Fertility Regimes to Manage Spring Dead Spot on ‘Tifway' Bermudagrass.

Spring dead spot (SDS) is a devastating disease which interrupts bermudagrass green-up in the spring.  Controlling this disease through a traditional fungicide program can cost $15,000 to $25,000 for one application.  The objectives of this research were to determine if manganese (Mn) or various nitrogen (N) rates can minimize SDS occurrence on Tifway bermudagrass and to determine the impact different light environments have on SDS development. The study was conducted at the Clemson University field research plots on Tifway bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] grown under shade.  Light treatments included full-sunlight and continuous full-day 55% shade.  Fertility treatments included N at 97.5 kg a.i. ha^-1 yr^-1 and 292.7 kg a.i. ha^-1 yr^-1 provided with 16-4-8 complete granular fertilizer and Mn (MnSO₄, 27.7 kg a.i. ha^-1) applied in June, August, and October.  Tifway plots were inoculated with the pathogen causing SDS Ophioshaerella korrae (J. Walker & A.A.Sm.) in September, 2006.  Data collection included visual turfgrass quality rated weekly from 1-9 (1=brown, dead turf, 7=acceptable quality, and 9=perfect, green turfgrass) based on color, density, texture, and uniformity of the bermudagrass surface.  Total clipping yield and shoot chlorophyll concentration were collected at the middle and end of the study.  Also, root total non-structural carbohydrates were collected at the conclusion of the study.  One year following inoculation of O. korrae, SDS symptoms were not noted.  Regardless, by mid-July, greatest chlorophyll concentration was sun-grown treatment fertilized with N at 292.7 kg a.i. ha^-1 yr^-1, while lowest chlorophyll concentration was noted when fertilized with N at 292.7 kg a.i. ha^-1 yr^-1 under shade.