Algal Spot (alga, Cephaleuros sp.): Light green to light orange spots develop on canes. Spots can merge to cover entire portions of canes. This disease has not been studied in detail, especially relating to overall damage. Copper type fungicides are recommended for control. (See Photo of Algal Spot)

Anthracnose (fungus – Elsinoe veneta): A common cane and foliage disease of blackberry and dewberry sometimes called dieback. The disease first appears in the spring as small purplish spots on new shoots and purple bordered spots on leaves. Spots on canes enlarge, usually develop an oval shape, and gradually turn gray. Ends of badly infected canes die back. Erect types are less susceptible than the more spreading types. Late dormant fungicide application will help prevent infection. (See Photo of Anthracnose)

Cane and Leaf Rust (fungus – Kuehneola uredinis): Small, lemon-yellow pustules develop on canes and leaves throughout summer. Cracking and drying of canes and spotting and drying of leaves result. The disease is not systemic and does not affect blooming. Prune out and burn infected canes. It is a minor fungal disease. (See Photo of Cane and Leaf Rust)

Fruit rots (fungi – Botrytis sp., Penicillium sp.): Mild, wet weather conditions are ideal for fruit rot fungi. Overripe fruit is most susceptible. Timely harvest and spacing plants for good air circulation help prevent fruit rots. Fungicides are available but should not be overused due to resistance development in the fungal populations.

Cane Gall, Crown Gall, and Hairy Root (bacteria – Agrobacterium rubi, Agrobacterium tumefaciens, Agrobacterium rhizogenes): Cane galls are large, bark splitting swellings in long masses. Crown gall consists of large warty galls on roots or at base of canes. Where hairy root is involved, small wiry roots grow singly or in bunches from the main root or base of stem. Remove and destroy affected plants. Avoid replanting where diseased plants were removed. Examine nursery stock for evidence of galls and hairy root. Do not plant stock with galls or plants that have had galls removed.

Nematodes Other Than Root Knot (Xiphinema spp and others): Xiphinema or dagger nematode damage results in root swelling especially at the tips. Symptoms can be confused with root knot nematode damage as seen on other crops. Dwarfed fruiting canes and smaller fruit result. Damage is more severe on light sandy soil. Severe nematode damage can be avoided by planting clean root cuttings in soil where only grasses or small grains have been allowed to grow for three to four years. Commercial producers in problem areas may need to consider a pre-plant fumigant. Root knot nematode is not a problem on caneberries. See Section on Nematodes. (See Photo of Nematodes)

Orange Rust (fungus – Gymnoconia peckiana or Kunkelia nitens): Symptoms first appear as small, yellow spots on both sides of leaves. These spots enlarge on the underside to form irregular shaped pustules that rupture to release masses of orange spores. The fungus becomes systemic in plants, and affected plants never recover. No fruit is produced. Diseased plants, including all roots, should be removed and burned when first noticed and before pustules break open. Control weed growth and remove fruiting canes after harvest to improve air circulation. Destroy wild brambles and dewberries in adjacent areas. Fungicides are not effective against this rust. Varieties vary in their susceptibility to this fungus. Most thorn type blackberries are resistant. (See Photo of Orange Rust)

Rosette (fungus – Cercosporella rubi): This disease is also called double blossom or witches’ broom. Symptoms appear in the spring as bunches or clusters of foliage at terminals or along fruiting canes. Flower buds are larger and redder than normal. Petals may be purplish, and sepals are much elongated. Infected flowers do not set fruit. Control rosette by removing infected canes as soon as they become noticeable. Destroy all wild berry plants in the vicinity. Remove and burn all fruiting canes soon after harvest and keep plants adequately spaced for good air circulation. Where heavy infection has occurred, mowing all canes to the ground may be necessary. The new thornless blackberry varieties, Navaho and A. (See Photo 1 and Photo 2 of Rosette)

Septoria Leafspot (fungus – Mycosphaerella rubi): A fungus disease causing symptoms similar to anthracnose leafspots. Spots tend to remain small with light brown or tan centers. Tiny black specks visible with a hand lens develop in centers of leafspots. Chemical control is not usually necessary.

Virus Diseases: Viruses transmission has not been determined. Diagnosis of specific viruses is difficult based on symptoms. Viral symptoms include mosaic on foliage, stunting, leaf curl, leaf distortion and sterility or partial sterility. Poorly developed fruit, known as nubbins, may occur with normal fruit in the same cluster. See section on Virus Diseases.