Download Disease Signs and Symptoms

Chapter 15 - Integrated Management of Weeds, Insects, Diseases & Other Pests
Plant Diseases
• Injury is loss of plant vigor resulting from an event
such as a lightning strike, hail damage, chemical
burn, or mechanical damage.
• Disease is suboptimal plant growth brought about
by a continuous irritant such as a pathogen.
– Or via chronic exposure to less than ideal growing
conditions.
• The source of continual disease irritation may be
abiotic (nonliving) or biotic (caused by a pathogen).
– Abiotic diseases are also referred to as noninfectious
diseases because they do not spread from plant to plant.
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Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 15 - Integrated Management of Weeds, Insects, Diseases & Other Pests
Plant Diseases
• Biotic diseases are caused by pathogens and are
often referred to as infectious diseases.
• Plant pathogens include viruses, bacteria, spiroplasmas, phytoplasmas, fungal-like organisms,
fungi, nematodes, and parasitic higher plants.
• Pathogens may infect all types of plant tissues and
can cause a wide variety of disease, ranging from
root rots and rusts to cankers, blights, and wilts.
• All plants all are susceptible to attack by at least
one pathogen in each of the groups listed.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 15 - Integrated Management of Weeds, Insects, Diseases & Other Pests
Plant Diseases
• Development of biotic disease symptoms on a plant
requires that the infectious agent must…
– Come into contact with a susceptible host (inoculation).
– Gain entrance or penetrate the host through either a
wound or a natural opening (stomata, lenticel, hydathode,
nectarthode) or via direct penetration of the host.
– Establish itself within the host;
– Grow and reproduce within or on the host.
– Be able to spread to other susceptible plants
(dissemination).
– Be able to survive prolonged periods of unfavorable
environmental conditions & absence of a susceptible host.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 15 - Integrated Management of Weeds, Insects, Diseases & Other Pests
Disease Signs and Symptoms
• The term sign is used when the pathogen or part of
the pathogen is observed in or on an infected plant.
• Symptoms are visual or detectable reactions or
plant alterations as the result of disease or injury.
– Symptoms often change as the disease progresses.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 15 - Integrated Management of Weeds, Insects, Diseases & Other Pests
Disease Signs and Symptoms
• Abnormal tissue coloration.
– Mosaic or mottling patterns may appear, especially with
virus diseases.
Nitrogen-deficient plants
often exhibit a generalized
chlorosis or yellowing.
Iron-deficient leaves often
exhibit interveinal chlorosis.
Phosphorus-deficient plants
are often purple.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 15 - Integrated Management of Weeds, Insects, Diseases & Other Pests
Disease Signs and Symptoms
• Wilting—if a pathogen interferes with water uptake
by the host plant, part or all of the plant may die.
– Verticillium and Fusarium
• Tissue death—necrotic (dead) tissue can appear in
leaves, stems, or root, as spots or as entire organs.
– Decay of soft succulent tissue, as in damping-off in young
seedlings, is common.
– Cankers caused by death of underlying tissue sometimes
appear as sunken, dead tissue on the trunks or limbs of
woody plants.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 15 - Integrated Management of Weeds, Insects, Diseases & Other Pests
Disease Signs and Symptoms
• Defoliation—as the disease progresses, the plant
may lose all its leaves and sometimes drop its fruit.
Figure 15-32 (A) Apple scab causing leaves of a cherry tree to die and drop off.
(B) Apple scab fungus emerging from inside an apple leaf.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 15 - Integrated Management of Weeds, Insects, Diseases & Other Pests
Disease Signs and Symptoms
• Abnormal increase in tissue size—some
diseases increase cell numbers or cell
size in the plant tissues, twisting and
curling the leaves or forming galls
on stems or roots.
• Dwarfing—pathogenic organisms can
reduce cell number or size, stunting
parts or all of the host plant.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Chapter 15 - Integrated Management of Weeds, Insects, Diseases & Other Pests
Disease Signs and Symptoms
• Replacement of host
plant tissue by tissue
of the infectious
organism
– Commonly when floral
parts/fruits are involved.
tab
Practical Horticulture 5th edition
By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky
© 2011, 2007, 2002, 1988 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458