Evaluating the Impact of Cultural Practices on Large Patch Severity on Zoysia Matrella (L.) Merr. ‘Cavalier'.

Large patch (LP) disease on zoysiagrass is caused by the fungal pathogen Rhizoctonia solani (Kühn), anastomosis group 2-2- LP. Large patch symptoms include blighted sheath tissue which produces orange/brown patches of dead turf that may exceed 20’ in diameter. The disease is expressed in the spring and fall and is most severe during extended periods with temperatures ranging from 21°C to 23°C, high humidity, and saturated soils. To date, the only peer-reviewed study conducted concluded that nitrogen source and rate have no effect on LP severity, however; many popular turfgrass management articles recommend lower rates of nitrogen with controlled release as a management practice to reduce LP severity.  In the present study, cup cuts of Zoysia matrella (L.) Merr. ‘Cavalier’ symptomatic and non- symptomatic of LP were taken from the field and maintained under greenhouse conditions. Fertility treatments were applied using 0.75 lbs of N (Urea)/ 1,000 ft² and 1.5 lbs of N (Urea)/ 1,000 ft² and plants were trimmed every other day or left untrimmed. Plants were placed in a growth chamber at near 100% humidity, 21-23°C temperature, and lighting at ca. 113 µmols^-1m^-2 for 21 days. Disease symptoms were quantified using digital imagery analysis. Data analysis was completed using the General Linear Models procedure of SAS (SAS  Inc., 9.1)  Mean percent pixel reduction was separated by the F-protected least significant differences (LSD) test at P  ≥ 0.05. The effect of mowing height was significant (P = 0.002) for green pixel reduction.  The greater reduction in percent green pixels (trimmed = 36.57 %; not trimmed = 4.54 % green pixel reduction) with the trimming treatment (1.27 cm height of cut), indicates that mowing height may influence the expression of large patch disease caused by R. spp.  The effect of nitrogen fertility on green pixel reduction was non-significant (P = 0.24).  The interaction between mowing height and nitrogen fertility was also non-significant (P = 0.11). These results refute conventional thought and support previous peer-reviewed findings that fertility does not have an effect on large patch severity.