Pathogens Covered

1
Pathogens Covered

• Pythium spp.
• Phytophthora spp.
• Fusarium solani
• Rhizoctonia solani

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Black Leg of GeraniumPythium spp.
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Pythium Root Rot of Impatiens
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Control

• Take special care during transplanting to avoid
  excessive planting depth and wounding of stem and
  root tissue.
• Avoid excessive soil compaction during the
  transplant operation.
• Water carefully avoid overwatering.
• Drench-applied fungicides can be effective in
  controlling this disease problem.

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Phytophthora Damping Off
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Phytophthora root rot

• Phytophthora root rot is caused by several
  species of fungi in the genus Phytophthora.
• Phytophthora cinnamomi is usually credited with
  causing the greatest damage to container- and
  field-grown woody ornamentals.
• P. parasitica, P. citricola, and possibly P.
  cactorum, are also known to attack woody plants,
  particularly azaleas and rhododendrons.
• Phytophthora cryptogea has been known to cause
  heavy damage on junipers in poorly drained
  landscape beds

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Phytophthora Root Rot Symptoms

• Phytophthora root rot greatly reduces the volume
  of the roots which are needed by the plant to
  absorb water and nutrients.
• The roots on diseased plants are brittle and
  brown to reddish-brown in color.
• A network of fine, discolored feeder roots may be
  confined to one area or include the entire root
  system. The fungus usually colonize the crown of
  the plants, often girdling the stem at or just
  above the soil line. A brown to reddish-brown
  discoloration of the tissues occurs just below
  the bark and may extend up the stem above the
  soil line.
• On some trees and large shrubs--such as
  dogwood--brown, water-soaked cankers oozing a
  dark-colored fluid or gum may develop at the soil
  line.

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Phytophthora Root Rot of Cineraria
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Phytophthora Root Rot Symptoms
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Phytophthora Root Rot Symptoms

• These symptoms can easily be confused with those
  of a nutritional disorder, overwatering, drought
  stress, and a number of other factors and so can
  be overlooked by the grower.
• Slight yellowing of the leaves followed quickly
  by permanent wilting and plant death are the
  symptoms usually associated with Phytophthora
  root rot on container-grown azaleas and
  rhododendrons
• In landscapes, established plants may show
  symptoms of general decline for one or more years
  before succumbing to root rot, while newly
  planted azaleas will quickly die.

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Phytophthora Root Rot Symptoms

• Symptoms vary according to the degree of root
  colonization by Phytophthora root rot fungi,
  plant age, plant susceptibility to root rot, and
  environmental stress.
• Typically, symptoms first appear on one plant and
  later on surrounding plants in both container
  areas and landscape beds. Some yellowing of the
  foliage, particularly at the shoot tips, leaf
  shed, slowed plant growth, and possibly limb
  dieback may occur in early stages of the disease
• However, it is not uncommon for liners or
  container-grown plants to remain almost
  symptomless until after transplanting into larger
  containers or landscape beds.

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Phytophthora Root Rot of Gardenia
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Phytophthora Symptoms

• The foliage of azaleas and rhododendrons may also
  be invaded by some Phytophthora root rot fungi.
• Irregular blotches which are first olive-colored
  and later brown, sometimes with a red margin,
  develop on the leaves.
• Diseased leaves are usually shed by the plant.
• Damage usually appears on limbs near the base of
  the plant.

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Phytophthora Crown Rot Holiday Cactus
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Phytophthora Crown Rot / Poinsettia
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Phytophthora / Poinsettia
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Disease Cycle

• Phytophthora spp. survive as resting structures
  (chlamydospores and oospores) and mycelia in
  diseased roots, crowns, and other crop debris.
• The resting structures are released into the soil
  or potting media from infested crop debris and
  are readily spread from pot to pot throughout
  propagation and container production areas by
  soil and splashing or flowing water.
• Recycled irrigation and runoff water has been
  implicated as a source of these fungi in
  rhododendron nurseries.

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Disease Cycle

• Heaviest losses to root rot in most container
  production nurseries usually occur on flat,
  poorly drained beds where water is allowed to
  stand around container bases
• Overwatering in the nursery or landscape will
  also contribute to losses from the disease.
• Phytophthora root rot is most commonly seen in
  field production nurseries and landscape
  plantings on poorly drained, waterlogged soils
  that are prone to flood. Disease development is
  usually slow or absent on well-drained sites.

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Control

• Prevention is the key to controlling Phytophthora
  root rot in commercial nursery stock. Once
  symptoms start to appear, much of the damage has
  already been done.
• No single control measure will ensure protection
  from Phytophthora.
• Several approaches must be directed at preventing
  the introduction and spread of these fungi and at
  preventing conditions favorable for disease
  development.
• These approaches include proper establishment and
  production practices, disease resistance and
  chemical control

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Fusarium Stem Rot - Dieffenbachia

• Caused by Fusarium solani
• Infection takes place at the soil line
• This is followed by the production of a brown
  spot.
• As the tissue dies, it becomes tan and falls
  away, removing tissue from the edge to the heavy
  center vein tissue

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Fusarium Stem Rot - Dieffenbachia
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Fusarium Wilt

• Caused by Fusarium solani
• Infection takes place in the roots
• Lower leaves turn yellow and wilt, followed by
  overall plant wilting and death of entire plant.
  Lower portion of stem near soil line turns dark
  brown-to-black with brown discoloration in
  vascular tissues.

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Fusarium Wilt -Chrysanthemum
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Fusarium Wilt -Chrysanthemum
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Fusarium Wilt -Tip Necrosis of lisianthus
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Fusarium Wilt -Tip Necrosis of lisianthus
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Management

• Planting disease-free cuttings, sterilization of
  potting soil and benches offer best means of
  control.
• Do not injure plants at the soil line.
• Apply iprodione (Kidon, Rovral, Chipco 26019) or
  etridiazole (Truban, Terrazole)
  Thiophanate-methyl (Banrot) to protect healthy
  plants.

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Anthracnose and brown leaf spot

• Caused by (Colletotrichum spp. or Leptosphaeria
  spp.)
• Occur throughout the world in greenhouse and
  indoor landscapes.

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Symptoms/Signs

• Symptoms of two leaf spots are very similar, with
  both occurring primarily during the cooler,
  winter months.
• Leaf spots are initially tan and water-soaked and
  may have a bright yellow halo.
• Fruiting bodies of the causal organism
  (Glomerella or Colletotrichum spp. anthracnose)
  or Leptosphaeria sp. (brown leaf spot) appear in
  concentric rings of tiny black specks within the
  leaf spot.

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Colletotrichum - Dieffenbachia
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Colletotrichum - cyclamen
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Colletotrichum -cyclamen
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Control -

• Keep foliage dry, and protect from cold water
  drips due to condensation on overhead structures.