Plant Health Problems
Diseases caused by Fungi:
Anthracnose, Pseudepeziza ribis.
The leaves are most commonly attacked although this disease can also occur on the fruit. The symptom on leaves is a scattered pattern of small red-brown to purplish spots that ooze masses of pink spores on the underside of the leaf. Red and white varieties are most susceptible.
Control can be achieved by raking and removing of infected leaves and fruit. It is also important to maintain good air circulation and maximize plant vigor. Use of fungicides is not effective or practical.
Powdery mildew, Sphaerotheca.
White powdery patches develop on leaves and shoots in early spring. These areas gradually turn a rusty brown as the spots age. Newly formed fruit are often infected and are covered with the white powdery growth characteristic of this disease. Infected fruit shrivel, crack and shatter. Species and cultivars vary in their susceptibility although European varieties are more susceptible than American ones.
Control can be achieved by pruning and removing of infected shoots. It is also important to maintain good air circulation and maximize plant vigor. Use of fungicides is not effective or practical.
Botrytis fruit rot, Botrytis cinerea.
Diagnostic symptoms appear as infected leaves and fruit are covered with a gray fuzzy mass of the fungus. This disease can result in extensive losses when wet weather occurs right before harvest.
Strategies to control this disease are aimed at methods that maximize air circulation and drying of the fruit and include pruning and thinning of the plants. When weather is favorable for disease, fungicide sprays are often necessary for effective control. Among the compounds registered for use in Connecticut is sulfur. Sprays are usually applied just before bloom and are repeated as necessary. Consult the label for dosage rates, safety precautions, and days to harvest intervals.
Cane blight, Botrysphaeria spp.
This disease occurs on the stems and can result in girdling and killing cankers. On the dead stems small, black fruiting pustules are produced and visible with a hand lens.
Pruning and removing infected canes back to healthy wood when the bark is dry is a key strategy for control. It is also helpful to maximize plant vigor by following sound cultural practices which include fertilizing, pruning, and watering.
White pine blister rust, Cronartium ribicola.
All species and varieties of currants are susceptible to one stage of the rust causing white pine blister rust. Symptoms appear as flat bright orange spots on the leaves in midsummer. Red currants are not very susceptible but black currants are very susceptible. Although this rust is of minor importance on currants, the fact that they are an alternate host for the white pine blister rust, probably the most serious disease of white pine, gives added importance to this disease on currants.
Although Connecticut no longer prohibits growing currants, many other New England states still limit their growth. Black currants (R. nigrum) are the most susceptible to this disease although hybrid, rust-resistant black currants are now available. These include Titanic, Consort, and Crusader. Chemical control is not effective.
Currant aphid, Cryptomyzus ribis.
This aphid is usually found on the underside of the tender terminal leaves which become more or less curled or blistered. Glossy black eggs on the twigs of the new growth carry the insect through the winter. These eggs hatch soon after the first leaves unfold. Many generations during the summer are born alive, most of them females without wings. When the aphids become overcrowded, winged females develop and migrate to other currant plants. The distorted and curled leaves often turn red and drop. After midsummer, the aphids become less abundant because of natural enemies, but enough females survive to lay eggs on the twigs in October.
Sprays of insecticidal soap, ultrafine horticultural oil or malathion, which are among the compounds registered for control of this pest in Connecticut, may be applied to the undersides of the leaves as soon as the aphids appear. Consult the label for dosage rates, safety precautions, and preharvest intervals.
Currant borer, Synanthedon tipuliformis.
Certain stems that appear to be unthrifty and finally die usually have the center or pith tunneled by the larva of this insect. The eggs are deposited singly on the bark. The fully grown larva is about ½" long and is white with brown head and legs. The adult is one of the clearwinged moths with a wingspread of about 3/4". The wings are transparent with opaque purplish margins. There is one generation each year, and the moths emerge in June. Sickly canes may be cut off and burned, if allowed, before June 1.
Currant fruit fly, Epochra canadensis.
This insect often causes serious injury to currant and gooseberry. The larva or maggot infests the berries, which may hang on the bushes or drop to the ground. There is only one generation each year, and the winter is passed in the pupa stage in the ground. The adult fly is about the size of the housefly, but is pale yellowish in color with banded wings. Two or three sprays or dusts of rotenone, which is among the compounds registered for use against this pest in Connecticut, at weekly intervals, starting when the blossoms fall, should control this pest. Consult the label for dosage rates, safety precautions, and preharvest intervals.
Currant stem girdler, Janus integer.
