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Statewide IPM Program, University of California




The posterior body portion of an arthropod.

abiotic disorder

Disease caused by factors other than pathogens, such as inappropriate cultural practices or adverse environmental conditions including nutrient deficiencies and pesticide phytotoxicity.


A pesticide for mites. Also called a miticide.


A simple, one-seeded fruit in which the seed is attached to the ovary wall at only one point, such as the "seed" on the surface of a strawberry.

acid equivalent (a.e.)

The acid portion of an active ingredient. A measure of pesticide potency used for herbicides (e.g., glyphosate) for which the amount of active ingredient is not a good measure of the amount of weed-killing ingredients; because the pesticide is formulated varying ways (e.g., an amine, ester, or salt), the amount of active ingredient can differ without changing the amount of the weed-killing component (the acid portion of the pesticide).

action threshold

The point at which a given pest is numerous enough that a management action (usually a pesticide application) is necessary to prevent economic loss or unacceptable damage. May also be called aesthetic threshold, economic threshold, or treatment threshold.

active ingredient (a.i.)

The component of a pesticide formulation that affects or kills the target pest or performs the pesticide’s function.

acute effect

An effect (e.g., illness or injury) that becomes apparent soon after an organism is exposed to the causal factor or substance, such as a pesticide.


A substance added to a pesticide to improve pesticide handling, performance, or safety, such as the mixing qualities or on-target coverage.


Arising from an unusual place, as in the case of roots growing from leaves or stems (“adventitious roots”).


A state of inactivity of an animal during dry or hot periods, typically during summer months. Also called estivation.

aggregation pheromone

A pheromone that attracts individuals of a given species for mating, defense, or other purposes. Aggregation pheromones are sometimes used to monitor or manage insect pests.

agricultural commissioner

The official in each California county responsible for enforcing federal and state pesticide regulations and issuing permits for restricted-use pesticides.


The white, spongy inner part of citrus fruit rind.


Basic, having a high pH or pH greater than 7.


The ability of a plant species to produce substances that are toxic to certain other plants.

allowable depletion

The proportion of available water in soil that can be used before irrigation is needed.


An instrument for measuring wind speed.


A plant that normally completes its life cycle of seed germination, vegetative growth, reproduction, and death in a single year.


An organism that releases toxins or otherwise changes conditions in a way that reduces the activity or growth of other organisms (especially pests).

antenna (plural: antennae)

The paired, segmented, sensory organs on each side of the head of certain arthropods, such as insects.


The pollen-producing organ of flowers.


A substance commonly used in rodenticides that prevents blood clotting, resulting in internal hemorrhaging.

apical dominance

Growth of the bud at the apex of a stem or tuber while growth of all other buds on the stem or tuber is inhibited.

apothecium (plural: apothecia)

Cup-shaped, spore-bearing structure produced by some fungi (e.g., Sclerotinia species) and lichens.


An underground formation of gravel, porous rock, or sand that contains water (groundwater).


An animal with jointed appendages and an external skeleton, such as a crab, insect, mite, or spider.


A spore produced within the saclike cell of the sexual state of a fungus.


The earlike projections at the base of leaves of some grasses that may be used to identify grass species.

available water

The amount of water held in the soil that can be extracted by plants.


A pesticide for pest birds.


A slender, bristlelike organ usually at the apex of a plant structure.


The upper (narrow) angle between a branch or leaf stalk and the stem from which it is growing.

axillary bud

An undeveloped branch or flower (bud) located in an axil.



Abbreviation for Bacillus thuringiensis.

Bacillus thuringiensis (Bt)

A group of bacteria that causes disease in certain insects. Formulations of several subspecies of Bacillus thuringiensis are used as insecticides, most commonly for caterpillars but for other pests as well (e.g., mosquito larvae).

bacterium (plural: bacteria)

A single-celled, microscopic organism that lacks a nucleus. Some bacteria cause animal or plant diseases.

bait station

A box or container designed to hold a mixture of attractive bait and pesticide to kill insects, rodents, or other pests and including baffles, small openings, or other design features to prevent access to the bait by nontarget animals.

band application

An application in which a material such as fertilizer or pesticide is applied in strips, usually to the planting bed or seed row.


