Orange Rust

A fungal disease with no treatment

Orange Rust disease is caused by a fungus Gymnoconia Interstitialis that moves systemically throughout infected blackberry plants, rendering them useless for future production. 
This blackberry disease is recognized easily by the large masses of orange colored spores produced in the spring on the leaves of affected plants. As leaf expansion is completed in late March or early April, large orange pustules form on the undersides of leaves, often causing distortion and upward leaf rolling. The pustules rupture and release spores for a period of about 60 days. Rust symptoms then disappear, but foliage remains sickly in appearance. All new canes produced on affected plants will be non-productive.
This fungus does not have a spore stage on an alternate host, but has its entire development on the blackberry plant. Masses of orange-colored spores are produced on the undersurface of the leaf. These spores are blown about and may infect other plants.
The fungus winters in the roots and stems of old plants. In the spring it grows up in the pith of the developing cane and out into the leaves, where it produces the spore masses described. The fungus is therefore perennial, and on this account when once established in a plant it cannot be eradicated.
Control of Orange Rust is limited to cultural practices that prevent spread of the disease and the use of resistant varieties. Remove all infested plants, including complete root systems, as soon as pustules become noticeable in the spring and before spores are released. Fungicidal sprays have not provided satisfactory control. Orange Rust can be controlled only by removing all infected plants (including their roots) when symptoms first appear! To prevent Orange Rust on blackberry plants use lime sulfur and copper sulfate. Good results was received with Cabrio, Pristine, or Rally fungicides apply in early spring and continue at 10- to 14-day intervals until early summer.
There are some new blackberry varieties with good resistance to Orange Rust disease.