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

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• Symptoms may

include tunnels in stalks or leaves, holes in leaves, chewed leaves, galls, leaf curling

Armywornon corn

Gypsy moth

Flea beetle on canola

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

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.

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

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

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

Corn borer egg mass

Frass of stalk borer

Sunflower beetle

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 Wilt

Leaf spot

Seeddiscoloration

Leaf spot Blight ornecrosis

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)

Mycelia and sclerotia

Rust spores

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 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

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 damagein 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 tissue.

• 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

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.