Ophiospharella Species that Cause Spring Dead Spot to…

Ophiospharella Species that Cause Spring Dead Spot to Respond Differently to Fungicides

By Wendell Hutchens, Jordan Booth, Kevin Hensler, David McCall, Ph.D.

Ophiosphaerella herpotricha and O. korrae are the two most common fungal species that cause the detrimental bermudagrass disease spring dead spot (SDS) in Virginia. Previous research has shown that they differ in aggressiveness, response to fertilizer type, ability to grow at certain pH ranges, and sensitivity to certain fungicides. The purpose of this project was to determine how natural populations of O. herpotricha and O. korrae respond in a field setting to various fungicides and fungicide groups.

Two trial locations were used for this study––one was a ‘Tifway 419’ hybrid bermudagrass fairway with a natural population of O. korrae and the other was a ‘Vamont’ bermudagrass fairway with a natural mixed population of both O. herpotricha and O. korrae. The following fungicide treatments were applied either once at full label rate or as a half rate twice (three to four weeks apart) in the fall of 2019: DMIs) Maxtima (mefentrifluconazole), Eagle (myclobutanil), Banner Maxx (propiconazole), Torque (tebuconazole); QoIs) Heritage (azoxystrobin), Fame SC (fluoxastrobin), Insignia (pyraclostrobin); SDHIs) Xzemplar (fluxapyroxad), Kabuto (isofetamid), Velista (penthiopyrad), and Posterity (pydiflumetofen). Plots were assessed three times in the spring and early summer of 2020 for percent necrosis. Data were transformed to area under the progress curve (AUPC) and means were separated.

Spring dead spot was suppressed more compared to the nontreated control in the mixed population than in the O. korrae population for nine of the eleven fungicides tested (Fig. 1). Kabuto, Maxtima, Velista, and Posterity generally provided the greatest SDS suppression and the SDHIs were the most efficacious fungicide class against SDS. These data suggest that certain fungicides are more efficacious than others against SDS and that fungicide selection for SDS should be made based on the Ophiosphaerella spp. population present.

FIGURE 1: Mean percent necrosis area under the progress curve for eleven different fungicides and the nontreated control. Maroon bars with upper-case letters compare the different fungicide treatments at the O. korrae population site and orange bars with lower-case letters compare the different fungicide treatments at the mixed population site. Bars with the same letters are not statistically different.