Botrytis Dieback and Fruit Rot (Botrytis cinerea): This disease commonly affects many plants. It can infect leaf and stem tissue but is most damaging when it infects flower and fruit tissue leading to fruit rot. It overwinters in dead leaves and plant debris and on stems. Inoculum is produced from fruiting structures on canes, from dead leaves, and from mummified berries in the spring.
Management: To help control the disease, choose a planting site with good air movement and prune out weak canes to speed the drying of plants. Also eliminate weeds to aid in quicker drying of foliage and fruit and harvest fruit before it is overripe. Fungicides should be applied during bloom, with additional applications made during harvest, if necessary. See the following Pest Management Table for specific recommendations and rates.
Powdery mildew (Podosphaera mors-uvae): This fungal disease overwinters on currant and gooseberry twigs. In early summer, a whitish, powdery growth appears on the surface of leaves, shoots, and branch tips. Infected berries become cracked and may shatter. Infected leaves may drop prematurely during hot weather. If left unchecked, the fungus can progress to the berries themselves. Later in summer, the growth may turn from white to brown. Warm, humid conditions with poor air circulation favor powdery mildew. Prune and dispose of infected branch and shoot tips in early spring. Severe infections can cause plants to become stunted and die. Some growers are experimenting with trellising gooseberries to improve disease management and harvestability. Certain horticultural oils (check labels) applied at first sign of mildew can prevent spread.
Management: Conditions of high humidity are most likely to lead to mildew problems. Any cultural practices like pruning and plant spacing that can help improve air circulation and reduce humidity will reduce incidence of mildew infections. Sprays are most necessary during humid or wet weather in the spring. Apply when the first signs of powdery mildew are apparent and repeat as necessary. If oil is used, multiple applications may delay ripening or reduce sugar accumulation in the berries. The oil kills powdery mildew colonies on contact, thus, high water volumes and thorough coverage of the leaves and developing fruit are essential for good results. Many common pesticides (including sulfur) are phytotoxic when applied with or close to oil sprays; check label for specific restrictions. See the following Pest Management Table for specific recommendations and rates.
Anthracnose Leaf Spot and Septoria Leaf Spot (Drepanopeziza ribis and Mycosphaerella ribis): These diseases can both become serious problems, especially in wet, humid years. Symptoms range from brown spots and yellowing on leaves, young shoots, and stems to early defoliation. The fungi overwinters in infected dead leaf tissue. Spores are released from this leaf debris in the spring and infect new leaf tissue. Small brown spots appear in early to mid-June and at this point both diseases are visually indistinguishable. Currant fruit may also become infected with Anthracnose. Severe infections cause berries to crack and drop.
Management: These diseases can be suppressed by raking out and removing infected leaves after they have fallen and apply mulch to cover any inoculum that might remain. Prune and trellis to improve air circulation and promote leaf drying will also help the control. Overhead irrigation creates conditions especially favorable leaf spot development, thus if it must be used, irrigate during morning hours to allow foliage to dry before the evening. Fungicides applied before bloom, after petal fall and after harvest are also recommended. See the following Pest Management Table for specific recommendations and rates.
White Pine Blister Rust (Cronartium ribicola): This disease is the primary reason for limited commercial production of Ribes in the North America. It is a complex disease that requires two hosts, susceptible varieties of Ribes and 5-needled pines (e.g., Eastern White Pine). Symptoms on Ribes consist of yellow to orange spots appear on less susceptible plants first in the spring. Larger patches of orange 'rust' appear on the underside of the leaves later in the summer. Symptoms are usually not severe on Ribes (although severe infections can defoliate plants), but infections in White Pines can lead to tree death.
Management: Black currants Ben Sarek, Consort, Crusader, Coronet and Titania are considered resistant. Titania is the most widely planted variety in New England (where it is permitted) and was considered immune to WPBR in the past. That immunity may no longer be stable and so some states are revising their regulations as related to allowing this and other 'immune' varieties. It is important to check with your local Extension Specialists to determine the most recent status of this disease. Gooseberries, red and white currants are generally less susceptible. Ribes species Red Lake, Jumbo Cherry and White Currant are known to be less susceptible than Red Jacket, Green Hansa, Poorman and Pixwell. Avoid planting in high-risk areas (Check with your University Extension office for help determining the risk category of your site) or within 1 mile of pine trees stands. If Rally fungicide is used for powdery mildew or anthracnose, it should also control white pine blister rust. See the following Pest Management Table for specific recommendations and rates.
Currant Cane Blight or Botryosphaeria Canker (Botryosphaeria ribis): The disease has been identified in NY and CT, but is likely present in other New England states. Initial symptoms appear as yellowing foliage and leaf wilting of young shoots during spring and summer. Affected shoots may resemble currant borer damage, but will have not borer larvae or exit holes. Once the cane is dead and no longer transporting nutrients, the fungus will make small (2mm in diameter) round black survival structures, stromata, which burst through the epidermis near tips of infected shoots. This disease causes canes to become extremely weak and consequently break off during high winds in the Fall and subsequent Winter. All currant varieties may be affected however gooseberries are not known to be affected.
Management: Watch for a rapid blight of young shoots during early fruit development, and scout mature canes for the small black survival structures prior to budbreak. Prune out and burn infected canes in spring. There are differences in resistance among cultivars, but it is variety specific and not linked to color traits.