Multi-State Evaluation of Dollar Spot Susceptibility in Creeping Bentgrass.

Dollar spot (Sclerotinia homoeocarpa) is a common disease on creeping bentgrass (Agrostis stolonifera) putting greens and fairways, and is typically treated using calendar-based preventative fungicides. This may lead to applications of more fungicide than necessary, causing environmental and economic concerns. The objectives of this research were to: 1) evaluate dollar spot susceptibility in commonly used commercial creeping bentgrass cultivars; 2) study environmental influences on dollar spot occurrence and severity; and 3) evaluate the suitability of a threshold-based fungicide application schedule for dollar spot control on a disease-resistant cultivar. The experiment was initiated in 2008 in nine states as a split-block design with three replicates. The whole-plot treatments were bentgrass cultivars and the sub-block treatments were two fungicide application regimes [ (no fungicide vs. a combination of boscalid and chlorothalonil applied when dollar spot was > 5% or 10% under putting green and fairway condition, respectively, in two of the three replicates in ‘Declaration’ (a S. homoeocarpa resistant cultivar)]. Dollar spot was observed in KS, IA, MI, WI, and IL in 2009. However, fungicide treatments were applied only in KS and IA due to the low disease pressure in other locations. The preliminary results showed that turfgrass quality and dollar spot occurrence and severity were affected by environmental conditions. ‘Crenshaw’ and ‘Declaration’ were the least and the most tolerant to dollar spot, respectively. Fungicide applications reduced dollar spot up to 36%. Variations in bentgrass quality were mostly due to the differences of disease sensitivity during summer.