Effects of summer cultivation and fertilization timing on large patch in zoysiagrass

Large patch disease in zoysiagrass has become more of a concern as use of the turfgrass has increased on golf courses.

Ken Obasa, Ph.D.; Jack Fry, Ph.D.; Dale Bremer, Ph.D.; Rodney St. John, Ph.D.; and Megan Kennelly, Ph.D.

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Effects of summer cultivation and fertilization timing on large patch in zoysiagrass: photo 1

Patches in large patch disease range in size from a few feet across
to 20 feet or more in diameter.
Photos by Megan Kennelly

Zoysiagrass (Zoysia japonica and Z. matrella) is being used increasingly often in golf course fairways and greens. Large patch, caused by Rhizoctonia solani AG 2-2 LP, is a common and severe disease of zoysiagrass. Patches range in size from a few feet across to 20 feet or more in diameter. On individual plants, the leaf blades develop a yelloworange color with rotting on the leaf sheaths. Large patch symptom development in zoysiagrass is favored by relatively cool and humid weather. In Kansas, large patch symptoms develop primarily in April-May and occasionally in September-October. Compacted and poorly drained soils and excessive and prolonged wetness near the leaf surface are optimal conditions for the development of large patch symptoms.

Effects of summer cultivation and fertilization timing on large patch in zoysiagrass: photo 2

On individual zoysiagrass plants affected by large patch disease, the leaf blades develop a yellow-orange color with rotting on the leaf sheaths.

Currently, large patch is primarily managed by fungicide application during fall and/ or spring. Cultural management practices do not provide an acceptable level of disease control, and few studies have examined the effects of cultural practices. Previous studies (2) have examined the effects of mowing height, nitrogen source and nitrogen application rates on large patch development and severity on zoysiagrass. They found that lower mowing heights resulted in more severe disease. In addition, large patch was not affected by nitrogen source (urea, urea formaldehyde, poultry litter, sewage sludge or bovine waste) or the two different application rates of 1.5 or 3.0 pounds nitrogen/1,000 square feet (7.32 or 14.64 grams/square meter) per year. The authors did not, however, study the effect of different fertilization timings such as early spring or late fall applications that may be used to prolong the length of season when the turf is green.

Effects of summer cultivation and fertilization timing on large patch in zoysiagrass: photo 3

The Rhizoctonia solani pathogen was grown
in the laboratory and then transferred to glass jars
of sterile oats, where it was allowed to grow
for two weeks before use.

Cultivation leads to improved soil moisture and oxygen conditions, resulting in improved root growth as well as increased microbial activity that is essential to the biodegradation of thatch. Aerating zoysiagrass turf in early spring when large patch is active has been anecdotally reported to result in new satellite infections on healthy turf by infected cores. The effects of cultivation in summer are not known, however. In addition, the effect of timing of nitrogen fertilization and cultivation on large patch development and severity in zoysiagrass is not known, although turfgrass managers have associated severe large patch outbreaks with excessive nitrogen fertilization.

The goal of this study was to evaluate the effect of cultivation on soil moisture, soil and thatch temperatures, and large patch development as well as evaluate the effect of timing of fertilization on large patch development.

Methods

Effects of summer cultivation and fertilization timing on large patch in zoysiagrass: photo 4

Research plots were inoculated by making a slice in the thatch and inserting 8-10 grams of oats in each spot. The turf slice was tamped back down and the area was irrigated to promote fungal growth.

The experiment was conducted at three Kansas locations: the Rocky Ford Turfgrass Research Center in Manhattan, the K-State Research and Extension Center for Horticultural Crops in Olathe, and the John C. Pair Horticulture Center in Haysville.

Inoculation

The plots were inoculated on Sept. 25, 2008, in Manhattan, Oct. 2 in Olathe and Oct. 3 in Haysville. The Rhizoctonia solani pathogen was grown on one-quarter-strength potato dextrose agar + antibiotics in the laboratory, transferred to glass jars of sterile oats and allowed to grow for two weeks before use. To inoculate the plots, a slice was made in the thatch and 8-10 grams of oats were inserted in each spot. The turf slice was tamped back down and the area was irrigated to promote fungal growth. Thermocouples and dual-probe sensors (1,3,7) were installed in the Manhattan site during 2009 and 2010 to determine the effect of cultural practices on soil temperature, thatch temperature and soil moisture content.

Effects of summer cultivation and fertilization timing on large patch in zoysiagrass: photo 5

At each of the three research sites (Haysville, Manhattan and Olathe, Kan.), there were four blocks of plots. Inoculated patches first became apparent in spring 2009.
Photos by Ken Obasa

Experimental design

The experiments were set up in a splitplot design, with cultivation vs. noncultivation as the main-plot factor with main plots 12 × 20 feet (3.6 × 6 meters). Fertility was the split-plot factor, with 12- × 10-foot (3.6- × 3-meter) plots. There were four inoculation sites (described above) per splitplot. There were four blocks at each of the three locations. Inoculated patches were apparent starting in spring 2009, expanding over time. The cultural practices and fertility regimes were initiated in summer 2008 and continued as shown in Table 1. Cultivation included core-aerification, verticutting and sand topdressing. Fertility was applied in spring and fall as plain urea at a rate of 1 pound nitrogen/1,000 square feet (4.88 grams/square meter) in spring and another 1 pound nitrogen/1,000 square feet in fall. In Manhattan, each spring and fall application was further split into two applications of 0.5 pound nitrogen/1,000 square feet (2.44 grams/square meter). Summer fertility was applied all at once as 2 pounds nitrogen/ 1,000 square feet (9.76 grams/square meter) as polymer-coated urea.

