yes, that is very likely. This disease is caused by a fungus called Gymnosporangium that infects both hawthorn and red cedar. There are also versions of Cedar apple rust, quince rust, and rust diseases that affect other plants.
The fungi can’t spread from cedar to cedar or appple to apple (or hawthorn to hawthorn), but must alternate between the two species to survive. In the spring orange spores from the cedar galls are carried by the wind to the apples.
In hot, wet or humid weather, the spores germinate and infect the leaves, the twigs and the fruit of the apple. Depending on the species of rust, the leaves will become spotted, or the leaves, twigs and fruit will become deformed with galls and the fruiting bodies of the fungi. The fruiting bodies develop on the affected plant parts, producing spores that are then blown back to the cedar trees. The fruiting bodies on the spores look like small orange koosh balls.
Some species or degrees of infection will not cause much damage, but others will cause severe defoliation.
Control can be accomplished by removing the alternate host, either nearby cedar trees or apples. A regularly scheduled fungicide program starting at bud break will also act as a preventive.
In The Garden,
Cindi Sullivan
