• Topics: Plant Pathology | Strawberry Diseases | Plant Disease Management Guide. Vegetable Crops | Peres, Natalia A

2011 Florida Plant Disease Management Guide: Strawberry¹

Alternaria Rot

Alternaria rot, caused by Alternaria tenuissima, occurs infrequently and is usually not important in most strawberry growing regions.

This rot affects ripe fruit in the field as well as post harvest. Lesions are irregular in shape and slightly sunken. Older lesions are circular, firm, sunken, and dark green to black due to sporulation of the fungus (Figure 1).

Management

Cultural: Do not leave over-ripe fruit in the field.

Figure 1. 

Alternaria Rot.

[Click thumbnail to enlarge.]

Angular Leaf Spot

Angular Leaf Spot (ALS), caused by Xanthomonas fragariae, is an important disease for winter strawberry production worldwide. The disease was reported first in Minnesota in 1960 and since then it has been found in almost all cultivated strawberry areas in the U.S.

Symptoms

The first symptoms of ALS begin as small, water-soaked lesions on the undersurface of the leaves (Figure 2). When moisture is high on the leaves, these lesions ooze sticky droplets of bacteria. As the disease develops, the lesions enlarge to form reddish-brown spots that later become necrotic. A practical way to recognize the disease is to place the leaves against a source of background light where the spots are seen as translucent. The tissue with older lesions eventually dies and dries up giving leaves a ragged appearance. If the disease invades the vascular system of the plant, the disease will be difficult to control and affected plants may wilt and die.

Figure 2. 

Angular Leaf Spot (ALS).

[Click thumbnail to enlarge.]

Causal organism

X. fragariae is a slow-growing, gram-negative, motile bacterium that is highly specific to wild and cultivated strawberry.

Disease cycle and epidemiology

The primary source of inoculum in a new field is contaminated transplants. Secondary inoculum comes from bacteria that exude from lesions under high moisture conditions. Bacteria can survive on dry infested leaves and tissue buried in the soil for up to 1 year. The pathogen can be spread easily by harvesting operations when wet and cool conditions favor the production of bacterial exudate. The pathogen also can be dispersed by rain and overhead sprinkler irrigation. Little is known regarding the epidemiology of ALS; however, development of the disease is favored by cool days (20°C/68°F) and cold nights (2-4°C/ 36-39°F).

Management

Cultural: The best way to control ALS is to use pathogen-free transplants. Harvesting and moving equipment through infected fields should be avoided when plants are wet. Minimizing the use of overhead sprinklers during plant establishment and for freeze protection may also reduce the spread and severity of the disease.

Chemical: See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Anthracnose Fruit Rot

Anthracnose fruit rot, caused by Colletotrichum acutatum, is an important disease for strawberry production worldwide. Although fruit rot is the most important symptom caused by C. acutatum, the fungus can also attack other parts of the plant including the crown, leaves, petioles, and roots.

Symptoms

Symptoms of anthracnose fruit rot appear as dark, sunken lesions on infected fruit. On green fruit, anthracnose lesions are small (1/16 to 1/8-inch across) hard, sunken, dark brown or black.Lesions on ripening fruit are larger (1/8 to 1/2 inch) hard, sunken, and tan to dark brown (Figure 3). During wet weather, the lesions become covered by sticky, light orange ooze composed of millions of spores (conidia) in a mucilaginous matrix. When conditions are favorable for infection, multiple lesions nearly cover the fruit and lesions may appear on petioles. Strawberry flowers are highly susceptible and blighted flowers turn brown and remain attached to the plant, a symptom also produced by the fungus Botrytis cinerea.

Figure 3. 

Anthracnose Fruit Rot.

[Click thumbnail to enlarge.]

Causal organism

C. acutatum produces orange masses of conidia that are hyaline, straight and usually with pointed ends. Molecular analysis of C. acutatum revealed that the population on strawberry reproduces asexually and has limited diversity. Other species of Colletotrichum, such as C. fragarie and C.gloeosporioides, cause anthracnose diseases of strawberry but are less frequently involved in fruit rot.

