| ||Currant Fruit Fly | Currant Aphid | Two Spotted Spider Mites | Gooseberry or Blind Bud Mite | Black Currant Gall Mite | Other insect pests on black currants
Authors: Dr. Ken Fry and Arden Delidais
An important part in the production of any fruit crop is to know what type of insects could cause production losses. A crop is at risk throughout the fruiting cycle. Insects can attack plants during flowering, fruit formation or just before harvest of the plump, juicy berries. To effectively control insects, the life cycle must be understood. For each insect listed, you will find the lifecycle and scouting techniques.
Currant Fruit Fly
Euphranta canadensis (Loew) (formerly known as Epochra canadensis)
Currant Fruit Fly Damage
The Currant Fruit Fly is widely distributed in western North America with sporadic records from the northeastern United States. The fly attacks red, white, and black currants and gooseberries. This species is not present in Europe.
The adult is somewhat smaller than a housefly and is pale to dark yellow in color. Its most striking feature is the banded pattern found on the wings. Adults feed on nectar from flowers and on honey-dew from aphids. Adults lay a single egg, approximately 1 mm long, under the skin in each developing fruit. Rarely will two eggs be laid in the same fruit. Egg-laying persists for up to month. Each adult will have between 3 and 17 ripe eggs at any one time and potentially can lay up to 165 eggs over her entire lifetime. Not all eggs survive; however, fruit that has been "stung" by the adult fly usually will drop prematurely. In 5-8 days pale-colored larvae hatch and feed on seeds inside the berry for 11-16 days. Larvae will feed on from as few as 2 to as many as 9 seeds. There are 3 larval instars. Late instar larvae will drill a small hole in the surface of the fruit through which to breathe.
Infested fruit ripen prematurely and may drop to the ground. Some fruit will remain on the plant until harvest. Once mature, the larva exits the fruit, burrows into the ground anywhere from 2-8 cm at the base of the plant and over winters as a pupa in the ground. The use of plastic mulch will likely result in the larvae burrowing right at the base of the plant or at the edge of the plastic. Adults emerge from the ground about mid-May to early June the next year. Time of emergence is dependant upon the type of soil and ground cover. In one study conducted in Maine, emergence was delayed up to 8 days in soil covered with manure.
Adult flies can be found where fruit occur on the plant. The adults will rest on the leaves at the centre of the plant, out of direct sunlight. Plants in shade will have more flies than plants in direct sunlight. Fruit that has dropped should be examined for any sign of egg-laying; elongate whitish eggs lying just under the surface of the fruit. The site of egg-laying might have a slight brownish tinge surrounding the wound.
Collection of fallen fruit has to be conducted on a daily basis to be effective at ridding the orchard of flies. This is an impractical solution. Rodents eat fallen fruit but are enough of a nuisance to preclude their enlistment as a biological control agent. Late picking of fruit to avoid maggoty fruit is an option. However, there is a risk of sun-scald. Late-maturing varieties are preferred by the currant fruit fly.
Cryptomyzus ribis (L.)
Aphids feed on the undersides of leaves and young shoots by sucking juices from the plant tissues. This feeding action usually results in a downward curling and crinkling of the leaves. Bronzing of the top surface of the leave is common. This particular species of aphid causes a puckering of the leaf surface.
During the growing season female aphids reproduce asexually and can produce many generations of live young if the environment is favorable. Winged females will be produced to migrate to other currants. At the end of the season, males are produced so that mating and egg laying occur. Aphids overwinter as shiny-black eggs in the crotches of buds and stems.
Look for shiny patches of liquid on the upper surfaces of leaves. This is aphid excrement or “honeydew”. It indicates that aphids are feeding on the underside of the leaf above. Aphids are attracted to yellow sticky traps. However, if you see winged aphids on the traps it means your aphid infestation is well established and already on the move.
The best way to scout for aphids is to walk the orchard looking at the undersides of leaves or on the stems of new growth. Do a random sampling of 10-15 bushes per row to get a good overview of the state of your orchard.
There are many natural predators and parasitoids of aphids, including ladybugs, green and brown lacewings, hover flies and wasps.
