Management of Bramble Diseases
Cane and Leaf Diseases
Anthracnose is caused by the fungus Elsinoe veneta. One of the
most common and widespread diseases of brambles in the United States,
anthracnose can infect red and black raspberries, blackberries,
dewberries, and loganberries. The disease is very destructive on black
and purple raspberries. On red raspberries, it can be common but is
usually not a serious problem. Disease losses can occur from
defoliation, general stunting and a decrease in cane vigor, reduction
in fruit yield and quality, and cane death. Resistance to anthracnose
is not available in most varieties. The use of fungicide (lime sulfur)
and cultural practices such as sanitation (removal of old and infected
canes) are key control methods.
Anthracnose can cause symptoms on canes, leaves, fruit and stems of
berry clusters. The most striking symptoms are on canes. A few days
after the fungus invades the succulent tissue of young canes, minute
purplish spots appear. These spots enlarge in diameter and become oval
or lens-shaped. The centers become somewhat sunken and are pale-buff to
an ash-gray color (Figure 27). Margins are somewhat raised and purple
to purple-brown. If numerous, the lesions may merge and cover large
portions of the cane. Diseased tissue extends down into the bark,
partly girdling the cane. As the canes dry in late summer and early
fall, diseased tissue often cracks. In the following year, fruit
produced on severely diseased canes may fail to develop to normal size
and may shrivel and dry, especially in a dry growing season.
Figure 27: Anthracnose lesions on black raspberry canes.
On leaves, anthracnose appears on the upper surface in
early- to mid summer as irregular, yellowish-white spots about 1/16
inch in diameter (Figure 28). The spots gradually enlarge and develop a
reddish-purple margin around a light-gray center. The centers of these
spots may drop out, producing a "Shot hole" effect. This "Shot hole"
symptom is more common on trailing blackberries and raspberries. On
blackberries, leaf spots may merge together producing large grayish
dead areas between the veins. Anthracnose does not usually cause much
damage to leaves of erect blackberries.
Figure 28: Anthracnose leaf symptoms on black raspberry.
The anthracnose fungus overwinters in the bark or within lesions on
infected canes (Figure 29). In early spring the fungus produces two
types of microscopic spores called conidia and ascospores. Conidia,
which are produced in small fungal fruiting structures called acervuli,
are the most common form of inoculum. Ascospores are comparatively
rare. Production of these spores coincides with the leafing out of
brambles in early spring. Spores are rain-splashed, blown, or carried
by insects to young, succulent, rapidly growing plant parts that are
susceptible to infection. The spores germinate in a film of water and
penetrate into the plant tissue. Symptoms appear about a week later.
Small pimple-like reproductive bodies are produced within lesions on
infected canes and the fungus overwinters there. These bodies produce
conidia for new infections the next spring, completing the disease
cycle. As canes age and harden, they become much less susceptible
Figure 29: Anthracnose disease cycle. Disease cycle of
Raspberry Anthracnose. Taken from the Compendium of Raspberry and
Blackberry Disease and Insects of the American Phytopatholical Society.
Used with permission.
Cane blight is caused by the fungus Leptosphaeria coniothyrium. Cane
blight is one of the more damaging diseases of raspberries. The disease
is most common on black raspberries, but also occurs on red and purple
cultivars. Cane blight occasionally occurs on blackberries and
dewberries. Cane blight can result in wilt and death of lateral shoots,
a general weakening of the cane, and reduced yield. It is usually most
severe during wet seasons. The fungus often invades the cane through
wounds. Any practice that reduces wounding on canes is beneficial for
control. Key control methods are the same as for anthracnose.
Dark brown to purplish cankers form on new canes near
the end of the season where pruning, insect, and other wounds are
present. The cankers enlarge and extend down the cane or encircle it,
causing lateral shoots to wilt and eventually die (Figure 30). On
second-year canes, the side branches may suddenly wilt and die, usually
between blossoming and fruit ripening. On close examination, dark brown
or purplish cankers can be observed on the main cane or branches below
the wilted area. Infected canes commonly become cracked and brittle and
break easily. Tiny black specks (pycnidia), which are reproductive
bodies of the cane blight fungus, develop in the brown cankered bark.