Disease cycle and epidemiology

Infected transplants are a common source of inoculum for production fields. C. acutatum apparently spreads first on the foliage, often without causing visible symptoms. Some conidia are formed on green leaves and petioles, and more are produced as the tissue ages and dies. Conidia are moved from the foliage to flowers and fruit by splashing water and harvesting operations. There, they germinate and infect tissues. As anthracnose lesions develop, abundant spores are formed that may be moved to other plants and new fields on equipment and harvesters. Warm wet weather favors infection and disease spread.

Management

Cultural: Transplants should be obtained from pathogen-free nurseries. Moving personnel and equipment from diseased fields into healthy fields should be avoided without proper cleaning and disinfestation. Carmine and Sweet Charlie cultivars are considered relatively resistant to anthracnose fruit rot. Strawberry Festival is moderately susceptible, and Camarosa and Treasure are highly susceptible.

Chemical: See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Botrytis Fruit Rot or Gray Mold

Botrytis fruit rot, also known as gray mold, caused by Botrytis cinerea, is one of the most important diseases of strawberry worldwide. B. cinerea is a cosmopolitan fungus that infects a wide range of fruit, vegetable, and weed species.

Symptoms

Botrytis fruit rot occurs in the field and after harvest. Infection occurs in the flowers and recently set fruitlets, but the symptoms are observed commonly on green and ripening fruit. Lesions begin as small, light brown spots that quickly enlarge and become covered with white fungal mycelia. Under moist conditions, gray-to-brown spores cover the lesions and the entire fruit may become mummified (Figure 4). When diseased fruit are disturbed, large numbers of spores are often released and are visible as gray puffs.

Figure 4. 

Botrytis Fruit Rot.

[Click thumbnail to enlarge.]

Causal organism

The pathogen produces hyaline, septate hyphae. Single-celled, multinucleated, ellipsoid conidia are produced on conidiophores. Conidia are hyaline individually but appear gray in mass.

Disease cycle and epidemiology

B. cinerea is a common colonizer of strawberry foliage in the nursery, and is also present on dying vegetation around strawberry fields. After runner transplants are planted, spores produced on old dying leaves rapidly colonize new emerging leaves without causing visible symptoms. These spores (conidia) are dispersed by air, water, and harvesters to infect flowers during the main bloom period in January and February. Cool to mild temperatures and prolonged leaf wetness promote spore production, germination, and infection of stamens, petals, and other floral parts. Flower infections often progress slowly, with lesions becoming visible on green and ripening fruit 2 to 4 weeks after infection. Direct infection of fruit by spores is not considered important in the field or after harvest. However, the pathogen also spreads from diseased fruit to healthy fruit by direct contact. As the epidemic progresses, diseased fruit, mummified fruit, and decayed flowers and pedicles become important new sources of inoculum. Botrytis fruit rot is especially damaging in annual production systems with prolonged flowering and fruiting cycles. The disease is favored by cool and wet weather. In Florida, the second crop of fruit that ripen in February and March are more seriously affected than the first crop of fruit that ripen in December-January.

Management

Cultural: Removal of infected fruit and plant debris can be used to reduce inoculum, but is not practical for control of Botrytis fruit rot. The cultivars Camarosa, Carmine and Treasure are less susceptible than Strawberry Festival and Sweet Charlie.

Chemical: Fungicides should be applied at peak bloom.

See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Colletotrichum Crown Rot

Colletotrichum crown rot, caused by Colletotrichum gloeosporioides or C. fragariae, is a serious disease in subtropical production regions. Although crown rot is observed in fields during the winter production season, it is most severe in nurseries in the southeastern United States and is one of the primary reasons that production of transplants for the Florida production season has been moved to cooler regions.

