Plant Health Problems
There are a number of diseases which are common to all species in the genus Rubus although their impact can vary from species to species.
Diseases caused by Fungi:
Anthracnose, Gloeosporium venetum.
On leaves, the fungus causes small circular white spots with purple borders. When infection is heavy, substantial defoliation may occur. On young canes, symptoms appear as purple spots. These spots enlarge and become sunken with age. These can kill the canes or can weaken them so that winter temperatures then complete the kill. In wet seasons, this fungus may kill the fruit stems and destroy part of the crop at picking time. Infected fruit appear shriveled, tan, and have a bitter flavor. Disease is often worse on black and purple raspberries although it can result in significant damage to red raspberries.
Improving air circulation to promote drying is very important for disease management. This is accomplished by good pruning and thinning practices. Infected canes should also be pruned and removed before new growth begins to eliminate the source of inoculum. When the planting has a history of disease, fungicide sprays can be applied as delayed dormant applications. Among the compounds registered for use in Connecticut are lime sulfur and copper. Consult the label for dosage rates, safety precautions, and days to harvest intervals.
Cane blight, Leptosphaeria coniothyrum.
The symptoms of this disease include weak growth and wilting of leaves. Cankers develop on the canes and appear as brown to purple lesions. Tissues in the affected areas are weak and bend easily. When the cankers girdle the stem, it wilts and dies. Infection is often associated with pruning wounds or other injuries. Black and purple raspberries are considered more susceptible than red raspberries although the disease can be serious on all types.
Disease management of cane blight is similar to that for anthracnose. This includes thinning practices that promote good air circulation as well as pruning and removing infected canes. Pruning is best done when 4 or 5 days of rain-free weather are predicted to promote good healing. When the planting has a history of disease, fungicide sprays can be applied as delayed dormant applications. Among the compounds registered for use in Connecticut are lime sulfur and copper. Consult the label for dosage rates, safety precautions, and days to harvest intervals.
Botrytis fruit rot, Botrytis cinerea.
Raspberry fruit are very susceptible to this fruit rot, especially during periods of rainy, wet weather. A diagnostic symptom is the presence of a gray fuzzy mass of the fungus covering the surface of ripening fruit. 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. It is also helpful to harvest ripe fruit regularly since overripe fruit are highly susceptible to infection. When weather is favorable for disease, fungicide sprays are often necessary for effective control. Among the compounds registered for use in Connecticut are potassium bicarbonate and iprodione. Sprays usually begin at bloom and are repeated as necessary. Consult the label for dosage rates, safety precautions, and days to harvest intervals.
Powdery mildew, Sphaerotheca.
Symptoms on the leaves appear as grayish white powdery patches, usually first evident on the lower surfaces. The fungus also infects emerging shoots which can result in distorted growth. When flower buds are infected, fruit quality can be reduced and in some cases, fruit are covered with fungal growth. Mildew infects red, black, and purple raspberries although blackberries are usually not affected.
Control can be achieved by pruning and removing of infected shoots. It is also important to maintain good air circulation. Cultivars vary in their resistance; for example, Latham, Royalty, and Logan are highly susceptible. Use of fungicides is not effective or practical.
Phytophthora root rot, Phytophthora spp.
This fungus attacks the roots and crown of plants and results in symptoms of general decline, wilting, and stunting. Leaves appear yellow and undersized. Symptoms are often most obvious in the spring and are most prevalent on plants in wet sites. Once infected, recovery is unlikely.
Prevention is the best method for control and site selection and good soil drainage are the most important strategies for disease management. It has also been demonstrated that planting on raised beds (8-12" high) is also effective for minimizing this disease. Cultivars vary in susceptibility although this is still uncertain in many cases. Black raspberry cultivars appear the least susceptible and purple raspberries appear less susceptible than red raspberries.
Diseases caused by Viruses:
Mosaic, Leaf curl, Crumbly berry, viruses.
Several virus diseases have been reported on raspberries. Symptoms are variable and include mosaic, mottle, leaf curl, dwarfing, and production of crumbly berries. Once infected, plants cannot be cured although symptoms can be masked by weather and high temperatures. Most of the common virus diseases are spread by insects, most frequently by aphids.
