366 J.L. BECKERMAN AND G.W. SUNDIN
production systems may have repercussions on disease transmission
within orchards. In this review, we discuss the interlinkage of apple
scab and fire blight with modern horticultural practices and impacts on
current disease management strategies.
II. IPM AND APPLE SCAB
A. History of Apple Scab
The earliest image of apple scab appears in “The Supper at Emmaus,”
a painting by Michelangelo Caravaggio (c. 1600) whereas the earliest
known report of apple scab was in 1819 (MacHardy 1996), almost 200
years later. Clearly, apple scab has long been recognized and associ-
ated with apples, but it is unclear when scab was first considered a
serious problem that warranted specific control measures. The earliest
documented efforts begin around the 1880s, when Bordeaux mixture,
used with success in vineyards, was then applied in the orchard, to
good effect (MacHardy 1996). During this time period, spraying equip-
ment was purchased by apple growers at a rapid pace to control insect
pests; the fact these same pieces of equipment could be used to con-
trol pathogens further drove demand. For example, in 1887, there were
fewer than 50 sprayers in the United States, and by 1892, there were
50,000 fruit growers using this equipment (Large 1962).
Prior to the 1800s, most apples in the United States were propagated
as seedlings or “natural varieties.” The apple industry in the United
States was started by plantings of seeds from cider mills from Europe.
Seedling propagation was promoted by John Chapman (a.k.a. Johnny
Appleseed) (Haley 1871). However, by 1835, initiation of the use of
clonal propagation in apple production underpinned changes in apple
scab epidemiology. The promotion of grafting of superior cultivars func-
tioned to limit the diversity of apple germplasm. “McIntosh,” one of
the first new world apple cultivars, was being clonally propagated as
early as 1835, in Nova Scotia, Canada, and became widely planted in
the northeastern United States. The desirability and expansion of the
highly scab susceptible “McIntosh” coincided with the identification
of apple scab as a problem requiring management. By 1912, scab was
identified as the most serious disease on apples, and the New Hamp-
shire pomologist C. Brooks wrote “Some varieties, such as McIntosh,
can scarcely be made to produce salable fruit without thoro [sic] treat-
ment for its prevention” (Brooks 1912). The continued selection and
expansion of a few apple genotypes such as “McIntosh,” “Delicious,”