Effects of summer cultivation and fertilization timing on large patch in zoysiagrass: photo 6

The cultural practices and fertility regimes were initiated in summer 2008 and continued through 2011. Cultivation practices included core-aerification, verticutting and sand topdressing.

Disease assessment

Disease was assessed by measuring patch sizes when patches had distinct margins, and patch size increase (radial patch expansion in inches per week) was calculated. When patches became large (merged together) or had poorly defined margins, disease was assessed by digital image analysis (4) with modifications (5,6). Patch symptoms within a 30- × 36-inch (76.20- × 91.44-centimeter) grid in the center of each plot were photographed weekly and analyzed to estimate turf infested with large patch disease (percentage of diseased, or non-green, turf), relative to healthy (green) turf.

Results

Effects of summer cultivation and fertilization timing on large patch in zoysiagrass: table 1

Microclimate

Cultivation had no effect on 5-inch (12.7-centimeter) soil temperature, thatch temperature or water content during 2009 or 2010 (data not shown).

Disease development

In 2009 we measured patch diameters for several weeks at all three locations. At all three sites, there was no effect of cultivation or timing of fertilization on patch size or the rate of patch expansion. Data from Haysville are presented in Figure 1. The other sites were similar.

In 2010 and 2011, we used only digital image analysis. The patches had become larger and had coalesced, making individual patch size measurements difficult. There was no effect of cultivation on disease at any site in 2010 or 2011. However, there were some significant effects of fertility in those years. In fall 2010 in Manhattan, the spring + fall fertility treatment had significantly less non-green turf than the summer fertility treatment (Table 2).

Effects of summer cultivation and fertilization timing on large patch in zoysiagrass: figure 1

Similarly, in Haysville, the spring + fall fertility treatment had less non-green turf than did the summer fertilization treatment on June 22, but this effect was not significant on July 7. In Haysville in spring 2011, the spring/fall fertility treatment again had less non-green turf than the summer fertility treatment (Table 2). In spring 2011 in Manhattan, there was a significant interaction among cultivation and fertility treatments. The cultivated spring + fall fertilization treatment had less non-green turf than both summer fertility treatments, and the noncultivated spring + fall fertilization treatment had less non-green turf than the noncultivated summer treatment (Table 2). There were no differences at the Olathe site in 2010 or 2011 (data not shown).

Discussion

Effects of summer cultivation and fertilization timing on large patch in zoysiagrass: table 2

This study was conducted over several years to examine the potential impact of the cultural practices over time. Cultivation did not affect disease based on patch size, patch size increase or digital image analysis, and it did not affect volumetric soil content or temperature. We hypothesized that cultivation might improve drainage and therefore reduce disease pressure, but this did not occur. We were not able to measure moisture right at the thatch or on the leaf sheaths, which may be a more informative area because that is where the pathogen infects the plant. However, instrumentation to measure moisture in those areas was lacking.

Fertilization in spring and fall was associated with slightly lower percentages of nongreen turf at Manhattan and Haysville, but not Olathe, in 2010 and 2011. Applications of nitrogen during spring and fall might have promoted more shoot re-growth within affected areas, thus masking the effects of disease.

Since effects were not consistent from year to year or site to site, spring or fall applications should still be approached with caution. Fall fertility may interfere with other processes of hardening off for winter. Furthermore, it is important to note that the effects of very early fertility, such as at the very initial signs of green-up, may be different from what we observed. Our spring fertility applications were made after the turf had already greened up significantly.

Funding

This work was funded by the United States Golf Association, the Kansas Turfgrass Foundation, the Kansas Golf Course Superintendents Association and the Heart of America Golf Course Superintendents Association.

Acknowledgments

The authors would like to thank W.W. Bockus, C.R. Little and B.K. Sandercock at Kansas State University for their thoughtful contributions to K. Obasa’s Ph.D. thesis associated with this work.

Literature cited

  1. Bremer, D.J. 2003. Evaluation of microlysimeters used in turfgrass evapotranspiration studies using the dual-probe heat-pulse technique. Agronomy Journal 95:1625-1632.
  2. Green, D.E. II, J.D. Fry, J.C. Pair and N.A. Tisserat. 1994. Influence of cultural practices on large patch disease of zoysiagrass. HortScience 29:186-188.
  3. Ham, J.M., and R.S. Senock. 1992. On the measurement of soil surface temperature. Soil Science Society of America Journal 56:370-377.
  4. Karcher, D.E., and M.D. Richardson. 2005. Batch analysis of digital images to evaluate turfgrass characteristics. Crop Science 45:1536-1539.
  5. Obasa K., J. Fry and M. Kennelly. 2012. Susceptibility of zoysiagrass germplasm to large patch caused by Rhizoctonia solani. HortScience 47:1252-1256.
  6. Obasa K., J. Fry, D. Bremer, R. St. John and M. Kennelly. 2013. Effect of cultivation and timing of nitrogen fertilization on large patch disease of zoysiagrass. Plant Disease 97:1075-1081.
  7. Song, Y., J.M. Ham, M.B. Kirkham and G.J. Kluitenberg. 1998. Measuring soil water content under turfgrass using the dual-probe heat-pulse technique. Journal of the American Society of Horticultural Science 123:937-941.

Kehinde Obasa is a postdoctoral research associate and Megan Kennelly is an associate professor in the department of plant pathology and Jack Fry and Dale Bremer are professors in the department of horticulture, forestry and recreation resources at Kansas State University; Rodney St. John is an agronomist with Ryan Lawn & Tree in Overland Park, Kan.