Agriculture Reference
In-Depth Information
century, since pesticides tend to give more reliable control of most foliar diseases.
However, the recent increase in sustainable and organic farming and problems relating
to pesticide use has led to an increase in scientifi c papers and non-refereed publications
relating to compost extracts and teas (Scheuerell & Mahaffee, 2002). A considerable
amount of work has been carried out to develop improved methods for preparation and
use of compost extracts and teas. Most of this work has been done in the United States
and much of it by commercial companies.
5.5
Current use of composts and compost extracts/
teas in crop production
Composts and manures are often used for the purposes of crop nutrition. Their application
specifi cally for the purpose of preventing or controlling crop pests or diseases in fi eld
crops is comparatively rare at present, although growers in the United States commonly
use composted bark in container growing media in order to reduce the incidence and
severity of root and stem-base diseases. Compost teas are currently being applied by
relatively small numbers of commercial growers, mainly to ornamental crops in the
Netherlands and the United Kingdom, and to edible and ornamental crops and private
gardens in the United States. Some growers are applying compost teas with the aim, or
partial aim, of preventing disease, but most currently apply them as a general crop tonic.
The science to support the reports of effi cacy of compost teas in suppressing plant disease
is limited at present. However, there are abundant anecdotal reports of the effi cacy of
compost tea in suppressing plant disease (Scheuerell & Mahaffee, 2002; www.attra.ncat.
org), and a compost tea industry has developed, particularly in the United States, which
makes largely unproven claims based on the ability of their compost teas and brewers
(used to make the teas) to suppress plant diseases.
5.6
Crop and soil health
5.6.1
Diseases in cropping systems
Conventionally grown crops, such as cereals are frequently grown in long-term
monocultures. This practice often results in heavy pest and/or disease pressure on the
crop, and the farmer usually relies on pesticides to maintain crop health and yield in
successive crops. Crop rotations can be used to reduce incidence and severity of pest and
disease attack (Abawi & Widmer, 2000). However, modern crop rotations are often short,
and contain species from a limited number of families, therefore there is a reliance on
pesticides to minimize crop losses due to pests and diseases. The less mobile soil-borne
diseases such as rhizoctonia root rot/stem canker of potatoes (
Rhizoctonia solani
) and
clubroot of brassicas (
Plasmodiophora brassicae
) can be partially controlled through the
use of balanced rotations, appropriate break crops and good soil husbandry. However, it
is often diffi cult to control root-inhabiting pathogens that survive saprophytically in soil
organic matter and exist for long periods in the absence of a host plant without using
fungicides. These pathogens include
Pythium
spp., some
Fusarium
and
Phytophthora
spp.
and
Sclerotium rolfsii
.
