More than 80 diseases have been recorded on soybean (Glycine max) in Australia, and of these only a handful have had a significant impact on commercial crops. Charcoal rot (caused byMacrophomina phaseolina), sclerotinia stem rot (Sclerotinia sclerotiorum) and phytophthora root rot (Phytophthora sojae) are the most important root and stem pathogens, whilst rust (Phakospora pachyrhizi) can be considered to be the worst foliar pathogen. Losses from these endemic diseases can be effectively managed through Integrated Disease Management strategies, including plant resistance, paddock selection, optimum planting density and timing, and in the case of rust, timely fungicide sprays. At least 17 pathotypes of Phytophthora sojaehave been recorded in Australia, and overseas several pathotypes of Phakopsora pachyrhiziare known. New pathotypes of these pathogens will appear when soybean varieties with a single gene for resistance are grown in regions and years favourable for disease development. Prior to 2012 powdery mildew (Erisyphe diffusa) had not been recorded in Australia, although there is evidence that the pathogen had been present before then. The disease’s potential future impact on production is unknown.
Among the diseases which are exotic to Australia, soybean cyst nematode (Heterodera glycines), sudden wilt syndrome (several Fusarium species), and brown spot (Mycosphaerella uspenskajae) are the greatest risk to the Australian soybean industry. The first two pathogens are soilborne, whilst the brown spot pathogen is seed- and stubble-borne, so their entry into Australia is possible in machinery and on boots contaminated with infested soil or stubble fragments. Surveillance of pathotypes of endemic diseases, of emerging endemic diseases such as powdery mildew, and of possible modes of entry of significant exotic soybean diseases into Australia needs to be conducted with vigilance.