Review of Soilborne Disease Management in Australian Vegetable Production
The strategic management of soilborne pathogens requires knowledge of their biology, their response to the presence or absence of a host, their host range, environmental influences on the host, the pathogen and their interaction. Soil type, health, physical and chemical structure also influence the impact of soilborne pathogens, and of those introduced to soil, eg. on planting material. Amongst vegetable growers, there is medium-high level awareness of integrated pest management (IPM) and integrated crop management (ICM) and the potential environmental, human and crop benefits potentially derived from these management approaches. The volume of information available on soilborne diseases of vegetables is such however, that few growers can synthesise the components relevant for their specific farming system and current disease threat. With consideration given to the determinants of key pathogen status, and the regional distribution of soilborne vegetable pathogens in Australia, we have concluded that the top five key pathogens (independently and in complexes) of vegetable crops today, are: Sclerotinia spp. (S. sclerotiorum and S. minor), Fusarium spp. (F. oxysporum and F. solani), Water moulds (primarily Pythium spp.), nematodes and Rhizoctonia spp. Risk assessment must underpin planting decisions. Our review suggests that growers at present do not have sufficient knowledge of some risk factors and influences on them; nor of the most timely and economic responses appropriate for their farming system. The responses may include not planting a site, planting a biofumigant crop, or changing the planting date or cultivar. Enabling technologies (i.e. DNA soil assays that can quantify some fungal pathogen and nematode soil populations; profile microbial communities etc.), are being used in other annual crop industries to inform grower decisions before planting. Vegetable growers in Australia are not lacking in options for the management of soilborne diseases. However, in the absence of informed risk assessment, vegetable growers are limited in their capacity to choose and integrate the most appropriate and reliable management options for their farming system. Synthetic chemicals and the use of tolerant/resistant cultivars where available, are therefore relied upon. Few other management options (cultural, chemical, biological, physical, genetic) have been sufficiently tested across farming systems with different soil types, disease pressures, and environmental conditions. In particular the relationship of inoculum density and disease incidence in different soil types and cultivars, is unknown for most of the identified key soilborne pathogens. Increased efforts and investment in extension material and services are strongly recommended. Growers will benefit significantly from practical knowledge packages. They should detail risk factors associated with these pathogens and how they may be assessed for whole farming systems; the economics of management options and inoculum reduction and avoidance measures; and the packages should be focussed on ‘adoption-ready’ knowledge rather than ‘early innovation’ information that cannot be implemented with any confidence. Investment in further development of risk assessment tools and technology, management options, cultivars, and inoculum reduction practices, is warranted. Some specific research on inoculum thresholds, and suppressive soil profiling and characterisation is also needed.