Compost fends off soil-borne disease

As well as helping to reduce the volume of waste shipped off to landfill, compost can have real health benefits - if you are a plant.

While compost’s benefits as a fertiliser and provider of nutrients are well established, its use as a fungicide and suppressor of other plant diseases is less well documented.

But a study commissioned by the Waste & Resources Action Plan (WRAP) looked at recent research into almost 50 types of disease affecting plants and concludes the evidence that compost made from garden or food waste helps suppress all manner of wilts, rots and turf disease is overwhelming.

The study was carried out by the University of Warwick’s horticultural research wing, Warwick HRI, and demonstrates that mixing compost into soil or peat to a level of 20 per cent or above enables ‘good’ microbes in the compost to fight off many common pathogens.

As well as being of value to the home gardener, the study suggests there are potential commercial benefits for agro-industrial use of compost.

Bacterial leafspot on radish crops and powdery mildew on barley could both be warded off by adding sufficient amounts of compost, for example.

The study looked at both container trials and field trials and found that in 74% of cases the compost had some beneficial effect at suppressing disease.

It also found that compost was in its prime when it came to fighting disease when it was between 12 and 15 months old.

Newly composted waste did not appear to have had enough time to allow useful bacteria cultures to develop, particularly when younger than six months, while compost seemed to reach its disease-combating sell by date after about two years, when it began losing potency.

There was also evidence that different kinds of compost varied in their efficiency at staving off different diseases.

Marketing compost has proved something of a headache to many producers in the past, who often end up giving the product away free of charge or for a very low price.

But the report concludes that there is a large potential market for compost in vegetable and ornamental crop production, turf grass top dressings and amateur gardening, so long as end-users can be convinced of its reliability as a weapon against plant disease.

Demonstrating such benefits will also help reduce dependency on chemical fungicides – a significant selling point for professional growers and amateur gardeners that offers obvious environmental benefits.

Sam Bond

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