Strawberry Diseases and Their Control
Fruit Disease Information Note No. 5
Charles W. Averre, Extension Plant Pathologist
Ronald K. Jones, Extension Plant Pathologist
Robert D. Milholland, Research Plant Pathologist

[Cultural Practices] [Leaf Diseases] [Fruit Diseases]
[Root Diseases]
[Crown Diseases]


Diseases are an important limiting factor in strawberry production in North Carolina. Control of these diseases involves a total cultural and disease prevention program. This program includes cultivar selection, use of certified planting stock, replacement of plants every 2 to 3 years, soil fumigation prior to planting, thinning plant stands after each harvest season plus disease, insect and weed control. Fungicide sprays are usually necessary prior to and during harvest to control fruit rot diseases. For assistance in identifying strawberry diseases see Diagnosis of Strawberry Diseases AG-386.

Cultural Practices

Following proper cultural practices suggested for your area of the state will provide conditions that promote vigorous plant growth. Crop rotation, thinning plant stands after the harvest season and frequent renewal of plantings are important cultural practices in a strawberry disease control program. Strawberries perform best on well-drained soils. Black plastic culture of California cultivars in eastern North Carolina appears to promote development of several diseases.

Cultivars

Grow cultivars known to be adapted to your part of the state. Many of these cultivars have resistance to some of the more common diseases. If a particular disease, such as red stele, has been a problem on your farm, select an adapted cultivar with resistance to that disease (Table 1). Diseases may be difficult to impossible to control on highly susceptible cultivars.

Certified Plants

The strawberry certification program offers some assurance to North Carolina fruit producers that the plants purchased from certified growers are true to variety and apparently free from injurious insects and serious diseases. No other single measure has contributed more to the control of strawberry diseases in North Carolina. Growers should ask for a certification tag on each cultivar of plants.

Table 1. Disease Reactions of Selected Cultivars.

Cultivar (origin)
Leaf spot
Leaf blight
Red stele
Anthracnose
Powdery Mildew
Albritton (NC)
R
R
S
S
R
All Star (MD)
S
S
R
VS
R
Apollo (NC)
R
R
S
R-I
R
Atlas (NC)
R
R
S
VS
R
Chandler (CA)
S
S
S
VS
R
Darrow (MD)
I
S
R
VS
R-I
Douglas (CA)
S
S
S
VS
R
Earlibelle (NC)
VR
VR
S
R-I
R
Earliglow (MD)
R
S
R
S
R
Marlate (MD)
R
R
R
U
R
Midway (MD)
S
S
R
U
R
Pajaro (CA)
S
S
S
VS
R
Prelude (NC)
R
R
R
S
R
Redchief (MD)
S
VS
R
VS
R
Rosanne (NC)
R
R
S
R
R
Scott (MD)
S
VS
R
VS
R
Sentinel (NC)
R
R
S
S
R
Sumner (NC)
R
R
S
S
R
Sunrise (MD)
VS
S
S
S
R
Surecrop (MD)
R
S
R
VS
R
Tenn Beauty (TN)
R
R
VS
VS
R
Titan (NC)
VR
VR
S
R
VS

VS=Very Susceptible; S=Susceptible; I=Intermediate; R=Resistant; VR=Very Resistant; U=Unknown
*Red Stele race Pf-2 occurring in NC soils.

Soil Fumigation

Strawberries in North Carolina should be grown in soil fumigated with a methyl bromide-chloropicrin mixture or SMDC (Vapam). Effective fumigation and the use of certified plants will control or reduce the damage from viruses, nematodes and red stele. Fumigation will also greatly reduce the weed population. At the time of fumigation, soil temperature 6 inches deep should not be less than 50 degrees Fahrenheit. At the time of fumigation, soil should have already been well prepared for planting and soil moisture should be adequate for seed germination for best fumigation results. The plastic cover should remain in place for at least 48 hours and plants can be set one week after the tarp is removed unless cold rainy weather prevails.

Leaf Diseases

Leaf diseases are not a serious problem on cultivars released by North Carolina State University. However, cultivars developed in California and those with resistance to red stele can be seriously affected by leafspot and leaf blight, respectively.

Scorch (Diplocarpon earliana) is the most common leaf disease in North Carolina, appearing as small dark-purple spots up to one-fourth of an inch in diameter on upper leaf surfaces. If the spots become numerous, the entire leaf dries up and dies. Similar spots may appear on leaf petioles and runners.

Powdery mildew (Sphaerotheca macularis) causes infected leaflets to curl upwards along the margins. The lower leaf surface may turn reddish on heavily infected leaflets. The white fluffy fungal growth is not as obvious on strawberry leaves as on many other plants infected by powdery mildews. The leaves of Titan are more susceptible to powdery mildew than other North Carolina recommended cultivars. The disease is often more damaging on plants growing in less than full sun. Powdery mildew can cause economic loss if it occurs on the fruit. Fruit infection occurs during bloom and shows up at harvest as a tan to rusty pink berry surface that often cracks as the fruit expands. Benomyl (Benlate 50W) should be used during bloom alone or in combination with captan for fruit rot control in plantings with Titan and to prevent powdery mildew damage to fruit.