A portion of a crop field bounded by levees.


A plant that completes its life cycle in two years and usually does not flower until the second growing season.

binomial sampling or presence/absence sampling

A sampling or monitoring method that involves recording only the presence or absence of a given organism (e.g., an insect pest) on a sample unit (e.g., a leaf), rather than counting the number of individuals.


The breaking down of a substance (e.g., a pesticide) by organisms (commonly microorganisms) in the environment.


An identifiable event that signals when to begin degree-day accumulation.

biological control or biocontrol

The reduction of an organism’s abundance or damage due to a natural enemy, such as a predator consuming (killing) prey. Biological control may occur naturally in the field or result from introduction or manipulation of natural enemies by people.

biotic disease

An unhealthy condition caused by a pathogen, such as a bacterium, fungus, phytoplasma, or virus.


A strain of a species that has certain biological characteristics distinguishing it from other individuals of that species. For example, certain populations of horseweed have genetic characters that make them resistant to the herbicide glyphosate; those are glyphosate-resistant biotypes.


A nut with no kernel, which consists of only the collapsed pellicle (skin).


Producing no grain or seed (e.g., individual florets of the rice panicle may be blanking).


A disease characterized by general and rapid death of plants or parts, such as branches, flowers, or leaves.

blind node

The first node formed on a strawberry runner that usually does not form a daughter plant.


To initiate the growth of flower structures.


A bulge in the upper leaf sheath caused by the expansion of the developing panicle.

Bordeaux mixture

A pesticide made of a mixture of copper sulfate and hydrated lime primarily used as a fungicide.

border harvesting

A harvesting method that leaves a strip of uncut hay along every other border. During the next harvest, these borders are mowed and the alternate borders are left standing.

borrow pits

Depressions on either side of a levee created when soil is removed from the field to build the levee.


Derived from plants or plant parts.


A modified leaf at the base of a flower.

broad-spectrum pesticide

A pesticide that kills a wide variety of unrelated species.

broadcast application

The application of a substance (e.g., fertilizer or pesticide) to an entire area (e.g., field or orchard).


A flowering vascular plant (angiosperm) in the dicot group, characterized by leaves that are usually broader than needles or grass leaves, with a network of intersecting veins instead of parallel veins. Broadleaf plants include many herbaceous species and nonconiferous shrubs and trees.


A small protrusion on the stem of a vascular plant that will later develop into a flower, leaf, or shoot. For example, a terminal bud is the primary growing point of a plant.

buffering capacity

The ability of soil or water to resist change in acidity (pH).


An underground storage organ of plants, composed chiefly of enlarged, fleshy leaf bases.


The circular, cupped portion of a fruit where the stem connects or was previously connected.


calcareous soil

Soil containing a high proportion of calcium carbonate.


To correct or standardize measuring devices. To properly adjust a sprayer's output.


An outer structure of a flower consisting of the sepals.


A thin layer of undifferentiated, actively dividing cells that produces new bark (phloem) on the outside and new wood (xylem) on the inside.


A dead, discolored, often sunken area (lesion) on a branch, root, stem, or trunk.


The leafy parts of plants or the outer layer of leaves.


A substance or agent capable of causing cancer.


The immature stage (larva) of a butterfly or moth (Lepidoptera).


Disfigurement or malformation of fruit, such as catfaced strawberries caused by lygus bug feeding or low temperatures.


A spikelike cluster of unisexual flowers, such as the male flowers of walnut.


An appendage resembling a tail on some insects (e.g., adult snakeflies) and other arthropods.

certified seed or planting stock

Seeds, tubers or young plants certified by a recognized authority to be free of specified pests or to contain less than a minimum number of specified pathogens or other pests.

certified transplants

Transplants (e.g., strawberry) that have received a certification tag from the California Department of Food and Agriculture. Production practices for these transplants must meet standards to be free of specified pests, such as viruses.


