Cedar-Apple Rust

 Written by Amy Ziems, Extension Educator – Plant Pathology

Pathogen

Cedar-apple rust is caused by Gymnosporangium juniper-virginianae is a fungal disease that affects apple, crabapples, hawthorns and junipers in Nebraska.  This pathogen requires both a member of the rose family (apple) and the Juniperus species to complete its life cycle.

Disease Symptoms

On apple, crabapple and hawthorn early symptoms are yellowish-orange spots on the upper leaf surface.  The spots vary in size depending on the susceptibility of the host and may be bordered by a red band or chlorotic halo.  Small, dark brown spots (spermoagonia) develop with the spots as they mature.  The fungus grows through the leaf and form long (1/4 inch) tendrils (aecia) on the lower leaf surfacedirectly below the orange spots.  Aecia have a papery texture and contain rust brown spores (aeciospores).

Fruit symptoms are similar to leaf symptoms.  Infection occurs near the calyx (blossom) end and spots are yellowish orange.  Rust spots are superficial, extending 1/4 inch or less into the flesh.  Brown spermatia are also produced on the fruit.  Although infection sites are superficial, their presence may reduce fruit quality by causing a decrease in size, distortion or premature abortion from the tree.

Yellowish-orange Spots on The Upper Leaf Surface	Aecia On The Lower Leaf Surface
Fruit Infection

Favorable Weather Conditions

Spores production and release from the juniper host are favored by wet weather during May and June when infection occurs on the apple, crabapple and hawthorn.

Control

Cultural

Planting resistant apple and crabapple species

Chemical

Fungicide applications on apple, crabapple, and hawthorn during the infection period of the rust fungicide gnerally from the pink stage of the blossome until petal drop (May and June).  Susceptible trees need to be sprayed regularly during this time.

Links

Description of symptoms observed on junipers.

For additional information, see the UNL Extension NebGuide, Cedar-apple and Related Rusts of Apple and Ornamentals (G1907)