Cane rust, often confused with orange rust, is a fungal disease that afflicts blackberries. This pathogen also goes by the name Kuehneola uredinis, and is most likely to affect specific blackberry cultivars, such as the olallieberry, Shawnee and Choctaw varieties. Cane rust eventually leads to reduced fruit production and defoliation of the plant if not properly treated. It is easily controlled with fungicides sprays and preventive plant care.
Cane Rust Basics
Cane rust spores travel on the breeze, infecting susceptible blackberry plant varieties. Affected plants display small yellow pustules on shoots and the undersides of leaves. Canes eventually split, and the plant loses its leaves. Fruit production may slow or stop all together, rendering blackberries inedible from falling fungal spores. Cane rust survives through the winter months in affected plants, causing damage to the following season’s crop. Fungal infections typically appear during the early summer. Cane rust spores are commonly confused with orange rust, another fungal disease that affects blackberries. However, orange rust affects only the leaves of the plant, and not the shoots.
Fungicide sprays are used to treat and prevent cane rust in blackberries. Certain brands are specially formulated and registered for use on blackberries. In addition to treating cane rust, myclobutanil fights powdery mildew. Some products made with pyraclostrobin and boscalid are effective for use up to two times during the growing season, and others can be used up until harvest. Liquid lime sulfur can be sprayed to reduce overwintering of cane rust in blackberries. It is most effective when followed with a treatment of fixed copper. However, lime sulfur’s foul, rotten egg odor may be a deterrent in some cases.
As a preventive measure for susceptible cultivars, spray fungicides on blackberry plants in the springtime when new green growth is approximately 1/4 inch long. Otherwise, spray plants at the very first sign of cane rust. If your blackberry plants have been affected by cane rust in the past, spray fungicides to reduce vulnerability. Most fungicides are utilized on a 7- to 14-day spraying schedule. Spray lime sulfur on blackberry plants during the winter months to stop cane rust from overwintering and affecting new growth in the spring. Following lime sulfur, an application of fixed copper is effective at the start of the growing season to keep cane rust away. Do not spray lime sulfur during the growing season, because this causes damage to new leaves and canes.
It is important to alternate the use of fungicides when spraying blackberries for cane rust. If you continue to use the same fungicide application, over time the fungal pathogen develops a resistance and does not respond to the treatment. Alternating these fungicides with each treatment interval ensures that the compound does its job in eliminating cane rust.
Carefully examine your blackberry plants and remove any unhealthy or diseased-looking canes and leaves to stop the spread of cane rust. Control the instance of fungal pathogens by mulching, removing weeds and making sure the plants have proper air circulation. When spraying fungicides, always wear protective clothing and pay attention to drift, which pollutes groundwater and can damage nearby vehicles or machines.
- University of California Agriculture & Natural Resources: Cane and Leaf Rust
- Small Fruits.org: Bramble Disease Control
- Louisiana State University Agricultural Center: Fruit Crops -- Blackberries
- LSU Ag Center: Growing Blackberries
- Pacific Northwest Plant Disease Management Handbook: Blackberry (Rubus sp.) -- Cane and Leaf Rust
- Ohio State University Extension: Brambles -- Production Management and Marketing
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