Cedar-Quince Rust

What is Cedar-Quince Rust?

Cedar-quince rust, caused by the fungus Gymnosporangium clavipes, requires two hosts to complete its life cycle: members of the Juniperus genus (such as eastern red cedar, J. virginiana) and plants within the family Rosaceae. While the disease is named for quince, it actually has a broader range of hosts within the Rosaceae family and affects:

• Malus (apple)
• Malus (crabapple)
• Juniperus (cedar)
• Crataegus (hawthorn)
• Amelanchier (serviceberry)
• Cydonia (quince),
• Chaenomeles (flowering quince),
• Pyrus (pear),
• Sorbus (mountain ash),
• Cotoneaster
• Aronia (chokeberry)

The fungus alternates between these two host groups, with the junipers being the primary hosts where the pathogen overwinters and the Rosaceae family plants being the secondary hosts affected during the growing season. The wide range of potential hosts contributes to the disease’s prevalence and the difficulty in managing it in landscapes where these plants are present.

Cedar-Quince Rust: How Does it Spread

Cedar-quince rust spreads through a complex lifecycle.

Overwintering and Initial Spread: The fungus overwinters as galls on juniper trees. During wet, warm spring weather, these galls produce orange, gelatinous spore horns, which release spores known as teliospores. These spores germinate to produce basidiospores.

Transmission to Secondary Hosts: The basidiospores are carried by the wind to the secondary hosts in the Rosaceae family. This is a crucial point in the spread of cedar-quince rust because the fungus requires a secondary host to continue its lifecycle. Once the spores land on susceptible tissue of these plants, they germinate, infecting the plant and causing disease symptoms.

Spreading Back to Primary Hosts: Later in the season, the infected Rosaceae plants produce spores of their own, called aeciospores, which are then spread by the wind back to the juniper hosts. Upon reaching the junipers, they infect the trees, forming galls where the fungus will overwinter and begin the cycle anew the following spring.

The spread of cedar-quince rust is heavily dependent on environmental conditions, particularly moisture and temperature. Wet, warm springs are conducive to the production and dissemination of spores, thus increasing the risk of infection. Human activity, such as the movement of infected plants, can also contribute to the spread of the disease. Additionally, the proximity of the hosts to each other can facilitate the transmission of the spores, making the disease more prevalent in areas where junipers and susceptible Rosaceae plants are grown in proximity.

Diseased Fruit on Hawthorn

Regions Impacted

Quince rust is mainly an issue in the eastern United States, where both the Rosaceae hosts and the alternate juniper hosts are present. The disease favors regions with temperate climates that experience cool, wet springs.

What are the Symptoms?

Cedar-quince rust presents distinct symptoms on its two different host plants.

On Junipers

• Galls: During the initial stages of infection, the most noticeable symptoms are the swellings or galls that form on the branches or twigs. These galls can vary in size from small bumps to large, multi-inch growths, usually becoming noticeable in the second year after infection.
• Spore Horns: In the spring, typically during wet weather, these galls produce orange to salmon-colored gelatinous structures known as telial horns. These horns are the spore-producing structures of the fungus and are a clear sign of cedar-quince rust.

On Rosaceae Plants

• Twigs and Thorns: Infected twigs and thorns exhibit swelling and cankers, often resulting in dieback. These areas might ooze orange spores during wet conditions in the spring.
• Fruits: Fruits develop rusty spots or blemishes, and in severe cases, they may become deformed or drop prematurely. The fruiting bodies may exude an orange, sticky substance.
• Leaves: While leaves are less commonly affected, they can show spots or lesions with a similar orange hue.
• Flowers: The petals can develop orange spots, and the entire flower structure may become distorted or blighted, impacting the fruiting potential of the plant.

Prompt identification of these symptoms is crucial for effective management and control of cedar-quince rust, especially since the disease can significantly impact the health and aesthetic appeal of the host plants, and in commercial settings, affect yield quality and quantity.

How to Control and Prevent Cedar-Quince Rust?

Controlling and preventing Cedar-Quince Rust involves integrated strategies since this pathogen requires two hosts to complete its life cycle. Here are measures you can take:

Cultural Control:

• Resistant Varieties: Planting rust-resistant varieties of susceptible plants is the most effective long-term solution.
• Proper Spacing: Ensure adequate air circulation by properly spacing plants and pruning to reduce humidity around the foliage, making conditions less favorable for fungal development.
• Watering: Water plants at soil level to avoid wetting the foliage, as moisture promotes fungal growth.
• Sanitation: Regularly clean up fallen debris, pruned materials, or infected fruits to reduce the potential for infection.

Physical Control:

• Removal of Galls: Prune out and destroy galls from junipers during the dormant season before they produce spores in the spring.
• Removal of Alternate Hosts: If feasible, remove nearby junipers or other alternate hosts, especially if they show signs of infection.

Chemical Control:

• Fungicides: Apply fungicides labeled for control of Gymnosporangium rusts. These are typically most effective when applied preventatively, just before the fungus starts producing spores. Repeat applications might be necessary throughout the season, following the product’s label for guidance on frequency and concentration.
• Timing: The most critical time for fungicide application is during the wet spring weather when juniper galls are producing spores.

Monitoring:

• Keep an eye on both types of host plants in the area, especially during the rainy season, for signs of rust. Early detection can significantly improve control outcomes.

Remember, it’s essential to follow local regulations and guidelines when implementing disease control measures, especially when using chemical controls. Also, consider consulting with a local extension service or a plant health professional for identification and management advice tailored to your specific region.