Stone Fruits

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Stone Fruits

• Prunus is a genus of trees and shrubs, including
  the plums, cherries, peaches, apricots and
  almonds.
• It is traditionally placed within the rose family
  Rosaceae as a subfamily
• The flowers are usually white to pink, with five
  petals and five sepals. The fruit of all Prunus
  species is a drupe with a relatively large
  "stone". Leaves are simple and usually
  lanceolate, unlobed and toothed along the margin.

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Stone fruits
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Peach Diseases

• Black knot
• Brown rot
• Perennial canker
• Peach scab

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Peach Diseases

• DISEASE Black knot
• PATHOGEN Apiosporina morbosa                 
  (Syn. Dibotryon morbosum)
• HOSTS members of the genus, Prunus,mainly
  affecting cultivated plum, prune and cherry and
  to a lesser extent wild plum and cherry.

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Significance

•  Black knot is a disease that is most severe on
  cultivated crops in orchard and ornamental
  planting situations.
• Black knot disease is mainly a problem in North
  America (Canada, the United States and Mexico)
  where it is indigenous.
• Black knot has been reported on 24 species of
  Prunus but is most commonly found on wild and
  cultivated plums and cherries. The disease can be
  found throughout North America but is most
  commonly found in the northeast.

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Black knot - Symptoms

• Thick, black, irregular swellings on the twigs.
  The presence of these symptoms is often first
  noticed in the winter season when they are
  unobscured by leaves. However, the fungal
  disease-causing agent has been present for quite
  some time.
• The pathogen's presence disrupts the normal
  growth of the twigs and a tumor-like growth forms
  at the infection site.
• The first symptoms appear as small, light brown
  swellings of the current or previous season's
  growth. The the swellings turn olive-green in
  color with a velvety texture in 2nd season. The
  knots darken and appear to have a hard, brittle
  texture.

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Symptoms
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Symptoms
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Disease Cycle
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Disease Cycle cont.

• Overwinters in the knots. The first ascospores
  are forcibly discharged at the time of bud break
  in early spring. Temperatures between 16C and
  27C (60-80F) are needed for discharge
  (continues until 2-3 wks. after bloom).
• Ascospores are spread by air currents and rain
  splashing. Mainly the succulent green shoots and,
  occasionally, wounded tissues are most
  susceptible.
• The knots develop very slowly, and by the end of
  the summer they appear only as small galls that
  might easily be overlooked. The following spring
  the knots enlarge very rapidly and are soft in
  texture with become greenish-brown color as
  conidia develop over their surfaces.

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Cultural Management

• Cultural management strategies are important in
  black knot management. Monitoring and pruning
  sources of inoculum. All shoots and branches
  bearing knots should be pruned out during the
  winter. This pruning should be completed before
  ascospore discharge begins in the spring.
• Winter is also a good time to look for and remove
  sources of inoculum in nearby wild Prunus species
  in hedgerows and woodlots.

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Management

• Genetic resistanceVarieties may vary in their
  ability to tolerate or resist an infection.
  Resistance is as important as fruit
  characteristics, tree size, and flowering time.
• Site selectionConsider the site location. Avoid
  planting new trees near areas with known problems
  such as abandoned orchards.
• Biological controlInterest in biocontrol agents
  is increasing because of the loss of certain
  fungicides registrations and the fact that
  applicators would prefer to reduce their exposure
  to pesticides.
• Chemical ManagementFungicides are normally only
  recommended for sites
• with valuable trees and/or severe infections
  levels.
• Fungicides work best as a protectant and are
  ineffective
• if cultural practices are not also employed.

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Brown rot

• PATHOGEN Monilinia fructicola, M.
  laxa,                   and M. fructigena
• HOSTS  Stone fruits (peach, nectarine, cherry,
  plum), almond, and occasionally some pome fruits
  (apple and pear)

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Brown rot

• The brown rot fungi cause a blight of blossoms
  and twigs and a soft decay of fruits of peaches,
  cherries, and plums. Thus, there are two distinct
  phases of this disease.
• Blossom and twig blight
• Fruit rot

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Blossom and twig blight

• This phase of the disease occurs in early spring
  when the trees are blooming, although twig blight
  also can occur during the fruit rot phase.
• The anthers and pistil of the flower are infected
  initially.
• Infected blossoms wilt, turn brown, and usually
  cling to the twig. Extension of the infection
  into the peduncle and twig results in a necrotic
  area in the woody tissue termed a canker.
• Under moist or humid conditions, ash-gray-brown
  colored sporodochia bearing conidia form on the
  surface of diseased blossoms and twigs. A gummy
  substance usually exudes from the cankers,
  causing the blighted flowers to adhere to the
  twig.

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Symptoms
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Symptoms
Blighted blossom, twig canker, gummy exudate,
and tufts of conidia.
Blossom and floral tube colonized by the fungus
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Fruit rot

• Fruit susceptibility to brown rot increases
  during the 2 to 3 week period prior to harvest.
  Increased susceptibility is associated with an
  increase in sugar content as the fruits ripen.
• Tan-brown, circular spots are visible on the
  fruit. Under humid conditions, ash-gray-brown
  masses of conidia develop on these lesions.
• If environmental conditions are wet and warm
  during fruit ripening, the entire crop can
  literally be destroyed overnight.
• Diseased fruit that do not fall to the ground
  dehydrate and become shriveled mummies that
  cling to the branch. Sometimes the fungal
  infection extends from the fruit into the twig
  and branch.

