of Bramble Diseases
Virus Diseases of
Red and black raspberries are susceptible to numerous
viruses. Raspberries probably suffer greater infection and more serious
damage from viruses than any other fruit crop in the United States.
Virus infection in raspberries can reduce fruit yields 70 percent or
more. There are four main virus-induced diseases of raspberries:
mosaic, leaf curl, streak, and tomato ringspot. Key control methods
include starting the planting with disease free (virus indexed) plants
and eradication of wild hosts as well as infected plants within the
Other disorders of raspberries can cause symptoms
similar to viruses. Late-spring frosts, mineral deficiencies (such as
iron and nitrogen), powdery mildew, pesticide injury, and feeding by
leafhoppers, aphids and mites can all cause symptoms similar to those
caused by various viruses. Positive identification of a bramble virus
or virus complex cannot be based on foliar symptoms alone. Greenhouse
and laboratory tests using specific scientific techniques are required
for positive identification of viruses.
This disease is caused by a virus complex (more than one
virus involved). Viruses of the mosaic complex (Rubus yellow net, black
raspberry necrosis, raspberry leaf mottle and raspberry leaf spot
virus) cause the greatest reduction in growth, vigor, fruit yield, and
quality of any of the bramble viruses. No raspberry plants are immune,
but black and purple cultivars are damaged more severely than red
cultivars. The symptoms of mosaic vary considerably, depending upon the
cultivar grown, which virus or viruses of the complex are involved, and
time of year. Symptoms are most evident on new canes during cooler
weather of spring and fall. Symptoms may disappear in the summer when
temperatures are high. This is an important point to remember when
considering control of virus diseases. Even though symptoms may
disappear temporarily, plants remain infected for life. Infected canes
are usually short and less vigorous than healthy canes. Leaves are
mottled with yellowish or light green spots on a darker green
background (Figure 55). On more susceptible cultivars, leaves become
puckered with large, dark-green blisters surrounded by yellowish or
yellowish-green tissue. Leaves that develop in hot weather may be
symptomless or show only faint mosaic pattern with yellow flecks in the
normal green color. Leaves formed in late summer show a fine,
yellowish, speckled mottling.
Figure 55: Mosaic virus symptoms on raspberry leaves.
Note the mottled areas of dark green and light green or yellow.
Mosaic-infected plants are often progressively more
stunted each year. In addition to leaf symptoms, the fruit yield is
reduced and may be dry, seedy (often crumbly), and lack flavor. On
black and purple raspberries, the tops of newly-infected canes often
curl downward, turn black, and die.
The raspberry mosaic virus complex is spread almost
exclusively by one species of insect, the large raspberry aphid
(Amophorophora agathonica). The aphid is widespread and feeds on the
undersides of leaves near the tip of the canes. The aphids become
contaminated with the viruses and can spread the viruses to healthy
plants up to a quarter of a mile or more away. The mosaic virus can
also be spread by commercial propagation from infected plants and
movement of the diseased nursery plants.
Leaf curl is less common than the mosaic complex, but it
is considerably more destructive. Infected plants are worthless and
should be destroyed immediately. The yield of infected raspberries can
be reduced up to 70 percent. Infected black raspberry plants may
degenerate and die after two or three years.
Leaf curl symptoms are easily recognized. Leaves on
infected plants are uniformly small, dark green, crinkled, and tightly
curled downward and inward. When diseased shoots first appear, they are
pale yellowish-green, but they soon turn dark green, become stiff and
brittle, and usually do not branch. Each year the plant loses more
vigor and is progressively more dwarfed. Fruiting laterals are shorter
and more upright than normal ones. Berries on infected plants may ripen
prematurely and are small, dry, seedy, and crumbly.
The raspberry leaf curl virus, the causal agent of
raspberry leaf curl disease, is spread exclusively by the small
raspberry aphid (Aphis rubicola). Heavy populations of this aphid can
cause severe inrolling of leaves even in the absence of the leaf curl
virus. Winged forms of the aphid can transmit the virus to healthy
raspberries from nearby infected brambles. Windborne aphids may spread
the disease several miles.