In wet weather, large numbers of microscopic spores (conidia) ooze out
of the pycnidia. This ooze gives the bark a dark-gray, smudgy
Figure 30: Cane blight lesion on thornless blackberry.
The pathogen survives over winter on infected or dead
canes (Figure 31). The following spring, conidia, formed in the
pycnidia, ooze from them during wet periods, and are blown, splashed by
rain, and carried by insects to nearby canes. Under moist conditions,
the spores germinate and penetrate into the plant through pruning
wounds, insect punctures, fruit stem breaks, and other wounds. After
entry, the fungus rapidly invades and kills bark and other cane
tissues. Pycnidia are formed in older cankers and complete the disease
cycle. Dead canes can continue to produce conidia and remain a source
of infection for several years.
Figure 31: Cane blight disease cycle. Taken from the
Compendium of Raspberry and Blackberry Diseaes and Insects of the
American Phytopathological Society. Used with permission.
Blight of Red Raspberries
Spur blight is caused by the fungus Didymella applanata. Spur blight
occurs only on red and purple raspberries. Spur blight has been
considered to be a serious disease of red raspberry; however, recent
studies in Scotland suggest that spur blight actually does little
damage to the cane. The extent of damage caused by spur blight in the
United States is not clearly understood. Key control methods are the
same as for anthracnose and cane blight.
Symptoms first appear on young canes in late spring or
early summer. Purple to brown areas (cankers) appear just below the
leaf or bud, usually on the lower portion of the stem (Figure 32).
These cankers expand, sometimes covering all of the area between two
leaves. In late summer or early fall, bark in the cankered cane area
splits lengthwise and fungal fruiting bodies, appearing as small black
specks, develop in the cankers. They are followed shortly by the
formation of many slightly larger, black, erupting spots, another form
of fungal fruiting body. Leaflets sometimes become infected and show
brown, wedge-shaped diseased areas, with the widest portion of the
wedge at the top of the leaf. Infected leaves may fall off, leaving
only petioles without leaf blades attached to the cane (Figure 33).
Figure 32: Typical symptoms of spur blight on red
Figure 33: Symptoms of spur blight on red raspberry
leaves. The "V-shaped" lesions are characteristic.
As diseased primocanes become fruiting canes (floricanes) during the
next season, the side branches growing from diseased buds are often
weak and withered and produce less fruit.
The fungus survives the winter in diseased canes (Figure 34). The
following spring and summer, during wet and rainy periods, spores are
released and carried by splashing rain and wind to nearby new growth.
There they germinate and produce new infections, where the fungus will
Figure 34: Spur blight disease cycle. Taken from the Compendium of
raspberry and Blackberry Diseases and Insects of the American
Phytopathological Society. Used with permission.
Leaf and Cane Spot
Septoria leaf and cane spot is caused by the fungus Septoria
rubi. The disease is common and can be quite severe in the southern
portions of the Midwest on erect and trailing blackberries and black
raspberries. Leaves and canes of severely infected plants become badly
spotted. The disease can cause premature defoliation which will produce
weak plants that are more susceptible to winter injury.
On leaves, Septoria leaf spot lesions have a whitish to
gray center surrounded by a brown to purple border (Figure 35). The
spots are circular and are about 1/8 inch in diameter. Tiny black
pycnidia (fungal fruiting bodies) form in the center of the spots. The
pycnidia are small; therefore, it may be necessary to use a magnifying
glass (10X hand lens) to see them. Leaf spots caused by Septoria are
similar to those of anthracnose. Spots on canes and petioles are
similar to those on leaves but are generally more elongated.
Figure 35: Septoria leaf spot on blackberry leaflet.
