Managing brown patch in tall fescue
Tall fescue (Festuca arundinacea) is widely used in the Transition Zone because it has relatively good drought and heat tolerance and is easy to establish from seed. The most common and important disease of tall fescue in this region is brown patch, caused by the fungus Rhizoctonia solani. Brown patch is primarily a mid-summer disease, but may occur anytime when night temperatures exceed 70°F and grass blades remain wet for periods of 10 hours or longer. Pythium blight, caused by Pythium aphanidermatum, also damages tall fescue during hot, wet, summer weather, but is not as common as brown patch in the northern Transition Zone.
Limited landfill space and the growing cost of waste disposal have increased the practice of returning grass clippings to the sward, often termed “grasscycling.” The influence of grasscycling on the development of brown patch and Pythium blight in tall fescue has not been determined. However, returning clippings has been shown to increase brown patch and Pythium blight in other turfgrasses, so it's possible that recycled grass clippings may provide a source of inoculum for disease development in tall fescue as well.
Irrigation timing and frequency may also affect brown patch development. Nighttime irrigation has been shown to promote brown patch. In one study at Kansas State University, we found that daily, early morning irrigation reduced brown patch in perennial ryegrass maintained under golf course fairway conditions compared to irrigation three days a week.
Fungicides are not routinely applied to control diseases in home lawns because of cost considerations. Labor costs increase due to the requirement for frequent scouting to determine if disease is present, and some fungicides may provide only 14 to 21 days of control, so multiple applications may be necessary. It is possible, however, that azoxystrobin (Syngenta's Heritage) and flutolanil (Aventis' Prostar), which are longer residual fungicides, may provide brown-patch control without increasing labor costs. Plus, the effectiveness of post-infection applications of chlorothalonil (Syngenta's Daconil Ultrex, whose registration for residential use was removed after the start of this study) for brown patch control deserved further study.
Because it generally occurs less frequently than brown patch, Pythium blight is not typically the target of fungicide applications on tall fescue lawns. However, it does occur in many instances, so we felt this deserved scrutiny as well.
The Kansas State study
To better define the effects of various cultural practices on brown patch occurrence in tall fescue, as well as explore whether certain fungicides are viable control options, we conducted a two-year study at Kansas State University. Our goals were to evaluate the effect of irrigation frequency (daily vs. every other day), clipping removal (collecting clippings vs. grasscycling) and fungicide application strategies on brown patch and Pythium blight development in tall fescue. We conducted the study at the Rocky Ford Research Center in Manhattan, Kan., during the summers of 1998 and 1999.
The tall fescue was comprised of a blend of 20 percent ‘Tomahawk’, 20 percent ‘Apache II’, 20 percent ‘Coronado’, 20 percent ‘Safari’, 15 percent ‘Barlexas’, and 5 percent ‘Tar Heel’ that had been seeded in September, 1997. The turf received 1 pound of nitrogen per 1,000 square feet from urea in September, October, April, May and June 1998 and 1999.
Irrigation was applied to replace water lost through evapotranspiration (ET) in 1998. In 1999, daily-irrigated turf received 0.2 inches per day, whereas turf irrigated on alternate days received 0.4 inches at each watering.
Clipping management treatments were set within irrigation blocks. Both subplots were mowed with a rotary mower every three to four days at a height of 3.5 inches.
One problem with incorporating fungicide treatments into lawn-servicing routines is the need for regular, frequent applications. Thus, we selected two fungicides known to have relatively long residual to see if application intervals could be extended. We applied fungicides within each mowing treatment, consisting of:
A preventive application of Heritage 50WG at 0.2 ounces per 1,000 square feet, at 35-day intervals (this is longer than recommended on the label).
A preventive application of ProStar 70WP (evaluated in 1999 only) at 2.2 ounces per 1,000 square feet, at 35-day intervals (this also is longer than recommended on the label).
A post-infection application of Daconil Ultrex 82.5DG at 4 ounces per 1,000 square feet, within 12 hours of the visible appearance of brown patch. Post-infection applications continued at two-week intervals during brown patch activity (i.e. when an increase in blighting had occurred since the last rating).
Heritage and ProStar were applied preventively every 35 days beginning May 29, 1998 and June 4, 1999. Post-infection treatments of Daconil Ultrex were applied on July 3 and 28, 1998, and June 24, July 26 and August 30, 1999. An untreated control was also included. Fungicides were applied with a CO
Plots were rated weekly for brown patch and Pythium blight. Disease development was a result of natural infection — we made no attempt to artificially inoculate the turf.
In 1998, a single, severe brown patch epidemic occurred beginning July (see figure 1, page 58), followed by two minor Pythium blight outbreaks in early August and September. In 1999, three moderate brown patch outbreaks resulted in blighted turf from mid-June through mid-September. Pythium blight also occurred from late July through early September.
