Agriculture Reference
In-Depth Information
impact of induced resistance and further studies are necessary to determine potential
effects of activators on soil microbial diversity.
4.2.1.11
Lettuce
Field applications of the commercial activator Oxycom™ (Redox Chemicals Inc.,
USA) reduced downy mildew (
Bremia lactucae
) and root rot (
Pythium
sp.) in lettuce
(Kim
et al.,
2001). In some cases, multiple Oxycom™ treatments compared favourably
with the industry standard fungicide regime. Four applications of ASM signifi cantly
reduced the level of powdery mildew (
Erysiphe cichoracearum
) on nine different let-
tuce cultivars that differed in susceptibility to the pathogen (Matheron & Porchas,
2000a). The use of ASM-fungicide mixtures also proved to be highly effective thus
demonstrating the potential to use ASM as part of a fungicide resistance management
programme (Matheron & Porchas, 2000b). In fi eld testing during 2001, ASM reduced
bacterial spot incidence in lettuce, caused by
Xanthomonas
campestris
pv.
vitians
, by
between 30% and 50% and this was equivalent to that obtained using a mixture of cop-
per sulphate (Cuprofi x
®
) and manganese ethylene bisdithiocarbamate (Maneb)
(
Bull &
Koike, 2005).
4.2.1.12
Cereals
ASM was originally registered as a plant tonic (Bion
®
) to control powdery mildew
(
Blumeria graminis
) on wheat (Gorlach
et al
., 1996). Unfortunately, the fi eld perfor-
mance of ASM in winter wheat was disappointing and the product exhibited variable
fi eld effi cacy when compared with conventional fungicides. The integrated use of ASM
with fungicides enabled a reduction in the frequency of fungicide applications in cereal
trials in Denmark (Jorgensen
et al
., 1997). Tank-mixing ASM with azoxystrobin provided
better control of powdery mildew (
B. graminis
f. sp.
tritici
) and leaf blotch (
Septoria
tritici
) on wheat than that achieved by either component alone (Stadnik & Buchenauer,
1999). However, the addition of the plant activator offered no benefi t in relation to grain
yield compared with fungicide only.
Iodus 40
®
(a.i. laminarin,
Goëmar, France) is registered for use on wheat to control
powdery mildew. Spray application with Iodus 40
®
(laminarin 1 g l
1
), 48 hours before
inoculation reduced mildew infection by 55% on wheat plantlets (Renard-Merlier
et al
,
2007). The ethanolic extract of
Reynoutria sachalinensis
, Milsana
®
, has been shown to
suppress powdery mildew on wheat by a combination of induced resistance and direct
antifungal activity (Randoux
et al.
, 2006). A single spray to run-off, 48 hours before
inoculation, reduced mildew infection on young glasshouse seedlings by 97%. A water-
soluble extract from
R. sachalinensis
has also shown fi eld effi cacy against powdery
mildew in wheat (Vechet
et al.,
2005).
Sonnemann
et al.
(2005) reported that mycorrhizal fungi and pathogenic nematodes
signifi cantly modulated the effect of ASM-induced resistance against powdery mildew
(
Blumeria graminis
f. sp.
hordei
) in glasshouse grown barley. ASM-treated plants showed
increased susceptibility to infection at higher levels of root infection. Although the results
can not be extrapolated to fi eld conditions, they do highlight the need to consider the
impact of soil biota on the effi cacy of plant activators.
