Production Regions
Washington red currant production is centered in Benton County, Washington. Small acreages also exist in western Washington. Most western Washington production is extremely small-scale or experimental in nature, therefore this profile focuses on the production and pest management concerns of the commercial industry in eastern Washington.
General Information
Currants are a high value-per-acre crop. These members of the Ribes genus, which includes red currants, black currants, and gooseberries, are not to be confused with zante currants, which are small dried grapes that resemble raisins. Of red, black, and white currants, only red currants (R. rubrum) are commercially produced in Washington State. Black currant trials have proven the species to be largely unacceptable; the plants produce less salable product than red currant plants and are more susceptible to pests (11). For the purposes of this profile, "currant" will be synonymous with "red currant."
Red currants have been shown to have considerable health benefits, including high vitamin C and potassium content. Given that the crop requires a low number of inputs and has a high return, interest in producing currants seems to be increasing in California, British Columbia, and parts of the eastern United States. The climate and soils of eastern Washington State make it a prime region for future expansion of the industry.
As of this writing, the market for red currants appears to be shrinking due to both a loss of processors and to competition from European suppliers. Processors have gone out of business in recent years due to problems with other juice berries.
Cultural Practices
Currants are berries borne on deciduous, weather-hardy shrubs that, in their natural state, are multi-stemmed and reach approximately 5 feet in height and 5 feet in width. While currants can be grown from seed, they are typically propagated for commercial production via hardwood cuttings taken from year-old wood. Plantings are made in unfumigated soil in the spring. The typical arrangement for new plantings is to arrange them alongside a 4-foot trellis with support wires suspended about 2 feet on both sides of the plants.
Established currant plants start growing in February of each year. (Plants do their growing between February and July. The rest of the year is essentially a dormancy period during which the plants store food for the following season.) Pruning takes place mid-February to mid-March. Growers prune to remove older wood and encourage new growth on spurs of productive, two- to three-year-old wood. Year-old plants are pruned at ground level to two or three stems (canes). In subsequent years (third and fourth season), all but two or three of the past year’s new stems are also trimmed to ground level, so the bush has two or three stems from each season. Older but productive stems may also be pruned to a shorter, more manageable length at this time. After four seasons, older, less productive stems may be removed. Plants are kept in production for 12 to 16 years, with peak yields at eight years. In a strong market, growers would turn over their acreage, removing old plants and replanting new currants, every 12 to 15 years. In practice, this does not take place in a moderately strong and weakening market such as the present situation in Washington State.
Red currants begin their single annual bloom in late March. Flowers occur near the base of stems and spurs one or more years old. Each flower bud opens to a number of small green flowers (as many as 20) joined together on a delicate, drooping 5 to 6-inch stem called a “strig.” Bees are introduced to the field for pollination in early April, coincident with the full-bloom period that generally occurs toward the end of the first week in April. The berries are subsequently borne in drooping clusters on these strigs.
Currants have high nitrogen requirements. Growers typically amend their soil with nitrogen (N), phosphorus (P), and potassium (K) in the spring.
Almost all of the currant crop in Washington is rill-irrigated. The plant’s shallow roots respond well to this irrigation method. While sprinkler irrigation does work on currant plants in eastern Washington, rill irrigation results in juicier, heavier berries. In the drier eastern Washington climate, the crop is irrigated from March through harvest. In years when water is plentiful, irrigation is extended as long as water lasts or until first frost.
Berries are ready for harvest when the fruit reaches 12 brix, about 90 to 100 days after first bloom. This occurs between the third week in June and the second week in July. Most of the crop is used for jelly and juice (2, 10). These berries are machine-harvested; harvesting machines are typically adapted from grape harvesters. Berries for processing go directly from the field to be frozen.
A small amount (less than 10% of the 2003 crop) is sold on the fresh market. These are harvested by hand about a week ahead of the currants intended for processing. Picking date is determined by the berries’ first reddening. At this stage, their sugar content is approximately 10 brix. Fresh market berries are picked by strigs, not as individual berries.
After harvest, routine off-season maintenance includes trellis repair in preparation for the coming spring. When the market is strong, an off-season pruning takes place to thin the weaker shoots.
Pests are listed in order of importance, with insects having the greatest impact on the industry, followed by weeds, then diseases. Within each category, an attempt has been made to list the pests in order of importance as well, although this can change from one season to the next.
Currant borer (CB) and currant stem girdler (CSG) are the primary pests of red currant in Washington. The larvae of both tunnel into the stems of the currant, causing progressive dieback and reduced yield (as much as 50%) if the insects are not controlled. Currant can also host other pests, but these do not result in economic damage at this time, so they are seldom controlled by Washington growers.
