Raspberry plants belong to the genus Rubus, most of which are in the subgenus Idaeobatus. Raspberries are a red composite fruit that are generally produced midsummer, but with different harvesting technology and cultivars, they are available year-round. They are prey to some plant diseases, which can damage or kill the plant. Fungal, bacterial and viral diseases can attack the plant, limiting both its yield and longevity. If infected with a viral disease, the plant is diseased for life. Identifying and treating disease may help save nearby raspberries before they fall victim.
Put on gardening gloves. Raspberry plants have fine thorns that could prick your hands.
Examine the raspberry plant gently for abnormalities.
Look for symptoms of anthracnose disease. There will be red-purple oval lesions, with a centre that turns pale brown or ash grey and a raised and purple surrounding, located on the primocanes. Purple-brown spots develop on the leaves. The lesions may cause the cane to become dry and cracked or to die. Infected primocanes may produce irregular, lateral branching and irregular fruit or suffer tip dieback.
Examine wounded or damaged canes for cane blight disease. If infected, you will see black, brown or grey lesions on the floricanes. The lesions contain black, bumpy pycnidia. The infected cane may be brittle or break near the lesion. The disease will cause the cane to wilt and eventually die, as well as the axillary buds and lateral branches.
Search for brown, V-shaped lesions with yellow borders surrounding the nodes on primocanes. These are signs of spur blight disease. Buds near infected buds may become inactive or fail and infected lateral shoots may not produce as many flowers. The lesions may turn silver to grey in winter.
Examine the plant for blossom blight and fruit rot, each of which are signs of grey mould. Damaged, bruised or wounded raspberry plants are susceptible to grey mould and cool, wet weather increases the likelihood of rot.
Study the plant for signs of verticillium, a soil-borne fungus infecting the raspberry's vascular tissue. Infected fruiting canes often have a stained red-brown sapwood. The canes wilt, have stunted growth, and eventually die. Sometimes the entire plant dies.
Look for water-soaked or dark green canes. These are symptoms of the bacterial disease "fireblight." You may see oozing from the cracks on infected canes, as well as a curled tip and colouring that later turns purple to black.
Examine the leaves for white, grey or tan spots, which signal raspberry leaf spot. Look for lesions with a centre that has fallen out, leaving a shot-hole appearance. Infected leaves may fall from the plant.
Turn the leaves of the plant over and search the bottom for a white to grey, powdery growth. This signals powdery mildew, which may occur yearly.
Continue studying the leaves. If you see orange-yellow spots, the plant may be infected with rust fungi. Rust fungi infects the leaves and canes, and sometimes infects the fruit.
Analyse the plant midsummer for signs of late leaf rust. It causes fine, light-yellow, powdery spores that appear on leaf petioles, cane shoots, calyces and the fruit.
Examine plants in low-lying, poorly drained areas for phytophthora root rot. You may see a few terminal canes wilting or large, entire canes wilting back.
Examine the raspberry leaves, looking for yellow-green mottling, blistering and browning on the tips. These are all signs of raspberry mosaic disease, which may also cause stunting of the leaves. Plant strength, fruit quality, hardiness in winter and fruit yield may all be reduced from the disease.
Identify "raspberry leaf curl," looking for curled and distorted dark green leaves. The plants are stunted and have branched excessively. The fruit crop becomes small, crumbly and seedy.
Identify symptoms of tomato ringspot virus. Infected plants display yellow rings, line patterns or veinal chlorosis on their leaves and stunted growth. The fruit yield is poor and crumbly.
Inspect the leaves for deformities and yellow areas. These are symptoms of the viral disease "tobacco streak."
Look over plants with a reduced fruit yield and reduced rigour. The plant may be suffering from "raspberry bushy dwarf," with symptoms that are often visible on leaves. The leaves develop interveinal chlorosis and irregular line or "oak leaf" patterns.
- Raspberries: What are Raspberries?
- University of Minnesota Extension; Raspberry Diseases; Chad J. Behrendt; 2000
- University of Illinois Extension; Virus Diseases of Brambles in the Midwest; 1996
- Michigan State University Extension; Raspberry Diseases in Michigan; Donald Ramsdell and Sandra Perry; 1994
- Cornell University; Managing Cane Diseases; Cathy Heidenreich
- Treat fungal diseases with a fungicide, following all manufacturer's instructions, and use an insecticide to prevent viral diseases. Destroy severely diseased and infected plants.
- Jupiterimages/Photos.com/Getty Images