To optimize yield potential, soybean farmers in Iowa are planting earlier in the growing season. Together with reduced tillage practices, this often means that seed germinate in cold, wet soils and are at risk for seed rot and damping off due to soil borne pathogens such as Pythium spp., Phytophthora sojae, Fusarium spp. and Rhizoctonia spp. Limited research has been done on the basic biology, and epidemiology of these important seedling pathogens of soybean.
Goss’s bacterial wilt and leaf blight (Goss’s wilt), caused by Clavibacter michiganensis subsp. nebraskensis (Cmn), has re-emerged in the Corn Belt as an economically important disease of corn. In 2011, the disease was widespread throughout Nebraska (confirmed in more than 67% of counties through 2010), Iowa (80 percent of counties), Illinois (30 percent of counties) and Minnesota (30 percent of counties). Numerous reports of the disease were also confirmed in northwest Indiana. Read more about Epidemiology of Goss's wilt of corn
Foliar fungicides have traditionally not been used in commercial corn because they have seldom been profitable. However, the use of foliar fungicides in hybrid corn production has increased dramatically in the past four years, primarily because of higher grain prices and physiological, yield-enhancing effects that are claimed by the agrochemical industry but are not related to reduced disease. Of concern is the fact that the use of fungicides has shifted attention from the sound use of integrated pest management (IPM) tactics for disease management, even those these tactics are designed to ensure efficient use of fungicides and maximize net return.
Phytophthora root rot (PRR), caused by Phytophthora sojae, is a considerable threat to soybean production in Iowa, particularly in wet summers. Currently, PRR is primarily managed by planting soybean varieties with genes that confer resistance (Rps genes) to P. sojae. The effectiveness of a resistance gene relies on its ability to recognize the pathogen’s corresponding avirulence gene (Avr). Using Rps genes as a management tool for PRR has had only short-term success because Avr genes in the pathogen continually evolve to escape detection by the plant. There are 15 known Rps genes in soybean, and the pathogen is classified into pathotypes depending on the combination of Rps genes they interact with in soybean. Most commercially available Phytophthora-resistant soybean varieties in Iowa have the Rps1k resistance gene. However, P. sojae continues to change genetically such that most resistant varieties are no longer completely effective. In recent years, Iowa producers have started to report losses to PRR on soybean resistant varieties with Rps1k. Read more about Integrated management of Phytophthora root and stem rot of soybeans