Small Fruit Diseases

Botrytis blight and fruit rot are common occurrences, especially in cool, humid weather on many crops throughout the world.

Mummy berry is the most serious and widespread disease of highbush, lowbush, and rabbiteye blueberries. It is most serious in the north following moist, spring weather conditions.

Only in recent years has Phomopsis twig blight and canker become an important disease of blueberries. Bushes that have been weakened by other factors are usually more prone to infection. In addition to twig blight and canker, the fungus causes a fruit rot.

Blueberries are susceptible to a number of virus and virus-like diseases. Virus diseases are spread to healthy blueberry plants by vectors that include primarily aphids, nematodes, leafhoppers, and occasionally honeybees, which can spread virus-infected pollen. Virus diseases also are spread by diseased plants from infected nursery stock. Once a bush is infected with a virus, it remains infected for the life of the plant.

Black root rot is known as a "disease complex," meaning that it can be caused by several factors.

Gray mold, or botrytis blight, is a common disease of a number of nonwoody plants worldwide and causes a greater loss of strawberry flowers and fruit than any other disease. It is found on green as well as ripening and harvested fruit.

There is a wide array of leaf spots that infect the cultivated strawberry and often wild strawberry species. Some are known as leaf spot (birds-eye leafspot), black leaf spot, Septoria leaf spot, Cercospora leaf spot, Alternaria leaf spot, red spot, and Angular leafspot. These leaf pathogens are caused by several fungi and may occur with other foliar diseases. Usually, disease development is favored by rain and warm, humid weather.

Leather or crown rot occurs in most temperate regions of the world on a wide variety of plants. Infection is favored by warm, wet weather and poorly drained soil. The fungus attacks berries in the field at all stages of growth. Fruit rot occurs when the berries come in contact with the soil. The pathogen may also cause a serious crown rot, which can develop along with the fruit rot.

Powdery mildew occurs on a wide range of hosts and almost everywhere the strawberry is grown. It is observed mostly as a foliage disease, but it occasionally causes a serious fruit rot. Severe foliar infection can damage leaves and reduce photosynthesis.

Red stele, or red core, is the most serious disease of strawberry. In areas with cool, moist soil conditions, especially soils heavy in clay that are saturated with water during cool weather, the disease is more prevalent. Red stele is caused by the soil-inhabiting fungus Phytophthora fragariae.

Verticillium wilt of strawberry, caused by the soilborne fungus Verticillium albo-atrum, occurs throughout the temperate zones of the world, infecting more than 300 kinds of cultivated plants. Its hosts are annual and perennial crops as well as weed species.

Anthracnose, commonly called "cane spot" or "gray bark," occurs in several species of Rubus. It is considered an extremely serious disease of black, purple, and susceptible varieties of red raspberry. Severe yield loss can result due to defoliation, wilting of lateral shoots, death of fruiting canes, and reduction in fruit size and quality.

Botrytis fruit rot or gray mold is the most common and most serious disease of Rubus species worldwide. The disease is caused by the fungus Botrytis cinerea. This pathogen has a wide host range and can survive on either living or dead tissue. It can overwinter on dead leaves, plant debris, and on the stems.

Crown and cane gall are bacterial diseases that seriously limit raspberry production in Pennsylvania. Crown gall is the more widespread of the two diseases and affects all brambles as well as apples, grapes, peaches, and roses. Only grass-like plants seem to be immune to crown gall.

Orange rust is a fungal disease that occurs only on brambles, particularly blackberries, dewberries, and black raspberries. This disease is not known to affect red or purple raspberries. This is a systemic disease. Once the plant is infected, the entire plant is infected for life.

Phytophthora root rot is now regarded as a major cause of declining red raspberry plantings. Blackberries and black raspberries appear to be less susceptible than red or purple raspberries. Wet soil conditions favor the development of the disease, which can often be observed in low-lying areas of a field. Declining plants previously diagnosed as suffering from "wet feet" or winter injury usually are infected by this root rot.

Blackberries are seldom severely infected by powdery mildew. It is occasionally a serious problem on susceptible varieties of red and black raspberries, especially the Black Hawk and Latham varieties. Infected plants may be stunted and less productive.

Red and purple raspberries are more affected by spur blight than black raspberries. Blackberries appear to be immune. In extremely overgrown and weedy plantings, the disease can cause a loss in yields, especially if excessive nitrogen is applied.

Verticillium wilt is caused by two common soilborne fungi. These fungi have a wide host range and attack more than 300 woody and herbaceous plants. The disease can be widespread and extremely destructive. Black raspberries are more susceptible to the disease than red raspberries. Blackberries also are attacked by the pathogen but are not as prone to wilting.

Virus diseases can seriously damage brambles, especially the raspberry, and can affect the lifetime of a planting. Once the plant is infected with the virus, the entire plant will be infected for the remainder of its life. Virus infections cause decreased productivity, so it is important to start a planting with healthy plant stock obtained from a reputable nursery.