Fruit IPM Extension Bulletin Fruit IPM Extension BulletinRaspberry Diseases in Michigan
Michigan State University Extension Bulletin E-1730
Donald Ramsdell and Sandra Perry,
Department of Botany and Plant Pathology
Major revision October 1994
Virus diseases are the main cause for losses in raspberry production. They are largely responsible for the decline in Michigan raspberry production from about 14,000 acres in 1950 to less than 1,000 acres in 1980. Certain steps can be taken to minimize virus infection and thereby maintain healthy plants and good production. Following are the most common raspberry diseases. For recommended pesticides, rates and times of application, see the Michigan Fruit Management Guide, Extension Bulletin E-154.
Raspberry Mosaic Virus
This
is the most widespread and damaging raspberry virus. All commonly grown cultivars can be
infected by the mosaic virus, except for Canby, which is resistant. Mosaic symptoms
consist of light green to dark green or yellow to green mottling of the leaves on infected
canes (Fig. 1A); blistering of leaves as well as a mosaic
pattern are also evident (Fig. 1B). The plants show a
progressive stunting of growth and poor yield. Fruits on infected bushes are small and
crumbly. The common raspberry aphid (a rather large, greenish aphid found on shoot tips
and on the undersides of the leaves) spreads the virus from diseased cultivated and wild
raspberry plants.
Raspberry Leaf Curl Virus
Leaves on infected canes are rounded, curl downward and are usually of a greasy,
dark green color (Fig. 2). Growth is stunted, and fruit
production is reduced. A small, yellow-green aphid found on the undersides of leaves
spreads this disease.
Tobacco Streak Virus
Tobacco streak virus symptoms are somewhat deformed leaves blotched with yellow
areas (Fig. 3) and poor fruit production. Since the virus is
pollen-borne, healthy plants can become infected by pollen from a diseased plant.
Tomato Ringspot Virus
This virus is widespread throughout the Michigan fruit growing area. It causes
disease in stone fruits (peaches, plums, cherries, etc.), pome fruits (apples, pears,
etc.), blueberries and grapes. Symptoms in raspberries are not very strong. A few leaves
on infected bushes may show some pale ringspots in the spring, but these later disappear.
The main effect is a general stunting of the bush, a general yellowing of leaves (Fig. 4) and production of small, crumbly fruit. Virtually all
raspberry varieties are susceptible. Tomato ringspot virus has a very wide range of hosts,
including many weeds such as dandelion, curly dock, plantain and chickweed. The virus is
spread by the dagger nematode Xiphinema americanum from the roots of diseased
raspberry bushes or weeds to the roots of healthy bushes.
Virus Disease Control: Purchase and plant only Certified Virus-Tested raspberry stock. Such stocks have been tested for the presence of known virus and other systemic diseases. If planting stocks are not certified, they probably will contain one or more of the viruses described in this publication. Plant stock in soil free of virus-vector nematodes (Xiphinema americanum - dagger nematode). If soil is found to contain this or other plant pathogenic nematodes, use a preplant soil fumigant. Locate new plantings 400 yards from other cultivated raspberries which may harbor the virus. Eliminate any wild raspberries (Rubus spp.) that are within this distance, using an appropriate herbicide. Use insecticides, such as Diazinon or Malathion, on a regular basis beginning in mid-May and ending after the first killing frost in the autumn. This helps prevent build-up of virus-carrying aphids. Pull out and burn any plants that show virus disease symptoms.
Fungal Diseases
Black and purple raspberry varieties are most seriously affected by anthracnose (Elsinoe
veneta), but the disease can be economically significant on red varieties also.
Symptoms appear on canes, leaves, and sometimes on the fruit. Infected canes show tiny
purple spots which progress to light gray round spots about 1/8 inch in diameter. The
spots enlarge to about 1/4 inch, have ash-gray centers and may have purple borders (Fig. 5A). As the canes age, the spots appear sunken and the borders
raised. Leaves will develop similar small round spots or lesions about 1/16 inch in
diameter (Fig. 5B)
.
