Effects of fungicide applications on root-infecting microorganisms and overwintering survival of perennial stevia

Abstract

Koehler, A.M. and Shew, H.D. 2018. Effects of fungicide applications on root-infecting microorganisms and overwintering survival of perennial stevia. Crop Protection 117:000–000.Stevia (Stevia rebaudiana) is a perennial species emerging as a new crop in the southeastern United States. In previous studies, application of quinone outside inhibitor (QoI) fungicides enhanced overwintering survival of stevia. Greenhouse and field trials were conducted to assess the effect of multiple fungicides on plant growth, root associated microorganisms, and overwintering survival. In greenhouse trials in the absence of soilborne pathogens, no differences in plant height, shoot weight, or root system ratings were observed among treatments. In two field trials screening seven combination fungicides and one biological control, significant increases in overwintering survival of plants treated with QoI fungicides were observed. Plants were dug from the fields monthly to destructively sample root crowns and species of Fusarium, Ceratobasidium, Pythium, and Macrophomina phaseolina were consistently isolated. Abundant microsclerotia from M. phaseolina were observed on stems of plants that did not survive winter. In seven sample months at each of the two field trials, non-fungicide treated plants had the lowest root weights. This study is one of the first to evaluate interactions between fungicide use and root associated fungi in a perennial crop and provides a framework to further investigate the role of root-associated fungi in overwintering survival.