© 2011, 2007, 2002, 1988 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ Practical Horticulture 5 th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky tab 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.

© 2011, 2007, 2002, 1988 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ Practical Horticulture 5 th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky tab 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, spiro- plasmas, 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.

© 2011, 2007, 2002, 1988 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ Practical Horticulture 5 th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky tab 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.

© 2011, 2007, 2002, 1988 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ Practical Horticulture 5 th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky tab 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.

© 2011, 2007, 2002, 1988 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ Practical Horticulture 5 th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky tab 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.

© 2011, 2007, 2002, 1988 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ Practical Horticulture 5 th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky tab 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.

© 2011, 2007, 2002, 1988 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ Practical Horticulture 5 th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky tab 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. (A) Apple scab causing leaves of a cherry tree to die and drop off. (B) Apple scab fungus emerging from inside an apple leaf. Figure 15-32

© 2011, 2007, 2002, 1988 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ Practical Horticulture 5 th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky tab 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.

© 2011, 2007, 2002, 1988 Pearson Education, Inc. Pearson Prentice Hall - Upper Saddle River, NJ Practical Horticulture 5 th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky tab 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.