Cane and Leaf Rust

Cane and leaf rust occurs on some blackberry cultivars, especially trailing varieties such as olallieberry. The first symptom of cane and leaf rust is lemon yellow pustules (uredinia) that split the bark of the fruiting canes of susceptible blackberries. Spores from these pustules (urediniospores) infect leaves and produce small yellow pustules (uredinia) on the underside of leaves during early summer. Defoliation can occur if infection is severe. Buff-colored telia develop among the uredinia on leaves in early fall.

It is important not to confuse this common blackberry disease with the less common but far more damaging orange rust, which causes plants to produce many small, weak shoots from the base of the plant.

On susceptible blackberry varieties leaf defoliation can be severe and result in the loss of plant vigor. Normally cane and leaf rust doesn't infect the fruit but masses of spores falling on fruit can render it unmarketable. Raspberries are hosts, but occurrence of this disease on this crop is rare. Wet spring conditions will favor disease development. The fungus overwinters on canes as mycelium or latent uredinia. Cane and leaf rust can be distinguished from orange rust by the presence of yellow pustules (uredinia) on both the canes and leaves. Orange rust has orange pustules on leaves only.

Control is best achieved by using cultural methods to reduce pathogen sources in combination with fungicides. Remove and dispose of fruit canes soon after harvest to reduce inoculum sources. Highly susceptible varieties with a history of this disease should receive applications of protective fungicides before the onset of disease symptoms and pathogen signs.

Removal of fruited canes after harvest and sprays of lime sulfur or some fixed coppers are acceptable management tools in an organically certified crop.

A recommended spray control program is a winter application of lime sulfur followed by fixed copper applied at green tip stage and then a treatment at bloom.