Two Spotted Spider Mites
Tetranychus urticae Koch
Spider mites feed on a wide range of crops, including weeds such as chickweed, wild mustard, and henbit. They infest black currants and chokecherries. The mite pierces the underside surface of the leaf and sucks out the chloroplasts. This results in a chlorotic spot, which is seen from the top of the leaf as stippling. If enough mites are present, small webbing on the underside can develop and leaves can turn brown and fall off. In severe enough infestations, webbing will be strung over foliage and stems. From the top view of the leaf, damage might be mistaken for nutrient deficiencies. However, an examination of the underside of the leaf with a 6 or 10 x glass will soon tell if mites are present.
When optimum temperatures of 30 to 32°C exist, life cycles from egg to adult can be complete in 8 to 12 days. The average female lives for 30 days and lays between 90 to 200 eggs. Populations build up quickly as in the summer of 2002.
When the daylight shortens, food supply diminishes and / or temperatures start to drop, the female turns yellowish orange, stops feeding and egg laying and leaves the black currant plant. This female hibernates on the ground in cracks and crevices under the leaf litter.
Spider mites can only be reliably scouted by using a hand lens and inspecting the undersides of leaves. They are usually found in drier areas unshaded foliage, row ends where wind dries out the bush). Spider mite infestations are patchy, often originating from weeds.
There is a wide range of natural control agents for spider mites. One biological control that can be purchased in Alberta is the predatory mite Amblyseius fallacis. It is to be applied at 7,000/acre on producing fields and 10,000/acre on newly established orchards. This predator is cold hardy and somewhat resistant to the softer pesticides.
Gooseberry or Blind Bud Mite
Cecidophyopsis grossulariae Collinge
Distribution, Biology & Damage:
This mite, an eriophyiid mite, is extremely small, visible only by using a hand lens. The mite is present in England and Europe and has recently been found in the northwest U.S. This species is not capable of transmitting the reversion virus, whereas the Black Currant Gall Mite, Cecidophyopsis ribis is a competent vector of the virus. The gooseberry mite has a broad host range, including black and red currants and gooseberries.
The mites feed on the undersides of leaves during the spring and summer. In the fall they migrate to the outer layers of the green scales of axillary buds causing some swelling. This is where they overwinter. Mite infestations have the potential to reduce cold-hardiness of dormant flower buds.
Although this mite is not considered to be widespread growers should keep a look out for it in their orchards. Work conducted in the U.S. indicates that the mite may not be able to overwinter under severe cold conditions. Air temperatures of -20°C and lower are sufficient to kill the mite.
Black Currant Gall Mite
Cecidophyopsis ribis Westw.
This eriophyiid mite is widely distributed in England and Europe. It is the single worst pest of black currants in Europe. Fortunately this species is not widespread in North America although it has been found sporadically through the years. The mite is the principle vector of reversion virus, a yield-reducing disease of black currants. The mites cause a gall to form in infested dormant buds.
Growers should keep an eye out for symptoms of this mite and the disease to ensure early detection should these pests be inadvertently introduced to Alberta. Common symptoms of the mite include galling of buds and of the disease include fewer serrations of the leaf edge and fewer number of leaf lobes, and smooth flower buds.
Other Insect Pests
Black Currant Leaf Curling Midge
Dasyneura tetensi (Rübsaamen).
This is a small, delicate fly that lays its eggs in the folds of young leaves. The larvae feed within the curled leaf dropping onto the soil to pupate 10-14 days later. There can be 2-3 generations in a season with larvae overwintering in the soil before pupating in the spring. Damage to production orchards does not affect yield. However, damage to nursery stock results in misshapen plants.
Synanthedon tipuliformis (Clerck)
This clear-winged moth attacks black and red currants and gooseberries. The adult female lays her eggs, commonly only one/stem, on the stem near to a bud or side shoot of 1-2 year old stems (never on current year growth). The larva hatches 8-10 days later and burrows into the pith, feeding until fall. The larva overwinters in the stem, pupates the following spring with the adult emerging in June or July.
Withering of leaves on young shoots and failure of fruit trusses to develop are symptoms of infestation. Pruning and burning infested stems control this pest. A pheromone is available to treat sticky traps for monitoring and control through mating disruption.
Dr. Ken Fry, Olds College