The Effects of Different Rates of Nitrogen and Iron Sulfate on Microdochium Patch Development on Trafficked Annual Bluegrass Putting Greens in the Absence of Fungicides.

Microdochium patch is a turfgrass disease in cool, humid regions caused by the pathogen Microdochium nivale. Currently, fungicide applications are the predominant method of control. Increasing pesticide restrictions have generated concern regarding management of Microdochium patch.  The objective of this research was to evaluate the effects of different rates of nitrogen and iron sulfate on Microdochium patch development on trafficked annual bluegrass (Poa annua) putting greens in the absence of fungicides. A field experiment was initiated in September 2013 and concluded in April 2015 on a sand-based putting green at the Oregon State University Lewis Brown Horticulture Farm, Corvallis, OR. Experimental design was a 2 by 3 by 5 randomized complete block design, with four replications.  Factors included year, nitrogen, and iron sulfate rates. Treatments were applied every two weeks from 26 September 2013 to 12 April 2014 and again from 22 September 2014 to 12 April 2015. No fungicides treatments were applied during the study. Nitrogen rates were 0.0, 4.88 and 9.76 Kg N ha^-1 and rates of iron sulfate were 0.0, 12.21, 24.41, 48.82, and 97.65 Kg FeSO₄ ha^-1. Traffic simulation was performed by walking over the plots with golf shoes 5 days a week to replicate 76 rounds of golf per day. Turf quality and turf color (1-9 scale, with 6 or greater considered acceptable), and percent disease (0-100%) data were collected weekly. Treatments receiving 0.0 Kg N ha^-1 in combination with 48.82 Kg FeSO₄ ha^-1, or 0.0 and 4.88 Kg N ha^-1 combined with 97.65 Kg FeSO₄ ha^-1 provided the greatest disease control, less than 1% disease. In spite of the disease suppression observed, no treatment received a turfgrass quality rating of 6.0 or greater.  Low turfgrass quality ratings were attributed either to turf thinning or blackening of the shoots resulting from iron sulfate applications.