Can the Right Potting Mix Replace
Fungicide? By Don
Comis June 15, 2007
Potting mixes custom-tailored to fight plant diseases can work much
better than systemic fungicides.
Agricultural Research Service (ARS) plant pathologists
Krause found this was true for a mix of peat, compost and the beneficial
fungus Trichoderma hamatum strain 382. Horst and Krause are at the ARS
Technology Research Unit in Wooster, Ohio. Locke is part of the unit's
Production Research Group in Toledo, Ohio.
In a test with begonias, the scientists found that the mix reduced
Botrytis gray mold, caused by the Botrytis cinerea fungus, better
than the standard fungicide chlorothalonil did. Botrytis gray mold is
the most common disease of greenhouse floral crops such as begonia, carnation,
chrysanthemum, cyclamen, geranium, impatiens, petunia and marigold.
The beneficial Trichoderma fungus seems to enter the plants
through the roots and spread through the entire plant internally. One advantage
of systemic biocontrolas opposed to spraying the plant leaves with a
solution containing beneficial fungiis that it doesn't leave a residue on
the plant that harms plant market value.
Begonias grown in this mix had much fewer gray mold symptoms and much
higher market value that those grown in straight peat and sprayed with
chlorothalonil. The improvement in plant quality and market value makes the
Trichoderma-compost mix very promising for greenhouse operations. Also,
Botrytis has developed resistance to several fungicides.
The Trichoderma fungus thwarts Botrytis on more than one
front. It prevents Botrytis from infecting fresh wounds, and produces
compounds that keep Botrytis spores from germinating.
Surprisingly, the compost mix had a similar effect even without
Trichoderma. This means there could be naturally occurring beneficial
fungi or other biocontrol agents in the compost.
But, growers need to add beneficial fungi like Trichoderma to
their mix, because they can't count on commercial composts to have them
about the research in the May/June 2007 issue of Agricultural Research
ARS is the U.S. Department of
Agriculture's chief scientific research agency.