Planting healthy, virus-free plants is helpful. Additionally, it is important to locate new plantings at a distance from wild Rubus species or from old plantings. Since red raspberries can be symptomless carriers of some viruses, they should not be planted near black or purple types. Removal of infected symptomatic plants is effective in reducing a source of inoculum.
Aphids, Aphis rubicola, Amphorophora rubi.
At least two species of aphids occur on raspberry, though they are seldom abundant, and their direct injury is not so much to be feared as the probability that they may transmit and spread mosaic and related diseases. These aphids are Aphis rubicola and Amphorophora rubi, and both are found infrequently on the undersides of the leaves. Control consists of spraying with horticultural oil, insecticidal soap or malathion, which are among the compounds registered for use against this pest in Connecticut. Consult the label for dosage rates, safety precautions, and preharvest intervals.
Blackberry knot gall, Diastrophus nebulosus.
This gall occurs on the stems of dewberry and blackberry. Each gall contains many larvae and varies from 1 to 3" long and from 1 to 1 1/2" in diameter. It is often deeply furrowed lengthwise and when first found is dark green, but later it turns to red and brown. No method of control is known other than removing and burning the galls, if allowed.
Blackberry leaf miner, Metallus rubi.
The larva of this sawfly is a miner in the leaves of blackberry and dewberry. The insect has two generations each year. Eggs are laid in blisters on the underside of the leaves in May and early June for the first generation, and in August for the second generation. The larvae mine along the leaf margins and tips of the leaf blades, making blotch mines that are usually confluent when several miners are at work in the same leaf. The adult is a nearly black sawfly about 1/6" long. Malathion and carbaryl are among the materials registered for use in Connecticut against this pest. Consult the label for dosage rates, safety precautions, and preharvest intervals.
Blackberry psyllid, Trioza tripunctata.
This jumping plant louse is a native of the wild blackberry, but occasionally it injures cultivated plants. The adult is about 1/6" long, yellowish brown, and each wing is marked by three yellowish brown bands. The adults live through the winter in protected places, appear on the plants soon after growth begins, and lay eggs in the hairs of leaf petioles and tender shoots. Both nymphs and adults puncture the stems and leaves causing a stunted and distorted growth sometimes called galls. The nymphs become fully grown late in the season and the adults overwinter. There is one annual generation. Control measures are seldom necessary.
Blackberry sawfly, Pamphilius dentatus.
Occasionally in Connecticut, the larvae of this insect devour blackberry leaves. The adults appear the latter half of May, and the females lay white oval eggs placed end to end beside the larger veins on the underside of the leaves. The larvae roll the leaves, fasten them by a web, and feed inside the web. They become fully grown the first half of July and are then about 3/4" long and of a bluish green color. They then enter the soil to overwinter. Adults emerge the following May.
For control, see Raspberry sawfly below.
European fruit lecanium, Parthenolecanium corni.
This scale often infests blackberry. These convex scales are considerably larger than San Jose or Forbes scales. They are rare in Connecticut and control usually is not required.
This beetle and others feeding while fruit is ripening, can be controlled to some extent by use of carbaryl or rotenone, which are among the compounds registered for use against this pest in Connecticut. Consult the label for dosage rates, safety precautions, and preharvest intervals.
Potato leafhopper, Empoasca fabae.
This leafhopper feeds on the undersides of the leaves. This insect is a serious pest in some years in Connecticut. It does not overwinter here, and the severity of infestation depends on the size of the migrating population and the weather. In addition to being a pest of brambles, it is also a pest of beans, alfalfa and potatoes. The adult is about 1/8 inch long and yellowish green. Nymphs are similar in color but have no wings. Both adults and nymphs are difficult to see because they move rapidly. Adults and nymphs may infest brambles and cause injury by sucking sap from the bottom side of leaves. This causes the young leaves to curl or gives them a white peppered appearance. Continued feeding results in a yellowing or browning of the leaves called "hopperburn." Among the compounds registered for control of this pest in Connecticut are pyrethrum, rotenone, or carbaryl. Repeated use of insecticides may lead to outbreaks of aphids.
