diagnosis & plant health master terms

acute

disorder or disease that occurs suddenly or over a short period of time

bacteria

single-celled organisms having a cell wall but no organized nucleus; a few species are plant pathogens

biotic disorders

plant problems caused by an infectious living agent

blight

any disease, regardless of the causal agent, that kills young plant-growing tissues

canker

localized diseased area, often shrunken and discolored, on stems and branches

causal agent

either an abiotic or a biotic agent that causes a disruption of a plant’s normal growth or physical properties

chlorosis

whitish or yellowish discoloration caused by lack of chlorophyll; often used in referring to a plant’s foliage

chronic

disorder or disease occurring over a long period of time

complex

a combination of factors that contributes to the stress or decline of a tree

conks

large spore-bearing structures of wood-decay fungi

dieback

condition in which the branches in the tree crown die from the tips toward the center

frass

partially decomposed wood excreted by insects; fecal material and/or wood shavings produced by insects

fungus

group of organisms from the kingdom Fungi, including yeasts, molds, mushrooms, and smuts; typically multicellular, parasitic, lack vascular tissue and chlorophyll, reproduce by spores

gall

swelling of plant tissues; frequently caused by insects, nematodes, fungi, or bacteria

gummosis

exudation of sap or gum, often in response to disease or insect damage

infectious

capable of being spread from plant to plant

leaf blotch

irregularly shaped areas of disease on plant foliage

leaf spot

patches of disease or other damage on plant foliage

necrosis

localized death of tissue in a living organism

nematode

microscopic roundworm; some feed on plant tissues and may cause disease

pathogen

causal agent of disease; usually refers to microorganisms

powdery mildew

white or grayish fungal growth on the surface of stems or foliage

root collar

area at the base of a tree’s trunk where the roots and trunk come together

rust

disease caused by a certain group of fungi; characterized by reddish brown spots on foliage and/or stem galls

scorch

browning and shriveling of foliage, especially at the leaf margin

sign

physical evidence of a causal agent (e.g., insect eggs, borer hole, frass)

stress

factor that negatively affects the health of a tree or plant

stunting

growth reduction of organisms, specifically plants or plant parts

symptom

a plant’s reaction to a disease or disorder (e.g., wilting, dieback)

vascular discoloration

darkening of the vascular tissues of woody plants in response to disease

virus

ultramicroscopic infectious agent that can reproduce only in living cells; some can cause disease

watersprout

upright adventitious shoot arising from the trunk or branches; also incorrectly called a sucker

wilt

loss of turgor pressure and subsequent drooping of leaves and young stems

witch’s broom

plant disorder characterized by shortening of internodes and proliferation of terminal shoots forming a dense brushlike mass of twigs

abiotic disorders

plant problems caused by noninfectious, environmental agents

abscission

leaf or fruit drop induced by hormonal changes

adventitious root

root that arises from a stem rather than from another root

aerobic respiration

process by which carbohydrates are converted into energy by using oxygen

allelopathy

chemical inhibition of growth or development of plants induced by allelochemicals

anaerobic fermentation

incomplete path of respiration in the absence of sufficient oxygen

compartmentalization

natural defense process in trees by which chemical and physical boundaries are created that limit the spread of disease and decay organisms

defoliation

loss of leaves from a tree or other plant by biological or mechanical means

frost cracks

longitudinal cracks in stems of trees and shrubs running parallel to wood grain; usually associated with extremely cold temperatures and previous wounds

fungicides

chemical compounds that are toxic to fungi

girdling roots

root that encircles all or part of the trunk or other roots; constricts vascular tissue and inhibits secondary growth and movement of water and photosynthates

hardened off

plant that has been allowed to gradually adapt to cold weather conditions

herbicide

pesticide used to kill, slow, or suppress plant growth by interfering with botanical pathways

insecticides

substances toxic to insects

osmotic potential

measure of the effect of solute particles on a substance’s ability to absorb or release water

permanent wilting point

point at which a plant cannot pull any more water from the soil and suffers permanent damage

physiological disorder

in plants, a disorder not caused by an insect, pathogen, or injury

phytotoxic

term to describe a compound that is poisonous to plants

sunscald

dead or injured bark and cambial tissues; results from cold bark temperatures followed by warm bark temperatures; often called southwest injury

systemic

moving throughout an organism after absorption; or affecting the entire organism

trunk flare

transition zone from trunk to roots where the trunk flares out into primary structural roots

venation

arrangement of veins in a leaf

honeydew

sticky substance secreted by certain insects when feeding upon plants

mycorrhizae

symbiotic association between certain fungi and the roots of a plant

phytoplasmas

mycoplasma-like organism; formerly known as MLOs

skeletonized

leaves that have had tissue removed from between the veins by insects

symbiotic

association of two different types of living organisms that is often but not always beneficial to each

vector

biotic or abiotic agent that transmits a pathogen

abiotic

nonliving

allelochemicals

substances produced naturally by plants as part of a defense against pests and other plants; may adversely affect growth and development of other plants

biotic

pertaining to living organisms

cellulose

complex carbohydrate found in cellular walls of the majority of plants, algae, and certain fungi

cuticle

waxy layer outside the epidermis of a leaf that retards water loss and resists insect damage

hardscape

constructed inanimate elements of a landscape such as walls, pathways, and seats

lignin

organic substance that impregnates certain cell walls to thicken and strengthen them; reduces susceptibility to decay and pest damage

mortality spiral

sequence of stressful events or conditions causing the decline and eventual death of a tree

phenols

naturally produced organic alcohols with acidic properties; one of several chemical defense compounds in trees

photosynthate

general term for the sugars and other carbohydrates produced during photosynthesis

photosynthesis

process by which light energy is used to form glucose from water and carbon dioxide in green plants

Plant Health Care (PHC)

comprehensive program to manage the health, structure, and appearance of plants in the landscape

pustules

small confined blister-like elevations

resource allocation

in plant physiology, distribution and use of photosynthates for various plant functions and processes

tannins

organic substances produced by trees; believed to be involved in a tree’s chemical defense processes

turgor pressure

pressure exerted on the cell wall by water within the cell vacuole

vigor

overall health; capacity to grow and resist stress

vitality

overall health; ability of a plant to deal effectively with stress