Agriculture Reference
In-Depth Information
incidence was reduced by 26%, 63%, and 74% in vines treated with 160, 320, and 480 g
of harpin ha
1
, respectively, compared with the untreated controls.
4.2.1.9
Onion
Several studies have shown that ASM has effi cacy against bacterial and viral diseases in
onions. Field trials by Gent
et al.
(2004) showed that four applications of ASM resulted
in a 34% reduction in the incidence of Iris yellow spot virus (IYSV) and also increased
the number of jumbo grade bulbs. Recent reports have suggested that the product will
soon be registered in Colorado for use in onions to manage IYSV (Lang
et al.,
2007).
ASM has also demonstrated potential to replace copper-based sprays that are routinely
used to manage xanthomonas leaf blight (
X. axonopodis
pv.
allii
) in onions (Gent &
Schwartz, 2005). Four weekly applications of ASM controlled xanthomonas leaf blight
as effectively as a copper oxychloride-mancozeb programme consisting of between
nine and twelve applications (Gent & Schwartz, 2005). In the absence of disease, ten
weekly applications of ASM reduced total bulb yield by up to 27%. However, this
result should be treated with caution as no yield reduction was observed when four
applications of ASM were applied at the recommended label rate. More recently, Lang
et al.
(2007) evaluated mixtures of bacteriophages and ASM to manage xanthomo-
nas leaf blight under glasshouse and fi eld conditions in Colorado. Two applications
of ASM integrated with bi-weekly bacteriophage (AgriPhage
®
, OmniLytics, USA)
applications reduced disease severity by up to 50% and were as effective as a multiple-
application copper-based programme. While this result is encouraging, this approach
would be more costly than the conventional programme and studies are required to
investigate strategies that make ASM/bacteriophage combinations more economically
attractive.
4.2.1.10
Potato
Foliar application of ASM, at 60 days of crop growth, reduced the severity of natural foliar
infections, mainly early blight (
Alternaria solani
), in 'Sebago' potatoes (Bokshi
et al.,
2003). However, the treatment did not induce resistance in tubers to postharvest inocula-
tion with the dry rot fungus (
Fusarium semitectum
). In glasshouse studies on 'Coliban',
ASM treatment signifi cantly reduced the severity of early blight and powdery mildew
(
Erysiphe cichoracearum
) on foliage and dry rot in tubers. Greater resistance to dry rot
was observed when foliage was treated at 30 days of crop growth than at 60 days. In
glasshouse studies, ASM treatment induced resistance to blackleg (
Pectobacterium caro-
tovorum
) in 'Asterix' and 'Baronese' potatoes, but not 'Monalisa' (Benelli
et al.,
2004).
More recently, Collins
et al.
(2006) investigated whether activation of systemic resistance
in potatoes would impact on rhizosphere populations in the fi eld. Repeated foliar applica-
tions of ASM and harpin did not affect rhizosphere microbial populations, but did affect
nematode densities. Non plant-parasitic nematodes increased in the harpin treatments and
decreased with ASM treatment compared with the control. Both treatments resulted in a
reduction of lesion nematodes (
Pratylenchus
spp.) and ASM reduced root knot nematodes
(
Meloidogyne chitwoodi
) by harvest. The use of ASM plus harpin reduced the nematode
infection index in comparison to the control. It is important to understand the ecological
