark brown border (Figure 2). When the leaves are wet or humidity is high, small amounts of gray cottony growth, called mycelium, may be seen growing amongst affected leaves in the turf canopy (Figure 3).
The months of June, July, and August tend to be the peak periods for brown patch activity in North Carolina. Warm nights combined with long periods of leaf wetness from afternoon thunderstorms, irrigation, or dew are ideal conditions for disease development. However, brown patch activity has been observed as early as March and as late as October. The disease may develop whenever night temperatures are consistently above 60°F combined with at least 10 consecutive hours of leaf wetness.
To make matters worse, the new turf-type varieties of tall fescue are generally more prone to brown patch than Kentucky 31, one of the first tall fescue varieties released in the United States. The dense canopy produced by the turf-types retains moisture and humidity for extended periods of time and enables the fungus to spread from plant to plant more easily. Due to the popularity of these turf-type varieties, effective management of brown patch is becoming more critical for landscape managers.
Although the turf-type tall fescues are generally more prone to brown patch than Kentucky 31, there is a wide range of susceptibility within the turf-type group (Figure 4). Turf-type varieties such as Falcon II, Millennium, and Endeavor exhibit good resistance to brown patch compared to highly susceptible varieties like Bonsai. Therefore, selection of a variety with improved brown patch resistance is an effective way to manage the disease long-term. Because tall fescue varieties change frequently, be sure to consult the National Turfgrass Evaluation Program (www.ntep.org) or Turffiles (www.turffiles.ncsu.edu) for the most up-to-date information when selecting a tall fescue variety.
Cultural practices also have a profound effect on brown patch development. Nitrogen fertilization, irrigation, and mowing are the most important factors to consider. For best results, tall fescue should be mown at heights between 2.5 and 3.5 inches. Brown patch can be encouraged by mowing heights that are either too low or too high. Mowing heights below 2.5" increase disease development by reducing the plant's ability to produce energy, whereas mowing heights higher than 3.5" create a turf canopy that is dense, matted, and holds moisture for extended periods.
Irrigation plays an important role because it serves as a source of leaf wetness, which the brown patch pathogen needs to infect tall fescue. Irrigation should not be applied just before sunset or just after sunrise - this will extend the duration of leaf wetness and encourage disease development. Instead, irrigation should be applied between midnight and 6 AM so as to avoid increases in leaf wetness. Also, irrigation should not be applied every day. Instead, irrigation should be applied "deep and infrequent", with sufficient water to wet the entire root zone every 3 to 4 days.
High levels of available nitrogen favor the spread of brown patch. Nitrogen induces tall fescue to produce soft, lush leaf tissue that is easily infected by the brown patch pathogen. Excessive foliar growth also results in a dense canopy that holds moisture and humidity for extended periods of time. It is important to note, however, that nitrogen does not cause brown patch to develop; it only makes the disease more severe. Many landscape managers are unfairly accused of causing brown patch to occur by fertilizing too much.
In general, tall fescue should not be fertilized with nitrogen in late spring or summer so as to discourage brown patch development. Following this type of program will result in yellowing and thinning of tall fescue during the summer as nitrogen is depleted from the soil. Turf in this condition is very resistant to brown patch, but is also not very pretty to look at! If fungicides are used to protect tall fescue from brown patch, then application of small amounts of slow-release nitrogen (= 0.25 lb N/1000 ft2/month) during the summer can help improve the quality of tall fescue turf. This practice, however, will encourage the development of other diseases, such as gray leaf spot and Pythium blight. Tall fescue that is fertilized during the summer should be monitored frequently for these diseases so that they may be controlled before widespread damage occurs.Selecting Fungicides for Brown Patch Control
Even with the use of a resistant variety and cultural practices, fungicides are often necessary to prevent unacceptable damage from brown patch. Several factors must be considered when selecting a fungicide. Cost is obviously one of the most important considerations. Fungicides vary tremendously in their cost per pound or per gallon (Table 2). However, since application rates vary as well, one must calculate the cost per 1000 ft2 or per acre in order to make an informed decision (Figure 5).
Several fungicide classes are available for brown patch control in tall fescue (Table 1). The choices are somewhat more limited in residential lawns because chlorothalonil, iprodione, and vinclozolin products are not labeled for application to these turf areas. All of the labeled fungicides provide good to excellent control of brown patch. However, they vary tremendously in residual control, or the number of days of disease control provided. Contact fungicides such as chlorothalonil and mancozeb are short-lived and must be reapplied every 7 to 14 days. The DMI, dicarboxamide, and benzimidazole fungicides are penetrant fungicides and provide longer-lasting control, up to 14 to 21 days.
Since the early 1990's, several new fungicide classes have been released on the turfgrass market. These new chemistries were developed in response to environmental concerns, and consequently are safe to the environment, highly effective, and provide extended periods of disease control. Two of these new fungicide classes - the QoIs (azoxystrobin, pyraclostrobin, and trifloxystrobin) and carboxamides (flutolanil) - are very effective for brown patch control and offer long periods of residual control, far exceeding those provided by the older classes described above.
