Mummy Berry Disease in Blueberries

Mummy berry is one of the most destructive diseases affecting blueberries in North America. It is caused by the fungus Monilinia vaccinii-corymbosi, which infects both wild and cultivated blueberry plants. The disease is especially common in regions with cool, wet spring weather, where conditions favor fungal growth and spore spread. Growers can suffer major crop losses because the disease damages young shoots, flowers, and fruit, eventually turning healthy berries into hard, shriveled “mummies.”

The disease cycle begins in early spring when overwintered mummy berries lying on the ground produce small fungal structures called apothecia. These cup-shaped structures release spores into the air during wet conditions. Wind carries the spores to newly developing blueberry shoots and leaves, causing a primary infection known as “shoot strike.” Infected shoots suddenly wilt and bend over in a distinctive shape called a “shepherd’s crook.” Leaves may show brown discoloration along the veins before becoming dry and necrotic. As the infection advances, gray fungal spores may appear on leaf stalks and infected tissue.

A second phase of infection occurs during flowering. Spores produced on infected shoots are spread by rain, wind, and pollinating insects such as bees. These spores infect blueberry blossoms, leading to “flower strikes.” Northern highbush blueberry varieties are particularly vulnerable during bloom. Once flowers become infected, the developing berries gradually change color from cream to pink, then shrink and harden into tan or whitish mummified fruit. Inside each mummy is a corky fungal mass that allows the pathogen to survive winter. The mummies fall to the ground, where they remain dormant until the next spring, restarting the disease cycle.

Managing mummy berry requires a combination of cultural and chemical controls. Growers often rake, cultivate, or apply mulch beneath bushes to bury fallen mummies and reduce the number of spores released the following season. Good air circulation and proper pruning can also lower humidity within blueberry plantings. Fungicides remain an important management tool, especially during early shoot growth and flowering. Modern disease management programs recommend rotating fungicides with different active ingredients to reduce the risk of fungicide resistance and maintain long-term effectiveness.
Mummy Berry Disease in Blueberries

Botrytis Blight: A Fungal Threat to Blueberry Crops

Botrytis blight, also known as gray mold, is a common fungal disease that affects blueberry plants worldwide. It is caused by Botrytis cinerea, a fungus notorious for infecting a wide range of crops, including strawberries, grapes, and tomatoes. The disease is most active in cool, wet, and humid conditions—typically during periods of prolonged rainfall or poor air circulation in dense canopies. When conditions are favorable, Botrytis can cause severe damage to blossoms, stems, and fruit, leading to significant economic losses for blueberry growers.

The disease usually begins during the flowering stage. As blueberry blossoms open, their corollas (petal tubes) age and become susceptible to infection. Ideally, the corolla should drop naturally after pollination, but if weather delays this process or if frost damages new growth, wounds may form that invite fungal invasion. Once infected, blossoms turn brown, shrivel, and often remain attached to the plant. Under humid conditions, they become covered with a characteristic gray, fuzzy mold.

Botrytis cinerea is an opportunistic pathogen that thrives on weakened or dying plant tissues. It survives in the environment as a saprophyte, feeding on dead leaves, pruned canes, or other plant debris. The fungus produces abundant spores that can easily spread through wind, rain, or mechanical contact during harvesting. Because spores are often present throughout the growing season, complete eradication is nearly impossible.

Symptoms of Botrytis blight vary depending on the infected plant part. Leaves may develop yellow spots that later turn brown and gray, while infected twigs can die back from flower blight. On ripening or stored berries, the disease manifests as soft, gray, moldy rot that causes fruit to shrivel and decay. Although postharvest fruit rot is common in regions where berries are stored for long periods, it is less of a concern in areas like Florida, where fruit moves rapidly from harvest to market.