The fungus overwinters as mycelium and pycnidia (fungal
fruiting bodies) in dead plant debris (leaves and stems) and on
infected canes. Pycnidia on infected canes from a nursery can be an
effective means for moving the fungus into new fields. In the spring,
spores (conidia) are produced inside the pycnidia. They are released in
high numbers and carried to young susceptible leaves and canes by
splashing or wind-driven rain. The fungus spores germinate in a film of
moisture and penetrate the leaf or cane tissue. As leaf and cane spots
form and age, new pycnidia form in the centers. These also produce and
release spores that can cause secondary infections throughout the
growing season. Although the environmental conditions required for
infection are not clearly understood, periods of rainfall are highly
conducive to disease development. After overwintering in infected canes
or debris, the fungus produces spores for new infections the following
spring, completing the disease cycle.
Rosette, or double blossom, is caused by the fungus Cercosporella
rubi. Rosette is a serious disease of many varieties of erect and
trailing blackberries, particularly in the humid southern United States
and the southern regions of the Midwest. The disease is not present in
the more northern regions of the Midwest. Rosette also occurs on red
and black raspberry but is seldom serious. Rosette infected blossoms do
not form berries and non-infected parts of the same cane may produce
poor quality fruit. The disease seriously reduces fruit quality and
yield. Once the disease is established in organic plantings, little can
be done to control it.
Symptoms of rosette disease are striking and may
completely change the plants' appearance due to a proliferation of
shoots. This proliferation of shoots is referred to as a witches'
broom. Buds on new canes of erect and trailing blackberries are
infected in early summer. Generally, no symptoms will develop until the
following spring, although a few "Witches' brooms" may develop during
warm spells in late fall. In the spring, numerous leafy sprouts develop
from infected buds (Figure 36). These shoots are generally smaller than
normal and have pale green foliage that later turns a bronze color.
Several of these witches' brooms may be formed on one cane. Unopened
infected flower buds are abnormally large and coarse and frequently
somewhat redder. Sepals enlarge and occasionally change into leaves.
Flower petals may become green and leaflike. As flower buds open,
petals are usually pinkish in color, wrinkled and twisted. Pistils are
usually larger and longer than normal and occasionally become
abnormally shaped. The fungus produces a whitish spore mass that can
cover the surface of the infected pistils and stamens. Berries do not
develop from infected blossoms. Non-infected parts of the same cane
often produce small, poor quality fruit. In some varieties the witches'
brooms symptoms may not be apparent; however, the fruit set in infected
blossoms is always impaired.
Figure 36: Symptoms of rosette disease on blackberry.
Young buds on vegetative canes are infected in early
spring (Figure 37). The double blossom fungus grows between the bud
scales and surrounds the embryonic tissues within the bud. As secondary
buds develop beside an infected bud, they are also invaded. After the
bud is colonized by the fungus, very little happens. Infected buds
usually remain symptomless until the next spring. A few infected buds
are sometimes forced out in an unusually warm late fall. The fungus
overwinters in infected buds. During the winter the fungus continues to
grow within the bud. Bud proliferation is induced. When infected buds
break dormancy in spring, they develop a large number of short,
abnormal and off-colored shoots (the witches' broom effect). Infected
flower buds usually produce abnormal blossoms upon which the fungus
produces its spores. These spores are carried by wind or insects to the
newly formed vegetative buds, which are only susceptible to infection
in early spring. The fungus infects these buds and overwinters in them
to cause new symptoms the next spring, thus completing the disease
Figure 37: Disease cycle of rosette. Taken from the
Compendium of Raspberry and Blackberry Diseases and Insects of the
American Phytopathological Society Used with Permission.
Powdery mildew is caused by the fungus Sphaerotheca macularis. Powdery
mildew affects susceptible cultivars of red, black, and purple
raspberries. Blackberries and their hybrids are usually not affected.
The disease can be severe (varying from year to year) on highly
susceptible cultivars, and these plants may be stunted and less
productive. The infection of flower buds reduces fruit quantity.
