Currant (Ribes)
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.
Insect Problems:
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.