Watering and feeding your apple tree are only a few tasks you need to accomplish to grow healthy apples. Cedar Apple Rust, which harms the tree and its fruit, is also something you need to watch out for. The question is, how do you go about it?
Continue reading to learn about this disease and how to protect your apple tree from getting infected.
What is Cedar Apple Rust?
Cedar Apple Rust is a disease caused by the fungus Gymnosporangium juniperi-virginianae, thriving mostly in North America’s Eastern region. The disease affects trees of the Rosaceae family, like the cedar, apple, pear, and quince. It causes stunted fruit growth and loss and may cause leaf drop.
Two living host species (the cedar and apple or crabapple trees) are needed for the disease’s full life cycle. This makes it stand out from other rust infections: It doesn’t live off of dead host species.
Pathogenic Life Cycle
Junipers and other conifer trees are where the fungus originates and remains during the winter. Aeciospores set the gall formation in motion, starting as ball-shaped growths 2 inches in diameter. They take two years to develop to produce and spread the spores fully.
When the spring rains fall, the galls swell. Then they secrete orange gelatinous tendrils called telial horns, where teliospores are produced. At these spores’ maturity, they become basidia, producing and releasing the infectious basidiospores.
In late spring or early fall, the wind will carry the basidiospores for over a mile to another host. Landing on apple or crabapple tree leaves that are wet for a few hours commences Cedar Apple Rust. Symptoms will appear after several weeks, depending on weather conditions.
One of the rust symptoms on the leaves includes fungal tubes. In mid-summer, the tubes will produce aecia, releasing aeciospores to be carried into the wind to junipers. The spores overwinter in the junipers until the following year, thus restarting the cycle!
Other Spreading Habits and Rules
Besides the wind, Cedar Apple Rust can also spread via splashing rain or irrigation. And garden tools like pruning shears will help spread the spores if you worked on an infected tree.
The nice thing about the disease’s spreading habits is that it can’t spread to and from the same species. An infected apple tree won’t infect another apple tree, and the same goes for the junipers.
Junipers vs. Eastern Red Cedars
The starting host trees for Cedar Apple Rust seem interchangeable. However, only one tree is accurately named between the juniper and the Eastern red cedar.
American cedars are not true cedars but are juniper varieties. For example, the most common host tree is the Eastern red cedar, the Juniperus virginiana. True cedars only grow in hot and arid regions in Asia; America’s climates aren’t enough for these trees.
The Eastern red cedar is the perfect juniper for the fungus to grow. Therefore, the disease is called Cedar Apple Rust instead of Juniper Apple Rust.
Cedar Apple Rust Symptoms
Apple tree leaves will have spots that start yellow and become bright orange or red with a red border. When the leaves are mature, small and raised black dots will form in the spots’ centers on the upper surface.
The lower surface of the leaves will show less-than-⅒-inch-long fringed finger-like fungal tubes sticking out below the leaf spots. These will cause the leaves to fall prematurely, especially during dry conditions.
You’ll know your apple tree has Cedar Apple Rust if the fruit has green or brown irregular spots with black dots. Fortunately, these slightly raised spots won’t extend into the fruit. Once the fruit matures, the spots will crack, and the fruit will become distorted or stunted in severe cases.
Another symptom is reduced production of fruit buds, not to mention apples dropping prematurely after a few seasons.
If you have juniper trees, Cedar Apple Rust is afoot if you see hideous galls growing on them in spring. Brown to orange gelatinous horns will incentivize you to go into a protective mode for your apples.
Preventing Cedar Apple Rust
One way to prevent the disease is by planting apple varieties resistant to rust. You could grow apples without worrying about protecting the tree from this infection. And since the spores can travel a long distance from their host, a resistant apple variety is your best option.
Another way is to avoid planting apple trees within a hundred yards of eastern red cedar or juniper trees. That goes for any tree that belongs in the Rosaceae family, whether it’s susceptible to Cedar Apple Rust or not. A good distance of at least 300 feet should make spreading difficult.
Proper watering and fertilizing without harming the roots and bark will also prevent your tree from becoming infected.
Understand that no fungicides will prevent or control the disease for trees grown for eating. The fungicidal treatment would be an option if you grew your apple tree solely for ornamental reasons. Otherwise, read ahead to the next section on treating Cedar Apple Rust.
Spray an apple tree or copper-based fungicide in the spring when the junipers’ galls release the spores. But first, you’ll need to check with your local nursery for the best fungicide.
You could also refer to your Agricultural Extension for other ways to control Cedar Apple Rust. After all, pollinators don’t take too kindly to fungicides, and you want them to pollinate your apple trees.
When you do spray, wait until new growth appears and closed flower buds show color. Then wear protective clothing and follow the directions on the fungicide’s label.
Treating Cedar Apple Rust
Even if the symptoms are present on your apple tree, you can still treat it. By combining methods of prevention and treatment, you may succeed in protecting your tree.
If you have any juniper trees nearby, inspect them. Prune any branches 4–6 inches below the galls so they can’t spread their spores to more trees. In between cuts, disinfect your pruning shears in 10% alcohol for half a minute so they don’t spread spores.
On an orchard, remove and destroy the junipers within a 2–5 mile radius. Depending on where you live, you could do this to any cedars or junipers that are near your apple tree. That would be easier since you’d prevent any more cases of Cedar Apple Rust in the future.
Prune your apple tree of infected branches to slow the spread if symptoms are showing. Do the same for the diseased leaves and fruits since they’re beyond saving. Rake up and dispose of fallen leaves, fruit, and other debris from under the trees afterward.
Frequently Asked Questions
1. What apple cultivars are resistant to this disease?
Apple varieties like Red Delicious and McIntosh Apples have a high resistance to Cedar Apple Rust. Some apple varieties may have moderate resistance if you can’t find the above-mentioned cultivars. These include the Granny Smith and Pink Lady cultivars.
If you want to grow rust-resistant crabapple trees, invest in varieties like the Snowdrift Crabapple, Thunderchild Crabapple, and Red Jade.
Make sure you select a variety that will thrive in your hardiness zone!
2. Is eating an apple from an infected tree dangerous?
It’s logical; eating a fruit that grew on an infected tree wouldn’t look like something to eat. As if Snow White biting an apple from an evil queen in disguise wasn’t a problem!
However, the only thing to worry about with an apple from a rust-infected tree is a slightly bitter taste. Cutting away the apple’s brown spots will suit you well if you want to avoid cringing as you eat. But safe or not, no one wants to buy an apple with questionable spots on it.
3. Could Cedar Apple Rust eventually kill my apple tree?
Rust doesn’t kill trees, but it will make them die easier. Of course, you’d have to sit back, do nothing, and let the infection thrive on the tree.
Any susceptible apple cultivar will endure damage to leaves and fruit when infected. In severe cases, Cedar Apple Rust will weaken the tree enough not to stand a chance against pests and diseases.
Nurture Your Apple Tree, Rust-Free!
You only want apples growing on your apple tree, not diseases like Cedar Apple Rust! Now that you know about this disease and what it can do to your tree, you’re prepared to protect it.
Check out our Apple Trees page to discover more ways to care for your tree and its delicious fruit!