Transcript d, daughter plant

Leading Producers of Strawberries
State
Harvested Acres*
California
25,000
Oregon
6,200
Florida
5,100
New York
3,800
North Carolina
2,400
Pennsylvania
1,500
Washington
1,500
LOUISIANA
1,100 1st in taste
*USDA 1995
Morphology
a, crown and leaf bases;
b, stolon (runner);
c, first (blind) runner node;
d, daughter plant;
e, secondary runner
Production Strategies
Matted Row System
Consists of rows 12 to 24 inches wide that are allowed to fill in or be renewed
with runner plants.
Fields are renewed or renovated each year. Fields planted in the matted row
system generally produce three to four profitable crops. If disease, insects,
or weeds heavily infest a planting, renovation may not be economically
justified.
Annual Hill Plasticulture
The annual hill system is a high-density system that grows strawberries as
annuals. This system consists of closely spaced plants in double rows
planted on raised beds covered with black plastic. Plasticulture is an annual
system of planting freshly plants in the fall. Plants and plastic are removed
after spring harvest and the process begins again the next fall.
Important Diseases
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Red Stele
Anthracnose and Black Leaf Spot
Botrytis Grey Mold
Mycosphaerella Leaf Spot
Many viruses, insects and regional nematodes
and numerous abiotic constraints that will not be
covered
Red Stele
Pathogen: Phytophthora fragariae
Distribution: Serious disease of strawberry in the northern
2/3 of the United States.
Many desirable commercial cultivars are highly
susceptible.
Thrives in poorly drained, cool, wet soils.
Symptoms
Aboveground: Symptoms of red stele rarely occur in the first year of
strawberry growth unless plants are infected before planting or if
conditions are suitable for rapid fungal growth.
The disease is first noticed during bloom of the second year. The
symptoms will be most noticeable in low or soil compacted areas of a
field where water drainage is poor.
Strawberry plants will show a general lack of vigor with poor runner
growth and small berries.
New leaves may appear bluish-green, while older leaves sometimes turn
red, orange or yellow. The leaves tend to wilt during warm weather or
drought stress.
Severely diseased plants may collapse prior to fruiting.
Although these aboveground symptoms are typical for red stele, they may
resemble symptoms caused by other types of root disorders; therefore, roots
also need to be examined.
Symptoms
Symptoms
Belowground: To correctly diagnose, roots should be sampled during
early spring and summer up until harvest.
Samples taken after harvest are not reliable because infected roots may
have already begun to decay.
If red stele is present, the roots will appear unbranched and will be lacking
feeder roots. This "rat-tail" appearance of the root is a diagnostic trait
of red stele.
Infected roots will have a reddish-brown core, but the outer tissue will be
white. The discoloration will begin at the root tip and move upwards,
but usually will not move into the crown.
This is in contrast to another root disease, black root rot, in which outer
root tissues are affected earlier than the inner (stele) root area. Normal
roots have both a white center and outer root surface
Symptoms
Red Stele,
& Rat tail appearance
Disease Cycle
The fungus is spread from one field, or area to another by the distribution of
nursery infected plants. Infection is then spread within the field by moving
water and by soil movement.
Once in the field, oospores in roots produce zoospores when soil moisture is
high, infecting the tips of the young, fleshy roots and destroying water- and
food-conducting tissues.
Infection and growth of the fungus in roots reduces the flow of water and
nutrients to the developing leaves and fruit causing drought-like symptoms in
the plant.
Disease Cycle
The optimum temp. for growth and infection is 57 F. When soil moisture is
high and the temperature is cool, plants show symptoms within 10 days after
infection.
The fungus is inactive at 40 F and above 86 F. The critical periods for
development and spread are in the spring and the fall.
As summer, soil temperatures rise, the fungus forms oospores in the stele of
infected roots. The fungus survives periods of hot, dry, or cold weather
primarily as these oospores
Disease Management
Pre-Plant
Soil drainage: the pathogen requires free water in order to develop.
Avoid low-lying areas, and, raised beds 10 inches or more.
Can persist in the soil for at feast 17 years, even in the absence of
strawberry plants = no crop rotation benefits.
Site Preparation: Cover crops can build organic matter in the soil (heavy,
compacted soils favor red stele).
Sanitation: Clean cultivators or equipment.
Planting: Exclusion and prevention. The pathogen is introduced most
frequently on infected-plants; therefore, mother plants should be
purchased from a reputable nursery.