Infected fruit may be lower in quality or unmarketable as a result of
the unsightly covering of mycelial growth. The key control method is to
avoid susceptible varieties. Sulfur will provide good control on
Infected leaves develop light green blotches on the
upper surface. Generally, the lower surface of the leaf directly
beneath these spots becomes covered by white, mycelial growth of the
powdery mildew fungus. The leaf spots may appear water-soaked. Infected
leaves are often mottled, and if surface growth of the fungus is
sparse, they often appear to be infected by a mosaic virus. Infected
shoot tips may also become covered with mycelial growth (Figure 38).
When severely infected, the shoots become long and spindly
(rat-tailed), with dwarfed leaves that are often curled upward at the
margins (Figure 39). Infected fruit may also become covered with a
white mycelial mat. When the disease is severe, the entire plant may be
Figure 38: Powdery mildew on blackberry leaves. Note the
leaves are covered with the white growth of the fungus.
Figure 39: Powdery mildew on blackberry. Note the
distortion of leaves.
The fungus overwinters as mycelium in buds on shoot tips
in Minnesota, but in California it has been reported to overwinter only
as cleistothecia (fungal fruiting structures), producing ascospores as
primary inoculum in the spring. Conidia are generally abundantly
produced on the surface of infected tissue, and these serve as
secondary inoculum for repeated cycles of infection throughout the
growing season. They are airborne and probably remain viable for no
more than 21 days. The development of this disease, like most other
powdery mildew diseases, is favored by warm, dry weather.
Orange rust is the most important of several rust
diseases that attack brambles. All varieties of black and purple
raspberries and most varieties of erect blackberries and trailing
blackberries are very susceptible. Orange rust does not affect red
raspberries. Orange rust is caused by two fungi that are almost
identical, except for a few differences in their life cycles. Arthuriomyces peckianus occurs
primarily in the northeastern quarter of the United States and is the
causal agent for the disease in the Midwest. Gymnoconia nitens is a microcyclic
(lacks certain spores) stage of A.
peckianus. G. nitens
is the more common rust pathogen on erect and trailing blackberries in
Unlike all other fungi that infect brambles, the orange
rust fungus grows "Systemically" throughout the roots, crown and shoots
of an infected plant, and is perennial inside the below-ground plant
parts. Once a plant is infected by orange rust, it is infected for
life. Orange rust does not normally kill plants, but causes them to be
so stunted and weakened that they produce little or no fruit. Key
control methods are cultural practices such as removing infected plants
early in the spring and eradication of wild hosts (brambles) near the
planting. Organic fungicides are not effective for control. In severely
infested areas, black raspberries or blackberries should probably not
be planted. Red raspberries are not susceptible.
Orange rust-infected plants can be easily identified
shortly after new growth appears in the spring. Newly formed shoots are
weak and spindly (Figure 40). The new leaves on such canes are stunted
or misshapen and pale green to yellowish (Figure 41). This is important
to remember when one considers control, because infected plants can be
easily identified and removed at this time. Within a few weeks, the
lower surface of infected leaves are covered with blister-like pustules
that are waxy at first but soon turn powdery and bright orange (Figure
42, 43). This bright orange, rusty appearance is what gives the disease
its name. Rusted leaves wither and drop in late spring or early summer.
Later in the season, the tips of infected young canes appear to have
outgrown the fungus and may appear normal. At this point, infected
plants are often difficult to identify. In reality, the plants are
systemically infected, and in the following years, infected canes will
be bushy and spindly, and will bear little or no fruit.
Figure 40: Black raspberry plants showing early season
symptoms of orange rust. Note the "Spindly" elongated shoots. Orange
pustules will develop on the underside of infected leaves.
Figure 41: Leaves on infected plants are usually yellow
(chlorotic) and smaller than leaves on healthy plants.
Figure 42: Orange rust symptoms on the underside of a
black raspberry leaf.
Figure 43: Close-up blister like pustules on the
underside of an infected black raspberry leaf. Pustules contain bright
orange masses of fungus spores.
