Agriculture Reference
In-Depth Information
9.8
Integrating Compost Teas in Disease Management
Adoption of compost tea as a means of biological control depends on strategies for
integrating it into existing crop and disease management that allow the timing and
number of applications to be optimised in relation to disease risk. How well the crop
protectant is applied to the crop surface can also influence efficacy. Spray technique
influences the distribution of spray droplet size and how well those droplets inter-
cept and cover the target plant tissue (Landers 2010 ). As such, biological control is
best implemented when there is a good understanding of disease epidemiology and
spray technology, including the key pathogen, crop and environmental factors driv-
ing disease development. Disease management tactics are also dictated by the level
of disease control considered acceptable by the farming business.
9.8.1
Seasonal Variation and Disease Thresholds
The extent of disease suppression using any form of crop protection is likely to vary
from one growing season to the next according to how the crop protectant inter-
acts with the prevailing environmental conditions, the arrival and concentration of
virulent pathogen inoculum and host growth factors affecting the susceptibility of
various plant tissues. In contrast, the level of acceptable disease control is defined
by the farming business and is influenced by the farming philosophy, business-style
and/or quality of produce demanded by customers and consumers. Evidence for
disease suppression from small-plot field experiments does not imply that applica-
tion of compost teas under commercial farming conditions would result in effective
disease control, as defined by the farmer. Nil-tolerance for a particular disease may
be necessary when customers reject a diseased crop on the basis of reduced produce
quality. Otherwise, there is usually a pre-determined disease severity, below which
there is no significant impact on the long-term sustainability of the farming busi-
ness. A certain frequency of crop failure may also be tolerated by some farmers
because high returns in abundant seasons maintain business viability.
9.8.2
Strategies for Implementation
The mechanism of action of compost tea will inform whether or not compost tea
is applied as a protectant, to prevent infection by a plant pathogen, and/or as a
post-infection eradicant or suppressant of pathogen colonisation. The first pro-
tective spray is usually timed in the weeks immediately preceding the expected
arrival of pathogen inoculum for primary infection of the host plant. Evidence of
environmental conditions favouring dispersal of primary inoculum and/or primary
infection might also be used to time a spray application (Magarey et al. 2002 ).
Monitoring for a low incidence of the first symptoms of disease can also be used;
however, this method may be unsuitable for those diseases where incidence and
severity increase rapidly under certain environmental conditions.
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