Symptoms

Symptoms caused by C. gloeosporioides and C. fragariae are virtually indistinguishable in the field. Plants infected initially show signs of water stress and may collapse relatively rapidly (2-3 days) at high temperatures. At cool temperatures, it may take weeks before plants collapse. The internal crowns of infected plants show a reddish-brown and firm rot when cut (Figure 5). Typically there are no lesions on foliage or stolons and symptoms may be confused with those of Phytophthora crown rot.

Figure 5. 

Colletotrichum Crown Rot.

[Click thumbnail to enlarge.]

Causal organisms

Conidia of C. gloeosporioides are barrel shaped with both ends rounded, whereas conidia of C. fragariae are narrower at one end and are slightly pointed. Setae of C. fragariae differ from those of C. gloeosporioides in that they function as phialides and conidia can often be observed at the points.

Disease cycle and epidemiology

Propagation of plants in Canada and northern states for the Florida production season has greatly reduced the incidence of crown rot. However, during the warm months at the beginning and end of the production season crown rot incidences of up to 5% occur in Florida fields. Recent studies have shown that inoculum for crown rot infections in Florida may be coming from non-cultivated hosts. Colletotrichum sp. responsible for crown rot do not appear to survive between seasons in subtropical production systems on plant debris since plants are usually killed immediately after the production season ends in the spring and the fungus disappears from crowns during the hot summer months.

Management

Cultural: Transplants from northern nurseries should be used for controlling crown rot. Reducing water on foliage by using drip irrigation will also limit dispersal of the pathogen. Treasure cultivar is considered highly resistant to crown rot. Sweet Charlie, Carmine, and Camino Real have moderate levels of resistance, and Strawberry Festival and Camarosa are highly susceptible.

Chemical: See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Leaf Scorch

Leaf scorch, caused by Diplocarpon earlianum, is a common leaf disease of strawberries worldwide.

Symptoms

Symptoms on leaves are numerous, irregularly shaped, purplish blotches that are 1/16 to 3/16 inch in diameter. Clusters of the blotches turn brownish, but never white or gray as in the case of common leaf spot. Dark, glistening acervuli appear in the lesions on the upper surfaces of the leaves. In severe cases, the leaf margins curl upward and the leaves dry to a tan color, progressing from the margins to the midrib, giving the leaf a scorched appearance.

Causal organism

The fungus is limited to species and cultivars of Fragaria although physiological and pathogenic specialization among isolates has been reported.

Disease cycle and epidemiology

Leaf scorch is favored by long periods of leaf wetness (12 h or more), frequent rain, and moderate temperatures (60-78°F). The severity of the disease is usually low in annual production systems.

Management

Cultural: Prolonged use of overhead irrigation should be avoided.

Chemical: See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Leaf Spot

Leaf spot, caused by Mycosphaerella fragariae, is one of the most common diseases of strawberries worldwide.

Symptoms

Leaf lesions are initially small, purplish-red and less than 1/8 inch in diameter. The spots may enlarge to 1/4 inch depending on the cultivar. On some, the lesions remain very small and numerous and the leaflets appear "rusty." On others, the lesions increase to 1/4 inch in diameter or larger and develop white or gray centers with reddish-purple to dark purple borders. Lesions may also form on fruit, calyces, petioles, and stolons. Severe infection can result in death of leaflets and defoliation of plants.

Causal organism

The fungus is considered to be pathogenic only to species and cultivars of Fragariae, although several races have been defined according to their effects on different cultivars.

Disease cycle and epidemiology

Older lesions provide inoculum to infect plants during the season. Conidia are produced during the entire season if weather conditions are favorable (50-86°F) and are splash disseminated.

Management

Cultural: Resistant cultivars and disease-free transplants should be used.

Chemical: See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Charcoal Rot

Charcoal rot, caused by Macrophomina phaseolina, was first reported in Florida in 2005.

Symptoms

Infected plants wilt, are stunted, and eventually die. The disease affects the plant roots and crown, and it can be difficult to distinguish from other crown diseases such as Colletotrichum and Phytophthora crown rots. Isolation in-laboratory is necessary for proper identification.

