Crop Science 41:1207-1211 (2001)
© 2001 Crop Science Society of America
TURFGRASS SCIENCE
Severity of Gray Leaf Spot in Perennial Ryegrass as Influenced by Mowing Height and Nitrogen Level
D. W. Williams*,a,
P. B. Burrusa and
P. Vincellib
a Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40546
b Dep. of Plant Pathology, Univ. of Kentucky, Lexington, KY 40546
* Corresponding author (dwilliam{at}ca.uky.edu)
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ABSTRACT
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Gray leaf spot [Pyricularia grisea (Cooke) Sacc.] has become a great concern for turf managers. Large losses of perennial ryegrass (Lolium perenne L.) turf caused by P. grisea epidemics have occurred in recent years. This field study was conducted to investigate the effects of two maintenance practices on the severity of gray leaf spot in perennial ryegrass managed as golf course fairways and roughs. The study was initiated in 1998 and repeated in 1999 at Lexington, KY. Treatments were two mowing heights (1.9 and 6.4 cm) with a split-plot treatment of monthly applications of water-soluble nitrogen (N) fertilizer between April and August at rates of 0, 36.6, and 73.2 kg N ha-1. Disease severity was rated visually as the percent of plot area blighted, and areas under disease progress curves (AUDPC) were compared statistically. There were no significant interactions (P 
0.05) between mowing heights and N rates in either year. In both years, AUDPC data showed no significant differences (P 0.05) due to the effects of mowing heights. The effect of N fertility was significant (P 
0.05) for both years. Plots treated with the highest N rate had significantly more gray leaf spot than those treated with the lowest N rate. Data indicated that turf managers may expect gray leaf spot to be equally severe between 1.9- and 6.4-cm mowing heights, and that applications of water-soluble N prior to or during environmental conditions conducive for gray leaf spot development should be avoided.
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INTRODUCTION
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GRAY LEAF SPOT has become a very important disease in perennial ryegrass turf. Serious epidemics have caused large losses of perennial ryegrass managed as fine turf throughout the mid-Atlantic and transitional climatic zones in the USA (Landschoot and Hoyland, 1992; Uddin et al., 1999; Vincelli, 1999). In Kentucky, the most serious losses occur in turf managed on golf courses, as opposed to athletic fields or home lawns. This is likely due to differences in the level of management practices found among these specific uses of turf.
Pyricularia grisea has long been known as a pathogen of several grass species. The fungus causes rice (Oryza sativa L.) blast, gray leaf spot of tall fescue (Festuca arundinacea Shreb.), perennial ryegrass, and St. Augustine grass (Stenotaphrum secudatum L.), and other species (Couch, 1995).
Trevathan (1982) reported significant differences in susceptibility among 315 cultivars of either Italian ryegrass (Lolium multiflorum L.) or perennial ryegrass to one isolate of P. grisea. Current evidence suggests that little natural resistance to P. grisea exists among available turf-type perennial ryegrass germplasms (Hofmann and Hamblin, 2000; Vaiciunas and Clarke, 1998).
Trevathan et al. (1994) investigated gray leaf spot of perennial ryegrass grown as a forage crop. They reported that 26°C was the optimum temperature for disease development along with extended periods of leaf wetness. They also reported increased disease incidence on younger plants relative to mature stands. They concluded that delaying late summer plantings of perennial ryegrass in to the autumn would reduce the potential for severe damage.
Landschoot and Hoyland (1992) described a serious gray leaf spot epidemic on perennial ryegrass fairways in southeastern Pennsylvania. Uddin et al. (1999) also reported another epidemic on golf fairways in Pennsylvania in 1998. A very serious epidemic was experienced in central Kentucky in 1995 (Vincelli, 1999). Early symptoms were patches of reddish-bronze to brown turf generally a few centimeters in diameter. Individual leaves showed either brown or gray lesions, sometimes surrounded by a dark brown halo. Additionally, bud leaves were observed to be wilted or twisted near the top, giving a fishhook appearance. Most tillers were killed during this epidemic. Total renovation of fairways was required on one golf course because of the destructive nature of the disease. Other smaller, less damaging outbreaks of gray leaf spot also have been noted in Kentucky. We have observed that most damage from gray leaf spot occurs from mid- to late August through September in most years. This is the optimum time of year for reseeding and/or renovation activities, as well as the first substantial application of N as part of an autumn fertility program for cool-season grasses. Both of these situations are typical causes for applications of water-soluble N at rates as high as 73 kg N ha-1.
