Disease Suppressive Composts

Matthew Ayres, SARDO, November 2007


Soil-borne disease currently accounts for a significant proportion of crop loss and failure on the Northern Adelaide Plains. The control of these diseases has been brought sharply into focus since the banning of the soil fumigant methyl-bromide due to its contribution to ozone-layer depletion. Since that time, growers have been seeking viable methods to control plant diseases. The addition of compost to soil may help provide a solution. 

Based at the South Australian Research and Development Institute (SARDI), Matthew Ayres is investigating the use of compost for disease suppression in vegetable crops on the Northern Adelaide Plains. Although relatively little examination of the role of compost in suppressing diseases of horticultural crops has been conducted in Australia, international research has shown great benefits when using compost incorporated into soils. Through the appropriate use of compost and specially developed compost formulations, it is envisioned that improved management of pests, disease and crop health can be achieved, with the potential for reduced reliance on chemical pesticides.

The main crops targeted are; capsicum, cucumber, tomato and eggplant. The main disease organisms targeted are fungi such as Fusarium, Pythium, and Rhizoctonia that cause wilts and root and stem rots. The effect of compost application on plant pathogenic nematodes will also be investigated. Laboratory, glasshouse and field experiments are underway to identify the composts that contribute most to disease suppression. 


Greenhouse Bioassays 

A number of plant bioassays (pot-trials), conducted in greenhouses at the Waite Institute, showed that significant suppression of soil-borne root and stem disease is possible using compost. In one trial, compost incorporation into soils known to contain disease reduced plant root-disease from 82% to 18% for tomatoes and from 98% to 26% for capsicum.

Scientists point out that these results are still to be validated in the field.


Field Trials 

Trials have recently been established in commercially-operating greenhouses at Virginia. Crops will be monitored for evidence of disease, and differences in disease incidence between treatments will be assessed. An attempt will also be made to assess differences in marketable yield and quality of crops between treatments.

Plant bioassays will run concurrently with the field trials in order to help determine the mechanisms involved in disease suppression.

Researchers are trying to identify the composts that contribute most to disease suppresion. Down the track, the group hopes to identify specific microbes which promote disease suppression and find ways to use those organisms to make the composts work more effectively.While the initial focus of the project is on intensive greenhouse crops, it is anticipated that compost applied to soils may have a major role to play in plant-disease suppression in field crops such as potatoes, carrots and lettuce.