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Symptoms
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Disease cycle
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Management of Brown Rot

• Orchard location is important. Trees planted in
  orchards having poor air movement, and thus slow
  drying conditions, are more likely to have
  blossom blight and brown rot.
• Sanitation practicesThe removal of diseased
  fruit mummies and blighted twigs from the trees
  and removal of fruit and mummies from the orchard
  floor can substantially reduce overwintering
  inoculum.
• Post-harvest controlPractices used during
  harvest can significantly impact the amount of
  fruit decay following harvest. Picking and
  handling fruit carefully to avoid injuries,
  cooling fruit promptly after harvest by
  hydrocooling or forced air cooling, using clean
  containers to hold the fruit, and timely
  harvesting
• FungicidesBlossom blight occurrence is very much
  dictated by the weather conditions. In areas
  where blossom infection occurs, 1 to 3 fungicide
  sprays beginning just as the blossoms open
  control blossom blight.

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Symptoms SIUC ARC 2001
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Perennial canker

• Also called Valsa canker, Cytospora canker,
  Leucostoma canker, and peach canker, is one of
  the most common and debilitating diseases of
  peach trees. Successful long-term production of
  peaches is seldom possible if the disease is not
  controlled.
• PATHOGEN Leucostoma cincta 
• HOSTS  Stone fruits (peach, nectarine, cherry,
  plum).

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Symptoms

• Somewhat variable depending on which part of the
  tree is attacked. The most conspicuous and
  pronounced symptoms usually appear on major
  scaffold limbs and older branches.
• Dark, sunken cankers expand along the limbs,
  producing large amounts of amber-colored or dark
  brown gum at their edges. As the cankers enlarge
  with age, infected tissues crack, dry out, and
  appear blackened affected limbs become
  progressively more girdled, lose their vigor, and
  eventually die.
• Gumming cankers can also be seen at other common
  sites of infection, including narrow-angled
  branch crotches, trunks injured by machinery,
  rodents, or insect pests, poorly healed pruning
  wounds, and leaf scars or winterkilled buds on
  young shoots.

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Symptoms
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Signs

• In the early spring, conidia are exuded in a
  sticky mass from pycnidia embedded in the wood.
  Perithecia sometimes are also formed in dead
  tissue after a couple of years, but the
  ascospores are considered to be of minor
  importance in the disease cycle.

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Signs
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Management

• 1. New plantings. Do not be establish next to old
  cankered blocks of peaches. Nursery stock should
  be canker free and not excessively large. Trees
  should be protected against peach tree borer
  before planting and promote wide-angle branching.
• 2. Pruning and training. It is critical to train
  in a manner that maintains wide branch angles and
  an open center to the tree. Two of the most
  common sites of canker initiation are
  narrow-angled branch crotches and the weak twigs
  that develop within tree centers.

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Management

• 3. Winter hardiness. Horticultural practices
  should be designed to promote hardening off in
  the fall and prevent winter injury.
• 4. Pest control. Brown rot, oriental fruit moth,
  peach tree borers, and rodents all cause cankers
  or injuries that can subsequently be invaded by
  the perennial canker fungi.
• 5. Canker eradication. During the pruning
  operation, remove all cankers on small branches
  or limbs, making a thinning cut at least 4 inches
  (10 cm) beneath the edge of the cankered zone.

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Peach scab

• PATHOGEN Cladosporium carpophilum  
• HOSTS  Stone fruits (peach, nectarine, cherry,
  plum).
• This disease can affect twigs and leaf petioles,
  but the most serious damage results from fruit
  infection.

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Symptoms

• First appear on fruit when they are half formed
  to nearly full grown, about six to seven weeks
  after petal fall.
• Small, round, olive-green spots about l/l6-l/8
  inch in diameter develop on the fruit.
• Spots are superficial and slowly enlarge. They
  may merge to form large, irregular blotches that
  turn velvety, dark olive-green or black.
• Severely infected fruit may be stunted, become
  misshapen, or crack open. When fruits crack open,
  they are often invaded by other fungi that rot
  the fruit.
• Leaves may also be infected by scab. Small (l/4
  inch), round, and yellowish-green to
  yellowish-brown spots develop on the underside of
  the leaf.

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Symptoms
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Symptoms
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Disease Cycle

• The fungus overwinters in lesions on twigs.
• Conidia are produced in the spring after
  petal-fall and are windblown or splashed about by
  rain.
• The conditions which favor disease development
  are temperatures above 60F for spore production,
  over 50F (optimal 72F to 86F) for spore
  germination, and between 36F and 95F for
  disease development. Most infection occurs at the
  shuck-split stage of growth, although the fruit
  remains susceptible through harvest.
• Spores from the fruit reinfect the twigs and
  leaves, completing the disease cycle.

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Management

• Fungicides - Most scab infection occurs between
  shuck-split and 6 weeks after shuck split. This
  period coincides with the peak spore production
  by the fungus.
• Fungicide sprays during bloom and petal fall are
  not necessary for scab control.
• Proper pruning increases air movement within the
  tree crown and decreases the likelihood of twig
  infection.