The
              Report

No. 85: Fungicides identified to fight protea disease


The full report
This is a summary of a full report Proteaceae - Managing Elsinoe Scab published by RIRDC (Pub. No. 00/64, DAV-116A) by A. Ziehrl, G. Berg, I. Pascoe and I. Porter; Ph: 03 9210 9222; Fax: 03 9800 3521.
The report is available in hardcopy (under wildflowers) or downloadable from this site.

Researchers have identified three fungicides to reduce the stem disease Elsinoe scab in South African Proteaceae. Almost a third of Australia™s production of this protea is currently infected at a cost to growers of about $600,000 a year.

Caused by Elsinoe spp, the disease produces scabby lesions on stems, leaves and flower heads and heavy infection can cause twisting or splitting of stems. Pruning of affected plants for disease control and/ or the disease itself can reduce production and in some cases, kill the host plants. The study to identify the fungicides was undertaken by researchers, Angelika Ziehrl, Gordon Berg, Ian Pascoe and Ian J. Porter, from Agriculture Victoria™s Department of Natural Resources and Environment.

It was funded by the Rural Industries Research and Development Corporation (RIRDC) and was prompted by a 1994/ 1995 study by the Institute for Horticultural Development on the incidence and economic impact of Elsinoe scab. RIRDC and the Australian Flora and Protea Growers™ Association (AFPGA) jointly funded the first study. That study found that Elsinoe scab was rated by survey respondents from both protea plantations and nurseries as the most serious disease affecting Proteaceae. It also showed the disease impacted on approximately 31 per cent of South African Proteaceae production in Australia, with existing management strategies for the disease having limited effectiveness.

The Study

This project aimed to develop an integrated control program for Elsinoe scab with objec- tives to:
 


The study also sought to develop an integrated control program for Elsinoe scab to reduce loss of revenue, cost of control and re-establishment, chemical usage, spread of the disease throughout the industry and the threat to developing export markets.

Research relied heavily on field trials to allow direct application of outcomes to commercial properties.

But extended and unusual weather conditions over nearly the entire period of one trial and high spore levels, impeded the collection of important data on conditions conducive to infection and disease development.

This was seen as a major drawback in understanding the disease and for developing further trials.

As a result, RIRDC funded a nine-month extension to the project with researchers then identifying key epidemiological factors through laboratory work.

The Results

Research conducted on Elsinoe scab in Victorian retail nurseries found that Australian isolates of Elsinoe spp. are the same species as those in South Africa. Also, the work shows some cultivars and selections of Proteaceae are more susceptible to infection than others. The effect of the disease on plant health and production can vary widely, even with the same level of initial infection.

Plants are more susceptible to the disease during the early stages of spring and autumn growth flushes.

Six of 11 retail nurseries surveyed had plants with visible symptoms of the disease. A further 17 per cent of plants developed symptoms later, increasing the number of nurseries with diseased plants to seven.

Within nurseries, disease levels appeared exacerbated by overcrowding of plants, overhead irrigation and high humidity - conditions favouring infection and disease progression, particularly on soft new shoots. Results of field trials showed Elsinoe spores may be present throughout most of the year on properties with high disease levels. Rain or overhead irrigation is required for at least primary infections to occur and moist warm conditions favour disease progression.

Spore germination on trial plants was significantly reduced at temperatures below 20 º C, although some germination did occur on soft new growth and under the pressure of high spore levels. The fungus isolated has the ability to infect other genera including Banksia and Dryandra spp.

In seeking to find measures to control the disease, nine fungicides were tested. Of these three - Octave®, Captan® and Dithane® - proved very good, reducing stem disease on flower shoots by 75 per cent. These fungicides also significantly reduced the number of se- verely affected stems per plant.

Of the remaining fungicides, two showed good results but the rest were only fair.

The study also identified that Proteaceae hosts can carry Elsinoe without showing symptoms. Developing a nursery hygiene program may help reduce the spread of the disease, and a suitable program should be based on training to minimise conditions that promote Elsinoe spread and survival.

As some Australian native Proteaceae were able to be infected with Elsinoe spp. isolated from South African varieties, and therefore have the ability to harbour the disease, a broad review of plant hygiene and distribution practices within the Australian Protea and Wildflower industries may be warranted.

The King Protea (Protea cynaroides),

The Study

The study indicates growers should use Octave®, Captan® or Dithane® to control Elsinoe scab. But they need to rotate the fungicides use to avoid pesticide resistance.

The work uncovered a range of implications for the Protea and wildflower industries in relation to severity and spread of Elsinoe scab. An integrated approach to managikng Elsinoe scab is required to minimise the severity and impact of the disease.

A survey of retail nurseries trading in South African Proteaceae indicated that more than 50 per cent of them stocked diseased plants. This suggests that Elsinoe scab is currently being spread to new sites and plantations through the sale of diseased plants.

Infection of Banksia spp. and Dryandra formosa by Elsinoe leucospermi isolates in the trials, should concern both the Protea and wildflower industries. If Elsinoe scab appeared on these commercial varieties, there is a possibility that the disease may become well established on native Australian flora and adversely affect production and sales.

A number of key issues were identified in this study as contributing to the economic loss attributed to Elsinoe scab and the spread of the disease throughout the Australian industry. These issues and some basic approaches and/ or remedies are listed in the following table:
 
Issue Management approach
1. Difficulty in disease identification  Contact a local agricultural advisory service
2. Trade of plants prior to symptom development after initial infection Use only reputable suppliers

Quarantine new stock for up to six months prior to planting, preferably with sprinkler irrigation to encourage symptoms of any existing disease 
3. Splash dispersal of spores  Avoid overhead irrigation
4. Physical disease transfer on property  Sterilise harvesting and pruning tools
5. Disease transfer through cuttings Do not use diseased plants for cuttings
6. Perpetuation of existing disease Prune out and destroy all infected material, paying particular attention to small non-productive shoots which have been shown to carry high levels of disease
7. Inadequate spray penetration and/or leaf stem coverage and droplet distribution  On-farm consultation and testing of spray methods (eg, with water sensitive strips), should be conducted together with equipment suppliers or other agricultural advisers 

Prune to allow greater spray penetration
8. Close proximity of plants Plan planting distances to allow maximum air circulation between mature plants

Increased spacing between pots will reduce the risk of disease transfer 
9. Susceptible varieties Use less susceptible cultivars and selections and/or conduct on-property selection trials for greater resistance to Elsinoe
10. Timing of spray application Do not wait for symptoms to appear on new shoot material. Apply fungicides when conditions and plant growth are likely to result in new infections (figure 10.1)

Primary infection may allow secondary infection to occur throughout the season
11. No fungicides registered for Elsinoe Seek all available information on control

Use fungicides within State registration and Label guidelines
12. High cost of fungicides Time sprays carefully to obtain maximum control and minimise the number applied

Use cost effective fungicides
13. Plant losses due to fungicide toxicity Test a few plants first for phytotoxicity 

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