Perennial ryegrass managed as golf turf may be considered to be under high or intensive maintenance. Two common cultural practices that turf managers can easily manipulate are mowing height and N fertility. Both of these practices are known to have significant effects on the severity of other fungal diseases. Applications of water-soluble forms of N may reduce the severity of dollar spot (Sclerotinia homoeocarpa F.T. Bennett) (Williams et al., 1996) and red thread [Laetisaria fuciformis (McAlpine) Burds.] (Couch, 1995). Conversely, high N fertility may enhance brown patch (Rhizoctonia solani Kühn) (Couch, 1995). Lower mowing heights can place additional stress on turf during summer, resulting in increased disease severity (Smiley et al., 1993). Mowing height also may have an impact on the microenvironment within the turfgrass canopy. Taller canopies may maintain higher levels of humidity within the lowest canopy regions for longer periods of time, which can be a more suitable environment for pathogen activity (Giesler et al., 2000). Moss and Trevathan (1987) reported an exponential increase of gray leaf spot lesions on perennial ryegrass with increasing periods of leaf wetness up to 24 h. Uddin et al. (1997) tested the effects of temperature and leaf wetness duration on the incidence of gray leaf spot on tall fescue. They reported that gray leaf spot occurred after leaf wetness durations equal to or greater than 8 h at all temperatures tested, and that disease incidence increased with increasing leaf wetness durations at all temperatures.
We have observed that gray leaf spot occurs on perennial ryegrass maintained at both typical rough and fairway mowing heights. Field observations have indicated that higher heights may be better able to recuperate from damage than lower heights, or that overall disease severity is less in higher mowing heights. As previously noted, damage from gray leaf spot sometimes is so severe on fairway-height turf that complete, postepidemic renovation is required. To date, we have not witnessed that level of gray leaf spot severity in rough-height perennial ryegrass in Kentucky, such that post-epidemic renovation was necessary.
Vaiciunas and Clarke (2000) tested the effects of a wide range of mowing heights (1.3, 1.9, 3.8, 6.4, and 8.9 cm), and four N rates (0, 0.7, 1.4, and 2.7 kg N 90 m-2) on gray leaf spot severity in perennial ryegrass and tall fescue. They reported that gray leaf spot severity in perennial ryegrass mowed at 8.9 cm was 52% higher than in perennial ryegrass mowed at 3.8 cm, and from 45 to 66% higher than perennial ryegrass mowed at 1.3 cm. They did not report differences between perennial ryegrass mowed at 3.8 and 1.3 cm, or among other mowing heights. They also reported that for 2 yr of the 3-yr study, disease severity was correlated positively with increasing N rates. They did, however, observe that, in 1 yr of the 3-yr study, increasing N resulted in decreased gray leaf spot when disease severity was low.
The mowing height response reported by Vaiciunas and Clarke (2000) was in perennial ryegrass mowed higher (8.9 cm) than might be found on most golf courses. There are no published studies examining the relationships between a narrower range of mowing heights and N fertility, and the severity of gray leaf spot in perennial ryegrass. The objectives of this study, therefore, were to investigate the effects of N fertility and mowing heights, as well as potential interactions, on the severity of gray leaf spot in perennial ryegrass. Specifically, a narrow range of mowing heights was chosen in an effort to closely approximate golf course roughs and fairways.
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MATERIALS AND METHODS
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The test site was the University of Kentucky Agricultural Experiment Station at Lexington, KY. Experiments were conducted in 1998 and 1999 on 12-yr-old monostands of turf-type perennial ryegrass (cultivar unknown). The soil was a Maury silt loam (fine, mixed, mesic Typic Paleudalf) with pH range of 6.3 to 6.9.