Currant Borer, Synanthedon tipuliformis
Currant borer adults are attractive, day-flying clearwing moths, blue-black in color with yellow markings. Typically, they complete one generation per year. In Benton County, currant borer (CB) adults emerge about the third week in May. Shortly thereafter, females lay single olive-brown eggs on older currant plants near the nodes or axillary buds, in pruning scars or exit wounds, and under loose bark. Eggs take about three weeks to hatch, after which the young larvae tunnel into and feed actively upon the central conductive stem tissues during the late summer and early fall. Larvae pass through about six instars, reaching 15 to 18 mm. in length at maturity, then shrinking to around 10 mm. before pupating in the spring. CB pupates in a thin, brownish/grey silken cocoon within the stem. The pupae start out cream-colored, become brown, then take on the coloration of the adult moth about two days before emergence the following May.
Historically, ethyl parathion was used effectively against CB (and CSG, see below) for many years but its use was cancelled on currants in 1991. Insecticides were applied when adults were seen flying in currant fields during May and June. However, because of a protracted emergence period and difficulties in obtaining good control, two or three applications were usually required over a four-to-six-week period. Multiple applications of these broad-spectrum insecticides tended to kill beneficial predators, often resulting in secondary outbreaks of spider mites. The mites, in turn, sometimes had to be controlled with a miticide after harvest of the currants in July.
Controls
Cultural
Pruning as described in the Cultural Practices section, above, eliminates much of the older wood habitat that CB favors.
Biological
Washington State University research has shown that mating disruption using twist-tie pheromone dispensers has a suppressant effect on populations of CB. This strategy is being used under an experimental use permit by all Benton County currant growers. They hang pheromone dispensers approximately the second week of May, a week before the emergence of the adult moth. Commercialization of the strategy will depend upon whether registrants find it economically feasible.
Chemical
Fenpropathrin (Danitol) was available under a Section 18 exemption beginning in 1997. In November 2003, the registrant petitioned the U.S. Environmental Protection Agency (EPA) to add currants to the main label. The rate on the Section 18 label was 10.67 fl. oz. product per acre, equivalent to 0.2 lb. active ingredient per acre (a.i./A). This rate is effective against CB. However, use of mating disruption has almost eliminated the need to apply Danitol with CB as its exclusive target. At this time, when Danitol is applied for CSG as described in the section following, CB is controlled as well. The timing of the second CSG application coincides with emergence of CB. Growers report that CB mating disruption has cut their total use of Danitol to about half what was used in the 1990s.
Currant Stem Girdler, Janus integer
Currant stem girdlers are slender sawflies 1/4 inch (male) to 1/2 inch (female) in length. They have a black head and thorax. Females’ abdomens are reddish orange on the front half and black on the back half, while males’ abdomens are brownish yellow. Both larvae and adults injure currant plants.
In Benton County, currant stem girdler (CSG) adults emerge around the edges of fields about the first week in May. Shortly thereafter, females begin laying eggs. The female lays one egg at a time, inserting it into the pith of a new shoot then climbing 1/2 to 1 inch up the shoot and girdling it with her saw-like ovipositor. Typically, this does not sever the stem completely, but rather leaves it dangling. It eventually dies and falls off.
A single female CSG can lay up to 30 eggs and girdle 30 shoots. The eggs hatch in about two weeks, and the larvae begin feeding on the pith of the shoot, injuring newer currant shoots with this tunneling and feeding action in much the same manner as currant borers injure older stems. The CSG larva reaches full growth by early September, at which time it begins making the cocoon in which it overwinters. In mid- to late April, it changes to a pupa just a few days before emerging as an adult.
The pest can be inconspicuous; without training and vigilance, sighting of the girdled shoots in early May is often the first indication that adult sawflies have emerged. This makes timing insecticide applications difficult. In an effort to be proactive, growers and fieldmen are making greater efforts to scout for the insect before damage occurs.
Historically, the application of ethyl parathion for CSG parallels its application for CB (see above).
Controls
Cultural
Growers scout for CSG in early May by looking for the emerging adults and the sawed-off stems around the periphery of the field. Sticky traps are sometimes employed. While pinching or cutting shoots below the girdle wound eliminates the problem, it is not practical as a means of control on a commercial scale.
Biological
No cultural or biological means are available for control of this pest, but research into mating disruption is underway.
Chemical
Fenpropathrin (Danitol) was available under a Section 18 exemption beginning in 1997. In November 2003, the registrant petitioned EPA to add currants to the main label. It is applied at 10.67 fl. oz. product/A (0.2 lb. a.i./A up to three times per season. The first application takes place when CSG first appears, typically the first or second week in May. This is often a border application only, as field borders are where the girdler generally appears first. Based on continued monitoring, a second application usually takes place late May or early June. This second application and a possible third (typically mid-June) are based upon the presence of CSG and may be a border application, a spot application, alternate row application, or an entire field application. Danitol is critical to the industry; losses of 50% or more could be incurred without it.
