DISEASES

INTERIOR PLANTS

Disease Definition

Disease- abnormality in structure or function caused by an infectious agent that injures or destroys

Often the most limiting factorConsider during plant selection

Two Disease Classifications

Infectious- damage which is caused by a pathogen or living organism

Noninfectious –physiological injury that destroys the plant’s value and are called disorders.

Disorders

Sunburn Overwatering

Terminology

Pathogen -organism causing disease: fungi bacteria viruses nematodes & mycoplasms- (not much of

a concern in the interior environment)Host - Organism the parasite lives on

Part of Nature

Normal part of natureCultivation increases diseases

cultural practices have changed uniform genetic background grown in pure stands

Suitable environment is usually wet, humid, and warm to hot

Method of Dispersal

Air currentsSplashing waterInsectsMitesCultural practices

Disease Triangle

There are 3 conditions necessary for disease to occur a susceptible host a virulent pathogen a favorable environment

These make up the disease triangle. If any one is missing, disease can not occur

Disease ComplexesDisease complex- multiple pathogens

occur when plant roots are damaged before stress

Successions occur Initial colonizers of the roots Successions of fungi Invasion of diverse saprophytes Tissue then supports other organisms

Disease Process

4 steps to the disease process: infection- organism enters the plant incubation- Pathogen inhabits the host

and without producing symptoms symptom development- interaction inoculum production- pathogen

produces propagules

Disease Control Agents

Prevent pathogen establishment Plant resistanceAlter the environment SanitationPesticides

Fungi

Most common Lacks chlorophyll; microscopic Germ spores, germ tube on plant surface,

penetration Fungus grows filaments called hyphae

(coll. the mycelium) Control with fungicides and watering

Fungal Disease Cycle

Bacteria

Tiny organisms that contain cytoplasm enclosed in a cell wall; no nuclei.

They do not require a living host for replication and growth.

Most are saprophytes; some are infectious Pathogenic species are usually bacillus

(rods), the others are spirilla or cocci Control by planting resistant species

Bacterial Disease Cycle

Viruses

Nucleic acid with a protein coat.Visible with an electron microscopeParasitic an multiply in living cellsPrimarily transmitted by feeding

activities or vectors Control by controlling the vector

Virus Disease Cycle

Fungal Rots

Root Rots - brown, mushy roots due to too much water.Wilt, yellowingAbscission of leaves from the

base up Death of the roots results

Root Rots

RhizoctoniaPythiumPhytophthoraSclerotiumFusarium

Rhizoctonia

Known as: damping-off, wire stem, head rot, crown rot

Attacks: Aglaonema, Begonia, Cissus, Chamaedorea, Hedera, Hoya, Peperomia, Philodendron

Reddish-brown myceliumHyphal branches at right angles

Rhizoctonia in Carnations

Pythium

Water mold favored by wet conditions Known as root rot, damping-off

Wilt; progressive yellowing from the base up; exterior of root sloughs off and leaves the core giving a thread-like appearance to the roots; dark color

Aglaonema, Aloe, Chamaedorea, Dieffenbachia, Pothos, Philodendron

Damping OffPythium – Root and stem rot

Unsterile soils, more water, poor air circulation

Spread by infested soil Brown roots and blackened stem Use dust protectants, improve

drainage

Pythium in Geranium

Lilium with Scortch or Pythium

Scorch on Lillium

Phytophthora

Phytophthora is closely related to Pythium and produces leaf spot Late blight, foliage blight, fruit rot,

crown rot, root rot Leaf damage, collapse of the plant Aglaonema, Dieffenbachia, Hedra,

Kalanchoe Peperomia, Saint Paulia

Sclerotium

Sclerotium - White fungus on the substrate surface and the plant; sclerotia (spore-like resting bodies) the size of mustard seeds Brassaia, Chamaedoria,

Dieffenbachia, Dracaena, Pothos, Peperomia.

Stem and Leaf Disease

Do not wet foliageNo excess waterSimilar to root rot with cause and

care

Powdery Mildew

Ersiphaceae - Powdery Mildew Change in temperature, cold and damp White powder on the leaves; younger

leaves curl; dwarfed and deformed foliage and flowers

Use fungicides

Powdery Mildew

Botrytis on Geranium

Botrytis – leaf spotleaf spot Moist atmosphere poor

cultural practice Prevention;

reduce humidity; resistance; avoid injury

Fusarium Wilt

Causes root rot Lower leaves turn yellow and

sometimes wilt; entire plant becomes chlorotic; roots blacken and mushy

Prevention is the best defense; aeration, pasteurization

Agalaonema, Asapragus, Dracaena, Spathiphyllum

Fusarium on Carnation

Verticillium Wilt

Soil borne; enters through roots & attacks the vascular system One of the most distructive fungi Yellow leaves which die from the

base to the top; whole plant stunted; no flowers

Culture-indexed cuttings

Verticillium on Chrysanthemum

Ascochyta Ray Blight

Fungus attacks flowers and buds Spores transported by splashing

water or air currents Completely rots the whole flower Sanitation; remove contaminated

materials

Ascochyta on Chrysanthemum

Rusts

Puccinia or Rust Red brown dusty spots on the

leaves Resistance is possible Sprays help

VIRUS

Virus Distortion Change of color Hard to treat Indexing of mums

Aster Yellows

Viral symptoms, leaf-hopper vector Green flowers Plant dies in a

few months Control the

insect