|Blackberry plant infected with Orange Rust.|
This image was taken yesterday in our research plots. It is typical of early season symptoms of Orange Rust (Gymnoconia nitens) in blackberry. The plants were weak and spindly with yellow leaves, some leaves will have an orange spots at the edges of the leaves. This was a numbered blackberry selection in the breeding program. Two plants in the plot were symptomatic, two others did not have any symptoms. The two infected plants were dug up, with as many roots as was possible and disposed of far from the caneberry fields.
From the SRSFC IPM guide:
Orange rust – Hosts affected: Navaho blackberry and black raspberry are very susceptible. Multiple spindly shoots that are light green in color, at first developing orange pustules on undersides of leaves only, indicate systemic infection of roots. Normal canes with orange spores indicate first-time infection. Disease control: Inspect planting thoroughly when new canes are 12-18 inches. Remove infected canes, recognized by weak growth and the presence of orange pustules. The varieties Cherokee, Cheyenne, Comanche, Choctaw (erect, thornless), Arapaho (erect, thornless), and Shawnee are considered resistant. The possibility of new races exists, as orange rust has been observed in all varieties. The varieties Darrow, Humble, and Navaho and black raspberries are susceptible. Wild blackberries should be eradicated within 0.25 mile of planting. Preventive fungicide applications are effective; however, once a plant shows symptoms, it has to be removed and destroyed.
For control recommendations see
Ohio State University has a publication describing this disease. Figure 3 is very similar to the one in this blog post.