Raspberry cane borer, Oberea bimaculata.
This insect is one of the longhorned beetles that appear in June. The female makes two rows of punctures around the tip of the shoot about half an inch apart, then lays an egg in the stem between the girdles. The tip wilts and this injury is thought to protect the egg from being injured by too rapid growth of the shoot. The egg hatches in early July and the grub burrows downward in the pith and overwinters in the cane only an inch or two below the girdle. During the second season, it continues to burrow downward, usually killing the cane, reaching the ground by the second winter. It overwinters in the burrow. The following spring it pupates in the burrow and the adult beetle may emerge in May or June. Two years are required for the complete life cycle. The adult beetle is about half an inch long and has black wingcovers and yellow thorax, usually with two or three black spots. For control, cut out and dispose of the wilted fruiting canes and wilted tips, cutting below the lower girdle.
Raspberry cane maggot, Pegomya rubivora.
The adult fly appears late in April. When raspberry shoots are a few inches tall, the fly lays an egg in the axil of one of the tip leaves. The egg soon hatches and the maggot crawls down the stem for a short distance, then goes into the stem and tunnels downward in the pith. It works its way nearly to the bark and cuts a tunnel around the shoot, thus girdling it, and the tip wilts. The maggot reaches maturity in late June or early July, pupates in the burrow, and the adult fly emerges the following spring. There is one generation each year. The only control is to cut several inches below the girdle and burn all wilted tips in May.
Raspberry crown or root borer, Bembica marginata.
The raspberry root or crown borer tunnels in the main roots and crowns of blackberry and raspberry plants. The adult is a clearwing moth having a wingspread of an inch, with transparent wings and black body crossed by four yellow bands. It emerges in July and August and deposits eggs underneath the leaves. During the first winter, the small larvae overwinter in blister-like elevations of the bark just beneath the soil level, or in crevices, or under flakes of bark at the base of the stems. In the spring, they tunnel in the stems and roots just beneath the bark, often girdling the plants. They overwinter in their burrows the second winter, and in the following spring, tunnel upward either in the pith or just under the bark. They finally reach a length of nearly an inch. In July, they burrow to the surface and pupate in the tunnel. When ready to emerge, the pupa works its way partly out of the tunnel when the case splits open and the moth escapes, leaving the pupae case protruding from the burrow. Infested bushes usually wilt at the top or die.
Drench diazinon, which is among the compounds registered for control of this pest in Connecticut, around the base of stems after harvest, or apply insect pathogenic nematodes in the autumn or spring. Consult the label for dosage rates, safety precautions, and preharvest intervals. Eliminating wild bramble hosts near desired plantings, and removing and burning infested plants will also help to control this pest.
Raspberry fruitworm, Byturus rubi.
Small brown beetles that eat holes in the tender terminal leaves and devour the blossoms often injure raspberry plants. The female lays eggs in May on the base of the blossom buds or on green fruit. The eggs soon hatch and the larvae work and develop inside the fruit and the fleshy receptacle, often causing the fruit to dry up. The larvae often adhere to the picked fruit. They are about 1/4" long, light yellow with a cross band of light brown on the back of each segment. The beetles are light brown, hairy, and about 1/6" long. Spraying with methoxychlor, diazinon or malathion, which are among the compounds registered for control of this pest in Connecticut, when blossom buds first appear, and again just before blossoms open, has been effective. Consult the label for dosage rates, safety precautions, and preharvest intervals. Damage tends to be more severe in weedy areas.
Raspberry sawfly, Monophadnoides
Serious injury is often caused by green spiny larvae, about 3/4" long, that feed on the leaves. The adult is a black sawfly about 1/4" long. In May, the adult lays eggs singly in the leaf tissue near a prominent vein. The eggs hatch in a week or so and the larvae feed on the leaves. When abundant, they may devour all of the foliage. They reach maturity in about 10 days, go into the ground where they overwinter, and pupate the following spring. There is one generation each season. The treatment is to spray with malathion or methoxychlor, which are among the compounds registered for control of this pest in Connecticut, before the plants bloom. Consult the labels for dosage rates, safety precautions, and preharvest intervals.
