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Cedar Apple Rust

How to Identify, Prevent, and Treat Cedar Apple Rust

What is Cedar Apple Rust?

Cedar apple rust is a fungal disease that affects apple, crabapple and cedar trees. It is caused by the fungus Gymnosporangium juniperi-virginianae and can cause significant damage if left untreated. The disease is most prevalent in areas with both cedar trees and apple or crabapple trees, as the fungus requires both hosts to complete its life cycle.

The fungus spends the winter on cedar, juniper, and other conifer trees in the form of hard, brown, ball-shaped galls that contain the fungal spores. In the spring, these galls release orange, gelatinous spore horns that are carried by the wind to apple and crabapple trees, where they infect leaves and fruit. Infected leaves develop yellow spots that eventually turn brown or black and may drop prematurely. The fruit can also be infected, causing raised spots or scab-like lesions that may deform or crack the fruit.

In late summer, the fungus produces a second type of spore that is carried back to the conifer trees, where it infects new branches and needles and forms new galls.

Main plants affected by Cedar apple rust include:

  1. Apple trees
  2. Cedar trees
  3. Crabapple trees
  4. Hawthorn trees
  5. Mountain ash trees
  6. Quince trees
  7. Serviceberry trees

The disease can spread from one type of host plant to another, allowing it to cause damage across multiple types of plants.

Cedar apple rust can cause significant damage to apple and crabapple trees, especially in areas with high humidity or frequent rain. It can weaken the tree and reduce fruit production, and severe infections could potentially kill the tree. Management of the disease involves a combination of cultural practices and fungicides. 

What are the Symptoms?

Cedar apple rust is characterized by the following symptoms:

  • Yellow spots on the leaves in early spring, which turn orange or brown later
  • Small, black dots on the undersides of the leaves
  • Small, yellowish-green spots or swellings on the fruit, which grow larger and turn brown or black
  • Twisted, distorted, or stunted leaves, fruit, and shoots in severe cases
  • Orange or brown, cup-shaped fungal structures that form on cedar trees in wet weather in the spring, which later produce brown, horn-like projections.

These symptoms usually appear on the plant in the spring and early summer and can continue to develop until the fruit matures.

How to Control and Prevent Cedar Apple Rust?

Controlling and preventing cedar apple rust involves several strategies, including:

  1. Removing nearby cedar trees: Since cedar apple rust needs both apple and cedar trees to complete its life cycle, removing the cedar trees near your apple trees (if they are less than 4 miles away) can significantly reduce the disease's occurrence.

  2. Planting resistant varieties: Some apple varieties are less susceptible to cedar apple rust than others. Consult with a local nursery or gardening expert to choose resistant apple varieties that will thrive in your area.

  3. Pruning infected branches: If you notice signs of cedar apple rust on your apple trees, remove and destroy any infected branches or twigs.

  4. Applying biofungicides:  There are several biofungicide products that can help control cedar apple rust, including:

  • Serenade Garden: This is a broad-spectrum, preventative biofungicide that uses a strain of the bacteria Bacillus subtilis to control fungal diseases.
  • Regalia: This is a plant extract biofungicide that is effective against a wide range of plant diseases, including cedar apple rust.
  • Actinovate: This biofungicide uses the beneficial bacteria Streptomyces lydicus to protect plants from a variety of fungal diseases, including cedar apple rust.
  • RootShield: This biofungicide contains a beneficial fungus that helps prevent the growth of harmful fungi in the soil, including those that cause cedar apple rust. 

It's important to read the label of any biofungicide product carefully and follow the instructions for use.

Applying Preventive sprays of copper-based fungicides: These fungicides work by preventing fungal spores from germinating on the surface of the plant, which in turn reduces the incidence of infection. Copper-based fungicides are considered to be relatively safe and effective and can be used as a preventative measure before the disease occurs or as a treatment if the disease has already taken hold. It's important to follow the manufacturer's instructions carefully when using any fungicide and to wear protective clothing and equipment to prevent exposure to the product.

Applying fungicides: Fungicides can be effective in controlling cedar apple rust if applied at the right time. Consult with a gardening expert to determine the best fungicide and application schedule for your apple trees.

Maintaining good cultural practices: Keeping your apple trees healthy and stress-free can help prevent cedar apple rust. Maintain good cultural practices such as proper watering and fertilization, and avoid damaging the trees' roots or bark.

By taking these measures, you can control and prevent cedar apple rust, ensuring healthy and productive apple trees for years to come.


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