SDHI (Succinate DeHydrognenase Inhibitor) fungicides represent a broad class of compounds that reduce the capacity of some fungal pathogens to infect turf. All compounds within the SDHI class affect slightly different target sites in the succinate dehydrogenase pathway. They are site-specific (interfering with a single metabolic function in sensitive fungi) and are all acropetal penetrants (they move upward and outward in the water stream). Resistance risk currently is listed as “moderate”. However, I would consider placing them in the “high risk” category when they are used against anthracnose and dollar spot pathogens. Each is assigned the same FRAC Code 7.
Although we are continually learning about their strengths and weaknesses, we already recognize that SDHI compounds differ widely in terms of spectrum of activity (Table 1). Prostar (flutolanil) is an excellent material for two common Rhizoctonia diseases (brown patch and large patch), but has no activity against dollar spot and anthracnose pathogens. Emerald (boscalid) is almost exclusively a dollar spot fungicide. The two new SDHI fungicides Xzemplar (fluxapyroxad, BASF) and Velista (penthiopyrad, Syngenta) also differ in activity.
Xzemplar’s clear strength is in dollar spot control, showing early signs excellent control and rapid turf recovery. As you know, I prefer the preventative approach for managing all turf disease issues. However, if you need a fungicide to quell an existing outbreak, Xzemplar at 0.26 fl oz/M will do a great job. I always caution against employing the “post-outbreak” or “curative” approach too often. Eventually, it will accelerate the evolution of fungicide-resistant pathogen populations.
Velista has a broader spectrum than other SDHI fungicides and is the only one with proven efficacy against anthracnose. The advantage here is that in mid-summer, when dollar spot and brown patch also threaten putting greens, Velista will help against all three diseases, without the growth regulation effect associated with some of our DMI fungicides.
When using SDHI compounds to target anthracnose and/or dollar spot pathogens, I recommend a tank mix with chlorothalonil—even the low label rate will improve control and reduce risk of resistance to site-specific fungicides.
SDHI fungicides and major turf disease targets: