Integrated Environmental Biotechnology - Environmental Biotechnology: Theory and Application - page 248

This, coupled with other fears regarding residual bromine in food and ground
water, has led to bans in Germany, Switzerland and the Netherlands, the latter
being, at one time, Europe's largest user of methyl bromide soil fumigation.
A number of alternative options are being explored, including soil pasturisa-
tion using steam, ultraviolet treatment and the development of resistant cultivars
using both selective breeding and genetic modification. The use of compost
extracts - so-called 'compost teas' - is also receiving serious consideration as a
means of crop-specific disease control. Their action appears to be twofold, firstly
as a protection against foliar diseases and secondly as an inoculant to restoring
or enhancing sub-optimal soil microbial communities.
Research projects in Germany, Israel, Japan, the UK, the US and elsewhere
have found that these extracts are very effective natural methods to suppress
or control a number of plant diseases thus reducing the demand for artificial
agro-chemical intervention (Table 10.1).
Direct competition with the relevant pathogen itself is one of a variety of
mechanisms believed to play a part in the overall disease suppression, along
with induced disease resistance, and the inhibited germination of spores. This is
thought to be brought about by means of the extract's action on the surface of the
leaves themselves and stimulatory effect on the associated circum-phyllospheric
micro-organisms. Bacteria, yeasts and fungi present in the extracts have been
shown to be active agents, while evidence points to a number of organic chem-
icals, including phenols and various amino acids, also 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

Table10.1 Plantdiseasesuppressionusingselectedcompostextracts
Compost extract

Suppressed disease

Bark compost extract a

Fusariumoxysporum
Fusarium wilt

Cattle compost extract b,c Botrytiscinerea

Grey mould of beans and strawberries

Horse compost extract b Phytophthorainfestans

Potato blight

Manure-straw compost extract d Plasmoparaviticola

Downy mildew of grapes
Sphaerothecafuliginea
Powdery mildew of cucumbers
Uncinulanecator
Powdery mildew of grapes

Spent mushroom compost extract e

Venturiaconidia
Apple scab

a Kai, Ueda and Sakaguchi (1990).
b Weltzein (1990).
c Elad and Shtienberg (1994).
d Weltzein, (1989).
e Cronin et al . (1996).