- SCAB AND FIRE BLIGHT OF APPLE 369
pressure). Within a decade after adoption of dodine, fungicide resis-
tance became a recognized problem in the apple scab pathogen,Ven-
turia inaequalis(Szkolnik and Gilpatrick 1969; Hewitt 1998). In 1971,
after 3 years of intensive benomyl use, resistance was first detected in a
southern Australian apple orchard (Wicks 1974.), followed by the iden-
tification of benomyl-resistantV. inaequalisisolates in Michigan in 1975
(Jones and Walker 1976).
The evolution of dodine and benomyl resistance preceded the release
of the SBI fungicides by a few years (with active ingredients like tri-
forine, fenarimol, propiconazole, triadimefon, and later myclobutanil).
These fungicides continued to provide a curative mode of action or
“kick-back” that was lacking in the protectant class of fungicides, (e.g.,
lime-sulfur, copper products, captan and mancozeb) making them more
desirable. More importantly, all of these fungicides, with their ability to
eradicate incipient infections gave growers a several day buffer against
poorly timed, or even slightly missed spray applications and allowed
growers to spray only when confirmed Mills infections had occurred.
Using SBIs in commercial orchards with low scab incidence in the pre-
vious year, the first fungicide applications could be applied as late as
the pink bud phenological stage, rather than starting 2–4 weeks earlier
at green tip (Gadoury et al. 1989). This approach was widely adopted,
reducing the five to eight early season fungicide applications typically
used when protectants were employed to four applications (Cooley and
Autio 1997).
Not surprisingly, as was observed with dodine in the late 1960s and
benomyl in the 1970s, resistance to SBI fungicides was first described
in the 1980s by Stanis and Jones (1985) and the phenomenon of fungi-
cide resistance repeated itself (Koller and Wilcox 1999). Again, just as
the introduction of SBI fungicides had softened the blow of resistance
to dodine and benomyl, the introduction of a new fungicide mode of
action, the strobilurins (Koller et al. 2005), gave growers an alternative
for the longer-term post-infection control of scab, though not allowing
as long a period of post-infection activity as the SBIs (Koller et al. 2005;
Cooley 2009). However, only a few years later, resistance to strobilurins
was identified in the orchards in Europe and later in North America
(Fontaine et al. 2009; Lesniak et al. 2011; Marine et al. 2012; Villani and
Cox 2014). For the first time since the introduction of dodine in 1958,
affected eastern and midwestern U.S. apple growers could no longer
rely on long-term post-infection control, and were faced with the possi-
bility that a single mistake or extreme weather event that occurred prior
to bloom could result in a season-long scab problem, necessitating addi-
tional applications of fungicide, a higher incidence of apple scab lesions