Integrated Management of Blueberry Diseases

Fruit Diseases

Mummy Berry (Monolinia vaccinii-corymbosi)

Mummy berry is becoming increasingly important is some parts of the Midwest; its severity varies from year to year. It is caused by a fungus which attacks new growth, foliage, and fruit and can cause extensive loss.

The fungus overwinters in mummified fruit on the ground (Figure 56). The mummies form cup or globe-shaped structures called apothecia. Apothecia produce spores that infect young tissue and cause rapid wilting. This is called leaf and twig blight, or bud and twig blight. These symptoms are difficult to distinguish from frost injury. These first infections form more spores, which are spread by rain, wind and bees to blossoms and other young tissue. The fungus infects and invades the developing fruit. The fruit becomes malformed looking like a pumpkin, and turns salmon or grey by midsummer (Figure 57). By fall, these fruit drop to the ground where they turn into mummies ready to produce apothecia the next spring.

 Figure 56: Mummy berry on blueberry.

Figure 57: Mummy berry disease cycle. Taken from Small Crop IPM Diseases Ident Sheet No. 3. We wish to thank the New York State Agricluture Experiment Station for use of this figure.

Management

Cultural controls are extremely important in organic production and can be used to reduce inoculum levels in the spring. In very small plantings, mummies can be raked up and burned. In larger plantings, mummies can be buried by cultivating or disking between rows or by covering them with a new layer of mulch at least 2 inches in thickness. Combining cultivation and an application of nitrogen in the spring speeds destruction of the mummies. The cultivation should be done just as apothecia start to emerge in the spring, which usually coincides with budbreak on the blueberry bushes.

Organic fungicides (sulfur and copper) are not effective for control of mummy berry.

Botrytis Blight/Gray Mold (Botrytis cinerea)

As with other small fruits, Botrytis primarily affects ripening fruit, although under certain circumstances the fungus can cause stem blight as well. Infection occurs primarily during bloom on flowers. The fungus survives the winter on dead twigs and in soil organic matter. It is present every year, but only causes severe damage during cool, wet periods of several days duration. The most critical period for infection is during bloom. The disease is more severe when excessive nitrogen has been used, where air circulation is poor, or when frost has injured blossoms. Rotted berries typically have a gray cast due to mycelium and spore-bearing structures present, which gives the disease its name. Stem symptoms are difficult to distinguish from those caused by Phomopsis. For positive diagnosis, the fungus usually must be isolated from infected tissue in a diagnostic laboratory. Cultivars possessing tight fruit clusters ("Weymouth","Blueray" and "Rancocas" are particularly susceptible to this disease.

Management

Any cultural practice that promotes faster drying of foliage and fruit in the planting should be beneficial for gray mold control. The use of excessive nitrogen should be avoided. Fertilization should be based on results for soil and foliar analysis. Organic fungicides (sulfur and copper) are of little value for gray mold control. Several biocontrol products are available for control of gray mold on small fruit crops (Table 1). In general, their efficacy under moderate to severe disease pressure needs to be determined.

Anthracnose (Colletotrichum gloeosporioides)

This fungus damages primarily fruit, but also infects twigs and spurs. It causes a salmon-or rust-colored berry rot. Infected fruit often exhibit a soft, sunken area near the calyx-end of the fruit. Spores spread to "Good" fruit during and after harvest, causing significant postharvest losses. Spores are spread mainly by rainwater. The disease is especially prevalent during hot, muggy weather and frequently occurs postharvest.

The anthracnose fungus overwinters in dead or diseased twigs, fruit spurs, and cankers. Spores are released in the spring and are spread by rain and wind. Blossoms, mature fruit and succulent tissue are infected; spores spread from these infections. Blossom clusters turn brown or black. Infected fruit shows bright pink spore masses at the blossom end. Stem cankers are rare, but when present are about 1/8" in diameter, with raised purple margins. Young girdled stems die back, resulting in a brown withering of the leaves. Cultivars in which the ripe fruit hangs for a long time on the bush prior to picking are especially susceptible. These include: "Berkeley", "Coville","Bluecrop," , "Blueray", and "Jersey". No cultivars are entirely resistant when the weather conditions are favorable for the disease development (warm and wet).

Management

Organic fungicides are of little value for controlling anthracnose. Pruning out small twigs and frequent harvesting are beneficial to control. Removing and destroying infected fruit should be beneficial. Old canes and small twigs should be removed in order to increase air circulation around the fruit clusters.