Greenhouse production of cucumbers and capsicums has developed rapidly in the last decade.
It provides larger urban areas of Australia with a ready supply of fresh products with minimal transport costs.
Other advantages are the more efficient use of water resources, fertilisers and reduced environmental degradation.
Protective structures provide a strategic capacity to feed large urban areas and market stability when adverse weather conditions affect outdoor production systems.
The project has focussed on major disease problems in greenhouse cucumbers and capsicums.
Extensive disease surveillance over the three year course of the project has updated Australian pathogen records.
New Australian records include the detection of a whitefly-transmitted virus, a fungal wilt disease and a fungal leaf spot on cucumbers.
Wilts associated with fungal root and stem rots were found to contribute to an estimated 30% of crop losses in cucumbers throughout Australia.
- We confirmed that Fusarium and Pythium isolates from diseased cucumbers were the causal agents.
- Fusarium isolates reproduced a root and stem rot disease in inoculated cucumber seedlings. Typical hypocotyl lesions formed as well as pink spore masses (sporodochia) on affected stems.
Vascular colonisation by Fusarium led to plants collapsing as observed in field surveys. Some control plants became infected late in the trials, confirming aerial transmission of this pathogen. Transmission was also demonstrated with sciarid flies and their larvae.
- Pythium isolates (P. irregulare, P. aphanidermatum and P.spinosum) were also shown to cause root rot diseases and resulted in many plants permanently wilting.
There appeared to be synergistic interactions between certain Fusarium and Pythium isolates. The combined inoculation of Fusarium and Pythium greatly increased the severity of disease expression, and hastened permanent wilting.
- The fungi, Fusarium oxysporum f. sp. radicis-cucumerinum and a range of Pythium species were found responsible for these extensive crop losses, often occurring in combination as a disease complex.
As a direct result of the crop surveys, trials into the control of this disease were initiated, in order to identify cultural, chemical and biological options.
- The integrated management of this disease through hygiene and sanitation, temperature and moisture control, chemical use and the introduction of microbial biological agents enabled greenhouse vegetable producers to reduce crop losses and maximise efficiency onfarm.
- Hygiene and sanitation proved crucial to the management of Fusarium root and stem rot, as the fungus was shown to be spread aerially and with sciarid flies.
- Reducing extremes in temperature and root zone moisture limits the potential for infection.
- Any of eight different species of the water mould Pythium were identified. Some are known to be associated with high temperatures and others with low temperatures.
- Of the chemical and microbial biocontrols evaluated, neither were found not to be curative. In some cases biocontrols halved losses in affected crops.
Chemicals performed better (losses one-sixth of untreated plants) but there are problems with the lack of relevant crop registrations and untested compatibility with other biocontrols. These factors inhibit their adoption in disease management programs.
The authors would like to thank the QLD, NSW, SA and WA greenhouse growers who cooperated in our disease surveys and in our on-farm trials.
Greenhouse Vegetables NSW, particularly the President, Mr Joe El-Boustani, supported and assisted with surveys and on-farm trials.
Vegetable IDOs in NSW (Dr Alison Anderson), QLD (Mathew Dent), SA (Craig Feutrill) and WA (David Ellement) assisted with disease surveys and extension activities.
Spray Gro Pty Ltd, Organic Crop Protectants Ltd and Bio-Care Technology Pty Ltd. supplied biological control products for evaluation.
Rijk Zwaan Ltd supplied cucumber seeds for trials and their staff, Steve Roberts, Phil Ritchie and Steve Natsias, assisted with disease surveys.
Within NSW Agriculture the following have contributed to this project. Mr Lowan Turton, Photographer, assisted with capturing images of disease symptoms and constructing the photographic montages used in this report.
Dr Idris Bachia and Lorraine Spohr undertook biometrical analyses.
Leigh James, Jeremy Badgery-Parker, Marilyn Steiner and Dr Stephen Goodwin collaborated with extension and training activities, and preparation of technical resources.
Technical support was provided for disease diagnostics, literature searches and greenhouse trials by: Dr Mary Ann Terras, Brenda Gorrie, Stacey Azzopardi, Melanie Scanes and Josh Jarvis.
This project was funded by Horticulture Australia Ltd through the National Vegetable R&D Levy and by NSW Agriculture.
The Australian Government provides matched funding for all HAL’s R&D activities.