Causal organism

Macrophomina phaseolina produces numerous dark oblong sclerotia on the isolation medium after 4 to 5 days incubation. Ostiolate pycnidia bearing relatively large, broadly ellipsoidal, hyaline conidia occasionally develop on host tissue after 8 to 10 days of incubation.

Management

Cultural: Planting should be avoided in fields with a history of Macrophomina diseases of other crops.

Phomopsis Leaf Blight and Phomopsis Soft Rot (Phomopsis obscurans )

Phomopsis leaf blight and Phomopsis soft rot, caused by Phomopsis obscurans, can occasionally cause serious problems on strawberry, especially on plants propagated in nurseries from the southeastern United States.

Symptoms

Lesions in the foliage are small initially and form circular, reddish-purple spots. Older spots can coalesce and form large V-shaped lesions with the widest part of the lesions at the leaf margin and the narrow base centered on a vein (Figure 6). Black specks of pycnidia often develop within the central areas of the older lesions. Initial symptoms on fruit are round, light pink, and water-soaked lesions (Figure 7). Frequently, two or more lesions may coalesce into large soft brown lesions with dark fruiting structures (pycnidia) on the surface. Over summer on plants propagated in Florida and the southeastern United States, the disease may also produce dark, sunken, and elongated lesions in the stolons and petioles while in the fruit production fields and similar in appearance to anthracnose.

Figure 6. 

Phomopsis Leaf Blight.

[Click thumbnail to enlarge.]

Figure 7. 

Phomopsis Soft Rot.

[Click thumbnail to enlarge.]

Disease cycle and epidemiology

Conidia of Phomopsis obscurans are spread by splashing water, harvesting operations, and equipment. The disease is favored by warm, wet conditions and can be the most severe during the summer on plants propagated in Florida and the southeastern United States. In fruit production fields in Florida, Phomopsis leaf blight will develop during the fall and early winter. The fruit rot phase of the disease typically develops in the fall and as the winter weather gets colder and drier in fields where leaf blight is present. Both the leaf blight and fruit rot caused by P. obscurans are rarely observed during the late season.

Management

Cultural: Transplants should be obtained from northern Canada or the western United States since leaf blight typically occurs on transplants propagated in the southeastern United States.

Chemical: See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Phytophthora Crown Rot

Phytophthora crown rot, caused by Phytophthora cactorum and P. citricola, can be a serious disease of annual production strawberry in Central Florida.

Symptoms

The disease is characterized by a sudden decline and wilt of plants. Reddish-brown coloration on the internal crown makes symptoms difficult to distinguish from those produced by Colletotrichum gloeosporioides or C. fragariae. Thus, isolation and characterization of the pathogen are important for proper identification.

Causal organism

In Florida, Phytophthora cactorum has historically been responsible for causing the disease, although P. citricola has been the primary cause of Phytophthora crown rot in recent years.

Disease cycle and epidemiology

Infected transplants are the primary source of inoculum for epidemics in Florida. The pathogen produces zoospores that infect strawberry plants under wet conditions. Phytophthora species produce oospores that may persist in infested soil and plant debris, although oospores have not been observed in Florida. Phytophthora cactorum also causes leather rot and the infected fruit may provide a source on inoculum. The disease is favored by warm temperatures and prolonged periods of wetness, conditions that are common during the plant establishment period (October) in Florida.

Management

Cultural: Use of disease-free transplants is the best way to control the disease.

Chemical: See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Phytoplasma Diseases

Several diseases of strawberry are caused by phytoplasmas. Some of the most common are aster yellows, green petal, bronze leaf wilt, and multiplier.

Symptoms

Phytoplasma diseases can be recognized by one or more characteristic symptoms, such as phyllody (Figure 8), stunting, and yellowing. Molecular techniques are necessary for detection and identification of phytoplasmas.

