Image: istockphoto.com/Dominique Rodrigue
Cedar-Apple Rust
There are any numbers of fungal diseases that can infect your apple trees. One of the most common and most serious is cedar apple rust. While most people resort to chemicals when this disease rears its ugly heads, there are effective organic methods of prevention and treatment.
Cedar-apple rust is a fungal disease that commonly afflicts apple and flowering crab apple trees (essentially similar fungi, cedar-hawthorn rust and cedar-quince rust, affect other members of the rosaceus family).
Its name hails from the fact that it spends part of its lifecycle on the apple tree and another portion on species of juniper, spreading effortlessly between the two. While its affects on the host juniper plant is minimal, the same cannot be said of apple and flowering crab trees.
Symptoms
Cedar-apple rust causes premature defoliation, which beyond unsightly also weakens a tree and reduces fruit set and yield the following year. Trees with severe defoliation are also susceptible to other diseases.
The fungus can also affect fruit, causing them to become distorted, develop deep pits, and to usually drop before harvest.
Stop if before it hits
Prevention, as they say, is the best medicine. In order to effectively stop apple-cedar rust before it strikes your fruit trees, one must first be able to identify the symptoms of the disease and understand its lifecycle.
The symptoms on apple and flowering apple are easily identified. In late spring or early summer, bright yellow-orange spots form on the upper surface of leaves. These spots gradually enlarge and turn orange or brown. They may be edged with a red band and small black lesions form in the center of the lesion. Sometimes, an oozing substance can be seen coming from the lesion. Eventually, an orange, cup-like fungal structure with tube-like projections forms on the bottom surface of the leaf directly beneath the lesion. Fruit may have brown spots
Starts in the spring
Fungal spores infect apple and flowering crab trees typically in April, most commonly during prolonged cool and wet periods. Rust lesions begin to develop one to three weeks after infection. In early summer (June or early July), spores are released from the lesions on infected apple trees that re-infect junipers, slowly creating galls in which the fungus over-winters. Spores released from an apple tree cannot infect another apple tree.The key to preventing apple-cedar rust is to disrupt the pattern.
Prevention
Ideally, one wouldn't have junipers or cedars in the same yard as apple/flowering crab trees. This minimizes the chance of infection, but it won't eliminate it entirely because spores can travel up to two miles in distance.
Inspect all junipers for fungal growths during the winter. Look for dark, reddish-brown, 1-inch growths (the galls) and remove them before the disease spreads to your apple trees. To be effective, this needs to be done before the orange, spore-laden 'horns' emerge from them in spring (March or early April).
Applying an organic fungicide like Soap-Shield® Fungicidal Soap two weeks before disease normally appears, or every seven to 10 days for as long as needed will help. You can also use Bordeaux Mixture or Copper Spray seven days after petal fall followed by another treatment two weeks later.
Autumn clean-up
If your trees are struck by apple-cedar rust, rake all infected leaves and fruit and remove them from the garden. Tolerant and resistant cultivars of flowering crab and apple are available, so you may want to look into these possibilities if rust is a severe or prolonged problem.
As a last resort, apply fungicides again in the spring to destroy the spores and make preventative measures more effective.
Andrew Hind is a freelance writer specializing in eco-friendly gardening.
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