Mid-season applications of Quadris with and without Warrior insecticide were evaluated in 2004 and 2005, and Headline, Folicur, Domark, or Headline plus Folicur were evaluated in 2006, 2007, and 2008 in 37 farm scale studies in Ohio. Producer cooperators selected fields, applied treatments at growth stage R3 and harvested fields. Each trial was rated at growth stage R5 or R6 for incidence and severity of brown spot and frogeye leaf spot. Aphids and foliar disease incidence was low in 2004. Soybean aphids were counted at stage R5 in 2005. Brown spot severity was reduced significantly by Headline in seven of the 13 locations. In the absence of soybean aphid, a single application of fungicide(s) increased yield significantly in only six of the 28 locations, of which only three had yield increases greater than 4.2 bu/acre. Populations of soybean aphids were high during 2005 at nine locations, and an insecticide application increased yield significantly at eight locations. These data indicated that foliar diseases and aphids contribute to yield loss in soybeans. However, more studies are required to determine action thresholds for brown spot and frogeye leaf spot. Accepted for publication 14 October 2010. Published 22 January 2010.

Brown spot, caused by Septoria glycines, is the most common foliar disease of soybean in Ohio, but its economic impact has not been assessed on modern cultivars. Therefore, the objectives of this study were to (i) evaluate the effect of S. glycines on soybean yield and (ii) evaluate the efficacy of strobilurin- and triazole-based fungicides on the control of brown spot. Yield loss associated with S. glycines was determined using weekly applications of chlorothalonil. The efficacy of azoxystrobin, pyraclostrobin, tebuconazole, and flutriafol alone and in combinations were also assessed using applications at the R3 and R5 growth stages at two locations over 3 years. Significantly different levels of brown spot developed following applications of chlorothalonil, with mean yield differences between treated and nontreated plots ranging from 196 to 293 kg/ha. Pyraclostrobin and azoxystrobin applied at the R3 growth stage significantly reduced final levels of brown spot; however, significant increases in yield occurred in only three of the six location-years. Triazoles, flutriafol and tebuconazole, applied at R3 or R5 did not significantly decrease levels of brown spot or impact yield. More data on the accurate timing of fungicides are still required to establish a long-term management program for this disease, and resistance to brown spot should be monitored in soybean cultivar development to prevent future yield losses.

No abstract

No abstract