Host Resistance: “Resistant varieties" are not resistant to all strains of P.
fragariae
Disease Management
Post - Plant
Use cultural practices which favor good plant growth and
development.
Avoid over irrigation.
Chemical: Soil fumigation with soil sterilants and/or pesticide
applications may be helpful in situations where resistant
varieties are not available or are not adapted.
Anthracnose and Black Leaf Spot
Pathogens: Colletotrichum acutatum, C. fragariae,
Distribution: Throughout the United States
The fungus may cause petiole and runner infections, flower
blight, and anthracnose crown rot.
Flowers and ripening fruit are very susceptible to anthracnose
fruit rot.
Symptoms
Lesions on stolons and petioles are sunken, firm, dark, and dry with
a sharp line separating healthy from diseased tissue. When a
runner is girdled by a lesion, the daughter plants beyond the
lesion wilt and die. Lesions on petioles also result in the death of
leaves.
Symptoms
Crown rot occurs when the fungus grows into crowns from
infected runners or petioles. Plants with crown rot may die in
the nursery or after being transferred to production fields.
Wilting plants with crown rot have a reddish brown, firm rot in the
interior of the crown.
Crown rot is sometimes difficult to identify just on the basis
of crown discoloration because crowns of dying strawberry
plants turn brown regardless of what kills them.
Symptoms and Signs
Fruit rot can occur on both ripe and unripe fruit. Infected tissue
on ripening fruit appears as round, firm, sunken, tan to brown
spots that turn into sunken black lesions with age.
The spots may remain a light tan color for a few days,
especially during wet weather. The entire fruit may become
infected, dried, and mummified.
Dark brown to black, firm lesions can occur on the green fruit.
Under humid conditions, salmon colored sporulation may be
visible on the lesions.
Progression of fruit lesion
Symptoms
Leaves: Lesions on leaves are small (<1/4"), round, and black
(sometimes light gray) often resembling ink spots.
Spots may become numerous on leaflets without causing leaf death
and often appear first on expanding leaves of runner plants.
The presence of leaf spot may be a warning signal that abundant
inoculum is present on other plant parts and fungicide applications
are needed.
Disease Development
Infected transplants and soil from infected transplants appear to be
the primary source of inoculum in most instances, especially in
annual production systems.
This may be especially true for C. fragariae, which has a limited
host range and does not survive in soil over the summer.
In perennial systems, the fungi may overseason in infected plants
and debris, providing inoculum for the following fruiting season.
Conidia may be dispersed in the field by wind-driven rain, splashing
water, insects, movement of workers, equipment or animals.
Disease Development
Disease development and spread is minimal in most cases under
cool, dry conditions.
Crown infections often occur in the nursery but do not appear until
after planting.
The fungus continues to develop in newly planted nursery infected
plants, which may suddenly die during warm weather in the fall
or early spring of the following year.
Infected berries eventually dry up and mummify and can become a
source of inoculum for the following season.
C. acutatum is known to survive in infected plant material for up to
nine months
Management
Difficult to control when conditions are favorable for infection during
harvest. Control measures must begin early in the season.
Disease-free planting material, however it is difficult to detect the fungus
in planting material because it causes latent infections.
Follow a protective fungicide program from transplanting through harvest.
Avoid overhead irrigation if possible.
If fruit rot occurs, remove all infected fruit at each harvest.
To prevent the spread of the disease, never move pickers from an infected
to a non-infested field.
When they are available, plant strawberry varieties resistant to anthracnose
(Resistant varieties are currently being developed).
Botrytis Grey Mold
One of the most common and serious diseases, in
wet seasons on unsprayed plants 80-90% losses of
flowers and fruit can occur
Causal agent – Botrytis cinerea
Symptoms and Signs
Young blossoms are very susceptible to infections. One or several
blossoms in a cluster may show blasting.
Soft, light brown lesion form at calyx end of fruit with lesions
without distinct borders
Produces light grey spores that are easily airborne.
Berries resting on soil or touching other decaying fruit often
infected
Good berries become a rotted mass within 48 hours
Berries soon dry out leaving dark brown, mummies covered with
grey-white fungal growth.
Single
or in
Clusters
Stages of
symptoms
Early Mummy
Disease Cycle
Fungus overwinters as minute, irregular, black fungal bodies
(sclerotia) and as dormant mycelium on dead leaves, stems, fruit
and on annual weeds.
