orange rust disease on blackberry foliage

Orange rust (Arthuriomyces peckianus)
Penn State Department of Plant Pathology & Environmental
Microbiology Archives, Penn State University, Bugwood.org

Updated: June 14, 2021

Anthracnose, cane blight, and spur blight (all stem cankers)

Spur blight on raspberry caused a canker on stem
Spur blight on a raspberry stem caused a canker
Photo: Mary Ann Hansen, Virginia Polytechnic Institute and State University, Bugwood.org
Small roundish anthracnose lesions on young raspberry cane
Small roundish anthracnose lesions on young raspberry cane
Photo: John Hartman, University of Kentucky, Bugwood.org
  • These are three fungal diseases that cause cankers on bramble canes, making them less vigorous and, in some cases, causing their death.
  • On overwintering red raspberry canes, spur blight appears as purple to brown cankers below the buds.
  • Anthracnose appears on most raspberries as gray spots or irregular cankers on the lower stems.
  • Cane blight shows as dark-brown to purple, sunken cankers with dark margins near pruning cuts or wounds. 
  • These three diseases can be routinely managed with good sanitation and one early-season lime sulfur treatment before new growth begins.

Gray mold (Botrytis)

diseased blackberry
Infected blackberry
  • The same fungus that causes gray mold on strawberries causes gray mold on bramble crops.
  • Specific fungicide sprays are usually not needed in the home garden planting where good sanitation is practiced (remove diseased fruit), except when the harvest period is wet.

Orange rust

orange rust fungus on raspberry leaves
Rust on raspberry
  • Orange rust occurs only on black raspberry and blackberry (red raspberry is immune) and is caused by a fungus that develops systemically through the plant long before symptoms appear.
  • The only control for this disease is the complete removal of the entire plant (including the roots) early in the season.
  • Characteristic symptoms are the development of spindly, thornless canes (on normally thorny cultivars) and the appearance of bright orange pustules on the undersides of leaves. 
  • To prevent the spread of the fungus, remove plants showing symptoms before the spore pustules mature and rupture.

Viruses

dark lines on bramble leaves
Photo: Blackberry Tobacco Ringspot Virus
John Fisher, Ohio Dept. of Ag., Bugwood.org
  • Viruses can cause a wide variety of symptoms including mottling, cupping, blistering, and yellow spotting of leaves.
  • These are often seen in young growth and can disappear later during hot weather.
  • A definitive diagnosis is important because late frosts, powdery mildew, mite injury, fungicide and herbicide sprays, and boron deficiency can cause the same symptoms.
  • Virus-infected plants need to be removed from the garden and disposed of in the trash.

Crown gall

brown hard galls on raspberry stem
Crown galls infecting canes
Photo: Eric Coombs, Oregon Department of Agriculture, Bugwood.org
  • Crown gall will occasionally infect brambles as the disease has a wide host range. It is caused by a soil-inhabiting bacterium, Agrobacterium tumeafaciens, which occurs worldwide and attacks over 600 plant species in more than 90 plant families.
  • The most obvious symptoms are the galls or growths that usually occur on the twigs, stems, and roots near the base of the plant at the soil line. Gall size can vary from small to large and are usually spongy when young, but they become hard and woody with age. 
  • Crown gall bacteria can be present in the soil, on contaminated tools, or carried by water to susceptible host plants. These bacteria can also survive in contaminated soil for years without a susceptible host.
  • Crown gall bacteria need fresh wounds to cause an infection, which can be caused by transplanting and cultivating activities, feeding damage from nematodes or soil insects.
  • Removal of galls will not cure infected plants because bacterial genes already inserted into the host's cells will continue to transform additional cells throughout the plant and produce galls in other locations.
  • Removal of infected plants will lower bacterial populations in the soil, however, low populations of soil bacteria still persist as surface colonies on many plant species regardless of their susceptibility to crown gall.  
  • If crown gall symptoms are already present on existing plants consider the selection of other nonsusceptible plant material.