Agriculture Reference
In-Depth Information
ensured wide adoption of synthetic fertilizers and highly effective fungicides (Gaud
1968
).
Today, fungicides and bactericides are applied to many food and ornamental
crops to prevent loss of yield and pre-harvest spoilage by fungal and bacterial plant
pathogens. Nevertheless, there has been resurgence of organic and biodynamic ag-
riculture, perhaps catalysed by the publication of Rachel Carson's 'Silent Spring'
(Carson
1962
). Retailers and consumers continue to demand reduced inputs of syn-
thetic fungicides because of concerns about the safety of pesticide residues in food
and the potential for negative effects on non-target organisms (Dagostin et al.
2011
).
Development of pathogen resistance to fungicides (Walker et al.
2013
) also provides
incentive to manage chemical inputs judiciously and to seek alternative materials.
Importantly, farmers in developing and developed countries seek to reduce the cost
of crop inputs and manage land for both economic and environmental sustainability.
A common objective of contemporary plant disease management is the integra-
tion of cultural and biological controls to reduce or eliminate the need for synthetic
chemicals. When applied to the soil or crop canopy, compost tea can be considered a
type of biological control that has potential to suppress a broad range of plant patho-
gens (Scheuerell and Mahaffee
2002
). Maheshwari (
2013
) also reported the appli-
cation and advantages of biocontrol in disease management. Disease suppression is
defined here as a statistically significant reduction in plant disease incidence and/
or severity relative to a non-treated or water-treated control. There are now at least
30 refereed scientific publications that have examined the effectiveness of foliar
applications of compost teas in detached-leaf assays, glasshouse and/or field trials.
This review provides a description of the characters of compost tea, methods of
production using open-windrow compost and variation in disease suppression ob-
served. A framework is proposed for evaluating the efficacy and safety of compost
teas when applied to a crop canopy. This framework draws on results of specific in-
vestigations that demonstrate a relevant principle relating to the theory or practice of
this type of biological control. Mechanisms for integrating compost tea in the man-
agement of fruit and foliar diseases in horticultural crops are then discussed, including
the practicalities of crop protection and factors affecting adoption by farmers.
9.2
Aerated and Non-Aerated Compost Tea
Scheuerell and Mahaffee (
2002
) describe two dominant methods for producing
compost teas. Aerated compost tea (ACT) results from any method in which wa-
ter is actively aerated during contact with the compost. Non-aerated compost tea
(NCT) results from any method that rarely disturbs the compost and water after
initial mixing. Both methods require a vessel, compost, water and filtration to en-
sure large particles do not block equipment used for spraying or fertigation. Whey,
rather than water, has also been used to prepare a pathogen-suppressive compost tea
(Pane et al.
2012
).
ACT is produced within 24-72 h using a custom-built vessel containing equip-
ment for continuous aeration of dechlorinated water to maintain the activity of
