Elemental sulfur is a commonly applied, effective powdery mildew control strategy in vineyards dating back two centuries (Forsyth, 1802). Bordelon et al. (2016) recommended a diverse and integrated management system for the control of powdery mildew. Such diversified approaches to powdery mildew management may reduce the risk of causal organisms developing resistance to some fungicides (Erickson and Wilcox, 1997). Elemental sulfur is also commonly used to control powdery mildew in organic production systems because it works relatively well under low inoculum conditions early in the season and will help to reduce applications of more effective but more resistance-prone material later in the season during peak disease infection (Savocchia et al., 2011; Smith et al., 2014). When applied to tolerant vines, sulfur is a relatively inexpensive and effective complement to other fungicides for effective control and prevention of resistance (Bordelon et al., 2016). Additionally, early applications of micronized sulfur have been recommended before the application of other fungicides (Smith et al., 2014).
Despite its historic usage, grape cultivars have responded differently when sprayed with sulfur (Shertz et al., 1980). Sulfur intolerant cultivars are generally fox grape derived; e.g., Concord (Bordelon et al., 2016). Many of the cultivars grown in the upper midwest and northern Great Plains regions of the United States have fox grape in their lineage; thus, they may exhibit sulfur phytotoxicity symptoms, but have not been tested to identify sulfur sensitivities or tolerances. With the increase in grape production in the upper midwest and northern Great Plains regions of the United States, more information on best management practices is needed for cultivation under these relatively new conditions and with nontraditional grapevine cultivars (Hatterman-Valenti et al., 2016).
If left uncontrolled, powdery mildew has been shown to cause premature leaf drop, stop the growth of berry epidermal tissue, reduce the rate of berry ripening, and slow periderm development (Gadoury et al., 2001, 2012). Such reductions in periderm development have been noted to decrease hardiness (Wolpert and Howell, 1986). These effects may be amplified in a region such as the northern Great Plains where short season length is inherently a limiting factor in production (Hatterman-Valenti et al., 2016). The following study was conducted to evaluate micronized sulfur phytotoxicity on winegrape cultivars commonly grown in the northern portion of the United States.
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