Cane Blight

Pathogen: Leptosphaeria coniothyrium

Symptoms, Life-cycle and Pest Management

The fungus overwinters on infected dead canes. In the spring spores are blown, splashed by rain, and carried by insects to nearby canes.  Under moist conditions the spores germinate and enter the plant through pruning wounds, insect damage, fruit stem breaks and other wounds. The fungus can then rapidly kill bark and other cane tissue.   Dark brown to purplish cankers form on the new canes near the end of the season. The cankers enlarge and extend down the cane or encircle it causing lateral shoots to wilt and eventually die. Infected canes commonly become cracked and brittle and break easily. This disease is usually most severe during wet seasons.

Anthracnose / Leaf Spot

Pathogen: Drepanopeziza ribis (syn. Pseudopeziza ribis) (asexual: Gloeosporidiella ribis)

Symptoms, Life-cycle and Pest Management

The fungus overwinters on fallen leaves in the form of fruiting bodies which can withstand severe winter conditions. The following spring these structures produce spores of a different type from those formed on the plant in the summer.  These spring spores attack the young leaves to start the infections for that season. Once the disease is present on the bush, it is spread further by the rain-splashed summer spores produced on the leaf spots.

The first symptoms appear on the leaves in early summer as they become spotted with very small, dark brown, round or irregular leaf spots develop, which, when abundant, may cause foliage to yellow and drop by midseason. Small, grayish bodies (acervuli) develop in leaf lesions. The disease reduces the plant’s vitality, growth, and productiveness. On currants, fruit as well as leaves may show spotting like fly specks. Severely infected berries crack open and drop also, the leaves fall and the bushes may become defoliated.

Remove and destroy dead leaves from under bushes. Cultivate under and around bushes to bury leaves before bud break in spring. Prune and thin bushes to provide better air circulation and drying conditions. Use a fall clean up and dormant spray to destroy inoculum from dead leaves.

San Jose Scale

Scientific name: Diaspidiotus (= Quadraspidiotus) perniciosus

Symptoms, Life-cycle and Pest Management

Female San Jose scales give birth to living young that emerge from under the edge of the scale covering. These tiny yellow crawlers wander in a random fashion until they find a suitable place to settle. Immediately upon settling, the crawlers insert their mouthparts into the host plant and begin feeding and secreting a white waxy material (white cap stage); eventually the waxy covering turns black and is known as the black cap stage. Later the covers turn various shades from gray to black.

They feed by sucking valuable plant juices, and in severe cases they affect the fruit as well. Scale insects are easily seen on the dormant wood. Prune out and destroy infested canes before new growth begins in the spring.

Powdery Mildew

Pathogen: Podosphaera mors-uvae (formerly Sphaerotheca mors-uvae)

Symptoms, Life-cycle and Pest Management

The fungus overwinters in pruned or broken twigs.  In the spring the spores are released and infect leaves and shoots.  Signs of the fungus are white patches on the surface of leaves, shoots and berries. The patches enlarge, merge, and develop white powdery masses of spores which can start new infections.  Eventually the fungus turns reddish brown and small black spore containing bodies develop.  This causes stunting and dieback of shoots and berries become off-color and rough.  In the fall, remove prunings and crop debris then spray with lime sulfur to kill overwintering spores.