Brambles (Rubus)
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.
Insect Problems
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.
Japanese beetle.
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
geniculatus.
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
lineolaris.
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.
Yellowjackets.
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.