best management practices

A set of recommended practices; in this case, recommended nursery practices to optimize plant health. Often abbreviated BMPs.

bleeding canker 

A symptom of infection on woody plant stems or tree trunks in which a dark, reddish ooze seeps through the bark. Certain Phytophthora species, other plant pathogens, and wounds can also cause this symptom.


Sudden, severe, and extensive spotting, discoloration, wilting, or destruction of leaves, flowers, stems, or entire plants.


Abbreviation: Best Management Practices.


A layer of tissue that lies between the bark and wood of woody plants; it consists of rapidly dividing cells that form the phloem and xylem.


A dry, dying, or dead, localized area on the stem of a woody plant.


A thick-walled, asexual spore important for an organism’s long-term survival.

contact fungicide

A fungicide that remains on the surface where it is applied; it has no after-infection activity (see also systemic fungicide).

crown (root crown)

Junction of root and stem of a plant, usually at the soil line; in grafted woody plants, the rootstock portion of the plant near the soil surface.


In Phytophthora, the resting structure that develops from a zoospore.


Determination of the cause of a problem.


Progressive death of shoots, leaves, or roots, beginning at the tips.

disease cycle

Succession of all events that occur in a disease, from initial infection of the plant by a pathogen, through disease spread, to overwintering or oversummering until another infection occurs.

disease triangle

The three important components necessary for disease: susceptible plant, virulent pathogen, and suitable environment.


To eliminate a pathogen from infected plant tissue.


To kill pathogens on the surfaces of tools, equipment, or plants.


Spread of a pathogen from diseased to healthy plants.


To kill (or inactivate or get rid of) an organism that might be in or on anything used in the nursery operation.


The combination of evaporation from soil and transpiration from plants.

flagellum (pl. flagella)

A hairlike, whiplike, or tinsel-like appendage of a zoospore that propels it through water.


Pertaining to leaves.


A gas or volatile substance used to kill or inhibit the growth of plant pathogens or other pests.

fungus (pl. fungi) 

An organism that is usually filamentous (forms hyphae), cannot photosynthesize,  has cell walls composed of chitin, and reproduces by sexual and/or asexual spores.


Chemical that kills or inhibits the growth of fungi or oomycetes.


Abbreviation: Hosts and Associated Plants. Refers to plants that are proven hosts for Phytophthora ramorum as well as plants from which P. ramorum has been detected. Both are subject to regulation.

host plant

Plant that is or can be infected by a pathogen.


Thread-like filaments that allow fungi and oomycetes to grow in plants and derive their food.

leaf spot

A disease-caused lesion in the leaf; the spot stops enlarging once it reaches a characteristic size.


Localized diseased area or wound.

life cycle

The stages in an organism’s growth and development.


The  network of hyphae that makes up the body of a fungus or oomycete.


The group of fungus-like organisms to which Phytophthora belongs.


A thick-walled spore important in an organism’s long-term survival; results from sexual recombination.


A disease-producing organism or agent.


Stalk portion of a leaf.


A genus of fungus-like organisms that cause plant diseases on nursery crops, food crops, and forest trees.


Referring to a host plant: Possessing properties that prevent or reduce disease development (see also susceptible). Referring to a pathogen: Acquired tolerance to a certain chemical such as a fungicide.


Softening, discoloration, and often disintegration of plant tissue as a result of infection.


A method for monitoring plant health based on regular visual inspection of the crop.


Indication of disease from direct observation of a pathogen or its parts (see also symptom).

sporangium (pl. sporangia)

Football-shaped structure that germinates from a chlamydospore or oospore and then releases zoospores.


A general term that refers to any reproductive structure of fungi, oomycetes, and some other organisms.


A symptom of disease characterized by a limited dead or dying area, as on leaves, flowers, and stems.


Prone to develop disease when infected by a pathogen (see also resistance).


Indication of disease by reaction of the host; e.g. canker, leaf spot, wilt (see also sign).

systemic fungicide

A fungicide that is absorbed into plant tissue and is moved around in the tissue (see also contact fungicide).


A group of similar cells forming a definite kind of structural material with a specific function; e.g., leaf tissue or stem tissue.


Swimming spore released from sporangia.