The disease is transmitted by grafting and by leafhoppers.

Figure 8. 

Phytoplasma-green petal.

[Click thumbnail to enlarge.]

Management

Cultural: Use of disease-free transplants.

Powdery Mildew

Powdery mildew, caused by Sphaerotheca macularis, occurs in most areas of the world where strawberries are grown. The disease is particularly severe on strawberries grown in greenhouses or plastic tunnels. In open fields in Central Florida, the disease is typically most severe in November and December and it may reappear in late February and March.

Symptoms

Early symptoms appear as small, white patches of fungus growing on the lower leaf surface. These patches can expand and coalesce to cover the entire leaf surface under favorable conditions. On some cultivars, irregularly shaped yellow or reddish brown spots will develop on colonized areas on the lower surface of the leaf and eventually appear on the upper surfaces. The edges of heavily infected leaflets curl upward (Figure 9). The fungus can also infect fruit and may reduce fruit quality and marketable yields.

Figure 9. 

Powdery Mildew.

[Click thumbnail to enlarge.]

Causal organism

Sphaerotheca macularis is an obligate parasite that only infects living tissue of wild or cultivated strawberry. The fungus produces chains of dry, hyaline conidia and, occasionally, cleistothecia containing ascospores on infected leaves.

Disease cycle and epidemiology

The fungus readily infects living, green leaves in the nursery. Thus, infected transplants are normally the primary source of inoculum for fruiting fields in Florida. When conditions are favorable, conidia produced on infected plants are wind-dispersed. Development and spread of powdery mildew is favored by moderate to high humidity and temperatures between 60° and 80° F. Rain, dew and overhead irrigation inhibit the fungus. Because dry conditions and high humidity are common in greenhouses and plastic tunnels, powdery mildew is typically more severe in protected culture.

Management

Cultural: Disease-free transplants should be used for controlling powdery mildew, although fields can become infected by conidia blown in from neighboring fields. Cultivars differ widely in their resistance to powdery mildew. Unfortunately, some of the most popular cultivars in Florida, Strawberry Festival, Camarosa, and Winter Dawn, are quite susceptible to the disease.

Chemical: See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Rhizopus Rot or Leak

Rhizopus rot or leak, caused by Rhizopus stolonifer, affects fruit and is most serious after harvest or in storage but can also occur in the field.

Symptoms

Infected fruits collapse and rapidly leak juice (Figure 10). A loose, cottony growth of mycelium (whiskers) grows over the surface of the fruit. Fruiting bodies (sporangia) appear as black dots scattered throughout the mycelium.

Figure 10. 

Rhizopus rot or leak.

[Click thumbnail to enlarge.]

Causal organism

Rhizopus spp. cause rots of various fruit and vegetable crops and physiological specialization has not been established.

Disease cycle and epidemiology

The fungus survives on crop debris and in the soil between seasons. Rhizopus can only infect through wounds. Under favorable conditions of high temperature and moisture, sporulation is rapid and abundant. Spores are disseminated by air and by insects.

Management

Cultural: Fruit should be handled carefully to avoid bruising. When possible, fruit should be picked during the morning, protected from the sun, and cooled rapidly before shipping.

Root Necrosis

Root necrosis, caused by Colletotrichum acutatum, has been observed in Florida since 2000. This fungus is widely known as a fruit rot pathogen, but also infects other strawberry tissues, including the roots.

Symptoms

Transplants with infected root systems often grow poorly or fail to become established after overhead irrigation is withdrawn. Few functional roots are found on infected plants even 1 to 2 weeks after transplant. Old structural roots are brown or black with few feeder roots, whereas new roots develop brown lesions, die back from the tip, or fail to emerge from the crown. In severe cases, C. acutatum enters the crown, causing a basal crown rot and eventually killing the plant. Plants in affected fields are stunted or irregular in size, flower late, and produce a poor early crop (Figure 11). Infected plants may recover during the cool winter months and produce normally in February and March if an outbreak of anthracnose fruit rot does not follow.