This insect is a sawfly that lays an egg in May in the new shoot and girdles or cuts it partly off an inch or less above the egg. These tips break off or hang from the canes. On the hatching of the egg, the young larva burrows downward in the pith to a distance of not more than 6 inches. About September 1, the larva reaches maturity, cleans out the lower end of the burrow, and eats a passageway to the outer bark. It passes the winter as a larva in the burrow and pupates in the spring. There is one generation each year. The only known remedy is to clip off and burn the tips of the canes.
Fourlined plant bug, Poecilocapsus lineatus.
This bug lays eggs in the soft stems. They hatch about the middle of May and the young bugs suck the sap from the tender leaves. They molt five times and when mature, about the middle of June, they have wings and are nearly 1/3" long. The insect body is yellow, marked lengthwise on the wings with four black stripes alternating with three green stripes. The injury to the leaves consists of sunken areas around the punctures. These areas later appear as circular transparent spots and finally as circular holes. This insect injures the new leaves of many different kinds of annual and perennial plants and shrubs. There is one generation each year. The nymphs can be managed by spraying with azadirachtin, ultrafine horticultural oil, insecticidal soap or malathion, which are among the compounds registered for control of this pest in Connecticut. Consult the label for dosage rates, safety precautions, and preharvest intervals.
Gooseberry spanworm, Cymatophora ribearia.
This insect occasionally feeds on gooseberry and currant. The larva is about an inch long when full-grown. It has the habit of a measuring worm and loops when it crawls. It is whitish with yellow stripes and black spots. It pupates in the ground and the moth emerges late in June. The moth has a wing spread of about 1 1/4" and is light tan with a row of parallel gray dashes across each wing. The eggs are laid on the bark in July and hatch the following spring. Treatment is seldom needed.
Imported currantworm, Nematus ribesii.
The adult sawflies emerge when the currant leaves first unfold, and lay white elongate eggs end to end in rows along the veins on the underside of the leaves of currant and gooseberry. The eggs hatch in a week or 10 days, and the larvae feed on the leaves, becoming full grown in 2 to 3 weeks, when they are about 3/4" long. During most of the feeding period, the larvae are grayish-green, covered with black spots but at the last molt, they lose the black spots and are a uniform green. They pupate beneath leaves or trash on the ground. A second generation begins in late June or early July. The first generation causes most of the injury; the second is of little account. Among the compounds registered for control of this pest in Connecticut, rotenone should be effective if sprayed when the first generation larvae begin to feed. If treatment seems necessary when the fruit is near maturity, pyrethrum may be used. Consult the label for dosage rates, safety precautions, and preharvest intervals.
San Jose scale, Quadraspidiotus perniciosus.
Large infestations of the San Jose scale can cause loss of vigor in currants. Partially-grown scales overwinter under their circular gray covering or scale on the twigs. They begin to feed as the sap starts to flow. When apple trees bloom, the males emerge from under their scales to mate with the immobile females. Females are circular and cone-shaped, and their circular scales are about 1/16" in diameter, with a raised center or nipple. The males are smaller and elongate, with the nipple not centered on the scale. Females give live birth to tiny bright yellow crawlers in June, usually about 3-5 weeks after the flower petals drop. The young crawlers quickly settle, insert their long mouthparts into the twigs, and then suck sap from twigs. As they grow, the crawlers secrete a waxy filament that becomes their scale or covering. Scales apparently have 2 generations per year, with the first in June and the second in August. Scales may be controlled by applying horticultural oil, which is among the compounds registered for control of this pest in Connecticut, as either a summer or dormant spray. Consult the label for dosage rates and safety precautions. To detect the yellow crawlers, wrap black tape coated with Vaseline around small branches. Adult flights may be detected with pheromone traps.
Scurfy scale, Chionaspis furfura
These whitish or light gray scales infest pear, apple, currant, and other trees and shrubs, reducing tree vigor. Scurfy scales pass the winter as purplish eggs under the shell of their mother. In Connecticut, the yellow crawlers hatch from eggs about the last week of May. They soon settle on the bark and insert their long mouthparts to suck the sap. The adult females are pear-shaped and about 1/10" long. The males are much smaller, long and narrow, with 3 longitudinal ridges or carinae. Dormant treatments with horticultural oil control these scales. A spray of insecticidal soap, which is among the compounds registered for control of this pest in Connecticut, early in June also will destroy the young. Consult the labels for dosage rates and safety precautions.
Twospotted spider mite, Tetranychus urticae.
This mite may be a serious problem on currants, especially if naturally occurring predators (predatory mites, six-spotted thrips, and mite destroyer ladybeetles) are disrupted with insecticides (such as rotenone). Ultrafine horticultural oil will control these mites while conserving natural predators. Consult the label for dosage rates, safety precautions, and preharvest intervals.