Diseases and Pests

Your best first line of defense against diseases and pests is to choose disease-resistant cultivars and to keep your plants healthy. Choose your site and prepare the soil carefully, paying special attention to good drainage. Make sure plants get adequate water, but avoid saturating the soil. Remove wild brambles, which can harbor diseases that can spread to your planting.

For more help identifying disease, pest, and other problems with raspberries, see www.hort.cornell.edu/diagnostic.

Choose disease-resistant cultivars and plant them in a well-drained site.

Mosaic virus. Aphids and leafhoppers infect and spread this disease through bramble plantings. Leaves become mottled with yellowish or light green blotches on a dark background. They also are smaller than normal and frequently deformed or cupped. The virus stunts infected plants, which produce dry fruit of poor quality.

Royalty, a purple raspberry cultivar, is immune to the aphid that transmits this virus. Black raspberries are very susceptible. Red raspberries can carry the virus without showing any symptoms, so do not plant black raspberries near red raspberries unless you are certain the red raspberries are virusfree.

To reduce the incidence of mosaic virus, plant only virus-indexed stock. Plantings located far away from wild brambles are less likely to become infected. Remove infected plants, because once infected, they cannot be cured.

Ringspot virus. This virus is transmitted by nematodes (tiny soil-dwelling, wormlike creatures) and causes berries to crumble when picked. Plants cannot be cured once they are infected. Plant only virus-indexed stock, and do not replant into a site where crumbly berry plants have been recently removed.

Phytophthora root rot. This disease causes plants to wilt or collapse during the heat of summer. It stunts leaves, which show poor color before wilting. Digging up plants will reveal that many of the roots are dead or chocolate-brown in color. This root-rotting disease is associated with wet sites. To avoid it, plant only in well-drained soils or on ridges or raised beds. Black raspberries are generally the least susceptible. Red raspberries vary in their susceptibility.

Verticillium wilt. This disease can be found in soil where strawberries or tomatoes, potatoes, peppers, eggplants, or other crops in the tomato family have been grown. It causes leaf wilting and yellowing from the bottom up and may appear on only a few canes of each plant. Verticillium wilt is most severe on black raspberries. Grow a cover crop of a grass species for a couple of years before planting raspberries if the site was once used to grow any of the susceptible crops listed above.

Spur blight, cane blight, and anthracnose. These diseases infect canes and weaken plants. Spur blight is identified by chocolate-brown or purple cankers around individual buds. Buds within the discolored areas fail to grow, or laterals from those buds collapse before fruiting. Cane blight cankers grow around the entire cane below wilting branches. Symptoms of anthrac-nose include small purple spots on young canes in the spring. The spots become sunken and turn gray with a purple border. This disease is most severe on black and purple raspberries.

To control these cane diseases, prune out and burn diseased canes before new canes emerge in the spring. Also, remove the fruiting canes after they have fruited, usually sometime in August. Fall-bearing raspberries that are mowed annually are not infected by these diseases.

Botrytis fruit rot. This fungus develops during cool rainy weather as a gray mold over the fruit. Practices that improve air circulation reduce its incidence. Fungicides are most effective when applied during bloom.

Orange rust. This disease affects black raspberries and blackberries, turning the undersides of new leaves orange in the spring. Plants produce new canes that are weak, spindly, and thornless. The disease is systemic in the plants, returning every year.

Raspberry cane borers. Adults of this insect pest appear in June. The first symptoms are wilting tips on new canes and laterals. Closer examination reveals two rows of punctures 1/2 inch apart encircling or girdling the stem. These marks are made by the female borer before she deposits her eggs between them. Larvae hatch from the eggs and burrow toward the base of the cane. They spend their second year in the roots and crown.

To avoid this insect, do not plant near wild brambles. When infestations occur, cut off the wilted tips below the girdle and crush the old stubs of canes in early spring.

Raspberry fruitworms. Early cultivars of red raspberries are most likely to be attacked by this pest. Larvae are usually first noticed at picking either inside the berry or on the receptacle. Infected fruit is usually unfit for consumption. The adults can severely injure leaves by eating holes in them.

Spider mites. These tiny pests are most prevalent during hot, dry weather. They are found on the undersides of leaves, preferring older, less succulent ones. Injury appears as bronzing on the leaf surface. Excessive fertilization can lead to high mite levels.

Blackberry leafminers. These insects feed on foliage, weakening the plant and causing poorly developed fruits. Larvae hatch from eggs laid in the leaf tissue and excavate large blotched "mines" between the leaf surfaces. Two generations occur each year—the first in late May and the second in late August.

Raspberry sawflies. Look for these small pale green larvae feeding first on the outer edges or undersides of the leaves and then chewing holes in the leaves. In heavy infestations, all leaf surfaces except the vein are destroyed.

Japanese beetles. These familiar insects chew leaves randomly in midseason. They prefer particular cultivars. Plantings near grub-infested turf are particularly susceptible.

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