In Tasmania, Sclerotinia diseases caused by S. sclerotiorum and S. minor have become widespread in the north-west and southern regions, where they affect many crops, such as beans, brassicas, carrots, lettuces, peas, potatoes and pyrethrum.
Sclerotinia produces sclerotia that can survive in soil over a long period of time. As a result, with intensive cropping, Sclerotinia inoculum in the soil can increase to such a high level that fungicide spray programs alone may not give adequate control of the disease in highly susceptible horticultural crops.
This project takes a new approach to examining and developing a long term Sclerotinia disease management strategy. The aims of the studies conducted in Tasmania were to evaluate and develop both short and long-term management strategies that are suitable for Sclerotinia control in horticultural crops.
Long-term strategies that were investigated included the evaluation of promising biological methods, such as commercial biocontrol agents, green manures and break crops.
The short-term strategies examined were pre-plant and post-plant chemical control methods to determine if there are other products that could be used in combination or in alternation with the current fungicide program.
The key research findings from trials conducted in Tasmania are detailed in this report.
As lettuce is the most susceptible crop to Sclerotinia wilt, almost all trials in Tasmania were conducted with lettuce as the benchmark crop.
Although Sclerotinia sclerotiorum can also cause Sclerotinia wilt, S. minor is the most common cause of lettuce wilt.
The areas of study examined in the Tasmanian trials were:
- effectiveness of bacteria and fungal biocontrol agents, used in pre- and post-plant treatments, for use in wilt disease management.
- effectiveness of alternative chemical soil treatments, used in pre-plant treatments, for use in wilt disease management.
- methods for improving Sclerotinia control on crops in the field after planting, with the use of new fungicides and fungicide mixtures containing materials that enhance plant defence systems.
- effectiveness of a range of green manure crops, including brassica green manures, for use in high Sclerotinia pressure areas, for long-term disease management. .
- Field trials conducted in Tasmania showed that the fungicide procymidone (sold as Sumisclex and Fortress) gave consistent and effective control of Sclerotinia disease caused by S. minor and S. sclerotiorum, under high disease pressure.
- Boscalid (BAS510-01F), a new class of fungicide, was shown to be highly effective against S. sclerotiorum and S. minor on bean, lettuce and pyrethrum crops in Tasmania.
- Effective fungicide application methods are essential for good disease control, with appropriate spray volume and timing in different types of horticultural crops.
Reducing plant susceptibility
- Agri-Fos (phosphorus acid) and MicroGyp (natural gypsum or calcium sulphate), consistently improved disease control when applied in combination with Sumisclex further reduce the percentage of diseased plants by 1% to 5%, when compared to Sumisclex alone.
- Plants have their own mechanisms for preventing fungal invasion, and an unhealthy crop with nutrient deficiencies is usually more susceptible to disease than a healthy crop.
- Contans, based on C. minitans biocontrol fungus, was identified as the most promising potential biocontrol agent for Sclerotinia.
- Under low disease pressure, Contans could provide early disease control when applied as a pre-plant soil treatment or post-plant spray applications.
- With many biocontrol agents, including Contans, their efficacy for prolonged Sclerotinia control appeared to be limited.
They appeared to be less effective under high disease pressure, and against actively growing Sclerotinia pathogens under favourable wet conditions, at the late crop stage.
- Under high disease pressure, fungicide applications following early biocontrol agent treatments are still recommended.
Brassica green manures
- This study indicated that brassica green manure plants that produce high plant biomass and high concentrations of biofumigants may offer advantages over non-brassica green manure plants for Sclerotinia disease control.
- BQ-Mulch, which produces high levels of isothiocyanates (ITCs) in roots, was found to be more effective for Sclerotinia control than Fumus, which produces high levels of ITCs in its foliage.
- The fumigating activities of green manures are likely to diminish rapidly and their effects for disease suppression are expected to be relatively short term.
- 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.
- This study showed that the high plant biomass and deep tap root systems of brassica green manures, helped reduce soil crusting, improved infiltration, increased organic matter and reduced sub-soil compaction.
- These overall soil improvement effects are likely to increase soil fertility and improve soil structural properties, thereby contributing to improved crop health and disease control.
Soil amendments with mustard meal, PERLKA and urea
- A preliminary laboratory test conducted in this study showed that cold pressed mustard meal, urea and PERLKA were highly effective in killing sclerotia of S. minor when applied at very high rates.
- These products are unlikely to replace post-plant fungicide applications but could be considered for use as an additional tool for an integrated disease management practice.
- Sclerotinia may cause seedling damping-off, and the susceptibility of seedlings appeared to be closely associated with plant architecture.
- Plant architecture could therefore be a useful guide when selecting plant varieties for use in crop rotations, particularly in ground that has high Sclerotinia pressure.
- Selection of paddocks that enable good air flow and rapid drying of crops, in order to minimize risk to Sclerotinia disease, are critical. Effective disease control can be difficult to achieve in the presence of field conditions that are highly conducive to the pathogen.
This study was conducted as part of project VG00048, led by Dr. Ian Porter of Primary Industries Research Victoria.
We would like to thank the Tasmanian growers, Mr. David Bovill, Mr. Richard Bovill, Mr. Colin Houston, Mr. Dennis Davis, and Mr. Jeremy Rockcliff, for providing trial sites, as well as their field staff for their assistance in planting and overall maintenance of the trial areas.
We are grateful to Mr. John Hill of Hills Transplant Pty Ltd, for his assistance in transplant treatments at the plant nursery.
Field trials at Cambridge and Margate in southern Tasmania were conducted with the assistance of Mr. Dennis Patten and Dr. Lee Peterson, Serve-Ag staff based in Hobart.
Other Serve-Ag staff, who also assisted in this project, are Peter Aird and Sarah Lamprey.
Mark Shakelton at CSIRO Entomology, Perth, conducted plant analysis for isothiocyanates in brassica green manure tissues.
The authors are grateful for the funding support provided by 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.