Volume 48 Number 1 Article 8 Pages: 35-35
Year 1994 Month 1
Title: Disease Management of Scab-Resistant Cultivars
Authors: L.P. Berkett, J.F. Costante, K.N. Bower, J. Clements and D. Schmitt
Citation
Abstract:
While 'disease resistant cultivars' are
immune to apple scab, they may be
affected by other fungal diseases such
as cedar apple rust, powdery mildew,
and frog-eye leaf spot that affect the
foliage and/or fruit.
Apple growers
need to know what diseases are poten
tial problems on the cultivars; they
also need information on how to effec
tively manage these diseases.
The ob
jective of this study was to determine
the incidence of foliar and fruit diseases
on scab-resistant trees treated with
minimal fungicides compared to nontreated
trees.
The investigation was
conducted in an orchard containing 8
scab-resistant cultivars and 2 scabsusceptible
cultivars.
Each cultivar
represented an individual block con
taining 5-13 trees.
Within each cultivar
block, the treatments (fungicide treat
ment versus no fungicide treatment)
were randomly assigned to the trees.
In 1988 and 1989, the fungicide treatment consisted of 6 applications of
benomyl and mancozeo applied be
tween the 'pink' phenological stage to
approximately 2-3 weeks after petal
fall.
In 1990 and 1991, myclobutanil
plus captan were applied at the pink
and petal fall phenological stages.
Each
year, disease incidence was assessed
on cluster and terminal foliage.
In
1990 and 1991, fruit were also evalu
ated.
The cultivars exhibited a range
of susceptibility to cedar apple rust.
On those cultivars that were less sus
ceptible to cedar apple rust, a 'frogeye
leaf spot' was more prevalent.
Fungicides did have a significant effect
on incidence of cedar apple rust and
leaf spotting.
Percentages of non-treat
ed fruit on which no disease symptoms
or disorders were detected at harvest
ranged from 523! on 'Nova Easygro' to
928! on 'Redfree' and 'Freedom' in
1990, and 50X on 'Freedom' to 992 on
'Liberty' in 1991.
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