Leaf blight (Dendrophoma obscurans) occurs on older strawberry leaves, and is more severe on red stele resistant cultivars. Spots are large, 1/2-1 inch in diameter, circular to oval in shape. Young spots are reddish-purple, enlarge with age and develop a brown center bordered by a purple zone. Small black fungal fruiting structures may be observed in the center of the spot. Lesions may also develop on runners of susceptible cultivars. This disease has been common for several years on red stele resistant cultivars.

Leafspot (Mycosphaerella fragariae) symptoms begin as round purple spots 1/8 to 1/4 inch in diameter on upper leaf surfaces. Later, the center of the spot becomes tan or gray, then almost white with a purple border. The disease can also occur on immature petioles, fruit stalks, runners and caps of susceptible cultivars. Several California cultivars are very susceptible, particularly when grown on black plastic.

Leaf blotch (Gnomonia fructicola) is characterized by purplish to brown blotches and in later stages by large necrotic spots. The spots often occur on the end of a leaflet and are wedge shaped. This fungus can also attack the fruit stalk, cap and fruit.

Fruit Diseases

Gray mold, the major fruit rot disease of strawberries, is caused by the fungus Botrytis cinerea. At times it causes 50 percent or more reduction in yield. It is most damaging to strawberries during periods of prolonged wet weather during bloom and the fruiting season. The disease often starts early in the season as a blossom blight. Later, losses from Botrytis can result from blighting of the buds and blooms and rotting of the green or ripe berries. The fungus progresses downward, killing berry, stems and leaves. In damp weather, the affected plant parts are covered with a fuzzy gray mass of spores of the fungus. The spores are able to germinate in water within a few hours and enter directly into the fruit or flower. The disease is very difficult to control in wet seasons particularly where plants are matted together, are excessively vigorous, and where there is an accumulation of over ripe fruit, dead leaves and stems. Good air circulation within the plant canopy should be provided to promote rapid drying of plants. To reduce loss from gray mold, fungicidal sprays should be applied just after new growth starts and repeated at 7-10 day intervals. During periods of frequent rains, it may be necessary to spray at 5-7 day intervals. Use captan 50% WP at 4 pounds per acre (4 tablespoons per gallon), benomyl 50% WP (Benlate) at 1 pound per acre, captan 2 pounds + benomyl 1 pound per acre or vinclozolin (Ronilan 50W) at 1 1/2 - 2 pounds per acre. Benomyl and vinclozolin can be used up to and during harvest (0 days between application and harvest). There is a four day re-entry restriction on captan, however. Workers must wear protective clothing while working in captan treated plantings for four days after each captan application. Growers should be encouraged to change captan to benomyl or vinclozolin one week before and during harvest.

Anthracnose fruit rot (Colletotrichum acutatum) can be a very destructive disease on California cultivars grown on black plastic. It has been reported to cause 60-75% fruit loss. The disease is most destructive during warm, wet weather. Anthracnose fruit rot appears as soft to firm brown to black spots on green fruit and dark purple spots on ripe fruit. On ripe fruit the spots enlarge rapidly until the entire fruit rots. The surface of lesion can become covered with pink to orange masses of spores. These spores are dispersed to other fruit in splashing water. During warm wet periods, on a highly susceptible cultivar such as Pajaro or Chandler, anthracnose can be extremely difficult to control. Captan may help reduce losses. (See gray mold for restrictions on captan).

Leather rot (Phytophthora cactorum) occurs occasionally on either green or ripe fruit in North Carolina. The rotted area is light brown in the center and shades into purple at the edge. In the late stages of decay, the fruit becomes tough and leathery. Captan is the most effective fungicide available at present.

Leak (Rhizopus nigricans) has been a very common and destructive post-harvest fruit rot of commercially picked and shipped berries, but is of much less importance now with good refrigeration and of little importance in pick-your-own or home plantings. The symptoms of leak are so characteristic that they are not easily confused with those of other fruits rots. The color of the infected ripe berry remains unchanged at first. Later, it changes to light brown. The berry becomes soft and watery and collapses flat with the juice running out, hence the common name leak. The rotted fruit and particularly packaged fruit soon becomes covered with white fluffy cottony fungus growth with black spore producing structures. The fungus enters the ripe fruit only through wounds.

