Integrated Environmental Biotechnology 251Table 10.1 Plant disease suppression using selected compost extracts
Compost extract Suppressed disease
Bark compost extract^1 Fusarium oxysporum
Fusarium Wilt
Cattle compost extract^2 ,^3 Botrytis cinerea
Grey Mould of beans and strawberries
Horse compost extract^2 Phytopthora infestans
Potato Blight
Manure–straw compost extract^4 Plasmopara viticola
Downy Mildew of grapes
Sphaerotheca fuliginea
Powdery Mildew of Cucumbers
Uncinula necator
Powdery Mildew of grapes
Spent mushroom compost extract^5 Venturia conidia
Apple Scab(^1) Kai, Ueda and Sakaguchi 1990.
(^2) Weltzein 1990.
(^3) Elad and Shtienberg 1994.
(^4) Weltzein 1989.
(^5) Croninet al. 1996.
having a role in the suppression effect. The exact nature of this action is not fully
understood, but it would seem to be principally a biological control, since it has
been known for some time that fine filtration and sterilisation by heat treatment,
significantly reduce the extract’s effectiveness (Trankner 1992).
Compost teas are prepared for use by either aerated or fermented extraction
methods. So-called ‘fermented’ extraction was the original, first developed in
Germany and it is not, in fact, a fermentative process at all. Actually an infusion
method, this requires a suspension of compost in water to be made, in a ratio
typically around 1:6 by volume. The resultant mixture is allowed to stand for
a given period, usually between 3–7 days, then coarsely filtered prior to being
used. The second method, which came out of research in Austria and the USA,
is more active and, with a typical cycle period of around 10–12 hours, derives
the product in much shorter time. The acceleration is achieved by increasing
the oxygen transfer to the extract during formation, initially by passing water
through compost, collecting the resultant liquor and recirculating it many times
to concentrate and aerate. Once prepared by either method, the finished product
is used as a foliar drench, typically applied to commercial crops at a rate of
around 1000 litres per hectare (100 gallons per acre).
The abilities of properly prepared biowaste composts themselves to suppress
and control soil-borne plant diseases, especially where mature compost is directly
mixed with the soil itself have been established (Serra-Wittling, Houot and Labou-
vette 1996). The efficacy of the protection given by this kind of incorporation
with soil known to be conducive to plant pathogens has also been demonstrated.