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September 2006

Compost Tea - Sharing experience

Extracted from an article reporting on the annual Great Britain and Ireland Conference of the International Plant Propagators Society held in 2006 at Grobbendonk, Belgium at the end of August. The article was included in "Plants and Propagators" Autumn 2006 - The Newsletter of the Great Britain and Ireland Region of the International Plant Propagators Society. This year's conference was on the theme 'Sustainable Plant Production'

A key session was on the use of Compost Teas, with the emphasis on their use to maintain a healthy population of beneficial micro-organisms both in the growing media and on plant leaves. There is increasing evidence that these out-compete and suppress the growth of pathogens and improve the plants' resistance to pests. However Compost Tea is not recommended or approved as a crop protection product.

John Summers of Tref Ego, one of the best-known suppliers of Compost Tea, said the material had a valuable role to play in propagation as well as production.

"This starts with the mother stock," he said. "Spraying mother plants with tea every 10 to 14 days will help to suppress Botrytis and leaf spots and means you won't carry these pathogens through into propagation. Use on the soil around stockplants improves fertiliser uptake by 30% which means stronger shoot growth and healthier cuttings."

John said that cuttings carrying a healthy microflora on their leaves would be less susceptible to Botrytis during propagation. "You can reduce Botrytis in propagation almost completely".

"Meanwhile, if you have tea in the propagation compost it means there is nutrition available at the point the roots begin to demand it. That timing can be critical and if nutrition is not there when the cutting needs it you get a second rate cutting - and that's not reversible".

"The developing roots then begin to produce exudates which trigger further microbial growth which in turn stimulates more root growth. Any pathogens that do enter the system then have a problem overcoming the plant."

John said using compost tea in a greenhouse could also have a dramatic effect on its ecology. "Your structure is alive with air-borne spores. Fungicides will only kill what is on the plant, not all the spores in the greenhouse. Tea applied in the house will begin to reduce the disease pressure - it can almost eliminate overwintering Botrytis."

John stressed that compost teas were not a new invention but were simply about re-learning how plants grow in their natural habitats - a view backed by Karel Eigenraam who spoke on using composts and compost teas in plant nutrition.

"The aim is to feed the microbes so that they in turn will make nutrients available to the plant. It will save lots of labour and chemicals - though small doses of chemical fertiliser can help and in a healthy soil or growing medium will be used very efficiently".

"A soil rich in beneficial microbes can also induce pest and disease resistance in plants. There will be fewer pest and disease problems although you may not be able to abandon chemical treatments completely. After using them, use compost teas to re-establish the food web in the soil or growing media."

Karel said growers using compost teas to manage their soils and growing media were telling him their crops were more uniform and ready for sale earlier, quality was improved and grafting results were better.

The full text of this article is included in Plants and Propagators, The Newsletter of the International Plant Propagators Society. Information on the International Plant Propagators Society are available from http://www.ipps.org.uk

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