Figure 11. 

Root Necrosis.

[Click thumbnail to enlarge.]

Causal organism

See anthracnose fruit rot.

Disease cycle and epidemiology

C. acutatum frequently colonizes leaves and petioles of runner plants in the nursery. Obvious symptoms may not be visible in the nursery environment, but if inoculum is allowed to build up and the weather is favorable, lesions may develop on the petioles. Little is known about how or when the pathogen spreads from colonized tissue above the ground to the root system below. However, C. acutatum grows freely in diseased tissues and has been isolated from the soil around diseased plants. Healthy plants are presumably contaminated by this inoculum during normal digging, trimming, and packing operations in the nursery. Cultivars that are highly susceptible to anthracnose fruit rot, e.g., Camarosa and Treasure, are susceptible to root necrosis disease as well. Early in the season, plant-to-plant disease spread is not thought to occur below ground as the root systems are relatively isolated. However, above-ground spread does occur and may be facilitated by overhead irrigation during establishment.

Management

Cultural: Disease-free transplants should be used.

Chemical: A pre-plant fungicide dip may suppress disease development when the disease is confirmed or when susceptible cultivars are being grown. See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Stem-End Rot and Leaf Blotch

Stem-end rot and leaf blotch, caused by Gnomonia comari, occur sporadically and may be found in association with Phomopsis obscurans.

Symptoms

Fruits can be affected at all stages. Characteristic symptoms on small fruits are irregular, brown areas on the surface and cessation of fruit development. On ripe fruits, the disease is characterized by a soft rot that is often invaded by secondary organisms. Leaf blotch lesions on young leaves are purple to brown and occasionally enlarge to form light-brown, necrotic spots on older leaves (Figure 12). The outer leaves may die resembling the symptoms of Verticillium wilt. Peduncles, petioles, and calyxes may also be affected.

Figure 12. 

Leaf Blotch.

[Click thumbnail to enlarge.]

Causal organism

G. comari infects numerous rosaceous species worldwide. Perithecia are globose and beaked, and ascospores are hyaline, straight or slightly curved, and septate.

Disease cycle and epidemiology

Fruit is infected by conidia and ascospores produced on other parts of the plant or on other hosts. The disease is spread by frequent rains or overhead irrigation. The fungus generally penetrates through stomata or wounds when humidity is high.

Management

Cultural: Some strawberry cultivars may be resistant but there is no information regarding the susceptibility of cultivars grown in Florida.

Chemical: See PPP-6 https://edis.ifas.ufl.edu/pdffiles/PG/PG10000.pdf.

Verticillium Wilt

Verticillium wilt, caused by Verticillium albo-atrum and V. dahliae, is an occasional problem in winter annual strawberry production. These pathogens have wide host ranges, and isolates that are pathogenic on potato and tomato are also pathogenic on strawberry.

Symptoms

Initial symptoms are wilting of the plant and browning of the margins and interveins of older leaves. Younger leaves may remain green, but develop slowly and the plant becomes stunted, declines, and ultimately dies (Figure 13). The crown of diseased plants develops necrotic streaking that appears similar to other crown rots. It is necessary to isolate the fungus to confirm its identity.

Figure 13. 

Verticillium Wilt.

[Click thumbnail to enlarge.]

Disease cycle and epidemiology

Infected transplants appear to be the primary source of inoculum for outbreaks of Verticillium crown rot in Florida. Disease spread from plant to plant seems unlikely, but infection may occur through root contact. The pathogen is favored by sudden weather changes such as increases in temperatures or lack of moisture.

Management

Cultural: The best method to control Verticillium wilt is to use disease-free transplants. Strawberry nurseries should avoid areas that were previously used for potato or tomato production. This fungus is likely to be more severe at high pHs, so care should be taken to not over lime the soil.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, Dean.

• Copyright 2012 |
• Site Feedback |
• About This Site