Diseased tissue frequently drops out leaving a shot-hole appearance. If the disease is not
controlled, canes become cracked and the druplets of the berries become infected,
resulting in worthless fruit. The fungus survives the winter in infected canes and
produces spores (both conidia and ascospores) in the spring at the time of leafing out.
The disease can become serious with abundant rain in late spring and early summer, or
under sprinkler irrigation.
Control: Use disease-free plants. After harvest, cut out and burn old fruiting
canes and new canes that show disease symptoms.
Spur
blight (Didymella applanata), is a serious disease of red raspberry varieties.
Infected canes release ascospores and conidia in May and June during rainy periods.
Conidia release continues throughout the growing season during wet weather. Small, brown
or purple spots appear around the nodes on the lower portions of the canes. These areas
turn brown, causing the leaf and flower buds to shrivel and die. Leaf lesions appear as
brown wedge-shaped areas. Diseased canes dry out and crack as they mature; the lesions
turn brownish purple and enlarge to cover much of the cane (Fig. 6A).
The symptoms of cane blight (Coniothyrium fuckelii) can easily be
confused with those of spur blight. Both diseases cause considerable damage to Michigan
raspberries. The fungus can live for several years in cane debris left in the field.
Spores release (both ascospores and conidia), and subsequent infection begins in the
spring. Conidial infection continues through- out the growing season during rainy weather.
Wounds from pruning, insect feeding or cane rubbing are the initial sites of infection.
Brown or black infected areas extend down one side of the cane for several inches (Fig. 6B). Fruiting canes infected the previous season have light
colored, cracked bark. Lateral shoots on infected canes grow poorly and may wilt and die
during hot weather.
Control: Never prune during wet weather. To prevent infection, canes should remain
dry for at least 3 days after pruning so wounds will callus. Prune out and burn infected
canes in the spring.
Orange rust
(Kunkelia nitens) attacks black and purple raspberries, but not red varieties.
Leaf symptoms develop toward the end of June. Infected leaves are small and yellowish with
orange pustules of waxy rust spores on the underside of the leaves (Fig.
7). The spores are shed and cause new infections over a 2- to 3-week period. Leaf
symptoms disappear from the field by mid- to late summer. The fungus invades all parts of
the plant (including the roots). Infected plants never recover. Newly infected canes are
weak, spindly and lack spines (thorns). Infected canes will not blossom the following
year.
Control: Plant rust-free raspberries. Remove and burn any plants that show
symptoms. Kill nearby wild raspberry plants. Fungicidal control is not effective.
Late
leaf rust (Pucciniastrum americanum) causes disease in red raspberries, usually
later in the season. Older (basal) leaves are covered with fine, light-yellow, powdery
masses of spores in midsummer (Fig. 8). The spore masses can
appear on leaf petioles, shoots, calyces (fruit caps) and even on the fruits. The
popularity of the 'Heritage' cultivar of red raspberry has made this disease more
prevalent. Rust disease builds up on the leaves of this fall bearing variety because of
the long growing season.
Control: No official control recommendations are available at the present time.
Verticillium Wilt
Verticillium wilt (Verticillium alboatrum) of raspberries is caused by a
soil borne fungus. The fungus penetrates the roots of raspberry plants and moves into the
cane through water conducting vessels. It is particularly damaging to black raspberries.
Leaves on infected fruiting canes turn yellow, gradually wither and fall. Symptoms begin
on lower portions of the canes and continue upward until the canes turn blue and die (Fig. 9).
Control: Use disease-free plants. Avoid planting raspberries for at least
three years in soil that has grown tomatoes, potatoes, peppers or eggplants. Remove and
burn diseased plants. Use a preplant soil fumigant if the Verticillium fungus is a problem
in the area to be planted. To control verticillium wilt disease in new plantings, fumigate
in late summer or early autumn (Consult Extension Bulletin E-154, Michigan Fruit
Management Guide). Apply with a shank applicator (Fig. 10) at a
depth of 8 inches, and immediately seal with a drag float or cultipacker. The soil should
be in excellent tilth and shouldn't have had a crop on it for about 6 months before
fumigation. Soil temperature should not be below 50F (at the 8-inch depth) at fumigation
time. Do not plant until the spring following late summer or autumn fumigation.
