374 J.L. BECKERMAN AND G.W. SUNDIN
attempted sole reliance of sanitation in an orchard with disease-
resistant apples, and found that it was not sufficient to provide adequate
disease control by itself, and that fungicides were needed to provide
acceptable control. However, with respect to sustainability, two appli-
cations of fungicide per season is a significant reduction compared to
the normal 12–20 applications necessary to manage an orchard with
conventional cultivars.
In an orchard with conventional cultivars, sanitation is an important
management component, and with respect to scab, is best directed at
the production of pseudothecia, the sexual fruiting bodies ofV. inae-
qualis, in the leaf litter. Growers recognized this as early as the 1880s
and recommended raking and burning leaves to reduce disease (Sutton
et al. 2000). Current cultural management options include mulching or
flail mowing leaf litter, applications of 5% urea to trees just prior to
leaf drop, or 5% urea applied to fallen leaves in autumn (Sutton et al.
2000). These practices facilitate leaf decomposition, thereby preventing
the development of pseudothecia in the following season. In addition
to sanitation, pruning trees to enhance air movement and increase sun-
light, reduces foliar wetness on leaves and fruit, reducing scab in con-
ventional orchards. These approaches have been found to significantly
reduce the number of fungicide applications needed for scab control
(Sutton et al. 2000).
Another cultural approach to manage apple scab involves the mixing
of susceptible cultivars with resistant cultivars that results in decreased
disease pressure (Didelot et al. 2007). However, other aspects of orchard
management (e.g., needs for cross-pollination of cultivars blooming at
similar times, management of other diseases, like fire blight or blister
spot), ease of applying thinners, ease of harvesting, etc. decrease apple
growers’ willingness to design such plantings simply to minimize dis-
ease pressure and/or optimize fungicide use. Any practical solutions for
sustainability and long-term management of apples require the recogni-
tion that biologically effective controls may not always be economically
feasible.
One of the most important cultural tactics to reduce fungicide inputs
into the apple management system was the adoption of dwarfing
rootstocks in high-density orchard systems (Rosenberger 2003). Over
the past 35+years, high-density orchards with 800–1500 trees per acre
or more have replaced old orchards with standard and semi-dwarf trees
that were planted at a density of 40–120 trees per acre. High-density
systems become more productive more quickly, typically in the second
year, unlike older production systems that may take a decade or longer
to reach full bearing capacity. Furthermore, large trees in old orchards