Two-Spotted Spider Mite, Tetranychus urticae
This pest is about 1/50-inch long, has eight legs, and is light tan or green. They overwinter as adults on weeds and debris at the base of host plants. Feeding by two-spotted spider mite can reduce plant vigor and impact yields. Before 1991, when ethyl parathion was widely used to control CSG and CB, its broad-spectrum activity tended to kill beneficial predators, often resulting in secondary outbreaks of spider mites. The mites, in turn, sometimes had to be controlled with a miticide after harvest of the currants in July.
Controls
Cultural/Biological
Growers avoid excessive use of broad-spectrum insecticides today, which conserves predators and eliminates the need to target spider mites.
Chemical
No miticides are registered.
Black Vine Weevil, Otiorhynchus sulcatus
This nocturnal insect is in the ground during the day but attacks currant plants at night, causing direct damage through its feeding activity, eating berries and lopping off strigs. It is prevalent mid- to late June, causing the most problem very close to harvest time in early July. There is some evidence that this pest is causing more damage and yield reduction than previously realized.
Fenpropathrin (Danitol) is effective against this pest, but is not registered for use against black vine weevil. Allowable use of this chemical against CB or CSG (see above) could help suppress black vine weevil, but the product has a 21-day PHI, which is too long to be effective during the weevil’s most damaging period.
If fenpropathrin (Danitol) were used as a barrier treatment (sprayed on the base of the canes at the wood/soil interface, a strategy used with success in recent trials on grapes), this might keep the weevils in the soil and off the plant.
Annual grasses are the most troublesome class of weeds for Washington currant growers. Individual weeds that cause the greatest problems are mallow (Malva spp.) and field bindweed (Convolvulus arvensis). Mallow, also known as button weed, is an annual broadleaf that often persists from year to year acting like a perennial. Field bindweed, also known as wild morning glory, is a perennial vine. Weeds in currants are not adequately addressed by available control measures. An effective grass weed control is a critical need of the industry.
Cultural/Mechanical
Grass, either naturally occurring or (more often) deliberately planted, is maintained between rows. This keeps the currant plants cooler by cutting down on reflected light and heat and also provides habitat for beneficial predator insects.
Chemical
Glyphosate (Roundup, other), a broad-spectrum herbicide, is typically applied twice per year: early spring and late fall. The late fall application takes place once the weather is cool and irrigation has ceased; it can occur as early as October or as late as December. If the late fall spraying is particularly efficacious, growers may skip the spring spraying. Otherwise, the spring spraying to control emerged winter annual weeds in an established field takes place in late March or early April. For new ground to be planted, glyphosate (Roundup) is applied to emerged weeds about 10 days before planting (planting takes place late March or early April). Growers typically mix 1.5 gallons of Roundup to 100 gallons of water plus 1.0 quart of Ad-Wet spreader and 7.0 lbs. ammonium sulfate. This mix is applied at 10 gal./A with excellent control results. As glyphosate can potentially damage currants and other non-target plants, it is applied as a directed spray, usually with a hooded sprayer, only on calm, windless days. About 12-16% of the total acreage receives a glyphosate treatment.
Napropamide (Devrinol) is labeled for soil application at 4.0 lb. a.i./A after transplanting but before weeds germinate, or before sawdust is applied. Growers report unsatisfactory results with this chemical and do not use it.
Oryzalin (Surflan) is labeled for application at 2.0 to 4.0 lb. a.i./A. It is applied after transplanting and once the soil has settled around the plants, then it is incorporated with irrigation or shallow (1- to 2-inch) cultivation. Oryzalin (Surflan) can also be used in established plantings prior to weed emergence. Growers report good efficacy on non-grass weeds, but the product does not have much residual action. This chemical is not effective on emerged grasses, but can be very effective on most annual grasses if it is applied before the grass weeds begin germination. It is picked up from the soil by the elongating shoot and roots. It will not control many weeds that have emerged and are actively growing. When used, this product is usually applied in a split application, i.e., twice at the 2.0 lb. a.i./A rate.
Disease control (particularly for powdery mildew and rust) is more of a factor in the wetter maritime climates of western Washington, but can be an issue in the drier eastern Washington climate where most of the state’s currant production occurs. Growers primarily use the Wilder cultivar, which has superior production characteristics as well as a degree of disease resistance.
Ribes species were once infamous as alternate hosts of white pine blister rust, a problem for all five-needle pines. To protect the lumber industry, a federal ban on cultivation of Ribes was put in place in the early 1900s, followed by specific state and regional restrictions in some areas. The federal ban was rescinded in 1966, and while several states continue to limit the cultivation of Ribes species, no restrictions exist in Washington State (12).
Powdery Mildew, Sphaerotheca spp.