The part of a rice field between two levees.


Exposure to temperatures low enough to induce biological processes that produce the consumed crop. Some crops must undergo specific chilling periods in order to produce vegetative growth or floral structures.


A thick-walled spore formed from the cell of a fungal hypha.


The green pigment of plants that captures the energy from sunlight, which is necessary for photosynthesis.


Bleaching or yellowing of normally green plant tissue.


The outer membrane of an insect egg.


Occurring frequently or over a long duration. Caused by frequent occurrence or long duration of a given condition (e.g., pesticide exposure and chronic toxicity).

chronic toxicity

The potential for a substance (e.g., a pesticide) to cause harm after multiple exposures (typically smaller amounts) over an extended period of time.

circulative virus

A virus that systemically infects its vector (e.g., an insect) and generally is transmitted for the remainder of the vector's life. Also called persistent virus.


A sheath, such as a covering of silk, formed by an insect larva as a chamber for pupation.


A group consisting of individuals that all have a common characteristic, typically consisting of individuals who are the same age.

cole crop

A crop within the crucifer family (Brassicaceae) harvested for either its leaves or head. Cole crops typically refers to different subspecies of Brassica oleracea (including broccoli, Brussels sprouts, cabbage, and cauliflower). Other Brassica, such as B. rapa (bok choy, tatsoi, and turnip), may also be considered cole crops.


A sheathlike structure enclosing the young shoot tip of a grass seedling.

collar region

In grasses, the region where the leaf blade and sheath meet; used in identifying species. In shrubs and trees, the trunk area at the soil line.

companion planting

The practice of planting certain plant species (e.g., herbs) in close association with other crop plants as an effort to repel pests or otherwise favor plant growth.

competitive exclusion agent

An organism capable of out competing other organisms to such an extent that it excludes the other organisms from the environment.

complete metamorphosis

A type of development in which there are four main life stages (egg, larva, pupa, and adult) and the larvae generally look distinctly different than the adults.

conidium (plural: conidia)

An asexual fungal spore formed by budding or fragmentation at the tip of a specialized hypha.


One of two tubular structures projecting from the top rear of an aphid's abdomen.


The tissue between the phloem and the epidermis in roots and stems.


A leaf formed within the seed and present on a seedling at germination. Also called a seed leaf. Cotyledons typically have a different appearance than true leaves.

cover crops

Crops that are primarily grown to improve the production system for a primary crop. Examples include grasses or legumes maintained in orchards or vineyards and legumes or other crops grown during the winter season to improve soil conditions.


The mobile first instar of certain types of insects, such as mealybugs, scales, and whiteflies.


Tiny hooks on the prolegs of caterpillars.

crop rotation

The practice of purposefully alternating crop species grown on the same plot of land, typically to improve soil conditions or manage pests.

cross resistance

A condition in which a pest population that has developed resistance to one type or group of pesticides is also resistant to another type or group of pesticides, even in the absence of exposure to the latter pesticides.


In trees or shrubs, may either mean the place where the main stem (trunk) and roots join at the soil line or the topmost limbs on a tree or shrub (the latter definition is commonly used in forestry). In strawberry, the shortened stem of a strawberry plant, from which fruit, leaves, and roots arise. The crown may also mean all the aboveground parts of the plant in some contexts.


The aboveground stem of grasses and sedges.


An identifiable strain within a plant species that is specifically bred for particular properties; sometimes used synonymously with variety.


Holding tubers under warm, humid conditions that favor wound healing. The process of drying a crop, such as to improve its storage.


The outer protective covering of arthropods and plants, which helps prevent moisture loss.


In cotton, a period of reduced growth and square production following a fruiting cycle.



