1. Module 4 - Get to the Cause! Biotic vs. Abiotic
Delineate time - development of damage
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 nonliving
Damage may have to be examined on several occasions to determine if the cause may be biotic or abiotic

2. 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

3. Biotic vs. Insects Identifying Insects
Symptoms may include tunnels in stalks or leaves, holes in leaves, chewed leaves, galls, leaf curling
Armyworn
on corn
Flea beetle on canola
Gypsy moth

4. Determine causes of plant damage
Abiotic causes of plant damage are non-living.
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

5. Environment injury includes:
Temperature extremes: too hot, too cold
Lightning
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.

6. 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 by:
Scattered patterns
Spread or movement over time; progressive

7. Get to the Cause! Biotic vs. Abiotic
Determine causes of plant damage Distinguishing Among Biotic (Living) Factors:
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

8. Biotic: Insects Identifying Insects
Signs include insect frass, webbing, egg masses, larvae, carcasses, moths, beetles
Knowledge of life cycles of insects assists in identifying the damaging insect
Frass of stalk borer
Corn borer egg mass
Sunflower beetle

9. 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.

10. Examples of Symptoms of Fungal Diseases
Leaf spot
Wilt
Leaf spot
Leaf spot
Blight or
necrosis
Seed
discoloration

11. 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

12. 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.

13. 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.

14. Virus diseases do not leave signs because they are visible only with the aid of powerful microscopes.
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

15. 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
damage in corn
Soybean cyst nematode damage
in soybean

16. 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.

17. Other Biotic Pests
Other organisms: Slugs and snails cause feeding damage or skeletonizing of soft leaf tissue.
Spider mites cause a stippling of leaf tissue, which ultimately turns bronze to brown, and eriophyid mites distort new growth.

18. 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

19. Genetics
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.