Two fungi, Sphaerotheca mors-uvae and S. macularis, have been known to cause the complex of symptoms known as powdery mildew on Washington currants. The disease appears as a white powdery growth on the young leaf surface and green shoots. Infected plants often are stunted. The fungal structures overwinter on stems and twigs, releasing ascospores around bloom, with symptoms visible as soon as 10 days later. Symptoms of this disease are generally seen on currants in early June.
Controls
Cultural
The cultivar Wilder is chosen most frequently because of its production characteristics and because it has fair resistance to diseases including powdery mildew.
Chemical
Lime Sulfur is labeled at 1.5 qt./100 gal. water for powdery mildew, but is typically applied at a rate of 2.5 gal./100 gal. water, which is the rate allowable for anthracnose control. This is done in combination with oil at the rate indicated below as a delayed dormant spray, about mid-March, when plants are at the green-tip stage.
Oil is typically applied at a rate of 3.0 gal./200 gal. water along with lime sulfur as described above.
Myclobutanil (Rally 40W) can be applied at 2.0 oz. a.i./A, but is only used in years when fungal diseases are an issue.
Anthracnose, Drepanopeziza ribis
Drepanopeziza ribis is a fungus that overwinters on dead leaves. Small, mushroom-like fruiting bodies appear on fallen leaves in spring, producing airborne spores that infect newly developing leaves, resulting in small, dark brown spots on the leaves. For this reason, the disease may also be called "leaf spot." When the spotting becomes profuse, foliage may yellow and drop by midseason, reducing the plants’ vitality, growth, and productiveness. Fruit as well as leaves may show spotting; severely infected currants crack open and drop. This disease is favored by wet climates and is therefore seldom a problem in the major commercial production areas of Washington, but can occur in small western Washington fields.
Controls
Cultural
Growers remove and destroy dead leaves from under and around plants. Some growers cultivate under and around plants to bury leaves before budbreak in spring. The pruning and thinning practices described under Cultural Practices provide better air circulation and drying conditions; this is especially important for disease control in the wetter climates of western Washington.
Chemical
Lime Sulfur is typically applied at a rate of 2.5 gal./100 gal. water in combination with oil at the rate indicated below as a delayed dormant spray, about mid-March, when plants are at the green-tip stage.
Oil is typically applied at a rate of 3.0 gal./200 gal. water along with lime sulfur as described above.
Myclobutanil (Rally 40W) can be applied at 2.0 oz. a.i./A, but is only used in years when fungal diseases are an issue.
Snakes, birds, rabbits and other rodents, and coyotes all populate currant fields in eastern Washington but their activities have not proven economically damaging to currants. Snakes and coyotes are beneficial as predators. Mice are the only economic problem in currants; they feed on plant roots and affect plant vigor. Mice also attract predators that, in turn, leave holes that can damage farm equipment. Growers sometimes bait for mice with zinc phosphide products used at label rates.
Critical NeedsGrowers need an effective annual grass-specific herbicide. Glyphosate’s broad-spectrum action is not always the appropriate tool for this problem. Herbicides that require multiple passes are problematic, as mechanical application of herbicide presents problems as the fruit matures. The fruit develops, gains weight and droops, then tends to gett caught in the weeds and broken off by the tractor or sprayer. Even airblast sprayers present issues, as the air they draw sucks and rearranges adjacent foliage.
Black vine weevil may be causing greater reduction of yield than growers have realized. This nocturnal pest may merit more study.
Control of currant borer and currant stem girdler is crucial. Pheromone-based mating disruption of currant stem girdler looks promising. If it can reach the success level of the mating disruption program for currant borer and both become commercially available, these, along with Danitol or an acceptable alternative, should provide a foundation for integrated pest management for this crop’s worst pests.
Sally O’Neal Coates
Washington State University
Washington State Pest Management
Resource Service
2710 University Drive
Richland, WA 99352
Phone: (509) 372-7378
Fax: (509) 372-7491
e-mail: scoates@tricity.wsu.edu
Dr. David James
Washington State University
Irrigated Agriculture
Research and Extension Center
24106 N. Bunn Road
Prosser, WA 99350
Phone: (509) 786-9280
Fax: (509) 786-9370
e-mail: david_james@wsu.edu
Entomology
Dr. David James, see above.
Weed Science
Dr. Robert Parker
Washington State University
Irrigated Agriculture Research and Extension Center
24106 N. Bunn Road
Prosser, WA 99350-9687
Phone: (509) 786-9234
Fax: (509) 786-9370
Email: rparker@wsu.edu
Industry Contact
Dennis Pleasant
Grower
11701 N. Pioneer Rd.
Prosser, WA 99350-6623
Phone: (509) 973-2443
e-mail: stepp@quicktel.com
Additional Resources
The International Ribes Association (TIRA)
P.O. Box 428
Boonville, CA 95415
Phone: (707) 895-2811
Website: http://www.msu.edu/user/sleightd/tira