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Science    Plant Pathology   Apple Rusts  Rust Diseases Three
different rust diseases can occur on apple. However, it is not
necessary to distinguish the subtle differences between these
rusts for the purposes of scouting, since the disease cycles and
control programs are similar for each.  Apple Rust  SYMPTOMS:
Small pale yellow spots appear on the upper surface of infected
leaves shortly after bloom. These spots gradually enlarge up to
1/4" in diameter, depending upon the apple variety and the
number of spots per leaf, and become bright yellow-orange in
color. By early or mid-summer, yellow spots will also be present
on the lower leaf surface; from these come small, orange-yellow
tubular fruiting bodies which eventually project downwards. As
the tubes mature, they split towards the base into narrow strips
and curl back on themselves to form cup-like structures. Within
these structures a ma