- SCAB AND FIRE BLIGHT OF APPLE 373
recent approval by the U.S. Department of Agriculture of Arctic apples
has resulted in the commercial release and potential future sales of a
genetically modified apple (Pollack 2015). Unfortunately, public accep-
tance of genetically modified organisms continues to be a contentious
issue within the United States and throughout the world, despite its
wide adoption in maize and soybean (Hu et al. 2004).
One issue that impacts breeding for disease resistance is the na ̈ıvet ́e
that sustainable apple production would be achieved through the intro-
duction (by classical or transgenic means) of scab-resistance genes
alone, that subsequent fungicide applications would be unnecessary
and that nonchemical controls would not be needed either (Holb 2008).
Regardless of how scab disease resistance is acquired, fungicides will
still be necessary to control all of the other fungal diseases (as they suf-
fer from over 100 reported disease problems) such as powdery mildew,
rusts, flyspeck, sooty blotch, and bitter rot, to name but a few. The selec-
tive pressure that any disease resistance places on the pathogen popu-
lation has shown that resistance will break down, and that new races of
the pathogen will evolve. Any disease-resistant cultivar will still require
additional applications of fungicide to protect against these new races
and minimize the risk of resistance breakdown.
If the 1970s were the zenith for breeding trees for disease resistance
and having effective fungicides for disease management, we have today
reached the nadir of having neither: only a handful of land grant insti-
tutions in the United States. have apple breeders working on disease
resistance, the major resistance gene relied upon for breeding has been
overcome, and the issues of fungicide resistance have become so severe
and widespread, that apple scab management today has more in com-
mon with the 1950s than the 1970s (Beckerman et al. 2015).
E. Cultural Control Methods for Apple Scab Management
Cultural management strategies provide a basis in plant disease man-
agement, and are often the first to be dispensed with when either new
resistant cultivars or highly effective fungicides become adopted by
growers. For apple production, cultural management includes sanita-
tion (removing overwintering inoculum) and adopting practices that
avoid or reduce plant disease. In general, cultural controls only become
relied upon when other options are not completely effective, or when
there are no alternative control methods.
Effective apple disease management requires a foundation of sanita-
tion to minimize the development of primary inoculum, thereby pre-
venting the primary infection event from occurring. Prokopy (2003)