Diseases Covered

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Diseases Covered

• Rhizoctonia Crown Rot and Blight
• Botrytis Blight
• Black Spot
• Daylily Rust

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Rhizoctonia crown and root rot.

• Caused by Rhizoctonia solani
• Root rot may develop either in the rooting cube
  or on rooted cuttings transplanted to pots as the
  crop is finished for retail. Infected roots
  become water-soaked then brown.
• Both root tips and sections of the root away from
  the tip may develop symptoms. Crown rot can
  develop on the stem as lesions expand from stem
  infections occurring during propagation.

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Rhizoctonia crown and root rot.

• Stem lesions may develop at a much slower pace on
  rooted plants, since this tissue is more hardened
  off and thus more resistant than stems of newly
  made cuttings.
• Foliar symptoms of crown and root rot include
  chlorosis, leaf necrosis, wilting, defoliation,
  and plant death, but often the most common
  symptom is stunting.
• Root rot infections may be initiated from lesions
  on stems or from inoculum introduced to the
  potting mix from debris surviving in the
  greenhouse.
• Generally, moist but not wet conditions in the
  potting mix favor development of Rhizoctonia
  crown and root rot on potted plants.
• Spacing plants with a full canopy too close
  together can result in moisture and soil
  temperatures favorable for development of disease
  due to shading of the container surface.

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Rhizoctonia Damping off
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Rhizoctonia Crown Rot Poinsettia
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Rhizoctonia Blight Begonia
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Rhizoctonia blight Impatiens
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Control

• Control of stem and root rot begins with thorough
  removal of all crop debris from the production
  facility at the end of a cropping cycle.
• Sanitation of work area and bench surfaces with
  surface disinfectants is important.
• During propagation, misting cycles should be
  monitored closely to avoid over wetting foliage
  of cuttings once newly made cuttings become
  turgid.
• In greenhouse production facilities with a
  history of Rhizoctonia stem and root rot, soaking
  dry rooting strips in a fungicide solution can
  protect cuttings from disease
• Generally one application of fungicide is
  sufficient to protect the crop during the
  propagation cycle.
• After transplanting, fungicide drenches may be
  needed at regular intervals to prevent crown and
  root rot

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Botrytis Blight

• CAUSAL ORGANISM Botrytis cinerea
• Botrytis blight is common in all parts of the
  world. This fungus is not a specific pathogen and
  can take advantage of many situations to produce
  a blight or rot condition on many hosts.
• It is an opportunist on cut or pruned rose canes
  and will infect flowers and buds.

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Symptoms/Signs

• The most common symptoms usually are seen on
  young flower buds which droop, turn black at the
  base and later produce the cottony grey-black
  mycelium of the fungus.
• Flowers can also be affected in the same way and
  cut ends will have the black canker like symptoms
  with presence of mycelium.
• Cool and wet conditions facilitate grey-black
  mycelial growth of Botrytis.

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Botrytis Stem Canker Impatiens, Poinsettia
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Botrytis Blight
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Botrytis Crown Rot - lisianthus
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Botrytis Blight GeraniumResults from infected
flowers
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Botrytis Dieback - Geranium
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Botrytis Blight
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Disease Cycle

• This fungus is not specific and will grow on many
  different plants and plant debris.
• Under cool wet conditions profuse sporulation
  results and spores are moved to roses by air
  currents or blowing rain.
• A minor wound in a bud or flower, or perhaps a
  pruning cut will provide the initial point of
  entry.
• As the infection progresses more sporulation
  results and additional sites become infected.
• The fungus is a low level parasite and will
  colonize wound sites as well as dead plant
  material.

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Control

• Prevention is the best means of control. This can
  be accomplished through intense sanitation
  procedures.
• By elimination of opportunistic colonization on
  dead plant material the amount of sporulation can
  be reduced.
• Good ventilation is also essential in reducing
  disease incidence. Some sprays may give short
  term relief but the fungus usually becomes
  quickly resistant.
• In greenhouse conditions special covers are used
  to reduce the levels of ultraviolet light
  required by the fungus for sporulation.
• In most cases, removal of infected plant parts
  and protection of wounds by chemicals is all that
  can be done until warmer and dryer conditions
  prove too unfavorable for continuing disease.

