Cedar Apple Rust

This is a gall, an abnormal growth on a juniper branch which is part of an intricate and often gross looking fungal infection passed between cedar and apple trees, aptly named cedar apple rust. Several species of trees can substitute for the cedars and apples. Junipers, hawthorns, crab apples etc can all carry the disease in its various life stages.

Understanding the life cycle of the disease is tricky, and the first step in attempting to curb it. Often people protecting their more valuable apple harvest will simply remove all of the cedars from their property to interrupt the disease in this stage of growth. While we have chosen to remove many of the cedars for this purpose, it is not reasonable to expect to be able to remove all of the cedars from the surrounding area. Spores can be carried by the wind for several miles and considering the fact that Gohn Greene Farms borders Oconee National Forest management of this pathogen cannot simply rely on the elimination of cedars.

These galls form on the junipers, having been infected from spores off of nearby apple, crab apple, quince or hawthorns. The galls almost look like baby pine cones when young and can be tricky to spot. Once they get to this size they're more readily identified and removal of them at this stage is one of the easier stages to interrupt in order to slow the spread of the disease. They're often golf ball sized, sometimes larger. This stage occurs in early Spring and soon the little orange spots visible in this picture will begin growing like little horns emanating from the gall in all directions.

Once the Spring rains start to fall with more regularity the gall and its horns transform into what I think is one of the more disgusting stages of life. They fill with moisture until they begin to droop, eventually becoming mucilaginous globs of goo hanging from the trees. The disease is most visible at this point, but the damage in this stage of its life cycle has already been done. Spores are carried by the wind to the apple trees just as their tender blossoms and leaves are emerging. Here the spores infect the fruits and leaves in just a few short hours. Solutions of garlic or nettle can be sprayed on the apple trees to increase resistance just prior to this stage of infection, but we haven't tried this method as of yet.

A couple of weeks later the spores which have successfully infected the upper leaf surfaces of the apple trees begin to emit tube like structures from the lower surface of the leaves in cup like arrangements. These tubes will then emit spores of their own over the summer, carrying the disease back to the junipers where they'll develop new galls over the course of a year. Two springs later the galls erupt to start the life cycle all over again.

At Gohn Greene Farms our apple trees are rather new and haven't been affected to any significant extent at this point. We've been removing galls from larger junipers and removing the smaller junipers entirely to limit the spread of the disease as effectively as possible before it becomes rampant. If it becomes a problem in future years we may try spraying with a garlic solution, but so far prevention of the galls from releasing their spores seems to be our main point of attack. Preventing them from turning into giant balls of snot has its aesthetic merits as well.