Non-target effects of strobilurin fungicide applications on creeping bentgrass putting greens during summer stress

Previous research has indicated that strobilurin fungicide applications may improve summer stress tolerance of creeping bentgrass (Agrostis stolonifera L.) putting greens. In this experiment, strobilurin fungicides were integrated within a summer fungicide program to evaluate disease severity and plant physiological effects. Fungicide programs were applied on a ‘Dominant Southern’ creeping bentgrass putting green; all of which consisted of five fungicide spray applications from June to August during 2011 and 2012. The 2^nd and 5^th application in each program consisted of a strobilurin fungicide. Strobilurin fungicides evaluated included pyraclostrobin, azoxystrobin, fluoxastrobin, or trifloxystrobin. The remaining fungicide applications were identical across programs. Measurements of visual quality, spectral reflectance, turfgrass cover, rooting characteristics, and disease severity were collected. The non-treated control was similar to treated plots in all parameters in 2011, and until 42 and 56 days after initial treatment (DAIT) the following year. At this time, fungicide programs began to exhibit greater visual quality, turfgrass cover, and spectral reflectance compared to the non-treated control. Differences in physiological effects coincided with the first observation of brown patch (Rhizoctonia Solani Kühn) in the experimental area. These data suggest that strobilurin fungicides exhibit excellent efficacy for disease control during summer, and that direct physiological effects may be transient and observable over the long term.

A 2-year field experiment was conducted to determine if applications of pyraclostrobin, azoxystrobin, fluoxastrobin, and trifloxystrobin could improve plant physiological effects of a ‘Dominant Southern’ creeping bentgrass putting green in the absence of visible foliar disease. Experimental units were arranged in a split-plot randomized complete block design. A fungicide mixture containing chlorothalonil and iprodione and a no fungicide treatment served as the whole-plots. Chlorothalonil and iprodione were applied at 14-day intervals. Sub-plots were treated with strobilurin fungicides (azoxystrobin, pyraclostrobin, fluoxastrobin, and trifloxystrobin) and a non-treated control. Sub-plots were applied at 14-day intervals. Neither differences in disease severity nor any physiological effect was observed on any assessment date over the course of two years. The results of this experiment suggest that while strobilurin fungicides perform well for disease control, detectable plant physiological effects under field conditions were limited.