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Black Spot

• Caused by the fungus Diplocarpon rosae. The
  disease can cause almost complete defoliation of
  bushes by early fall.
• It produces a weakened bush on which cane
  dieback, stem canker, and winter injury can
  become severe.

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Symptoms

• Circular black spots ranging from 1/16 inch to
  1/2 inch in diameter appear generally on leaves
  upper sides.
• The spots are frequently surrounded by a yellow
  halo. Infected leaves characteristically turn
  yellow and fall prematurely.
• This leaf spot can be distinguished from others
  by the fringed margin and consistently black
  color.
• Cane infection produces a reddish-purple spot.
• In many varieties, pale flower color is
  indirectly caused by infection.

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Disease Cycle

• Black spot is spread by splashing water.
  Infection occurs after leaves are wet for several
  hours.
• Therefore, the disease is more serious during
  periods of rainfall.

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Control

• A preventive program for black spot should begin
  with a thorough cleanup in the fall. Diseased
  leaves on the ground should be raked and
  destroyed.
• All diseased canes should be pruned off by
  cutting several inches into good wood.
• A fungicide program should start in the summer
  just before leaves become spotted. From then
  until frost, the leaves may require a protective
  fungicide coating. When the leaves are growing
  rapidly or during rainy weather, it may be
  necessary to spray the plants two times a week.
• However, if growth is less rapid and rains are
  less frequent, spraying at 7 to 10 day intervals
  is usually sufficient

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Daylily Rust

• Daylily rust is caused by the fungus Puccinia
  hemerocallidis and affects the leaves and scapes.
  
• It is not a new disease of daylilies, having been
  reported previously in China, Taiwan, Korea,
  Japan and Russia.
• Unfortunately, the disease has now arrived in
  North America, and was first identified in the
  southeastern United States in August 2000. 
  Because of widespread shipping of infected
  plants, by late 2001 daylily rust had been
  identified in approximately 30 US States, Canada
  and Australia.  In nature, however, the main
  method of rust spread is by wind borne spores

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Daylily Rust

• While daylily rust may kill the foliage on some
  cultivars, it is unlikely in the short term to
  actually kill the infected plant. However, it is
  not yet known what the effects of continuous
  infection will be on individual daylilies

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Symptoms
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Symptoms and Signs
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Symptoms and Signs
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Disease Cycle
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Disease Cycle

• It is not known where the rust overwinters.
• It has successfully overwintered in some States
  of USDA Hardiness Zone 7 and milder as of April
  2002 .
• There are three possible ways that this rust may
  survive the winter.
• The first is as urediospores, the orange powder
  produced from the spots (known as pustules) on
  daylily leaves.
• Some rusts overwinter as mycelium (the strands
  which form the body of the fungus inside the
  leaf) but this can only take place where the
  plant tissue remains alive.
• The third means by which rusts can overwinter is
  in the form of teliospores.

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Disease Cycle

• Teliospores are typically hardier and more
  durable than the urediospores and lie dormant on
  dead daylily leaves over winter.
• These new spores must be transported by the wind
  or other means to a plant of the alternate host,
  Patrinia, which is a perennial plant also of
  Asian origin. Thus it is possible that in
  climates where the rust cannot survive the winter
  as mycelium or urediospores, it may still be able
  to continue the infection in the subsequent year
  if there is a plant of Patrinia in the vicinity.
• Patrinia is not common at the moment in North
  America, but several species are being offered
  for sale both as plants and seeds. Not only does
  it pose a threat to daylilies as far as
  overwintering of the rust is concerned, but the
  rust life cycle stage on Patrinia is a form of
  sexual reproduction which may increase the
  chances of new races of daylily rust developing.

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Control

• Cultivar selection
• It is generally recommended to remove the foliage
  from all plants discovered to have rust, cutting
  just above the soil level.
• Fungicide applications mancozeb, chlorothalonil,
  azoxystrobin and triadimefon
• Overhead watering should be avoided wherever
  possible