False Cypress Diseases

False Cypress is relatively free of diseases that require complicated treatments or ongoing maintenance. The 5 most common diseases are easily treatable and avoidable with cultural and mechanical means. Canker, Juniper Blight, Rust, and Witch's Broom are treated with careful and hygienic pruning.

Crown and root rot is another name for the pathogen Phytophthora. This disease can kill trees and shrubs starting at the root system and is often not noticed in the top growth until it is too late. Sadly the only way to treat Phytophthora is to remove all the plant material. While this seems dramatic, preventing the disease is as easy as growing your false cypress in a well-draining location.  

Canker 

Cankers on a tree or shrub can be caused by a range of problems. Mechanical damage to branches can leave scars where the plant overgrows tissue to compensate. Fungi or bacteria can also cause the overgrowth of plant tissue which results in cankers forming. The woody plants are adept at sectioning off and compartmentalizing any damage on branches and stems to stop canker from spreading. Some species of False Cypress are particularly prone to canker when placed planted outside of their preferred growing conditions. 

Identifying Canker 

Dead parts of tree and shrub branches or trunks and even roots. All cankers are oval or oblong with excess growth around the edges that defines the damaged area. Cankers sometimes ooze sap or can encircle an entire branch resulting in the death of the plant above the canker. 

Treating Canker 

Cultural treatment is the only treatment recommended for False Cypress displaying signs of canker. Remove any damaged stems and branches early to protect undamaged parts of the shrub. Make cuts at least 4 inches (10cm) away from areas where canker has formed.

Sterilize any pruning equipment used to remove canker growth. Growing healthy plants greatly reduces the chances of pests and diseases. Remember that a plant growing in the right place will be healthy and low maintenance. Always research the correct growing conditions for additions to your landscape. 

Collar and Crown Rot

Collar and Crown Rot is caused by the Phytophthora water mold and can cause both top growth dieback and root infections that result in complete plant death. The Phytophthora is active in soils that are cool and remain damp or soggy due to poor drainage. The smallest hairlike roots are affected first and transport the disease to other parts of the root system eventually traveling to other parts of the plant.

The roots begin to die off until there is little root system left to support the top growth. Phytophthora spp. Travel easily between plants in wet soils and are also easily introduced to the garden by planting infected plant material.

Identifying Collar and Crown Rot

Top growth will show signs of wilting or dieback typically in one area of the shrub. Smaller plants typically show signs across the whole plant. Lower branches may have a black or brownish streaking on the inside when pruned which indicates the spreading of the organism. The root system will have black or brown sections (dead roots) or a root system that is entirely too small compared to the size of the top growth. 

Treating Collar and Crown Rot

Unfortunately, by the time a False Cypress is showing signs of Phytophthora it may be too late to save the plant and the best treatment will be to remove as much of the root system and top growth as possible. Prevention is the cure for this disease. Ensure that planting areas have plenty of drainage year round and that the False cypress is planted in full to part shade to encourage the strongest growth.

Overwatering could cause issues with root rots, particularly for young shrubs. Look for species of trees and shrubs that are resistant to Phytophthora and always fully inspect any new plants rots system for signs of dieback before planting in your established garden beds.  

Juniper Blight

Juniper Blight is a spore-forming fungal disease that can overwinter easily on infected plants, only becoming visible when temperatures rise and humidity is high in the late spring or early summer. Many varieties of False Cypress can be affected although new growth or immature shrubs are the main targets. Established, mature plants are rarely permanently damaged and able to withstand the fungus with mechanical and cultural treatments. 

Identifying Juniper Blight

New shoots begin to turn brown and dry out soon after appearing. The fungal spores remain on the dead plant material and are washed to other parts of the plant either by supplemental overhead watering or natural precipitation. Whole branches will be killed off over time. The spores easily overwinter on any dead plant material, even still attached to the plant. 