Different areas of perennial ryegrass were used each year. The experimental design in both years was a randomized complete block split-plot with three replications. Whole plots were 1.8 by 9.1 m, and split-plots were 1.8 by 3.0 m. Whole plot treatments were mowing heights and split-plots were N levels. Mowing heights were 1.9 and 6.4 cm to simulate golf course fairways and roughs, respectively. Fairway-height plots were mowed 3 d wk-1 and rough-height plots were mowed 1 d wk-1. Nitrogen (0, 36.6, and 73.2 kg N ha-1) was applied as urea (46-0-0) once every 30 d beginning 1 April and continuing through 1 August of both years. Plots were irrigated immediately with approximately 0.6 cm water after N applications.
Plots were inoculated with P. grisea grown on sterile grain, which was applied by hand at the rate of 96.7 kg grain ha-1. Inoculum was prepared by soaking equal parts of oat (Avena sativa L.) and barley (Hordeum vulgare L.) in water overnight in 3.6-L plastic jugs. Jugs containing grain were autoclaved for 1 hr on two consecutive days, infested with a local isolate of P. grisea, and incubated at room temperature (approximately 20–22°C) for 2 wk. Jugs were shaken daily to mix the inoculum during the first week of growth. Plots were inoculated on 30 July 1998 and on 26 July 1999.
Irrigation was supplied as needed to prevent drought stress prior to inoculation, and daily following inoculation for the duration of the epidemics in an effort to provide environmental conditions conducive to disease development. Irrigation to supply 0.6 cm water was applied during the day, generally between 1000 and 1300 h.
Split-plots were evaluated for percent of plot area blighted by P. grisea. All ratings were taken as visual estimates where 0 = no blighting and 100 = entire plot area blighted. Blighted tissue was confirmed for P. grisea in the lab and no other pathogens were detected. The area under disease progress curves (AUDPC) (Campbell and Madden, 1990) was calculated for each treatment within each year of the study with the dates and disease severity means for each year expressed in Fig. 1 and 2. Statistical analyses were performed by ANOVA of SAS (SAS Inc., Cary NC). Means and AUDPC data were separated by the F-protected least significant differences (LSD) test at P 0.05.
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Fig. 1. Effect of mowing heights on the severity of gray leaf spot in perennial ryegrass in 1998. Bars labeled with the same letter within observation dates were not significantly different (P 0.05).
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Fig. 2. Effect of N levels on the severity of gray leaf spot in perennial ryegrass in 1998. Bars labeled with the same letter within observation dates were not significantly different (P 0.05).
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RESULTS
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Gray leaf spot severity was much greater in 1998 than in 1999. Environmental conditions were near average for Kentucky during August in 1998 (Table 1). Conditions in 1999 were much warmer and/or drier than average during both July and August. The warmer and drier conditions during 1999 likely resulted in less favorable environmental conditions for gray leaf spot development. Because of the difference in environmental conditions among years, data from both years were pooled for analysis. No significant differences using pooled data were found relative to the results reported below.
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Table 1. Temperature, dew point, and precipitation data at research site during July and August of 1998 and 1999.
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1998
In 1998, the main effect of mowing height was significant beginning 8 August (Fig. 1). Gray leaf spot severity was significantly higher (P 0.05) in the fairway height turf when compared to the rough height turf on 8 and 10 August, with means of 44 and 26% of plots blighted, respectively. As the epidemic progressed, mowing height differences decreased and eventually reversed order by 14 August. By the end of the rating period (28 August), gray leaf spot severity was 58 and 69% plot area blighted for the fairway and rough heights, respectively (Fig. 1), but the difference was not significant (P 0.05). Similarly, there were no significant differences (P 0.05) in AUDPC values among mowing heights (Table 2). Hence, under the conditions of this study, mowing heights did not affect significantly gray leaf spot severity in 1998.
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Table 2. Area under disease progress curves (AUDPC) for epidemics of gray leaf spot in perennial ryegrass as influenced by mowing heights and N levels in 1998 and 1999 .
