(Courtesy of and adapted with modifications from the University of Wisconsin)
Under most conditions, insects are not perennially serious pests of currants and gooseberries; however, certain insects occasionally will become abundant enough to cause serious damage if left uncontrolled.
The currant aphid, Cryptomyzus ribis (L.), overwinters in the egg stage on plant stems. Eggs hatch in early spring, and the insects feed by sucking out the plant juices, which results in stunted and distorted new growth. As leaves continue to develop, they will be crinkled with downturned edges. Areas between veins on the upper leaf surface may be reddened. As the aphids feed, they excrete excess sugar and water in small droplets called honeydew. Ants may feed on this, and a black fungus (sooty mold)often grows on it. The aphids themselves are small (up to about 2 millimeters), green, and usually found in colonies. Other aphid species also occasionally feed on currants and gooseberries.
Aphids often are kept under good natural control by predators such as ladybugs, small parasitic wasps, and even some insect diseases. In some areas or during certain years, these natural controls may not be adequate, and you might choose to use a chemical spray. Dormant sprays are effective, as are summer horticultural oil or insecticidal soap if applied when the aphids are first seen.
The damaging stage of the currant borer, Synanthedon tipuliformis (Clerk), is a pale, yellow, wormlike larva that tunnels through the pith of the cane. A member of the clear-winged moth family, the wasp-like adult lays its eggs on the canes in early June. After hatching, the worm enters the cane and feeds all season. It overwinters in the larval stage in the cane, emerging as the adult moth the following spring. Feeding damage will kill the cane; the first symptom is yellowing foliage on individual canes in late spring. Red currants are attacked most frequently.
Cut out and destroy infested canes as early as possible. Once the larvae bore into canes, chemical control is not possible.
Imported Currant Worm
The imported currant worm, Nematis ribesii (Scopoli), is the most serious insect pest of currants and gooseberries, with the latter being the favored host. Foliage is consumed by several small, spotted, caterpillar-like larvae. The adults are sawflies about the size of a housefly. Two generations hatch each year, causing damage in the spring and again in late summer.
Bacillus thuringiensis-based products and/or a broad-spectrum insecticide should control this insect. Start looking for damage shortly after the leaves have fully expanded. The second generation usually is less severe than the first and does not require treatment.
Currant Stem Girdler
Adult sawflies, Janus integer (Norton), make numerous punctures in canes during egg laying in spring, resulting in drooping and wilting of new shoots in late spring. Further damage occurs as the larvae tunnel through the canes. This insect also attacks poplar and willow trees, and damage usually is more severe near stands of these trees. Removing and destroying infested canes at the first sign of wilting is the best control.
Fourlined Plant Bug
The fourlined plant bug, Poecilocapsus lineatus (Fabricus), is yellowish green with four dark stripes on its back. It is quite active and runs and flies readily. It sucks plant juices from leaves and young stem growth, causing deformed and brown foliage. Older leaves will be spotted with many tiny, light spots. This insect feeds on numerous wild hosts, and damage occurs most frequently when such plants are allowed to grow near currants and gooseberries.
In areas where plant bugs have been a problem, they can be controlled by an early season application of pyrethrum-based or pyrethroid compounds.
The larval stage of the gooseberry fruitworm, Zophodia convolutella (Hübier), is a greenish worm with darker stripes along the sides. The worms feed by hollowing out the insides of the fruit of both currants and gooseberries; each worm consumes several berries. The adult is a moth.
Bacillus thuringiensis-based products and/or a broad-spectrum insecticide should control this insect. Make two applications 10 days apart, starting at early fruit development.
Currant Fruit Fly
Fruits infested by the currant fruit fly, Epochra canadensis (Loew), drop early and have dark spots surrounded by a red area. Small, white maggots will be found in such fruit. Late-maturing varieties are preferred by this insect.
The removal and burial or the destruction of dropped fruit will keep populations from building. The insecticide program for gooseberry fruitworm also will control fruit flies.
San Jose Scale
The adult San Jose scale, Quadraspidiotus pernicious (Comstock), is a small, grayish, disk-shaped speck about 2 millimeters across with a raised spot in the center. It is found most frequently on the canes. For most of its life, the scale insect is incapable of movement and merely sits and sucks out the plant juices. Heavily infested plants will have canes encrusted with scales. In such cases, single canes or even entire plants will be killed.
Dormant sprays of lime sulfur or superior oil will control San Jose scale.