Tar spot (Phyllachora maydis), gray leaf spot (Cercospora zeae-maydis), southern rust (Puccinia polysora), and northern corn leaf blight (Exserohilum turcicum) are foliar diseases that can significantly reduce corn (Zea mays) yields in Indiana. The obje...

Fusarium head blight (FHB) is a destructive disease of wheat and other small-grain cereals. FHB causes reduction in crop yield due to premature bleaching of spikes. Additionally, it deteriorates the crop quality due to production of mycotoxins. An integrated management strategy is needed to effectively manage this disease. One of the most important strategies in the FHB management toolbox is chemical control. Fungicides start losing their efficacy over time due to the development of fungicide resistance in the pathogens. This necessitates the development and testing of new fungicides with multiple active ingredients or modes of action. In this 3-year study, we evaluated the effectiveness of a new fungicide with multiple active ingredients, Sphaerex (a proprietary mix of metconazole and prothioconazole), in an FHB-susceptible soft red winter wheat cultivar, Shirley, in the eastern United States. Sphaerex provided significantly better control over untreated plots for FHB incidence, FHB severity, and deoxynivalenol (DON) content across all 3 years. The level of control of FHB and DON by Sphaerex was found to be similar to that provided by other standard FHB fungicides. The yield of the fungicide-treated plots was statistically similar to that of the untreated plots.

Tar spot of corn, caused by the fungus Phyllachora maydis, is an economically important foliar disease recently reported in the United States and Canada. Due to the recent introduction of Phyllachora maydis, the impacts of cultural management practices on disease development are still unknown. Separate field studies were conducted to determine the effects of nitrogen (N) application rate and plant density on disease development. Field trials were conducted across six site years in Michigan with two corn hybrids of differing disease susceptibility. The relative area under the disease progress curve was used to compare disease development between N application rates and plant densities. Nitrogen application rate had no significant effect on disease at any location. Plant density and disease had a significant (P < 0.05) inverse relationship at five of six site years, with an average 41% decrease in the relative area under the disease progress curve for every 1,000 plants per hectare increase. The economically optimal planting density ranged from 73 to 77 thousand plants per hectare for US$150 to 300 per metric ton corn prices, demonstrating that relatively low planting densities were more profitable despite greater disease. Therefore, other disease management practices including hybrid selection may be more effective at protecting yield than increasing plant density.