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The effect of N levels was significant on two of four observation dates. Plots treated with no N had significantly less (P 0.05) gray leaf spot than did plots receiving 73.2 kg N ha-1 on 8 and 14 August (Fig. 2). Differences between AUDPC for N treatments also were significant with the 0 kg N ha-1 rate having significantly less disease than the 73.2 kg N ha-1 rate (Table 2). The intermediate rate (36.6 kg N ha-1) was not significantly different (P 0.05) from either the lower or higher rate (Table 2).
1999
There were no significant differences due to the effect of mowing height on either observation date in 1999 (Fig. 3). In general, plots mowed at 1.9 cm had slightly more disease injury than those mowed at 6.4 cm. This also was the case early in 1998 when gray leaf spot severity was relatively low. Comparisons of 1999 AUDPC data (Table 2) also indicated no significant differences between the two mowing heights. Differences in blighting among N levels were significant on the second, but not the first observation date (P < 0.05). Plots treated with 0 kg N ha-1 mo-1 had significantly less gray leaf spot on 31 August when compared to plots receiving both 36.6 and 73.2 N kg ha-1 month-1 (Fig. 3). The AUDPC data also showed that split plots receiving the low N rate had significantly less gray leaf spot than split plots receiving the two higher N rates (Table 2).
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Fig. 3. Effects of N levels and mowing heights on the severity of gray leaf spot in perennial ryegrass in 1999. Bars labeled with the same letter within both treatment and observation dates were not significantly different (P 0.05).
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DISCUSSION
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Our results showed no interactive effects among mowing heights and N levels. The mowing heights evaluated in this study would likely simulate the heights normally found on golf courses. However, fairways and roughs are difficult to simulate because of trees, topography, etc. Mowing heights are often dictated by player demands. Golf course superintendents usually cannot impose large changes in mowing heights because of the impact on playability. On the basis of the results of this study, and the limited ability of golf turf managers to adjust mowing heights, manipulation of mowing heights as a cultural practice to reduce gray leaf spot severity cannot be recommended. It should be noted, however, that proper mowing frequencies relative to mowing heights (i.e., the lower the mowing height, the more frequently turf should be mowed) will improve general turf health, and should be practiced throughout the growing season.
Our results did not agree with those of Vaiciunas and Clarke (2000), who reported increased gray leaf spot severity at higher mowing heights (8.9 cm) than were imposed in this study. Considering these discrepancies, additional studies are necessary to investigate relationships between mowing height and gray leaf spot severity.
Gray leaf spot in Kentucky has been observed at both mowing heights on golf courses, but has appeared to be most destructive on fairways. This could possibly be explained by differences in maintenance practices between fairways and roughs. Fairways are normally irrigated, whereas rough areas rarely are. Turf areas under irrigation would likely provide a much better environment for blighting by P. grisea than would nonirrigated turf. Longer periods of leaf wetness would be expected to occur in irrigated vs. non-irrigated turf, regardless of mowing heights. Natural leaf wetness results from the accumulation of dew during diurnal cycles of nighttime cooling. Dew on turf consists of condensed atmospheric water vapor (
75%) and guttation/exudation from leaves (25%) (Williams et al., 1998). Monteith (1963) reported that under certain field conditions (e.g., short, dense canopies and low wind velocities) water vapor from moist soils is the dominant source of atmospheric condensation on plant leaves. Additionally, guttation and exudation of moisture from leaves is a function of soil moisture and plant water status (Taiz and Zeiger, 1991). Therefore, turf under regular irrigation (i.e., fairways) will be predisposed to heavier and more frequent accumulations of natural leaf wetness than will nonirrigated areas.
Additionally, fairways normally will receive more frequent applications of N relative to rough areas. It was clear that under the conditions of this study, increasing N fertility resulted in increased gray leaf spot severity. This was true in both years and both mowing heights. Our results agree with previous studies that evaluated the effects of N on diseases incited by P. grisea. Vaiciunas and Clarke (2000) found that increasing N levels increased gray leaf spot severity in perennial ryegrass under moderate to high disease pressure. Long et al. (2000) also reported an increase of rice blast as N rates were increased. Therefore, turf managers should avoid significant applications of water-soluble N prior to or during the occurrence of environmental conditions that are conducive for gray leaf spot. This would be especially important in areas where prior disease incidence indicates the presence of potentially viable inoculum, and in situations where preventative fungicide applications are not used.