Effective management of Botrytis blight involves maintaining good air circulation, removing dead plant material, and avoiding overhead irrigation. While sanitation alone cannot eliminate the disease, it remains an essential component of integrated fungal control strategies to protect blueberry yields and quality.
Botrytis Blight: A Fungal Threat to Blueberry Crops

Managing Pests and Diseases in Blueberry Cultivation

Blueberry plants, prized for their delicious, antioxidant-rich fruit, face challenges from a range of pests and diseases that threaten yield and quality. Among the most damaging pests is the blueberry maggot (Rhagoletis mendax). The maggot’s larvae burrow into the berries, rendering them soft, discolored, and unsuitable for sale. This pest is especially prevalent in regions with humid summers. Another major pest is the spotted wing drosophila (Drosophila suzukii), an invasive species notorious for its ability to infest ripening fruit. Unlike most fruit flies, it targets unripe berries, leading to early fruit decay and economic losses.

Diseases pose an equally significant threat. Mummy berry disease, caused by the fungus Monilinia vaccinii-corymbosi, is a persistent issue. It affects blooms and developing fruit, leading to shriveled, grayish berries that drop prematurely. This disease can spread rapidly under cool, wet spring conditions. Another common fungal threat is anthracnose fruit rot, caused by Colletotrichum species. This disease results in soft, sunken lesions on ripe fruit and can devastate crops during warm, wet periods.

Soil-borne diseases further complicate blueberry cultivation. Phytophthora root rot, caused by Phytophthora cinnamomi, thrives in poorly drained soils. Infected plants exhibit symptoms like stunted growth, leaf yellowing, and eventual death, particularly in young bushes. This pathogen can persist in the soil for years, making it a long-term threat.

To combat these issues, integrated pest management (IPM) is vital. Cultural controls, such as planting in well-drained soil and pruning to enhance air circulation, reduce disease pressure. Regular sanitation, including the removal of infected plant material, helps curb fungal spread. Biological controls, like introducing natural predators or parasitoids, are gaining traction for pests like the spotted wing drosophila. Chemical interventions, including fungicides and insecticides, remain critical but must be applied judiciously to prevent resistance.

Advancements in monitoring technology, such as pheromone traps and disease prediction models, enable growers to detect problems early, minimizing damage. By adopting a holistic approach, growers can protect their crops and ensure sustainable production in an increasingly challenging environment.
Managing Pests and Diseases in Blueberry Cultivation

Blueberry maggot

Alternaria fruit rot on blueberries

Alternaria species are an abundant, ubiquitous component in the environment and are a natural part of the fungal micro-flora. At least 20% of all agricultural spoilage is caused by Alternaria species. Fruit rot caused by Alternaria species is one of the most important factors affecting the post-harvest quality and shelf life of blueberries.

Alternaria can infect the fruit beginning at the end of bloom and throughout the fruit development stage, up until harvest. Infections remain latent until the fruit ripens. In the field, sporulation by Alternaria spp. will often appear on ripe fruit, as sunken areas near the calyx covered with a dark green, velvety growth. Infected fruits exhibit a shriveling or caving-in of the side of the berry and become watery in storage.

The growth of Alternaria species in blueberries is especially problematic since it could result in accumulation of mycotoxins. The major Alternaria mycotoxins belong to three structural classes: the tetramic acid derivative, tenuazonic acid (TA); the dibenzopyrone derivatives, alternariol (AOH), alternariol methylether (AME) and altenuene; and the perylene derivatives, the altertoxins.

Alternaria fruit rot is a primary issue when fruit is not harvested in a timely fashion and overripens on the bush.
Alternaria fruit rot on blueberries

Phytophthora root rot in blueberry plant

The most common disease of blueberry, Phytophthora root rot, can cause severe dieback and often results in plant death.

Phytophthora root rot, caused primarily by the oomycete Phytophthora cinnamomi, is a soilborne disease affecting blueberry.

Phytophthora disease is a plant pathogen that spreads to trees and plants by contaminating their roots. This disease is easily transmitted from plant to plant; it spreads by water irrigation, gardening tools, and human activity.