Rednecked cane borer, Agrilus ruficollis.
Swellings from 1 to 3" long are often made by the larvae of this insect on the new canes. The adult is 1/3" long, with blue-black wing covers and reddish or copper colored thorax. There is only one annual generation, and the beetles, though present on the bushes from May to August, are most abundant in June. The female lays eggs in the bark near a leaf stalk. Each larva burrows upward in the sapwood and goes around the twig several times in a spiral course forming swellings or galls. The larva overwinters in the pith, where it completes its growth and pupates the following spring. When the annual pruning takes place, all infested canes should be removed and disposed of.
Rose scale, Aulacaspis rosae.
This scale infests rose and blackberry. Dormant and, if needed, summer sprays of ultra-fine horticultural oil, which is among the compounds registered for control of this pest in Connecticut, will be effective against this pest. Consult the label for dosage rates, safety precautions, and preharvest intervals.
Strawberry bud weevil, Anthonomus signatus.
This weevil will occasionally damage raspberries. This weevil lays an egg in the flower bud, then eats the pedicel partly off. In severe infestations, this insect may cause a loss of 50 to 60 percent of the crop. The beetle is about 1/10" long, and varies in color from black to reddish brown. The larva feeds almost entirely on pollen and the eggs are laid almost wholly in the buds of staminate varieties. The adult overwinters and there is only one generation each year. This insect injury may for the most part be avoided by planting a large proportion of varieties with imperfect flowers for the main crop. Some perfect flowered varieties will be necessary for pollination. A spray of methoxychlor, which is among the compounds registered for control of this pest, can be used only at blossom bud break. Consult the label for dosage rates and safety precautions.
Tarnished plant bug, Lygus
This 1/4" long true bug has the characteristic X pattern on its back, is brownish mottled with yellow and is very active. Both adults and nymphs suck plant sap from flower and fruit. Nymphs are smaller and bright green. Sections of the fruit that have been injured fail to develop. Since tarnished plant bugs also feed on many weeds, keeping a mowed area around the planting may reduce the population. Insecticides applied for control of other pests of brambles will normally control this bug.
Tree cricket, Oecanthus nigricornis.
Of several species of tree crickets occurring in Connecticut, this one has the habit of laying its eggs in small twigs of raspberry and blackberry canes. These punctures either kill the cane above this point or so weaken it that the fruit cannot develop. The canes often break off at the egg laying punctures. This tree cricket is yellow with black legs and antennae and is about 5/8" long. In pruning the canes, those containing eggs should be cut off and disposed of. Methoxychlor or carbaryl, which are among the compounds registered for control of this pest in Connecticut, applied late August to mid-September can manage these crickets. Consult the label for dosage rates, safety precautions, and preharvest intervals.
Twospotted spider mite, Tetranychus urticae.
This general pest also feeds on raspberries. Foliar damage caused by the twospotted mite is similar to that caused by the European red mite. Mature females spend the winter on the lower portion of tree trunks or in the ground cover. The young nymphs feed first on herbaceous plants, then move upwards into trees and shrubs as the season progresses. As the common name indicates, the summer adults have a dark spot on each side of the body. Twospotted mites can develop through many generations, depending on the temperature. Their abundance usually peaks in August. Many beneficial insects and mites feed on twospotted mites. In home orchards, control usually is not necessary.
These inch-long yellow and black wasps, along with their white and black relatives called the bald-faced hornets, love to feed on ripening fruit. They are particular problems in dry years and in fall raspberries when their populations are high. They will sting easily and so are a danger and nuisance to pickers.
Controls need to be in place before berries begin to ripen. Traps can be placed around the perimeter of the planting. Harvest all berries as they ripen. Since food is brought back to the nest, where feasible, insects can be followed back to the nest. If the nest is nearby and accessible it can be destroyed using hornet and wasp sprays.