Root Diseases

Red stele (Phytophthora fragariae), a very serious fungus disease of strawberries, attacks plants during the cool part of the year, but above-ground symptoms are most apparent from March to July. The fungus persists for many years in the soil, and it occurs most frequently in poorly drained areas. The causal fungus spreads from one area to another in the roots of infected plants and within an area in surface water or in soil carried on farm implements. Red stele affected plants become stunted and wilt in dry weather. Older leaves turn yellow or red particularly along the margin. The symptom that helps to identify red stele is the brick red discoloration in the center (stele) of live white roots. The red color may extend the length of the root, or it may show up for only a short distance above the dead root tip. This symptom is obvious only during winter and spring. The discoloration does not extend into the crown of the plant. Infected plants usually die by June or July. To reduce losses, strawberries should not be planted in fields where red stele has occurred. Use only certified plants and select well-drained sites for strawberries. Fumigate planting sites with methyl bromide-chloropicrin mixtures or SMDC (Vapam) before planting. If strawberries must be reset in fields where red stele has been a problem, fumigate with methyl bromide plus use a resistant cultivar that is adapted to your area (Table 1).

Verticillium wilt (Verticillium albo-atrum) of strawberry occurs infrequently in North Carolina. The symptoms are similar to those for red stele except Verticillium does not cause red discoloration in the roots. Control is the same as for red stele. Most of the red stele resistant cultivars are also resistant to Verticillium.

Black root rot is a name for a general condition of older plantings for which several fungi and nematodes are associated. Normal strawberry roots are white, but naturally turn dark on the surface with age. The root system of a plant affected by black root rot is smaller with black lesions or with the roots completely black. Such plants become stunted and produce few berries and runners. Control by resetting with certified plants, avoid poorly drained sites, rotate planting sites and fumigate.

Nematodes, including Northern root knot (Meloidogyne hapla), lesion (Pratylenchus sp.) and sting (Belonolaimus sp.) nematode damage strawberries in North Carolina. The common or southern root knot nematode (M. incognita) does not damage strawberries. Affected plants are stunted, older leaves die and few runners are produced. Symptoms often appear during the summer and usually occur in spots or areas within a field. On affected plants, roots may be short and stubby, with root tips swollen. The root tip stops growing and several branch roots develop just behind the root tip. Roots die completely in later stages. Damage is often more severe on sandy soil than on clay soil. Control by avoiding infested sites or by fumigating with methyl bromide-chloropicrin mixture, Vorlex, or SDMC (Vapam) before planting and by using certified plants.

Crown Diseases

Anthracnose (Colletotrichum acutatum, C. gloeosporioides and Glomerella cingulata) crown or runner rot is the most serious fungus disease in North Carolina on California cultivars grown on black plastic. It causes less damage on cultivars grown on the matted row system. Anthracnose attacks the mature crown, fruit and runner plants. Symptoms on infected runners are elongated black lesions often with a gray center. Eventually, the entire runner and runner plant dies and turns black. The fungus may enter the crown and causes reddish-brown discolored areas in the center of the crown. Infected plants wilt during mid-day and soon die. The fungus is carried over from year to year in crowns that became infected in late summer. Disease development is favored by temperatures of 80 F and higher. The fungus produces masses of spores on diseased plant tissues and these spores are spread to nearby plants in splashing water. The disease often begins in wet spots in a field. During periods of hot rainy weather or frequent irrigation, the disease builds up rapidly. With cooler weather in late summer and fall, the fungus becomes less active. Anthracnose can cause severe fruit rot on highly susceptible cultivars on black plastic. The fungus is carried over in infected plants and does not over winter in the soil. Therefore, healthy plants for transplanting are essential. Plant stands should be thinned immediately after the picking season. Avoid excessive irrigation and fertilization during the summer months. Most cultivars are susceptible to this disease; however, Apollo and Titan appear to be somewhat tolerant.

Leaflet blight and crown rot (Hanesia lythria) has, in some wet summer seasons, caused considerable damage to plants. It also has been reported to cause a tan to brown rot of the berries. The typical early stage of the disease is a wilting and drooping of the three leaflets and eventual death of the entire leaf at the point of leaflet attachment to the petiole. Abundant spore production by the fungus occurs at that point. The fungus progresses down the petiole into the crown. Many weed hosts have been reported for this fungus. Some strawberry cultivars such as Albritton, Earlibelle, Titan and Atlas are much more resistant than Surecrop, Guardian, Floria 90 and others.

Table 2. Major strawberry diseases on black plastic: causes, symptoms, prevalence and control in North Carolina.