For years, turf managers have been instructed to irrigate deeply and infrequently to maintain good turf quality and reduce diseases. In our experiment, we did not detect differences in brown patch severity between daily and alternate day irrigation regimes. Therefore, it appears that the timing (i.e. morning vs. evening) and not frequency of irrigation has a larger impact on brown patch development. For example, nightly watering will likely extend leaf wetness duration and increase brown patch severity.
We hypothesized that daily, early morning applications of water might actually decrease brown patch by removing dew and guttation droplets from tall fescue leaves and hasten early morning leaf drying. This also turned out not to be the case. The higher mowing heights and dense canopy structure of tall fescue may have prevented efficient dew removal and rapid drying of leaves following early morning irrigation.
The use of mulching mowers that return clippings to the sward is recommended, especially in higher mowed turfgrasses in residential landscapes, because it recycles nutrients contained in leaf blades and reduces the disposal of clippings in landfills. However, concern exists that returning diseased clippings may increase the severity of certain fungal diseases. Further, the nitrogen contained in clippings could stimulate turf growth and encourage either brown patch or Pythium. We did not observe increases in brown patch or Pythium blight in tall fescue associated with grasscycling.
Three Heritage applications at 35-day intervals beginning in early June provided almost complete control of brown patch in each year (see Figure 1, page 58). Periodic preventive applications of Heritage could be integrated into existing landscape maintenance programs relatively easily because turfgrass managers often return to residential lawns at four to five week intervals for fertilizer, herbicide or insecticide applications.
ProStar prevented brown patch for about 3 to 4 weeks, and then infection increased. Therefore, a more frequent 21- to 28-day schedule would be required with ProStar (as recommended on its label).
Heritage is currently labeled for control of Pythium on various turfgrass species. However, we found that Heritage treatments increased Pythium blight on tall fescue in both years and especially in daily irrigated plots in 1999. It is possible that the low rates and extended application intervals of Heritage that we used were not sufficient to suppress Pythium blight. (Heritage is labeled for Pythium control at 0.4 ounces per 1,000 square feet with a 10 to 14 day schedule — our applications used 0.2 ounces.) However, turf treated with Heritage was more dense (based on tiller counts) in mid-summer than either the Daconil Ultrex-treated or untreated plots, probably as a result of superior brown patch control. Lush, dense turf favors Pythium blight development, so this may have been a contributing factor.
Post-infection fungicide applications are commonly used by turf managers to control brown patch on tall fescue in residential landscapes. In our study, tall fescue often exhibited more than 10 percent blighting before a post-infection application could be made. While post-infection applications of Daconil Ultrex (no longer labeled for residential lawns) suppressed further brown patch development, the overall damage to the plots was still unacceptable. This lack of control would likely be true for any fungicide used in a post-infection schedule because of the lag time between infection and symptom development.
Brown patch and Pythium blight resulted in greater than 10 percent turf blighting for three or more weeks during a four-month period in each year of the study. This level and duration of blighting may be unacceptable in high-maintenance lawns. However, for homeowners that can tolerate severe levels of blighting, we found that turf exhibited complete recovery the following spring even when no fungicides were used. Hence, neither brown patch nor Pythium blight outbreaks resulted in death of turfgrass crowns in our study.
To summarize, lawn-care operators have three options when it comes to brown patch management in tall fescue lawns.
Customers who are willing to accept the temporary loss of turf quality associated with severe (more than 50 percent) blighting can decide to use no fungicides. Although severe blighting may occur, we observed good recovery in the fall and spring following the disease outbreak.
A post-infection fungicide application may save expenses on chemicals (compared to a preventive schedule) but could increase labor associated with frequent scouting. Further, customers should be prepared to tolerate a moderate level of blighting (20 to 50 percent) when this strategy is employed. Another consideration is that some of the most effective post-infection fungicides, such as Daconil Ultrex and Chipco 26019, are no longer labeled for use on residential lawns (though several others remain available).
Customers that demand high quality throughout the summer may be willing to cover the cost of a preventive fungicide schedule. We observed that Heritage applied every 35 days provided excellent brown patch control. Be aware that if turf is mowed at less than 2 inches and irrigated frequently, Pythium blight may increase using this strategy. ProStar could also be used in a preventive program, but a more frequent application schedule would be required (every 21 to 28 days).
Finally, brown patch was not influenced in our study by irrigation frequency (daily vs. alternate day) or how clippings are managed (collected or grasscycled).
Dr. Jack Fry is professor of turfgrass science; Derek Settle is a graduate research assistant; and Dr. Ned Tisserat is professor of turfgrass pathology, all at Kansas State University (Manhattan, Kan.).
This research was sponsored, in part, by the Kansas Turfgrass Foundation.
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