If you grow currants, you should know about currant sawflies.
Currants make delicious jellies, pies, sauces, and even wine, but currant sawfly larvae can completely strip the leaves from your currant plants in only a few days.
Also known as imported currantworms and common gooseberry sawflies, these pests feed on gooseberries and other members of the Ribes family. Native to Europe, this pest is now found throughout North America.
Currant sawfly identification
If you see chewed holes in the leaves of your currant bushes, take a closer look. There are several pests that can cause this damage. It may be currant borers (Synanthedon tipuliformis), currant spanworms (Itame ribearia), the Epochra ribearia maggot, gooseberry fruitworms (Zophodia convolutella), or currant sawflies (Nematus ribesii). Sawflies tend to feed in groups, while those other pests do not.
Like other sawflies, adult currant sawflies look like a cross between a wasp and a fly. The larvae grow to 3” in length, but their coloration makes them difficult to see. They start out green with black heads. As they grow, they develop yellowish ends and black spots.
Currant sawfly lifecycle
Adult currant sawflies lay tiny, oval white eggs on the underside of leaves and there can be three generations each year. The first brood emerges after the first leaves appear in spring, the second occurs in early summer, and a third generation may occur, weather permitting. In each generation, feeding is very heavy and rapid.
To make matters worse, feeding often begins on the lower, inner reaches of the shrub, so you may not even notice the damage right away. Be sure to inspect plants regularly for signs of feeding and look on the underside of leaves for eggs.
How to control currant sawflies
Before you take any drastic measures, you need to know that the larval stages of currant sawflies look a lot like little green caterpillars. The distinction is important because control measures are different for moth and sawfly larvae. Take a closer look. If you have one, grab a hand lens or magnifying glass. If if you see 6 or more pairs of hookless legs, it’s a sawfly. Caterpillars have tiny hooks on their stubby legs and they usually have only 3 pairs of prolegs.
You can treat moth larvae infestations with Bacillus thuringiensis (Bt). That treatment will not work against sawflies. Commercial growers spray plants with Malathion as soon as currant sawflies appear. Your best choice for controlling currant sawflies is to spray infested plants with insecticidal soap and handpick currantworms as they are seen.
Currants are edible plants, native to the northern hemisphere.
Not to be mistaken with the tiny black raisins made from black Corinth grapes, currants are members of the Ribes family, along with gooseberries and jostaberries (a cross between currants and gooseberries).
Most Americans are unfamiliar with currants because they were banned in 1920. This ban was put in place because currants are co-hosts, along with white pine, to white pine blister rust (Cronartium ribicola). This fungal disease was devastating to white pines on the east coast. That ban was lifted, in 1966, as resistant cultivars were developed.
The small, pea-sized fruits can be red, pink, white, or black and are produced in clusters called ‘strigs’. Currants are tart, so they are not usually eaten fresh. They are more commonly used for jams, jellies, pies, syrups, wine and brandy. The flowers are also edible.
Currant plants are thornless, deciduous shrubs that make excellent additions to native gardens. They are drought tolerant and provide food and shelter to many indigenous birds. Native Americans frequently used currants as both food and medicine. In particular, they used currant roots to treat menstrual and menopausal problems. Scientists have found that currant roots and seeds contain high levels of gamma-Linolenic acid, a chemical known to be effective for those same issues.
According to Wikipedia, there are black currants, red currants, and white currants. According to the University of Massachusetts, “Species are Ribes rubrum (most red currants and some whites), R. petraeum (white), R. vulgare (pink, white, and red), and R. nigrum and R. ussurienses (black). Native currants… belong to the species R. odoratum."
My order of Golden Currants (Ribes aureum) just arrived. Clearly, there is some confusion. Here’s the bottom line, as well as I can figure:
How to grow currants
Traditionally, currants grow in cool climates with fertile, well-drained soil, where they are found in full sun or partial shade. In areas with hotter summers, like the Bay Area, currants prefer heavier soil and more shade. Mulch can be used to keep roots cool and moist in summer. Most currant bushes reach 3 to 5 feet in height, but they can go as tall as 9 feet, under ideal conditions. Currents can be grown in large containers. Currants are normally purchased as bare root stock or young saplings that were propagated from hardwood cuttings. These young currant bushes need a lot of water to get established, but are very drought tolerant later on. Currents also need a lot of potassium. Our Bay Area soil tends to have plenty of that, so no treatment is needed around here. Most currant plants are self-pollinating, but production is significantly higher per plant with multiple plants nearby.
Currants can be pruned as shrubs or trees, depending on your preferences and the plant’s location. Currants should be pruned once a year in winter using a method called renewal pruning. Renewal pruning ensures that there are fruit-producing 2- and 3-year old stems each year. Use the following pruning schedule on currants:
Pests & diseases of currants
Aphids, mites, currant borers, and the larva of some moths and butterflies are really the only pests that bother currants. Problems are more commonly caused by mineral imbalances in the soil or improper irrigation. Rust, powdery mildew, anthracnose, and leaf spot can sometimes appear on currants.
Since currant flowers tend to appear early in the season, sometimes as early as February, they provide pollen and nectar to our earliest pollinators. This helps set the stage for a more productive year overall. Each bush can produce up to 10 pounds of fruit, so it won’t hurt to leave some behind for the birds.
Add some native golden currants to your California garden in early spring or late fall for many years of fruit and flowers!
You can grow a surprising amount of food in your own yard. Ask me how!