Environmental and Edaphic Factors that Influence Spring Dead Spot Epidemics.

Spring dead spot (SDS) (Ophiosphaerella spp.) is a soilborne disease of warm-season turfgrasses grown where winter dormancy occurs. The edaphic factors that influence where SDS epidemics occur are not well defined. A study was conducted during the spring of 2020 and repeated in the spring of 2021 on four 'TifSport' hybrid bermudagrass (Cynodon dactylon × transvaalensis) golf course fairways expressing SDS symptoms in Cape Charles, VA, U.S.A. SDS within each fairway was mapped from aerial imagery collected in the spring of 2019 with a 20 MP CMOS 4k true color sensor mounted on a DJI Phantom 4 Pro drone. Three disease intensity zones were designated from the maps (low, moderate, high) based on the density of SDS patches in an area. Disease incidence and severity, soil samples, surface firmness, thatch depth, and organic matter measurements were taken from 10 plots within each disease intensity zone from each of the four fairways (n = 120). Multivariate pairwise correlation analyses (P < 0.1) and best subset stepwise regression analyses were conducted to determine which edaphic factors most influenced the SDS epidemic within each fairway and each year. Edaphic factors that correlated with an increase in SDS or were selected for the best fitting model varied across holes and years. However, in certain cases, soil pH and thatch depth were predictors for an increase in SDS. No factors were consistently associated with SDS occurrence, but results from this foundational study of SDS epidemics can guide future research to relate edaphic factors to SDS disease development.

Soil surfactants influence fungicide movement in United States Golf Association putting green soil.

The management of root and crown diseases of turfgrasses is challenging. To manage these diseases, golf course superintendents and other turfgrass managers often spray fungicides at a high carrier volume and irrigate after application to move fungicides into the root zone. Furthermore, previous research has demonstrated that soil surfactants can increase fungicide movement and distribution in soil. Two laboratory experiments were conducted using lysimeters, which were coated with sand on their inner walls to prevent preferential flow and contained 90/10% sand/peat moss (v/v), to determine the effects of soil surfactants on movement of selected fungicides in soil. The soil surface in the first experiment was treated three times at 2-wk intervals with one of three soil surfactants: Aquifer (propoxylated polyethylene glycols), Fleet (polyoxyalkylene polymers), and Revolution (modified alkylated polyol). The soil in the second experiment was treated with only Revolution four times at 2- to 3-wk intervals. Immediately after the final surfactant application, soil columns were treated with 14 C-labeled fungicide. 14 C-Myclobutanil was applied in the first experiment, and 14 C-azoxystrobin and 14 C-propiconazole were applied in the second experiment. In the first experiment, 14 percent units more of the recovered 14 C-myclobutanil was detected in the 5- to 7.6-cm sampling depth, and >4 percent units more was detected in the 7.6- to 10.2-cm depth after soil surfactant application compared with the fungicide-alone treatment. Each soil surfactant also yielded >28% more leachate than the nontreated control. In the second experiment, the total recovered 14 C-azoxystrobin and 14 C-propiconazole in the 7.6- to 10.2-cm depth increased by 2.8 and 1.9 percent units, respectively, compared with soil treated with fungicide alone. These data indicate that soil surfactant inclusion may increase fungicide distribution in soil, which may enhance the efficacy of fungicides in suppressing root and crown diseases.