VG00013 Leek Diseases

Leeks belong to the Allium family and
are likely to be prone to similar diseases that attack onions, but little is known about diseases of leeks in Australia..

Diseases have been reported on commercial crops in Australia and the spread of these problems could jeopardise further development of the industry and affect the maintenance of existing domestic and export markets.

The aims of this project were to determine the main disease problems of
leeks in Australia, develop management strategies to control these diseases and to ensure that this new
information and technology is adopted by the industry.

Summary :

Extensive surveys of leek plantings in Australia identified two main diseases, Fusarium foot rot (Fusarium avenaceum and F. oxysporum) and Bacterial blight (Pseudomonas syringae pv. porri) as the cause of significant economic crop losses..

Lesser diseases included :

• Leaf blight (Stemphylium botryosum), while widespread in all states, only caused cosmetic damage.
• Purple blotch (Alternaria porri) was found in Victoria and Queensland, and while severe infection can reduce marketability most damage was also cosmetic.
• Others included Smudge (Colletotrichum circinans), Botrytis leaf spot (Botrytis cinerea), Pink root (Pyrenochaeta terrestris) and Oedema (caused by environmental conditions).
• Viruses including Leek Yellow Stripe, Shallot Latent and Onion Yellow Dwarf were found on leeks in Australia however they were not widespread.
• Other organisms found associated with infection from Fusarium and Pseudomonas included onion maggot and 3 species of parasitic nematodes

Surveys also showed that seedlings can often be infected with Fusarium without showing symptoms.

All commonly planted varieties were susceptible and trials showed that planting infected seedlings increased seedling mortality and Fusarium infection at harvest.

Bacterial blight caused by Pseudomonas syringae pv. porri was shown to be seed borne in leek seeds planted in Australia.

Preliminary studies showed that soaking seed in hot water eliminated the bacteria from the seed, but the treatment severely reduced germination.

Recommendations :

This project has shown that Fusarium foot rot and Bacterial blight are the two most economically important diseases of leeks in Australia.

Seed treatments need to be further evaluated to determine the efficacy of physical and chemical treatments in eliminating pathogens from seed.

Further testing also needs to be done on the use of chemical and biological treatments to reduce or prevent plants becoming infected with Fusarium in the nursery and after planting in the field.

Studies should also continue to evaluate fungicides and spray programs for the control of Alternaria and Stemphylium, as these two pathogens may become more important in the future particularly if there is climate change.

Studies need to be carried out to evaluate seed treatments for the control of bacterial infection in seed, and whether these treatments effect germination.

The spread of bacterial blight in plantings needs to be evaluated and whether different copper formulations can reduce spread and infection levels.

As a results of these studies growers should:

1. Use disease free seed – from a known source and that has been treated and properly certified as disease free.
2. Ensure that seedlings are grown in pasteurised or treated soil.
3. Ensure that seedlings are grown in a “clean” environment.
4. Obtain seedlings from a reputable source.
5. Avoid trimming the leaves of seedlings or other operations in the nursery that could spread bacteria through seedling batches.
6. Drench seedlings with a suspension of prochloraz or carbendazim to reduce the likelihood of soil infection with Fusarium.
7. Avoid injuring seedlings at planting.

Acknowledgements :

We wish to thank the leek growers of Australia and related industry personnel for participating and
being involved in the surveys.

The leek growers in South Australia and Victoria for their co-operation
and help in allowing field trials to be conducted on their properties.

A special thank you to the leek
growers of South Australia for allowing the extensive surveying of plantings and providing seedlings,
especially John Cranwell for all his time, effort and guidance during the course of the project.

All the technical staff at the Plant Research Centre and the Lenswood Research Centre for their help in
undertaking this project.

We wish to thank Michael Priest, Dr Ric Cother and Dorothy Noble from the New South Wales DPI
for identifying leek pathogens throughout the project.

This project has been facilitated by South Australian State Government and Horticulture Australia Limited (HAL) in partnership with AUSVEG and has been funded by the National Vegetable Research and Development Levy.

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