Volume 48 Number 1 Article 21 Pages: 47-47
Year 1994 Month 1
Title: Non-Target Effect of a Fungicide Spray Program on Phytophagous and Predacious Mite Populations in a Scab Resistant Apple Orchard
Authors: K.M. Bower, L.P. Berkett and J.F. Costante
Citation
Abstract:
Scab resistant cultivars can reduce
the need for fungicides in apple production.
However, management of
powdery mildew, cedar apple rust
and frog-eye leaf spot may require
limited fungicide use.
Since fungicides
can have mite suppressive activity, it
is important to determine the impact
this reduction would have on mite
populations.
This study, conducted
during 1988 and 1989, investigated the
impact of a fungicide spray program
(6 applications of benomyl and mancozeb
versus no fungicide application)
on phytophagous and predacious mite
populations in a Vermont apple or
chard.
Levels of mite infestation were
determined on 4 scab resistant cultivars and 2 scab susceptible cultivars
by counting motile phytophagous and
predacious mites on leaf samples collected on 16 dates in each growing
season.
Data were evaluated separ
ately for each cultivar, on each assess
ment date arid over time, using an
analysis of variance with a completely
randomized design.
Within each cultivar
there were 3-5 single tree replicates per treatment.
The impact of the fun
gicide spray program on predacious
mite populations were clearly evident
in both years.
Approximately four
weeks after the last fungicide applica
tion, significantly higher predacious
mite populations were detected on
non-treated trees.
Out of the 56 sam
ples for all cultivars in which there
was a significant difference in preda
cious mites, on 54 of those incidences
(96.42), the mean number of preda
cious mites was significantly higher on
non-fungicide treated trees.
In 1988,
few significant differences in phyto
phagous mite populations within culti
vars were detected.
However, incidences where there were significant
differences in phytophagous mite pop
ulations increased in 1989; in the
majority of the incidences, populations
were significantly higher on fungicide
treated trees.
This study shows that a
fungicide spray program consisting of
6 applications can impact the mite
populations on apple trees and documents the potential benefit of eliminating fungicide applications.
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