Death of seedlings caused by one or more pathogens that weaken the stem or root.

daughter plants

Vegetative progeny of plants that reproduce via rhizomes, stolons, tubers, or other structures. In strawberry, daughter plants develop along the runners produced by the original strawberry plant (called the mother plant).


The term applied to cultivars, such as of strawberry, that produce flower buds more or less independently of day length.

degree-day (DD)

A unit combining temperature and time used in monitoring growth and development of organisms. May also be called a heat unit.


Opening naturally and regularly along lines of weakness. In fruits, opening along sutures to release seeds.

delayed dormancy

The period in tree fruit and nut crops that begins when buds begin to swell and continues until the beginning of green tip development or just before the emergence of new leaves.


Having stems and branches that stop growing at a certain point, usually after producing flowers. In cotton, this term is applied to varieties with a distinct interruption in growth following fruit set. In tomato, this term applies to varieties that grow into compact, bush-type forms and for which fruit ripens all at once.

developmental threshold

The lowest temperature at which growth occurs in a given species.


A period of physiologically controlled dormancy or inactivity in insects or other invertebrates.


A plant that has two cotyledons, or embryonic leaves, which are the first leaves to appear from a germinating seed.


An unhealthy condition (e.g., that caused by a pathogenic bacteria, fungus, or virus) that impairs the function or performance of an organism. In the case of crops, disease impairs a plant's economic value.


A period of inactivity or slowed function, such as that seasonally or during periods of adverse environmental conditions. For many tree fruit and nut crops, dormancy occurs during the winter.

dough stage

A stage in grain (seed) development when the grain turns from a liquid to a soft doughy consistency before hardening.

drag off

The practice of removing soil from the tops of potato hills before sprout emergence.


The aerial dispersal of a substance, such as a pesticide, beyond the intended application area.


Stunting of plant growth, such as smaller-than-normal leaves and stems.


economic threshold

The point at which a pest has become numerous or damaging enough to require a management action (e.g., pesticide application) to prevent intolerable economic loss. The point at which the damage caused by a pest exceeds the cost of taking a management action to reduce the pest's abundance or subsequent damage. May also be called action threshold or treatment threshold.


A parasite that lives on the outside of its host.


A parasite that lives inside its host.


The tissue containing stored food in a seed that surrounds the embryo and is eventually digested by the embryo as it grows.

entomopathogenic nematodes

Nematodes that infect and, in combination with symbiotic bacteria, kill insects.


The part of an embryo or seedling above the attachment point of the cotyledon(s).


The outermost layer of living cells on the surface of an animal or plant.


A state of inactivity during the summer months or dry or hot weather. Also called aestivation.


The loss of soil moisture due to the combination of evaporation from the soil surface and transpiration by plants.


In strawberries, producing flowers and fruit throughout year as long as temperatures are favorable.


The act of keeping pests away from crops, structures, or other areas, commonly by using barriers such as fencing, row covers, or screens.

extrafloral nectary

A nectary located outside the flower.


In potato, a collection of buds on the surface of the tuber that can sprout and form a new stem when conditions are favorable.



Allowing cultivated land to lie dormant, with no crops growing on it, for an extended time period, such as during one growing season.

feeder roots

The youngest roots with root hairs, which are most important in the absorption of nutrients and water.

field capacity

The amount of moisture left in the soil after saturation and excess water has drained away via infiltration, percolation, and runoff.

flag leaf

The terminal leaf of a grass plant. The last emerging leaf below the grain head.


Outer part of the rind of citrus fruit, bearing oil glands and pigments.


The period of flying activity of moths or other adult insects of a given generation.


In grasses, an individual flower in a grass spikelet. In head-forming cole crops, one of the flowering stems making up the head of broccoli or cabbage. In plants in the sunflower family (Asteraceae), one of the small flowers within the inflorescence.

flower bud

A bud in which flower parts are contained.


The leaves of a plant.


The feces of insects.

fruiting bodies

In fungi, reproductive structures that produce spores.