Phytophthora Root Rot
Phytophthora root rot (Phytophthora erythroseptica
or P. cactorum) is of minor importance in Michigan. The fungus lives in the soil
and may infect raspberry roots in fields with low-lying, poorly drained areas. Symptoms
appear in the summer and consist of either wilting back of entire large canes (Fig. 11) or wilt of only a few terminals.
Control: Plant bushes in sandy, well-drained soils. Install drainage tile or dig
drainage ditches where soil is poorly drained. No effective post infection chemical
treatment program exists at this time.
Botrytis & Penicillium
Botrytis (Botrytis cinerea) or Grey mold symptoms on ripening fruit appear as a gray, fuzzy mold on the fruit surface. Penicillium rot (Penicillium sp.) consists of whitish areas on the surface of ripening fruit. Warm, wet weather favors disease development.
Crown Gall and Cane Gall
The bacteria of crown and cane gall (Agrobacterium sp.) cause galls on
roots (Fig. 12) or on canes. Infected bushes become weakened,
stunted or unproductive as a result of the gall tissue interfering with water and nutrient
flow in the plants. The bacteria can live in the soil for years and infect raspberry
plants through root wounds. Infested soil may be splashed higher up on the plant,
producing cane galls. Nursery stock may arrive already infected with crown gall which then
serve as an inoculum source for uninfested soil.
Control: Check planting stock for suspicious swellings or galls on roots and canes.
Dip the stocks in a suspension of Galltrol or other brand of antagonistic Agrobacterium
sp. at planting time. This is a nonpathogenic strain of the bacterium that protects the
plants against infection by the naturally pathogenic strains that may be in the soil at
the planting site. The antagonistic strains act only to protect disease free plants from
future infection by the crown gall bacterium; they cannot cure infected plants.
Several species of nematodes cause economic loss in Michigan
raspberries. Xiphinema americanum (the dagger nematode) is a root-infecting
pathogenic nematode and also acts as a virus vector by spreading tomato ringspot virus.
Root knot nematode (Meloidogyne spp.) causes galling symptoms and stunting of
plants. The root galls are usually smaller than those caused by crown gall bacteria.
Stubby root nematode (Trichodorus spp.) causes a stunting and stubbiness of roots
and thereby weakens plants. The ring nematode (Criconemella spp.) is found in
high populations in the raspberry root zone, but its importance is not known. The lesion
nematode (Pratylenchus spp.) is very damaging because it feeds inside the roots,
causing considerable root destruction. Bushes infected with the lesion nematode become
very stunted and may die. Nematodes feeding on raspberry roots cause wounds which allow
soil fungi, i.e. Verticillium sp. and Phytophthora sp., to more easily
infect the roots.
Control: Plant clean stock. Nursery stock can be a source of nematode infestation.
Ask the nursery that sells the stock to provide a copy of nematode soil tests from their
growing sites. Before planting, take soil samples as described in MSU Extension Bulletin
E-2199, Detecting and Avoiding Nematode Problems. Fumigate the soil if pathogenic or virus
vector nematodes are present.
MSU is an Affirmative-Action/Equal-Opportunity Institution. Extension
programs and materials are available to all without regard to race, color, national
origin, sex, disability, age or religion.
Issued in furtherance of Extension work in agriculture and home economics, acts of May 8
and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Gail L. Imig,
Extension Director, Michigan State University, E. Lansing, MI 48824.
This information is for educational purposes only. References to commercial products or
trade names does not imply endorsement by the MSU Extension or bias against those not
mentioned. This bulletin becomes public property upon publication and may be printed
verbatim with credit to MSU. Reprinting cannot be used to endorse or advertise a
commercial product or company. Produced by Outreach Communications and printed on recycled
paper using vegetable-based inks.
Major revision, destroy previous editions-10:94-4M-TCM.
Many MSU Extension data bases are available on CD-ROM or in other formats. For more information about this data base please contact
