Agriculture Reference
In-Depth Information
source and the fermentation method. For example, Weltzein (1990) showed that late
blight lesions (
Phytophthora infestans
) on detached tomato leaves were suppressed
to the greatest extent by 7- and 14-day fermentations, as opposed to 1-, 2- and 28-day
fermentations. There is a lack of published data to support the statements made in popular
literature concerning the effect of fermentation time on the disease-suppressive properties
of compost teas. Ingham (1999, 2003) claims that optimum fermentation times coincide
with the presence of maximum active microbial biomass in the teas as they ferment,
which is usually 18-36 hours. Others have suggested that whilst 24 hour fermentations
are best for compost teas which are intended for use primarily as fertilizers, fermenta-
tion times of 7-14 days are better when producing compost teas with optimal disease-
suppressive properties.
5.8.1.4
Fermentation nutrients
Most compost teas produced for research purposes or for use in gardens or on commer-
cial crops are produced with added nutrients (i.e. nutrients other than those present in the
compost). There are many compost tea recipes, the authors of which claim will produce
compost teas, which enhance the growth of specifi c microbial groups, or will result in
particular bacteria:fungi ratios. Several brewer manufacturers also sell proprietary formu-
lations of nutrients, which they claim will help produce teas with particular properties.
However, there is very little published scientifi c evidence to support the effi cacy claims
made for most of the recipes or proprietary nutrient formulations.
A wide range of nutrients have been added to compost extracts and teas prior to
fermentation, primarily in attempts to see whether the disease-suppressive properties of the
teas were enhanced. Nutrients used to date include sucrose, malt, yeast extract, peptone,
starch, nutrient broth, humic acid, kelp, molasses and rock dust (Mahaffee & Scheuerell,
2006). The addition of fermentation nutrients has been shown in some cases to enhance
the disease-suppressive properties of the teas (Ketterer, 1990; Sackenheim
et al.
, 1994;
Scheuerell & Mahaffee, 2004, 2006), to reduce the disease-suppressive properties (Urban &
Trankner, 1993; Scheuerell & Mahaffee, 2004), or in other cases to have no effects on
disease-suppressive properties (Elad & Shtienberg, 1994).
5.8.1.5
Dilution
Very few investigations have been carried out to determine whether dilution of compost
extracts and teas (with water) affects their ability to suppress disease. Many small-
scale growers apply compost tea at the rate of 50 L ha
1
, according to instructions in
the Compost Tea Brewing Manual (Ingham, 2003). However, the cost and practical
problems associated with applying them at this rate on a large scale would likely be
prohibitive. Most published studies relate to a single pathogen, and no overall conclu-
sion relating to the effect of dilution has been reached. Some workers have found that
the disease-suppressive properties of compost tea could be maintained after dilution
dependent on compost source (Elad & Shtienberg, 1994), whereas others found that
dilution decreased disease-suppressive properties of the tea (Scheuerell & Mahaffee,
2004).
