Reports on Plant Diseases |
RPD No. 709 - Spur Blight & Cane Blight of Raspberries
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May 2000
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[ Spur
Blight Symptoms ] [ Spur Blight Disease Cycle ]
[ Cane Blight Symptoms ] [ Cane Blight
Disease Cycle ] [ Control ]
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Spur and cane blights are common, serious diseases of raspberries in
Illinois, especially during wet seasons. These blights often occur together
on red raspberries, weakening the canes and reducing yield.
Spur blight is caused by the fungus Didymella applanata (the imperfect
stage is an unnamed Phoma sp.). This disease is more common and
serious on red raspberries and to a lesser extent on black and purple
raspberries and loganberries. Blackberries and dewberries are highly resistant
to this disease. Spur blight can cause yield losses in several ways. It
can blight the fruit bearing spurs, cause premature leaf drop, and kill
buds on the canes that later develop into fruit bearing side branches.
In addition, berries produced on diseased canes may be dry, small, and
seedy. Affected canes may be more vulnerable to winter injury than uninfected
ones.
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Click on image for
larger version
Figure 1.
Red raspberry canes
showing spur blight infections
(dark areas). Note dead buds
and black specks - fungus
fruiting bodies.
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Spur Blight Symptoms
Chocolate brown, dark blue, or purplish spots with encircling bands form on
the new canes and leaf petioles in the late spring or early summer, usually
at a bud or leaf attachment (Figure 1). The infected areas, which vary from
half an inch to several inches long, gradually enlarge until the cane is girdled.
By late summer the bark in the cankered area dries up, and the canes may crack
and split lengthwise. Speck-sized, black reproductive bodies (pycnidia) of the
fungus develop in the dead bark. Later in the fall, the bark in these areas
turns silvery gray, and numerous black pustules containing perithecia (another
reproductive structure of the fungus) form on the lesion. Many buds on fruiting
canes that were infected the previous year shrivel and die. Surviving infected
buds develop small, weak, lateral shoots with stunted yellow leaves that wither
and die early in the season.
Leaves sometimes become infected and show brown, angular or wedge-shaped areas.
The widest part of the wedge is toward the margin or tip of the leaflet. Spur
blight spreads into the leaf petiole and into the cane at the point of attachment.
Leaflets on diseased canes turn yellow and drop prematurely, sometimes leaving
the petiole (leaf stem) attached to the cane.
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The fungus survives on infected canes during winter. The following spring and
summer, during wet and rainy periods, spores are released and carried by splashing
rain and wind to nearby canes and leaves, where they germinate and penetrate
plant tissue. Infections commonly occur where the leaf petiole is attached to
the stem.
Large numbers of spores (conidia) ooze from pycnidia during warm, wet weather.
These spores are washed and splashed to other canes, where new infection occurs
through wounded or unwounded tissue.
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Cane blight is caused by the fungus Leptosphaeri coniothyrium (the imperfect
stage, Coniothyrium fuckelii). This disease, more common on black raspberries,
also occurs on red and purple varieties but rarely attacks blackberries and
dewberries. Cane blight can result in wilt and death of lateral shoots, a general
weakening of the cane, and reduced yield.
Cane Blight Symptoms
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Click on image for
larger version
Figure 2.
Cane blight on
black raspberry - note
gray spore
masses.
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Toward the end of the season, dark brown to purplish black cankers form
where pruning, insect, and other wounds occurred on young canes. The cankers
enlarge and encircle the cane causing the lateral shoots to wilt and die.
On second-year canes, the side branches may suddenly wilt and die, usually
between blossom time and fruit ripening. Close examination reveals the
presence of cankers on the branches or the main cane where insect injury,
pruning wound, or other type of wound has occurred. Infected canes commonly
become cracked and brittle, and break easily. Numerous black specks (pycnidia),
the reproductive bodies of the fungus, develop in the cankers. In wet
weather, large numbers of microscopic, olive-colored spores (conidia)
ooze from the pycnidia, giving the bark a characteristic dark gray, smudgy
appearance.