Residual control is an important consideration for landscape managers, as it is not profitable or logistically feasible to apply fungicides every 7 or 14 days. The new QoI and carboximide fungicides represent a potential solution to this problem. However, landscape managers have been slow to adopt the use of these products due to a lack of specific recommendations for their use in tall fescue landscapes.Optimizing Application Rates for Brown Patch Control
In 2003 and 2004, field experiments were conducted in the Charlotte and Raleigh areas in an effort to develop specific recommendations for brown patch control in tall fescue. Our goals were to identify fungicides that provided 28 days of disease control and to identify the lowest possible rates that could be applied on this interval. Although some landscape managers may wish to apply fungicides more or less frequently, we have found that most desire a product that will reliably provide 28 days of control.
The experiments were initiated in early June of each year with an application of each tested product at the appropriate rate. Fungicides were applied in 3 gal H2O per 1000 ft2 with TeeJet 8004 nozzles operated at 40 psi. The treatments were then re-applied twice on 28 day intervals. The percentage of each 5' by 6' plot that was exhibiting brown patch symptoms was measured every 14 days from early June through late August.
2003 Results. Brown patch pressure was high during June of 2003, reaching a peak in early July (Figure 6). Untreated plots exhibited an average of 80% brown patch injury on 2 July. The fungicides 3336 and Eagle failed to provide significant suppression of brown patch on this date (Figure 7). SysStar (3 oz) and ProStar (3 oz) provided the best brown patch control in this trial, maintaining brown patch incidence to 1% or less. Insignia (0.9 oz) and Heritage (0.2 oz) both maintained brown patch to less than 5%, which can be considered a typical damage threshold for most tall fescue landscapes. Also providing good brown patch control were Insignia (0.5), Compass (0.25 oz), and Heritage (0.1). Banner Maxx (2 fl oz), Bayleton (1 oz), and Compass (0.15 oz) did not provide acceptable control of brown patch in 2003.
2004 Results. Based on the 2003 results, more trials were conducted in 2004 to identify the lowest possible rates of ProStar, SysStar, and Insignia that would provide 28 days of brown patch control (Figure 8). In 2004, Heritage (0.2 oz) was the only treatment to provide 100% control of brown patch. ProStar (2.25 oz), Insignia (0.9, 0.7, and 0.5 oz), and Heritage (0.1 oz) also maintained brown patch below 5%. Reduced rates of SysStar (2.25 and 1 oz) and ProStar (1.5 and 1 oz) provided good brown patch control but did not maintain disease incidence below 5%.
In our trials, Insignia, Heritage, ProStar, and SysStar have proven to be the most effective for control of brown patch in tall fescue when applied on 28 day intervals. Heritage applications at the low label rate (0.2 oz/1000 ft2) have consistently provided excellent control of brown patch for 28 days. Applications at half of the low label rate (0.1 oz/1000 ft2) also show some promise, however, additional research is needed before we can recommend this rate for use in the field.
ProStar and SysStar are very effective brown patch products when applied at the high label rates (3 oz/1000 ft2). Reduced rates of ProStar, down to 2.25 oz/1000 ft2 have also provided excellent control, whereas reduced rates of SysStar have not been effective. This can be explained by the higher flutolanil content in ProStar (70%) than in SysStar (51%).
Insignia is the newest addition to the QoI fungicide family and recently received approval for application to landscape turfgrasses. The 0.7 and 0.9 oz per 1000 ft2 rates of this product have consistently provided good control of brown patch when applied on 28 day intervals. The 0.5 oz rate has been less consistent, but may be an option when disease pressure is low or where a brown patch resistant variety has been planted.
Of the QoI fungicides, Compass provides the shortest residual control and has not provided 28 days of brown patch control in our trials. It is important to note that the Compass label recommends applications on 21 day intervals, and the product is very effective when applied on these shorter intervals. This product represents an additional option for landscape managers if applications are made on shorter intervals. However, analysis of cost per day (Table 2) demonstrates that Heritage or Insignia applications on 28 day intervals are more cost-effective than Compass applications in 21 day intervals.
Although much less common than brown patch, Pythium blight and gray leaf spot warrant consideration when developing a fungicide program for tall fescue landscapes. The QoI and benzimidazole fungicides provide excellent control of gray leaf spot, but the carboxamides have no activity against this disease. Heritage, Compass, Insignia, or SysStar would therefore provide excellent control of both gray leaf spot and brown patch. Unfortunately, the fungicides that are used for brown patch control have little to no activity against Pythium blight. Heritage and Insignia have some Pythium activity but will only suppress the disease for 7 to 10 days. Since the development of Pythium blight is very unpredictable, the best strategy for management of this disease is to monitor frequently and apply a true Pythium fungicide, such as mefanoxam (Subdue Maxx, Mefanoxam) or propamocarb (Banol) when disease activity is detected.**April 2005