Module 4 - Biotic or Abiotic

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					  Module 4 - Get to the Cause!
             Biotic vs. Abiotic
Delineate time - development of
  – Progressive spread of damage on a plant or to
    other plants suggests a biotic or living cause
  – Damage that does not spread on a plant or to
    other plants suggests the cause is abiotic or
  – Damage may have to be examined on several
    occasions to determine if the cause may be
    biotic or abiotic
         Get to the Cause!
             Biotic vs. Abiotic

Determine causes of plant damage
 – Patterns of damage in space and time will
   indicate whether cause of damage is
   biotic (living) or abiotic (nonliving)
 – Identification of causes is assisted by
   • use of proper field equipment
   • proper field monitoring
           Biotic vs. Insects
Identifying Insects                    Armyworn
                                       on corn
• Symptoms may
  include tunnels in
  stalks or leaves,
  holes in leaves,                     Flea beetle on canola
  chewed leaves, galls,
  leaf curling

                          Gypsy moth
Determine causes of plant damage

• Abiotic causes of plant damage are non-
  – Generally are distributed uniformly across a
    plant or field and are repeated
  – Don’t spread or move with time
  – May be from mechanical factors such as
    cultivator injury; physical factors such as
    environment; or chemical factors such as
    pesticide or nutrient problems
  Environment injury includes:
Temperature extremes: too hot, too cold
Storm situations with hail, wind or tornado
Wind injury
Frost damage
Moisture extremes: too much, too little

 Since some environmental injuries can
 resemble other biotic or abiotic causes,
 flag off area to see if damage spreads.
           Get to the Cause!
             Biotic vs. Abiotic

Determine causes of plant damage
• Biotic
• Biotic factors are living factors, such as
  pathogens, insects or weeds, characterized
  – Scattered patterns
  – Spread or movement over time; progressive
            Get to the Cause!
               Biotic vs. Abiotic
Determine causes of plant damage
     Distinguishing Among Biotic (Living)
  – To further identify which living factor is causing
    the damage, make a closer examination of
    symptoms and signs of the living organism.
• Symptoms: visible abnormalities such as
  wilts, rots, galls, chlorosis, leaf spots
• Signs: presence of actual organism or direct
  evidence of organism, such as spores, insect
  egg masses, insect frass, nematode cysts,
  weed seedling
                  Biotic: Insects
Identifying Insects
• Signs include insect frass, webbing, egg
  masses, larvae, carcasses, moths, beetles
                      Frass of stalk borer

Corn borer egg mass                          Sunflower beetle

• Knowledge of life cycles of insects assists in
  identifying the damaging insect
           Biotic: Diseases
Identifying Diseases
• Organisms causing diseases include
  fungi, bacteria, viruses, nematodes
• Symptoms are plants’ reaction to the
  disease organism
• Symptoms of fungal diseases may
  include leaf spots, leaf blights, stem or
  fruit rots, necrotic rings, chlorotic
  spots, discolored seeds, root rots, wilt.
Examples of Symptoms of Fungal Diseases

                                               Leaf spot
  Leaf spot

                Leaf spot
                                   Blight or
        Signs of Fungal Diseases
• Signs of fungal diseases include visible
  presence of the organism, such as rust
  pustules, mycelial growth (fuzzy spots),
  spores, sclerotia (black fungal bodies)
                        Rust spores
Mycelia and sclerotia
          Bacterial Diseases
• Bacterial disease organisms enter through
  wounds or natural plant openings
• Symptoms of bacterial diseases may include
  water-soaking, interveinal spots, shiny
  lesions, wilt, discoloration of leaves, galls,
  slimy wet rots.
           Virus Diseases
• Virus diseases are caused by
  submicroscopic virus bodies that infect
  plant cells. Common symptoms include
  mottling or mosaic color patterns, or
  purple color, stunting, distortion.
• Virus diseases do not leave signs because
  they are visible only with the aid of powerful
• Insects, mites, fungi or nematodes often
  vector or transmit viruses; the presence of
  these organisms may provide clues that a
  virus disease is present.

       Grain aphid           Wheat curl mite
                             1/100 inch long
            Nematode Diseases
• Nematodes are microscopic roundworms that
  damage plant tissues as they feed. Many feed
  on or in root tissues; a few feed on above-
  ground parts.
• Nematode symptoms may include stunting,
  poor stand, poor vigor, chlorosis or necrosis.

  Dagger nematode causes stand   Soybean cyst nematode damage
  damage in corn                 in soybean
• Nematode signs include the microscopic
  roundworm body of the nematode.
• Some nematodes also produce a reproductive
  cyst that is visible with the naked eye on
  roots. Plants with suspected nematode problems generally
  are diagnosed based on detection of nematodes.
           Other Biotic Pests
• Other organisms: Slugs and snails cause
  feeding damage or skeletonizing of soft leaf
• Spider mites cause a stippling of leaf tissue,
  which ultimately turns bronze to brown, and
  eriophyid mites distort new growth.
         Animal Damage
• Small or large mammals or birds may
  cause animal damage, which includes
  chewing bark, leaves, branches or
  stems. Birds cause punctures or
  missing flower parts and seeds.

                     Bird damage to rice and sorghum
• Genetic abnormalities are rare but they
  may mimic plant diseases. These often
  are associated with an individual plant
  or hybrid. They include phenomena
  such as unusual color patterns,
  unusual growths or lack of thorns.

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