If you have ever looked at your juniper trees and noticed a strange orange ball with tentacles growing, you may have thought it was something out of this world. No, it’s not an alien invasion, it’s cedar-apple rust.
Despite the name, this disease affects both apple (and crabapple) trees and certain types of junipers, including the widely planted eastern red cedar. It looks different on each host tree – but the two are connected in the same disease cycle. Here’s how to spot the signs early and keep it from spreading across your landscape.
Key Takeaways:
- Cedar-apple rust is a fungal disease that requires both juniper trees (like eastern red cedar) and apple or crabapple trees to complete its life cycle, with spores traveling between the two hosts.
- The disease causes bright yellow or orange spots on apple tree leaves and fruit, while junipers develop brown or red galls that release yellow tendrils during rainy weather.
- While cedar-apple rust won’t kill trees, it damages the ornamental value of hosts and ruins apple fruit production.
- Prevention methods include separating the two host species, planting resistant apple varieties (like red delicious or empire), pruning for better airflow, and sometimes using fungicides.
- Treatment involves professional pruning of juniper galls in late winter before spore release and applying fungicides under expert guidance.
Apple trees are one of the main targets of cedar-apple rust.
What Is Cedar-Apple Rust?
Cedar-apple rust (Gymnosporangium juniperi-virginianae) is a fungal disease that requires two hosts. In this disease’s case, it needs a juniper tree (commonly the eastern red cedar) and a member of the Rosaceae family (typically an apple or crabapple tree). Without both species, the fungus will die.
While cedar-apple rust is not a deadly tree disease, it can still cause damage and demands attention. It will harm the ornamental value of your trees and can damage the fruit.
The fungus causing rust spends a year on a juniper before spreading. The rust organism overwinters in gall tissue in a juniper, waiting for warmer, rainy spring weather. These conditions will allow the gall to produce spore horns.
The horns release spores that the wind carries from the juniper to the apple tree. These spores can travel for miles, though it’s typical that they will only travel a few hundred feet.
The spores then begin to grow on the apple tree, infecting fruit, leaves, and even young branches in some instances.
PRO TIP: Cedar-apple rust is just one of a few kinds of rust that can attack trees. Other rust diseases include quince rust and hawthorn rust. Keep a lookout for symptoms of these if you have quince or hawthorns on your property.
Symptoms and Damage of Cedar-Apple Rust
Symptoms on your trees will appear differently depending on whether you are looking at an eastern red cedar or an apple tree.
Apple and Crabapple Symptoms and Damage
The most obvious symptoms on apple trees are the bright yellow or orange spots that develop on the leaves. You’ll first be able to spot them in the late spring, and they will continue to grow throughout the summer. Severe infections will cause some leaves to drop, especially if we have dry weather in the summer.
Tiny galls, usually under an inch in length, will appear on new growth and potentially stunt future growth. You’ll also find yellow and orange spots on fruit, which will likely be larger than the ones on leaves. The rust will lead to ruined fruit and premature drop.
Juniper Symptoms and Damage
Homeowners can observe symptoms on their eastern red cedars by the middle of spring. The trees will develop galls on the needles with a brown or red color. They are small, some no larger than a single pea.
The galls develop small pits, which become especially noticeable after rain. During damp weather, they produce bright orange, jelly-like tendrils that many people describe as looking like orange goo on cedar trees, slimy orange growths, or even alien-like blobs. These structures release spores that can infect nearby apple and crabapple trees. When the weather dries out, the tendrils retract back into the gall until the next round of moisture.
Galls can stay on trees for years, causing some branch dieback. The damage to your junipers is mostly minor from these galls.
Management of Cedar-Apple Rust in Southeastern Pennsylvania
Though cedar-apple rust won’t kill your trees, that doesn’t mean it is something you can ignore. Many homeowners in Southeastern Pennsylvania grow eastern red cedars and apple trees for their ornamental value, and cedar-apple rust will destroy much of that value. Additionally, the disease will damage the fruit, ruining one of the best benefits of growing apple trees on your property.
How to Prevent Cedar-Apple Rust
The easiest way to prevent cedar-apple rust on your trees is to remove one of the two species causing the disease. While there’s no guarantee cedar-apple rust will occur if you have eastern red cedars and apples on your property, putting both trees close together is asking for trouble.
If you do plan to grow apples and junipers together, consider planting a resistant apple species, such as:
- Red delicious
- Empire
- McIntosh
- Niagara
- Spartan
Preventive pruning to promote air flow and light penetration will also help reduce the damp conditions that allow the fungus to thrive. Fungicides for preventing cedar-apple rust are an option, though we mostly recommend using them only for high-value trees.
How to Treat Cedar-Apple Rust
If cedar-apple rust is already showing up on your trees, timing matters. Fungicides can help, but they’re most effective when used before symptoms appear – and not every tree needs treatment. An arborist can help you decide if it’s worth applying or if there’s a better approach.
The best move you can make is pruning infected junipers in late winter. That’s when the galls are visible but inactive, and cutting them out before they produce spores in spring will help limit how much the disease spreads. Improving airflow between trees and removing dead or dense branches can also make your landscape less favorable for rust to take hold.
This isn’t something you fix once and forget. It’s more about managing the environment around your trees so they stay healthier year after year.
Frequently Asked Questions About Tree Diseases in Southeastern Pennsylvania
We’ve answered some common questions homeowners have when we diagnose their trees with cedar-apple rust so you can better understand the disease.
Can I use fungicides myself to combat cedar-apple rust?
We recommend leaving any chemical use to professionals. You may not have access to the fungicides you need, and using them to treat cedar-apple rust requires a delicate touch. Birds and pollinators are attracted to apple trees, and reckless use of fungicides could harm them.
If I treat cedar-apple rust with fungicide, do I still need to worry about other diseases?
Yes, cedar-apple rust isn’t the only issue trees face in Southeastern Pennsylvania. Apple and ornamental trees are vulnerable to several other diseases that show up in similar ways: leaf spots, early leaf drop, or fruit damage. Some other problems to keep an eye out for include:
Will my neighbor’s juniper tree cause cedar-apple rust in my apple tree?
Depending on how close your trees are to your neighbors, yes, a neighbor’s juniper may cause cedar-apple rust. To combat this, consider planting a resistant cultivar of apple tree or choosing another fruit tree. Alternatively, talk with your neighbor about it to ensure you are both looking for the signs of cedar-apple rust developing so you can stop it.
Need Help Managing Cedar-Apple Rust? Call Clauser Tree Care
After you’ve spent years working on and cultivating your apple or junipers, you don’t want all that effort to go to waste when the tree appears unsightly from cedar-apple rust. If you need help diagnosing the problem with your trees or assistance with pruning away the galls to protect your trees, the team at Clauser Tree Care can help.
We employ ISA Certified Arborists who provide expertise on all aspects of tree care and can help you determine what’s wrong with the trees on your property and rectify the problem. Call us today at 215-542-8291 or request a quote online.
About Clauser Tree Care
From who you talk to on the phone in our office, to our courteous and experienced work crews who provide your service, all of the hard-working team members at Clauser Tree Care strive for complete client satisfaction. Our job is simply not done until you are pleased with the experience that you have had working with our company. Founded more than 25 years ago on the principles of honest work and arboricultural best practices, we strive for a higher standard of care for a greener future.