Disease
Plant parts affected
Symptoms
Occurence
Importance*
Control and Comments
Gray mold (Botrytis cinerea) fruit, blooms fruit rot
general
1
fungicide, cultural
Anthracnose (Colletotrichum spp.) runner, crown death of plants
common
1
certified plants, cultural
Anthracnose (Colletotrichum acutatum) fruit fruit rot
common
1
fungicides
Leafspot (Mycosphaerella fragariae) leaves leafspot
general
2
resistant cultivar
Northern root-knot nematode (Meloidogyne hapla) roots stunting
occasional
3
fumigate, certified plants, rotation
Leaf scorch (Diplocarpon earliana) leaves leafspot
general
3
resistant cultivar
Powdery mildew (Spaerotheca sp.) leaves, fruit leaf roll
common on Titan
3
full sun, fungicides, resistance
Petiole Rot (Botrytis cinerea) Petiole base dead leaves
late winter
3
 
Leaf blight (Phomopsis obscurans) leaves, runners leafspot
general
3
resistant cultivars
Red stele (Phytophthora fragariae) roots, crown root rot, stunting
rare
4
resistance, certified plants, fumigate, rotation
Bud rot (Rhizoctonia sp.) crown crown rot
occasional
4
cultural practices, severe if plants set too deep
Black root rot (Several fungi) roots stunting
rare
5
cultural, fumigation, rotation
Lesion nematode (Pratylenchus sp.) roots stunting
rare
5
soil fumigation, certified plants, rotation
Crown rot (Sclerotium rolfsii) crown plant death
rare
5
cultural practices, rotation
Dwarf (foliar nematode, Aphelenchoides sp.) bud, leaves crimping of bud
rare
5
soil fumigation, certified plants
Yellow, crinkle, mottle (virus) foliage stunting
rare
5
certified plants
Sting nematode (Belonolaimus sp.) roots stunting
occasional
5
soil fumigation, certified plants, rotation
Leather rot (Phytophthora cactorum) fruit fruit rot
sporadic
5
fumigation, rotation
June yellows (genetic) foliage yellows
rare
5
resistant cultivar
Hard rot (Rhizoctonia solani) fruit fruit rot
rare
5
resistant cultivar
Leak (Rhizopus sp.) fruit fruit
rare
5
resistant cultivar
Leaf blotch (Gnomonia sp.) leaves, fruit leafspot, fruit rot
occasional
5
resistant cultivar

*This is a general rating and any one of these diseases can be very damaging on an individual planting - (1 - most important and 5 - least important).

Table 2. Major strawberry diseases on matted row: causes, symptoms, prevalence and control in North Carolina.

Disease
Plant parts affected
Symptoms
Occurence
Importance*
Control and Comments
Gray mold (Botrytis cinerea) fruit, blooms fruit rot general
1
fungicide, cultural
Red stele (Phytophthora fragariae) roots, crown root rot, stunting occasional
1
resistance, certified plants, fumigate, rotation
Black root rot (Several fungi) roots stunting rare
1
cultural, fumigation, rotation
Northern root-knot nematode (Meloidogyne hapla) roots stunting occasional
2
fumigate, certified plants, rotation
Leaf scorch (Diplocarpon earliana) leaves, runners leafspot general
2
resistant cultivar, fungicide
Powdery mildew (Spaerotheca sp.) leaves, fruit leaf roll common on Titan
3
full sun, fungicides, resistance
Anthracnose (Colletotrichum sp.) runner, crown death of plants occasional
3
certified plants, cultural
Lesion nematode (Pratylenchus sp.) roots stunting common in mountain areas
3
soil fumigation, certified plants, rotation
Crown rot (Sclerotium rolfsii) crown plant death occasional
4
cultural practices, rotation
Leafspot (Mycosphaerella fragariae) leaves leafspot general
4
resistant cultivar, fungicides
Leaf blight (Phomopsis obscurans) leaves, runners leafspot general
4
resistant cultivars
Bud rot (Rhizoctonia sp.) crown crown rot, fruit rot rare
5
cultural practices, severe if plants set too deep
Dwarf (foliar nematode, Aphelenchoides sp.) bud, leaves crimping of bud rare
5
soil fumigation, certified plants
Yellow, crinkle, mottle (virus) foliage stunting rare
5
certified plants
Sting nematode (Belonolaimus sp.) roots stunting occasional
5
soil fumigation, certified plants, rotation
Leather rot (Phytophthora cactorum) fruit fruit rot sporadic
5
fumigation, rotation
June yellows (genetic) foliage yellows rare
5
resistant cultivar
Hard rot (Rhizoctonia solani) fruit fruit rot rare
5
resistant cultivar
Leak (Rhizopus sp.) fruit fruit rot rare
5
resistant cultivar
Leaf blotch (Gnomonia sp.) leaves, fruit leafspot, fruit rot occasional
5
resistant cultivar

*This is a general rating and any one of these diseases can be very damaging on an individual planting - (1 - most important and 5 - least important).

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Recommendations of specific chemicals are based upon information on the manufactuer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data. All recommendations for pesticide use were legal at the time of publication, but the status of registration and use patterns are subject to change by actions of state and federal regulatory agencies. 04/91/1000

Published by North Carolina Cooperative Extension Service, Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Reformatted February 2002 by Tom C. Creswell