Cedar Apple Rust: A Disturbing Discovery

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By Mark M. Hall – My family and I returned home from church on a rainy Sunday in May. It had been pouring for hours, but just as I pulled into the driveway, the rain stopped, and the sun shone brightly through a break in the clouds. I drove the car slowly along our gravel lane, while we soaked in the beauty of God’s Creation. Everywhere wildflowers were blooming in a variety of colors, and the grass had turned a vibrant green. Water droplets sparkled as they fell from the trees that lined the way. 

Yes, all the familiar signs of spring were indeed there to admire and appreciate. Mesmerized, I leaned forward, arms resting on top of the steering wheel, when I noticed something hideous above us, in the cedar tree. I was so horrified by what I saw that I felt the hair on the back of my neck stand up. Stuck to its branches were brown, dimpled orbs about two inches in diameter from which slimy, orange tentacles extended in every direction. It looked as though we had been invaded by some alien life form. “What in the world was that?” we asked in disbelief. We had never seen anything like it! 

Wasting no time parking the car, we ran straight back to the cedar for another look. “What could this possibly be?” we still wondered aloud while examining the gooey weirdness clinging to our tree. “Some kind of fungus, maybe?” It was quite possibly the strangest thing we had ever seen. Filled with curiosity, we were determined to identify the freaky-looking things. Immediately, my wife went inside the house to do some research, while I checked the side yard for any crop circles.  

We discovered that this was a sticky fungal growth indicative of Gymnosporangium juniperi-virginianae, a tree disease otherwise known as cedar apple rust. Its many gelatinous appendages, called telial horns, produce spores that are released by wind or rain. Two specific types of trees are required to complete the life cycle of the fungus, and its spores cycle back and forth between those two types. On one side of this rotation is a juniper, often an eastern redcedar, like ours, and on the other side is an apple, a crabapple, a hawthorn, or a quince. These spores can reach a tree several miles away, but most infections develop within several hundred feet. Unfortunately, our apple tree stood right across the driveway from our poor cedar. 

Gymnosporangium juniperi-virginianae known as cedar apple rust orange fungi.

After more study, we examined our apple tree, where we saw the telltale yellowish-orange spots beginning to form on its leaves. Before long, the fungus would grow down through each leaf and create brown, hollow bumps on the bottom surface of each one. There, more spores would be produced and blown back to the cedar tree, where the infection would spread, weakening and potentially killing the cedar. 

Later that summer, the leaves prematurely fell from the apple tree and the fruit itself showed signs of the disease. The apples were spotted with yellowish-orange discoloration that was similar to the spots on the leaves, most of the apples were misshapen and smaller than usual, and many of the apples dropped off the tree before ripening completely.  

The front view of a leaf infected with cedar apple rust.

Fortunately, there is a measure of good news. If the nasty galls have not spread all over the cedar, the infestation may be controlled without tearing down the tree. In late winter or early spring, each infected cedar branch should be cut off four to six inches below the gall. The pruning shears must be disinfected with bleach between cuttings to limit the spread of the infection.  

Both the cedar tree and the apple tree must be treated with a fungicide or biofungicide — specifically a product that is effective against rust. Some of these products are approved for organic farming, and some of them are non-toxic to bees and other beneficial backyard bugs as well. When treating the apple tree, it is essential to use a product that is approved for use on fruit trees. 

The apple tree must be treated every one to two weeks for a total of three to four applications each spring. These treatments need to be started just before the apple blossoms open and continue until the petals begin to drop. The cedar tree must be repeatedly treated from mid-summer through the end of summer, following the product label instructions. These treatments minimize the disease, but they are unable to eliminate the infection. Therefore, treatments will need to be continued every year unless one tree type or the other is removed. 

We were not so fortunate. You see, the galls were spread all over our cedar. Sadly, this was not a surprise, for we had learned that the fungus spreads rapidly during an especially rainy spring. We love harvesting fresh, juicy apples from our backyard each fall, so we decided to remove the extensively infected cedar. Highly disappointed, I fired up the chainsaw, and soon the tree was no more. 

Obviously, our story did not have a fairy tale ending. We miss our cedar, with its stringy, reddish-brown bark, the dense network of branches, and pretty, blue, berry-like cones. If we ever plant another juniper or apple tree, we will certainly investigate the rust-resistant varieties that are available at many nurseries. However, I am glad to report that our apple tree has made a comeback in production … and that we were not visited by extra-terrestrials!  

Have you had to deal with cedar apple rust on your property? How did you treat it? We would love to hear from you in the comments below.

Originally published in the July/August 2021 issue of Countryside & Small Stock Journal and regularly vetted for accuracy.

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