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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North Carolina Insect Notes
For assistance with a specific problem, contact your local
North Carolina Cooperative Extension Service
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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