Effect of Nitrogen and Spring Fungicide Application on Large Patch Severity in Zoysiagrass.

Large patch is the most limiting disease on zoysiagrass fairways and lawns in the upper transition zone. Ideally, a management strategy integrating cultural practices would reduce the need for multiple fungicide applications to control this disease. This field research is designed to evaluate the impact of different nitrogen sources applied during large patch activity in the spring and fall.  Plots were arranged in a randomized complete block design with four replications. Treatments included nitrogen source (CaNO₃, (NH₄)₂SO₄, and urea), nitrogen application timing, and fungicide. Nitrogen was applied in fall, spring, both fall and spring, or only in summer. Spring and fall treatments were applied at a rate of 24 kg N/ha when five-day average soil temperatures first reached 18°C. Summer-only nitrogen treatments were applied monthly in June, July, and August at 32 kg N/ha. Fall and spring treatments received additional nitrogen in the summer to total 96 kg N/ha per annum of the same nitrogen source. A separate spring treatment of 144 kg N/ha of a controlled release fertilizer (Duration™ 120 d) was also evaluated. Duplicate plots of each treatment received one fungicide application of tebuconazole at 0.824 kg ai/ha when spring fertility was applied. Nitrogen source did not impact large patch development. Large patch severity was minimal in fall 2014 and 2015. Fall nitrogen applications in both years increased the percentage of green turf in the late fall compared to summer or spring only treatments, but did not affect spring green-up. Plots receiving nitrogen in the spring of 2015 had a higher percentage of green turf and less visual large patch than summer- and fall-only plots. Tebuconazole significantly reduced large patch outbreaks compared to non-fungicide treated plots. A management strategy incorporating nitrogen and fungicide applications during the spring infection period may be effective in improving zoysiagrass quality and reducing large patch severity.