In late May to early June, wind and perhaps rain-splash
spreads the bright orange aeciospores from the pustules on infected
leaves to healthy susceptible leaves where they infect only localized
areas of individual mature leaves (Figure 44). When environmental
conditions favorable for infection occur, the spores germinate and
penetrate the leaf. About 21-40 days after infection, small, brownish
black telia develop on the underside of infected leaflets. The
teliospores borne in these telia germinate to produce a basidium, which
in turn produces basidiospores. In blackberries these spores then
infect buds on cane tips as they root. They also may infect buds or new
shoots being formed at the crowns of healthy plants in the summer. The
fungus becomes systemic in these young plants, growing into the crown
at the base of the infected shoot, and into newly formed roots. As a
result, a few canes from the crown will show rust the following year.
The fungus overwinters as systemic, perennial mycelium within the host.
Figure 44: Orange rust disease cycle. Taken from the
Compendium of Raspberry and Blackberry Diseases and Insects of the
American Phytopathological Society. Used with Permission.
Orange rust is favored by low temperatures and high
humidity. Temperatures ranging from 43 to 72 F favor penetration and
development of the fungus, but higher temperatures decrease the
percentage of spore germination. At 77 F, aeciospores germinate very
slowly, and disease development is greatly retarded. Spore germination
and plant penetration have not been observed at 86 F. Aeciospores
require long periods of leaf wetness before they germinate, penetrate,
and infect plants.
Late leaf rust, caused by the fungus Pucciniastrum americanum, can cause
serious damage to susceptible red raspberry cultivars. Economic losses
occur from fruit infection and premature defoliation. Because it
usually appears late in the season and only occasionally in a severe
form, some consider it to be a minor disease. The wild red raspberry, Rubus strigosus, in the eastern
United States is very susceptible to this rust. A number of cultivars
originating from this species also are highly susceptible. While late
leaf rust occurs throughout the northern half of the United States and
southern Canada, it is more common east of the Mississippi River. In
recent years, its occurrence has increased in the northern areas of the
Midwest and it has caused significant losses. The rust does not occur
on black raspberries or blackberries. Organic fungicides are not
effective for control. Once established in the planting, little can be
done to control it.
On mature leaves, late leaf rust causes small chlorotic or yellow spots
to form on the upper leaf surface (Figure 45). These spots may turn
brown before leaves die in the fall. Unless the disease is severe,
foliar infections can be rather inconspicuous. Small pustules filled
with powdery spores (not waxy like orange rust spores) are formed on
the undersides of infected leaves (Figure 46). These spore masses may
also occur on leaf petioles, canes, and even on the fruit. Infected
fruit are worthless; thus, yield of marketable fruit is reduced (Figure
47). Badly infected leaves may drop prematurely, and in years when the
disease is severe, canes may be defoliated by September.
Figure 45: Symptoms of late leaf rust on the upper
surface of red raspberry leaves. Note the chlorotic spots.
Figure 46: Symptoms of late leaf rust on the lower
surface of red raspberry leaves. Note the masses of powdery yellow
Figure 47: Late leaf rust symptoms on red raspberry
fruit. Note the pustules on individual drupelets.
Unlike the orange rust fungus, the late leaf rust fungus is not
systemic. The rust fungus produces two types of spores (urediniospores
and teliospores) only on raspberries (Figure 48). The alternate host
for the rust is white spruce (Picea canadensis), on which another type
of spore (aeciospore) is produced. The rust apparently does not need
the aeciospores stage to survive on raspberries, because the disease is
found year after year in regions remote from any spruce trees. The
fungus probably overwinters on raspberry canes and, in the following
season, produces urediniospores that serve as the source of primary
inoculum for new infections.
Figure 48: Late leaf rust disease cycle. Taken from the
Compendium of Raspberry Diseases and Insects of the American.
Phytopathological Society. Used with Permission.
The small, numerous, light-yellow spots seen on the
undersurfaces of the leaves are the uredinial pustules that contain the
urediniospores of the fungus. These spores are capable of causing new
infections throughout the growing season. Black, one-celled teliospores
may be found later in the season intermingled with the uredinial
pustules. They are capable of infecting the alternate host (spruce)
through the production of yet another type of spore (basidiospore), but
probably play little part in the life cycle of the rust on Rubus.