VG00048 Brassica green manure conference paper 2004

Sclerotinia diseases are among the most difficult soilborne pathogens to control.

Chemical control methods for these pathogens usually offer only temporary crop protection against infection, and have little or no effect on the long term viability of sclerotia.

Biological control by antagonistic and parasitic microbes to plant pathogens has been associated with Sclerotinia control in some soils and is often related to increase in organic matter.

Organic matter is vital as a food source and haven to beneficial microorganisms that are related to disease suppression, soil structure, improvement in soil properties and crop health.

The use of green manures in between successive crops helps maintain or increase organic matter in soils.

However, little is known of the effects of different types of green manures on Sclerotinia wilt on lettuces.

Brassica plants are known to produce different types and levels of biofumigant chemicals, collectively known as isothiocyanates

This study has shown that high plant biomass and deep tap root system, which reduced soil crusting, improved infiltration, increased organic matter and reduced subsoil compaction.

These soil improvements may contribute to disease management and crop health.

Discussion:

• This study indicates that brassica green manure plants that produce high concentrations of biofumigants offer advantages over non-brassica green manure plants for disease control.
• Fodder rapes, which produce high levels of ITCs in their roots are more effective for Sclerotinia control than mustards, which produce high levels of ITCs in their foliage.
• Brassica green manures did not eliminate S. minor inoculum in soil, and short-term disease suppression is believed to be the mode of action against Sclerotinia.
• As ITCs levels will diminish rapidly after incorporation into soil, their effects for disease suppression are expected to be relatively short term.
• As a result, brassica green manures did not control Sclerotinia infection at later crop stages.
• Under conditions that are ideal for the Sclerotinia disease, fungicide control methods should also be used in conjunction with brassica green manures for disease management.
• Other benefits from green manures that can produce longer lasting effects are often overlooked.

Acknowledgements :

The authors thank Mark Shakelton at CSIRO Entomology, Perth, conducted plant analysis for isothiocyanates.

The authors acknowledge the financial support of Horticulture Australia Limited (HAL)
in partnership with AUSVEG through the National Vegetable Research and Development Levy.

The Australian Government provides matched funding for all HAL’s R&D activities.