Treating Juniper Blight

Remove infected plant material as quickly as possible to prevent spreading. Only use drip irrigation or a soaker hose for supplemental watering as overhead watering spreads the fungal spores. Buy varieties that are specifically listed as resistant to Juniper Blight. Always carefully inspect new plant material before planting it in the garden.

Copper-based fungicides can be used as a preventative on highly susceptible plants, although applications will need to be started early in the spring while the weather is still cool and continue for 6 weeks. Always follow the manufacturer's instructions and make sure that your particular plant species is listed for use. 2

Rust

Rust occurs during the mild but cooler months of the spring and fall. Wet or humid conditions help the fungal spores to spread easily over false cypress foliage. Windy conditions help the spores to travel between plants. The rust begins as small copper or rust-colored dots and grows quickly causing yellowing of affected leaves (needles).

Rust fungi are species specific although many have multiple forms of spores that occur throughout the growing season. Rust is usually a cosmetic problem rarely causing growth issues for well-established False Cypress shrubs and trees.  

Identifying Rust

Small orange or rusty colored dots form on the leaf scales or bark of the stems and branches. As the spores grow they will fuse together giving the plant a streaky orange look. Affected leaves (needles) will turn yellow and may fall off the plant. Galls can form and bark may show signs of sap oozing in heavily infected shrubs. Even though these symptoms are unpleasant, rust rarely kills False Cypress. 

Treating Rust

Pruning out the affected branches or stems is the best way to treat rust. Make cuts that do not weaken the plant and disinfect your pruning equipment between cuts. Rust spores can survive on plants such as some weeds even though they are not visibility affecting the host plant. Keeping surrounding garden areas well-weeded will help reduce the incidence of fungal disease.

Reducing the amount of overhead watering also helps to restrict the movement of rust spores. Using drip irrigation or soaker hoses helps to keep the foliage dry and gets water right to the plant root zone reducing the amount of overall weed growth in a garden border.

Witch’s Broom

Unusual growth coming from the tips of a False Cypress is commonly referred to as a Witch’s Broom. Plants that are affected either have a genetic mutation that causes the excess growth or it is the result of an initial fungal infection that had not been treated. False Cypress typically develops overgrowth as a reaction to a fungal infection like rust or an infestation of dwarf mistletoe.

Over the years many new and exciting dwarf conifers have been developed as the result of Witch’s Broom growths. Witch’s Broom in False Cypress rarely ends in the death of the shrub and is easily treated without any chemical intervention.  

Identifying Witch's Broom

The ends of branches will have unusually dense branching, oddly flattened stems, or changes in the shape and texture of the conifer needles. Growth is typically slow but may begin to girdle the circumference of the branch it is attached to. Severe girdling can result in the death of the whole branch if not treated early. 

Treating Witch’s Broom

Pruning the excessive growth is the only treatment for Witch’s Broom. Make clean cuts well below the broom so retain the natural shape of the false cypress. Brooms can be left in place if there is no girdling or the growth is not objectionable.

Always practice good garden hygiene when pruning false cypress and clean tools between cuts if the plant has had any type of fungal or mildew infection recently. 

Common False Cypress Disease Chart

DiseaseIdentifyingTreating
Canker Oblong areas that may be sunken with thick edges on branches and trunks Proper regular pruning of dead plant material, ensure your plant has the proper growing conditions
Collar and Crown Rot Wilted top growth, dieback of the root system, root system too small to support the amount of top growth Buy Phytophthora-resistant cultivars and species, improve drainage of the planting site, and do not overwater new plants
Juniper Blight Brown, dead growth at the tips which spreads over time to kill off whole branches Prune out infected plant material, avoid overhead watering
Rust Small orange specks or dots on the scale like leaves Prune away infected stems and branches, and avoid overhead watering to keep spore spread to a minimum.
Witch’s Broom Growth at the tips of branches is markedly different in needle texture, color, or growth habit than the rest of the plant Remove well below the protruding section, typically a secondary infection or a genetic mutation

Sources:

“How to Manage pests and Disease in Gardens and Landscape”, University of California Agricultural and Natural Resources. www.ipm.ucanr.edu