Raspberry streak, caused by tobacco streak virus, is
generally a minor, but widespread disease. It is presently limited to
northern Ohio, western Pennsylvania, and western New York. Streak
affects only black raspberries.
The most obvious symptom of the disease is numerous
purplish streaks that appear on the lower parts of infected canes.
Usually, the streaks are less than an inch long. Terminal leaves on
infected canes are often hooked or recurved, twisted or rolled, and
darker green than normal. Leaves on the lower positions of the cane may
show yellowing along veins and mottling. Fruits on infected canes are
smaller than normal, dull, seedy, and crumbly and lack flavor. The
individual drupelets often ripen unevenly, giving the fruit a blotched
This virus disease occurs only in red raspberries and is
widespread in the major red raspberry-producing areas of the Pacific
Coast and northeastern United States. Infected plants may appear
normal, but they are usually somewhat less vigorous than healthy
plants. The most obvious symptom of the disease is the production of
small, crumbly berries that fall apart when touched. The crumbly berry
is caused by the failure of some of the tiny fruitlets (druplets),
which make up the fruit, to develop.
The tomato ringspot virus can affect many other species
of woody and herbaceous plants. This virus is transmitted through the
soil by the dagger nematode (Xiphinema americanum).
of Virus Diseases
Always start new plantings with the highest-quality
plants available. Use only certified, disease-free, virus-indexed
stock. Avoid obtaining uninspected plants from friends or neighbors.
Select a planting site that is sunny and fertile and has good air and
water drainage. Destroy all wild and neglected raspberries and other
brambles located within 500 to 1,000 feet of your planting site.
Do not plant black or purple raspberries near red
raspberries, even though the red raspberries appear to be healthy. Red
raspberries may have latent infections. This means that they can be
infected, but do not show symptoms. Even though infected plants are
symptomless, the virus can still be transmitted from them to healthy
plants. If black and red raspberries are planted together, separate
them as far apart as possible. If possible, plant black raspberries
upwind from reds. The reason for this is the aphids that transmit
viruses are generally blown or carried by wind rather than by active
flight. Therefore, you do not want aphids to be blown from your red
raspberries to your more susceptible black raspberries.
Go through the raspberry planting at least twice a year
and remove all plants showing any virus symptoms. This should be done
once about mid-June and again in August or September. Before removing
infected plants, kill all aphids on them by spraying infected plants
with an insecticide a day or two before removal. Dig out the diseased
plants, including roots, and dispose of them away from the planting
site. In established plantings, where more than 5 to 10 percent of the
plants show visible virus symptoms, removal of infected plants probably
will not pay. In this case, maintain the planting until fruit yield
becomes unprofitable, then destroy it. It is unwise to establish new
plantings next to old, infected ones. Maintain strict aphid control at
all times, especially in late spring and early summer when aphid
populations are highest.
If the virus is transmitted by nematodes, the nematodes
must be controlled in order to control the disease. Have the soil
tested for plant parasitic nematodes before planting. Samples should be
taken in July of the year preceding planting. Spring samples, taken
when soils are cold, are not accurate and do not give the grower
sufficient time to apply a preplant nematicide. Information on
collecting soil samples and submitting them for analysis is available
from your Extension service.
In an organic disease management program where emphasis
is placed on reducing overall fungicide use, it is essential to
identify any available disease resistance and use it. Unfortunately,
resistance to most of the major diseases is not available in most
commercially grown raspberry and blackberry cultivars in the Midwest.
Thus, the disease management program must rely mainly on the use of
cultural practices and efficient fungicide use. Whereas resistant
cultivars are not generally available for most diseases, cultivars do
vary greatly in their level of susceptibility to certain diseases. If
resistance is not available, those cultivars that are highly
susceptible to important diseases should at least be avoided.