This fungus-like organism has an extremely wide host range and infects a large number of tree and shrub species including other ericaceous plants (such as rhododendron and madrone) and many conifers. The leaves of blueberry plants appear drought stressed. Trees or plants often wilt and die rapidly with the first warm weather of the season. Leaves may turn dull green, yellow, or in some cases red or purplish.

Wet, poorly-drained soil is one of the principal contributors to the growth and spread of this disease. Blueberry roots are shallow and like a lot of moisture, but when blueberry roots are too wet for too long, this disease organism can move in. Wilting and apparent nutrient deficiency symptoms on infected plants indicate the roots are not working correctly.

The pathogen kills plants by growing from the roots up through the root crown and into the lower trunk, where it kills the inner bark and causes a browning of the outer layer of sapwood.
Phytophthora root rot in blueberry plant

Armillaria root rot

Armillaria root rot, also known as shoestring root rot, is caused by a number of Armillaria species, most notably Armillaria mellea and Armillaria gallica. It is also known as the honey toadstool or bootlace fungus, is a widespread and often destructive disease that can affect an extremely wide range of plants.

The disease is a rare disease of blueberries in the United States, but it can cause serious damage where it occurs.

They are most commonly found in forests and natural areas where they infect a variety of trees and shrubs. Therefore, the disease is most common in newly established blueberry fields that are planted on land recently cleared of native vegetation.

Armillaria survives as mycelium and rhizomorphs on old roots and stumps. The fungus spreads between bushes by root-to-root contact and can also survive on wood chip mulches.

What are the symptoms? Infected plants are low in vigor and may appear to be suffering from a nutrient deficiency.

Leaves are small and chlorotic, and branches wilt suddenly. The entire plant may be affected or only individual canes may exhibit symptoms of the disease. Plants decline slowly over several years or die within a short time. Occasionally, after an infected tree has died, honey-coloured clusters of toadstools grow from the base of the tree.
Armillaria root rot

Crown gall of blueberry plants

Crown gall is an occasional problem in propagation beds and new plantings, but is seldom seen in mature plantings.

Agrobacterium species were first classified by means of a pathogenicity based-taxonomy in A. tumefaciens, those strains that induce crown-gall. This bacterium has the widest host range of any plant pathogen. It is capable of causing tumors, or “galls,” on virtually all plant species, except the monocots (grasses).

Galls are most common at the bases of canes or on major roots, but they occasionally form on branches higher in the bush. It can cause severe problems on blueberry. These galls may be scattered in discrete masses on infected roots and branches or they may occur in long linear strips of contiguous bumps. Galls can also completely encircle the branch.

In blueberry, strains of Agrobacterium biovar 1 (i.e., Agrobacterium tumefaciens species complex), R. rhizogenes, and A. rubi were reported as causal agents of the disease.
Crown gall of blueberry plants

Bacterial canker of blueberry plant

This disease is caused by the bacterium Pseudomonas syringae pv. Syringae. It is a minor stem disease that occurs mainly in western North America.

Pseudomonas syringae is a naturally present environmental bacterium that can survive on the surface of the stem; it only infects the plant if it enters the stem through wounds, such as from frost damage, or through natural openings, such as leaf scars.

The bacterium multiplies in buds and on expanding aerial plant tissues as an epiphyte during the late fall and into the spring months.

Cankers can extend the entire length of the stem or girdle stems. Cankers can kill buds, and if a canker girdles the stem, the stem portion above the canker dies. Leaves turn orange (or black) and wilt after buds have leafed out.

Bacterial canker can be particularly severe on young plants in new plantings because a high proportion of the wood is succulent and susceptible to disease.

The bacteria survive on the buds and bark and enter the plant through wounds caused by frost or pruning. Only 1-yearold stems are attacked. The bacteria can be spread by wind, rain, insects, propagation wood, and pruning tools.

Disease severity and symptom expression is favored by factors including poor nutrition, plant parasitic nematodes, sandy soils, and by climatic factors such as late spring frosts and cool, wet growing conditions.
Bacterial canker of blueberry plant