Agriculture Reference
In-Depth Information
The benefit of using compost tea amended with nutrients appears to depend on
the pathosystem. The most consistent ACT for suppression of damping-off on field-
grown cucumbers caused by
Pythium ultimum
was ACT amended with kelp, hu-
mic acids and rock dust (Scheuerell and Mahaffee
2004
). In another pathosystem,
Scheuerell and Mahaffee (
2006
) illustrated no significant difference between ACT
and ACT amended with nutrients for grey mould suppression on geranium, regard-
less of an increase in microbial numbers with additional nutrients.
Adjuvants are mixed with synthetic fungicides to reduce the surface tension of
the spray droplets, helping the fungicide to adhere and increase its surface area on
the leaf or fruit surface and/or penetration of the leaf cuticle (Steurbaut
1993
; Zab-
kiewicz
2007
). Materials compatible with organic agriculture include fish hydroly-
sate (de Ong
1927
), vegetable oils and polysaccharides, although the benefit of each
as an adjuvant needs to be determined empirically. Spray adjuvants, including Ka-
raya gum and Yucca extract, have been shown to increase the effectiveness of ACTs
in reducing
B. cinerea
development on glasshouse grown geranium (Scheuerell and
Mahaffee
2006
). In grapevine, however, adjuvants used as wetter-spreaders and
penetrants have been shown to disintegrate the epicuticular waxes on berry surfac-
es, causing greater susceptibility to
B. cinerea
infection and depletion of the number
of microorganisms on the fruit surface (Marois et al.
1987
; Rogiers et al.
2005
).
9.4.5
Storage
Practitioners expect to use compost tea soon after preparation meaning that product
'shelf life' is not a major concern; however, there may be occasions where a tea
needs to be stored and/or transported to another location. Research is needed to de-
termine the viability of microorganisms in compost tea during storage and transport,
as well as changes in biological, chemical and physical characters resulting from
microbial competition, parasitism and/or antibiosis. Foregoing commercialisation
of bio-fungicides, experiments are required to determine the formulation that results
in long-term survival or integrity of the active component/s. Abadias et al. (
2001
),
for example, found that that the greatest survival rate and viability of
Candida sake
occurred when the biocontrol agent was freeze-dried and stored in lactose and skim
milk. Compost tea, in contrast, comprises not only component microorganisms but
the medium in which these microorganisms are sustained. The potential to con-
centrate and store compost tea produced in large quantities to maintain its disease-
suppressive qualities is unknown.
9.4.6
Dilution Prior to Application
Some practitioners may seek to dilute a batch of compost tea with water to allow
the same volume of tea to be applied over a greater area of a horticultural crop.
Palmer et al. (
2010b
) evaluated the mean germination proportion of
Botrytis cinerea