Treatment with a pesticide that either is a gas or becomes a gas after it is applied.


A pesticide for fungi.

fungus (plural: fungi)

A multicellular organism (e.g., mildew, mold, rust, or smut) that lacks chlorophyll and derives its nutrients from other organisms. The fungal body generally consists of filamentous strands called mycelium.



Localized swelling or outgrowth of plant tissue, often formed by a plant in response to the action of an insect, pathogen, or other organism.

girdle (v.)

To damage or kill a ring of tissue around a root or stem in a way that interrupts the transport of nutrients and water and commonly results in the death of plant parts above or below the girdle or even the entire plant.


Each of two membranous bracts (leaflike structures) below a grass spikelet or the single bract surrounding the florets of a sedge.


A bitter-tasting plant compound that can be present at potentially toxic concentrations in the foliage of plants in the Solanaceae family and in the epidermis of potatoes.


A substance poisonous to many animals, produced by numerous small glands in most cotton varieties.

graft union

Place where the rootstock joins the scion, or top part of grafted trees, shrubs, or vines.

ground cover

Any of various low- and dense-growing, spreading plants, such as ivy and pachysandra. Plants used for covering the ground, such as substitutes for turfgrass.



The inflorescence of certain plants, such as cole crops, grasses, small grains, and sunflowers.

heat unit

See degree-day.


A pesticide for undesirable vegetation (weeds).

hibernaculum (plural: hibernacula)

A shelter occupied during the winter by a dormant insect, notably peach twig borer, or other animal.


An excretion from insects, such as aphids, mealybugs, soft scales, and whiteflies, consisting of modified plant sap and composed mostly of sugars and water.


An increase in the reproduction of an organism that can occur after sublethal exposure to certain pesticides.

horticultural oils

Highly refined petroleum (or seed-derived) oils that are manufactured specifically to manage (e.g., kill or repel) pests on plants.


An animal, plant, or other organism that provides sustenance for a parasite or pathogen.

host resistance

The ability of a host plant or animal to ward off or resist attack by pests or to be able to tolerate damage from pests.

hypha (plural: hyphae)

A filament that is the vegetative, structural unit (mycelium) of a fungus.


The portion of an embryo or seedling between the cotyledons and the developing root. The stem of a germinating seedling.



Unable to become diseased or infected by a given pathogen.

incomplete metamorphosis

A type of arthropod development that consists of three life stages (egg, nymph, and adult) and has nymphs that commonly resemble the adults.


To move a substance, such as an herbicide or plant matter, into the soil, commonly by cultivation or irrigation.


Having a growth pattern in which stems continue growing indefinitely. For flower clusters, this term means that the lower flowers of the cluster open first, and the terminal ones open last.


Testing a plant for a pathogen infection (commonly viruses) by grafting tissue from it onto another plant (an indicator plant) that readily develops characteristic symptoms if the pathogen is present.


The entry into a host and establishment of a pathogen.


The presence of pests in a field or other area or on a given host.


A flower cluster.

inner bark

In older trees, the living part of the bark; the phloem.


Any part or stage of a pathogen that can infect a host, such as spores or virus particles.


Containing no carbon. Generally used to describe substances (e.g., pesticides) that are of mineral origin.


One of the larval or nymph stages of an immature insect between successive molts. For example, the first instar is between hatching and the first molt.

integrated pest management (IPM)

A pest management strategy that focuses on long-term prevention or suppression of pests or their damage through a combination of techniques, such as biological control, habitat manipulation, modification of cultural practices, and use of resistant varieties. Pesticides are used only after monitoring indicates they are needed according to established guidelines if available, and treatments are made with the goal of removing only the target organism or preventing its damage. Pesticides are selected and applied in a manner that minimizes risks to human health, nontarget organisms, and the environment.


The portion of a stem between two nodes.


An animal having no spine or internal skeleton, such as an earthworm or insect.



The elongation of rice internodes before flowering.