In spring, sclerotia produces conidia, wind, splashing water, human
activity spread throughout the patch depositing on blossoms,
stems young fruit and leaves.
Some plant parts may be infected in 3 hours. Temp 70-80, free
moisture (rain, dew, fog, irrigation) are ideal for germination and
infection.
Fungus can penetrate unbroken skin of fruit.
Single berry may contaminate many others in field or after
harvesting.
Factors Favoring Disease
Moderate temperatures and long wetting periods or
periods of humidity during bloom.
Prolonged rainy and cloudy periods just before and
during harvest.
Dense foliage and wide rows keep plant wet longer, all
varieties are susceptible but some are much more than
others.
Disease Management
Avoid narrow rows
Encourage air flow
Apply fungicides
Mulching with clean straw
Black polyethylene sheeting
Limiting cultivation from early bloom until after harvest
Avoid wounding plants
Care in handling berries
Refrigeration of berries
Mycosphaerella Leaf Spot
One of the most common and widespread diseases of
strawberry.
Mycosphaerella fragariae is also the cause of black seed
disease of strawberry fruit, which occurs occasionally in
North America where Mycosphaerella leaf spot is
present.
Prior to the development of resistant cultivars and
improved control programs, leaf spot was the most
economically important strawberry disease.
Symptoms
Leaves: Leaf symptoms vary with strawberry cultivar, strain of the
fungus, and environmental conditions.
Leaf lesions or "spots" are small and round (3-8 mm diameter), dark
purple to reddish, and are found on the upper leaf surfaces. The
center of the spots becomes tan to gray to almost white, while the
broad margins remain dark purple.
Lesion centers on younger leaves stay light brown, with a definite
reddish purple to rusty brown margin.
Numerous spots may coalesce and cause death of the leaf.
In warm humid weather, atypical solid rusty brown lesions without
purple borders or light colored centers may form on young leaves.
Lesions are evident on the undersurface of the leaf but are less
intense in color, appearing as indistinct tan or bluish areas.
Symptoms
Leaf stems (petioles), runners, fruit stalks (pedicels), berry caps
(calyxes): Almost identical to those on leaves. pathogen.
Fruit: Superficial black spots (6 mm in diameter) form on ripe
berries under moist conditions. These spots surround groups of
seeds (achenes) on the fruit surface. The surrounding tissue
becomes brownish black, hard and leathery, however, no general
decay of the infected berry occurs.
Usually only 1-2 spots occur on a berry but some may have as many
as 8-10 "black-seed". Symptoms are most conspicuous on white,
unripe fruit and on ripe fruit of light colored cultivars.
Economic losses in this case are due to unattractiveness of "black
seed" spots on fruit, rather than fruit rot.
Signs of the pathogen
Late in the season, dark specks (sclerotia and/or
perithecia) may be seen in older lesions.
Disease Cycle - North
In northern growing regions, the life cycle is somewhat
different.
Three sources of primary inoculum may be present: conidia
overwintering on living leaves, conidia from overwintering
sclerotia, and ascospores.
Abundant conidia, produced in early summer on lesions on both
upper and lower leaf surfaces and lesions on other plant
parts, are spread primarily by water splash.
Sclerotia are produced during the winter on dead infected
leaves. These may also produce abundant conidia in the
spring.
Disease Cycle - North
Conidia also develop on occasion from the bases of perithecia.
Perithecia are produced on upper surfaces of overwintered
leaves. Forcibly discharged ascospores from these perithecia
are wind disseminated.
It is not known if these ascospores serve as an important source
of primary inoculum, but they are most probably a means by
which genetically different strains of the fungus may travel
long distances.
M. fragariae establishes in the stigma at the time of flowering
and then grows to the achene. From there it infects
surrounding berry (receptacle) tissue. Conidia produced in
leaf infections are probably the primary inoculum source for
fruit infections.
Disease Cycle
Disease Management
Plant in well drained soil with good circulation and exposure.
Choose disease resistant cultivars suitable for the region.
Plant only disease free plants purchased from reliable nurseries.
Apply nitrogen fertilizers only at renovation to reduce succulent new
leaf tissue which is more susceptible.
Remove older or infected leaves before setting runners in new
plantings.
Removing and burning all debris at renovation (after harvest) helps to
reduce overwintering inoculum
Fungicide spray schedule - Thoroughly cover all above ground plant
parts with spray, especially undersides of leaves