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NOTES
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Published with the approval of the Director, Kentucky Agric. Exp. Stn. as publication 00-06-87.
Received for publication July 8, 2000.
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REFERENCES
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- Campbell, C.L., and L.C. Madden. 1990. Introduction to plant disease epidemiology. John Wiley and Sons, Inc., New York.
- Couch, H.B. 1995. Diseases of turfgrasses. 3rd ed. Krieger Publishing Company, Malabar, FL.
- Giesler, L.J., G.Y. Yuen, and G.L. Horst. 2000. Canopy microenvironments and applied bacteria population dynamics in shaded tall fescue. Crop Sci. 40:1325–1332.[Abstract/Free Full Text]
- Hoffman, N.E., and A.M. Hamblin. 2000. Progress in identifying resistance to gray leaf spot in perennial ryegrass. p. 161–162. In Agronomy abstracts. ASA, Madison, WI.
- Landschoot, P.J., and B.F. Hoyland. 1992. Gray leaf spot of perennial ryegrass turf in Pennsylvania. Plant Dis. 76:1280–1282.
- Long, D.H., F.N. Lee, and D.O. TeBeest. 2000. Effect of nitrogen fertilization on disease progress of rice blast on susceptible and resistant cultivars. Plant Dis. 84:403–409.
- Monteith, J.L. 1963. Dew, facts and fallacies: Water relations of plants. Blackwell, London.
- Moss, M.A., and L.E. Trevathan. 1987. Environmental conditions conducive to infection of ryegrass by Pyricularia grisea. Phytopathology 77:863–866.
- SAS Institute. 1985. SAS user's guide: Statistics. 5th ed. SAS Inst., Cary, NC.
- Smiley, R.W., P.H. Dernoeden, and B.B. Clarke. 1993. Compendium of turfgrass diseases. APS Press, Pilot Knob, MN.
- Taiz, L., and E. Zeiger. 1991. Plant physiology. The Benjamin/Cummings Publishing Company, Inc., Redwood City, CA.
- Trevathan, L.E., M.A. Moss, and D. Blasingame. 1994. Ryegrass blast. Plant Dis. 78:113–117.
- Trevathan, L.E. 1982. Response of ryegrass introductions to artificial inoculation with Pyricularia grisea under greenhouse conditions. Plant Dis. 66:696–697.
- Uddin, W., L.L. Burpee, and K.L. Stevenson. 1997. Influence of temperature and leaf wetness duration on development of gray leaf spot (blast) of tall fescue. p. 137–138. In Agronomy abstracts. ASA, Madison, WI.
- Uddin, W., M.D. Soika, F.E. Moorman, and G. Viji. 1999. A serious outbreak of blast disease (gray leaf spot) of perennial ryegrass in golf course fairways in Pennsylvania. Plant Dis. 83:783.
- Vaiciunas, S., and B.B. Clarke. 1998. Impact of cultural practices and genotype on the development of gray leaf spot in cool-season turfgrasses. p. 140. In Agronomy abstracts. ASA, Madison, WI.
- Vaiciunas, S., and B.B. Clarke. 2000. Impact of management practices on the development of gray leaf spot in cool-season turfgrasses. Proc. Rutgers Turfgrass Symposium, New Brunswick, NJ.
- Vincelli, P. 1999. Gray leaf spot. An emerging disease of perennial ryegrass. Turfgrass Trends 7:1–8.
- Williams, D.W., A.J. Powell, Jr., P. Vincelli, and C.T. Dougherty. 1996. Dollar spot on bentgrass influenced by displacement of leaf surface moisture, nitrogen, and clipping removal. Crop Sci. 36:1304– 1309.[Abstract/Free Full Text]
- Williams, D.W., A.J. Powell, Jr., C.T. Dougherty, and P. Vincelli. 1998. Separation and quantitation of the sources of dew on creeping bentgrass. Crop Sci. 38:1613–1617.[Abstract/Free Full Text]
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