PHOTO TCC
Cedar-Apple
Rust, caused by the fungal disease, Gymnosporangium juniperi-virginianae is another serious and
disfiguring disease of ornamental and fruit apples. Rust fungi are evolved
complex organisms that require two hosts to complete their life cycle.
The first host of this
disease is Eastern red cedar, Juniperus virginiana,where the rust forms ball like structures with
fungal telial horns that forcibly eject the spores that spread the disease to
apples. Although these bright orange horned goo balls are quite alarming they
are usually not noticed on the juniper or mistaken for fruit or cones. Once the
spores from the juniper travel to the leaves of apples the real unsightly
damage occurs.
On apples the spores
germinate and after a week or two cause orange pustules on the leaves of susceptible
apples. Rainy wet weather in the spring is ideal for the germination on
junipers and the spread and infection to apples.
Once in the apple leaf,
given a short period of wet weather, the leaf lesions form fruiting structures
in mid to late summer and re-infect the juniper host where the disease over
winters.
Cultural control, includes
removal of junipers in the vicinity of apples as well as planting disease
resistant varieties of apples. Avoiding mass plantings of apples and junipers
in landscapes reduces the amount of disease inoculum and the potential for
severe outbreaks.
There are a number of fungicides
that are labeled for control of Cedar-Apple Rust. Typically they require
several applications starting at bud break and continuing every two weeks to
get suitable control. Fungicides may also be applied to junipers in mid to late
summer to reduce the back transmission from the apples to the junipers.
Your
I.S.A. Certified Arborist is up to date on the latest research on Cedar Apple
Rust and can help preserve your apple trees.
