INTERIOR PLANTS
DISEASES
Disease Definition
Disease-
abnormality in structure
or function caused by an
infectious agent that injures or
destroys
Often the most limiting factor
Consider 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 nature
 Cultivation 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
currents
 Splashing water
 Insects
 Mites
 Cultural 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 Complexes
 Disease
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 resistance
 Alter the environment
 Sanitation
 Pesticides
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 microscope
 Parasitic an multiply in living cells
 Primarily 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, yellowing
 Abscission of leaves from the
base up
 Death of the roots results
Root Rots
Rhizoctonia
Pythium
Phytophthora
Sclerotium
Fusarium
Rhizoctonia
Known as: damping-off, wire
stem, head rot, crown rot
Attacks: Aglaonema, Begonia,
Cissus, Chamaedorea, Hedera,
Hoya, Peperomia, Philodendron
Reddish-brown mycelium
Hyphal 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 Off
– 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
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 foliage
 No excess water
 Similar 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
– leaf spot
 Moist atmosphere poor
cultural practice
 Prevention;
reduce humidity;
resistance;
avoid injury
 Botrytis
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