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Blackberry Cultivar Susceptibility
Cause Kuehneola uredinis, a fungus that affects 'Black Diamond', 'Chehalem' and 'Evergreen' blackberries. Rust can be particularly severe on 'Chehalem'. This fungus forms several spore types, which can infect leaves of floricanes and primocanes. The fungus is not systemic in the plant. Wet conditions favor disease development.
Symptoms Elongate, yellow pustules (uredinia) form on floricanes in late spring. Canes become brittle and break easily. Spores from these lesions infect leaves and produce small, yellow pustules (uredinia) on the undersides of leaves. Without a good comparison one might describe the color as orangish. Premature defoliation can occur if severe. Buff-colored pustules (telia) develop among the uredinia on leaves in fall. These produce other spores, which infect leaves on primocanes, which develop pustules, called spermagonia and aecia. Pustules may also be seen on fruit. Might be confused with orange rust, which has bright-orange uredinia or with blackberry rust.
Cultural control
- An alternate-year fruiting program reduces disease pressure.
- Remove old fruiting canes after harvest.
Chemical control Focus on cultural controls for best results.
- Apply dormant lime sulfur spray in winter to trellised canes.
- Rex Lime Sulfur Solution (28%) at 6 to 8 gal/100 gal water/A (especially important for 'Chehalem'). 48-hr reentry. O
- Sulforix at 3 gal/100 gal water. 48-hr reentry.
- Apply at green tip and again just before blossoms open.
- Abound at 6 to 15.5 fl oz/A is registered for Phragmidium spp. and may be useful. Do not apply with silicone-based surfactants. May be applied on the day of harvest. Group 11 fungicide. 4-hr reentry.
- Fixed coppers such as Nu-Cop, C-O-C-S, Nordox, Cuprofix, or Kocide most with a 48-hr reentry. O
- Quadris at 10 to 15.5 fl oz/A. Do not apply with silicone-based surfactants. May be applied on the day of harvest. Group 11 fungicide. 4-hr reentry.
- QuiltXcel at 14 to 21 fl oz/A is registered for Phragmidium violaceum and may be useful. Do not use within 30 days of harvest. Sprayers should not be used on apples. Group 3 + 11 fungicide. 12-hr reentry.
- Rally 40 WSP at 1.25 to 3 oz/A. Applications may be made up to the day of harvest. Group 3 fungicide. 24-hr reentry.
- Spectracide Immunox Multi-Purpose Fungicide Spray Concentrate for Gardens at 0.67 fl oz/gal water. May be applied up to the day of harvest. Group 3 fungicide. H
Note: Some registered products offer only suppression of this disease and thus are not recommended for use. These products include Cabrio.
Reference Fischer, G.W. and Johnson, F. 1950. Cane and leaf rust, Kuehneola uredinis (Link) Arth., of blackberries in western Washington. Phytopathology 40:199-204.