While Liberty is considered resistant to CAR, it's interesting to
note that leaf spotting induced by CAR and subsequent leaf drop is
quite prevalent in the Hudson Valley in years where CAR conditions
are high.
D. Rosenberger pointed this out in a 2000 'Scaffolds' article (in quotes)
"In areas where cedar apple rust is prevalent, rust-induced leaf
spotting can be confused with frog-eye leaf spot. Cultivars such as
Empire, Cortland, and Liberty that are considered resistant to cedar
apple rust can develop rust-induced leaf spotting. Rust spores can
germinate on the foliage of rust-resistant cultivars. The rust fungus
then invades a few cells and may even appear macroscopically as a
pin-point yellow or orange spot on the upper leaf surface. However,
the infected leaf cells soon die because of incompatible
host-pathogen interactions within rust-resistant cultivars. The host
cells that are killed or damaged by the rust infections are
subsequently invaded by Botryosphaeria, Alternaria, or Phomopsis.
These fungi use the dead or dying cells as a food base to get energy
for invading adjacent healthy tissue.
Rust-induced leaf spots are indistinguishable from frog-eye leaf
spot except that rust-induced leaf spots are usually more uniformly
distributed throughout the tree canopy. Sometimes the original
orange-yellow rust lesion is visible in the center of the brown leaf
spots initiated by rust infections. There is no reason to spray trees
after these leaf spots appear because infected leaves do not produce
inoculum for secondary infections."
http://www.nysaes.cornell.edu/ent/scaffolds/2000/6.5_disease.html
--
Peter J. Jentsch
Extension Associate
Department of Entomology
Cornell University's Hudson Valley Lab
3357 Rt. 9W; PO box 727
Highland, NY 12528
email: [EMAIL PROTECTED]
Phone 845-691-7151
Mobile: 845-417-7465
http://www.nysaes.cornell.edu/ent/faculty/jentsch/