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The pathogen survives over winter on infected or dead canes. The following
spring, conidia, formed in pycnidia, ooze out during wet periods. These spores
are rain splashed, blown, and carried by insects to nearby canes. Under moist
conditions these conidia will quickly germinate and penetrate any type of wound,
rapidly killing cane tissue. Infection occurs at almost any time of the growing
season. Pycnidia are formed in the dead portions of the older cankers. Dead
canes continue to produce conidia and remain a source of infection for several
years.
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These blights are not difficult to control if the following suggestions are
followed.
- Select a sunny planting location with good soil drainage and air circulation.
Avoid shady areas. The longer the canes and foliage remain wet from dew, rain,
etc. the greater the chance for spur blight and cane blight development.
- Plant certified, No. 1 grade, one-year-old, substantially virus-free
stock. When setting out new plants in the early spring, cut off the "handles"
(old cane stubs) at ground level and destroy them. Before new shoots
appear, remove and destroy all dead and winter-injured canes from established
plantings. Also remove all wild or neglected raspberries and blackberries
in the area.
- Fertilize raspberries to maintain plant vigor, but avoid using an excessive
amount of fertilizer.
- Keep the fruit-planting and surrounding region free of weeds and cultivate
carefully to reduce root injury. Keep the rows about 12 to 18 inches (30
to 46 cm) wide for air circulation, to allow penetration of sunlight, and
to improve spray coverage.
- Remove and destroy all old fruit canes immediately after harvest.
Thin the new canes to about 6 for staked-hill plantings, or 4 to 6 inches
(10 to 15 cm) apart for hedgerow plantings. Remove all weak, short, spindly,
and injured canes.
- Topping canes and other pruning to reduce excess growth should be done
in dry, clear weather so the wounds will have a chance to heal before rain
is expected. Weak, broken, or infected lateral branches on fruiting canes
should be cut back to healthy wood.
- Follow the spray schedule outlined in "Illinois Commercial Small Fruit
and Grape Spray Guide", Circular ICSG-2, and "Illinois Homeowners' Guide to
Pest Management", Circular 1354. Thorough coverage of all canes and foliage
with each application is essential for blight control and for successful fruit
production. If possible, apply the sprays a day or two before rain is predicted.
In the spring, spray when the buds show no more than 3\8 inch (1 cm) of
green at the tips. For this spray only, use liquid lime-sulfur or
copper hydroxide 50 WP. Copper hydroxide is available for use on raspberries
as Blueshield 50 WP or Kocide 50 WP. Both products have a 48 hour reentry
interval. This spray also helps control anthracnose, certain insects, and
mites. Delaying this spray after more than 3/4 inch of growth of new shoots
will burn exposed foliage.
Where disease has been severe, spray with Captan or Benlate according to
label recommendations. Spray when the new canes are 6 to 8 inches (15 to
20 cm) tall; when shoots are 12 to 15 inches high (30 to 38 cm) or just
before the blossoms open on the fruiting canes; just after bloom, as soon
as the petals fall; and just after the fruit has been harvested and old
canes removed. The first two sprays of Benlate or Captan may not be needed
where these blights and anthracnose are not severe and the liquid lime-sulfur
has been properly applied.
- Keep raspberry plantings free of insects such as crown borers, stem girdlers,
aphids, fruitworms, rose scale, sawflies, plant bugs, tree crickets, picnic
and sap beetles, and mites. Most suggested insecticides and miticides,
except for liquid lime-sulfur, may be safely mixed and applied at the same
time. Follow all the manufacturer's directions.
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Further information concerning fruit diseases can be obtained
by contacting Mohammad Babadoost, Extension Specialist in Plant Pathology, Fruit
and Vegetable Diseases, Department of Crop Sciences, University of Illinois,
Urbana-Champaign.
University of Illinois Extension provides equal
opportunities in programs and employment.
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