An immature form of a nematode, insect, or other animal.



larva (plural: larvae)

The immature form of an insect that hatches from an egg, feeds, and then enters a pupal stage. The first-stage immature of mites is also called a larva, although mites do not develop a pupal stage.


The information and directions for use, storage, and disposal of a pesticide, typically found on a pesticide container. The pesticide label is a legal document that users must follow.


Producing no visible symptoms (generally refers to an infection or a pathogen).

latent period

The time between when a vector acquires a pathogen and when the vector becomes able to transmit the pathogen to a new host. The time between infection of a host plant and production of inoculum by the pathogen.

layby application

An application, such as of fertilizer or herbicide, after the crop is well established. An application at the latest time in the season when it is still possible to pass through the field with a tractor.

leaching fraction

The proportion of applied irrigation water that is added to meet the crop's leaching requirement. A measure of the excess water that is applied during an irrigation event.

leaching requirement

The amount of water in excess of a crop's evapotranspiration requirement that is needed to maintain maximum yield by moving (leaching) harmful salts down below the root zone.

leaf area index

A measure of how much foliage there is. The ratio between the total leaf surface area of a plant and the surface area of ground that is covered by the plant's leaves.

leaf margin

The outer edge of the leaf.


Natural openings in the surface of a stem or tuber, which can open and close and allow gas exchange, similar to leaf stomata.


Of or pertaining to butterflies and moths (order Lepidoptera).


Localized area of diseased or discolored tissue.


In many grasses, a short membranous projection on the inner side of the leaf blade at the junction where the leaf blade and leaf sheath meet.


One of the seed chambers in a plant ovary or cotton boll.


The toppling of plants (e.g., a grain or leaves of a bulb crop) before harvest, which can be caused by rain, wildlife, or wind.



Jaws. The forward-most pair of mouthparts of an insect.


The fecal pellet excreted by a larva before pupation.


The collection of cells at a growing point of a plant that are capable of cell division.


A change in form that takes place during development (typically for insects) from an immature to an adult.

microbial pesticides

Bacteria, fungi, viruses, or other microorganisms that are commercially produced to kill or otherwise reduce the abundance or damage of pests, such as invertebrates, plant pathogens, or weeds.


An organism of microscopic size, such as a bacterium, phytoplasma, or virus.


Generation of new, disease-free plants from tiny pieces of meristem tissue.

microsclerotia (singular: microsclerotium)

Very small sclerotia, such as those produced by Verticillium wilt fungi.

milk stage

The early stage of grain development when the grain is filled with a milky liquid.

mineral oils

Highly refined petroleum (or seed-derived) oils that are manufactured specifically to manage (e.g., kill or repel) pests on plants. Synonymous with horticultural oils.


A small tuber produced under greenhouse conditions on a small potato plant generated by micropropagation.


A pesticide for mites. Also called acaricide.


A pesticide for pest mollusks, such as slugs and snails.


In insects and other arthropods, the forming of a new cuticle (skin) that precedes shedding (ecdysis) of the old skin. Molting is a part of the process of development into a larger and older instar, or metamorphosis into the next life stage.


Carefully gathering and recording information on the abundance, development, and growth of organisms (typically pests or crops) or other factors (e.g., crop damage), often utilizing very specific procedures and commonly on a regular basis over a period of time.


A plant that has one cotyledon when it germinates from the seed.


A layer of material placed on the soil surface to prevent weed growth and improve the health of a crop or other desirable plants.


An unharvested nut remaining on the tree. For aphids, psyllids, and some other insects, the crusty skin remaining after the inside of the insect has been consumed by a parasite.


A change in the genetic code of a cell or an organism. A change in the structure of a gene.

mycelium (plural: mycelia)

The vegetative structure of a fungus, consisting of a mass of slender filaments called hyphae.


A living organism smaller than a bacterium that has a unit membrane but no cell wall. The newer generally accepted term is phytoplasma.

mycorrhiza (plural: mycorrhizae)

A fungus that grows in a symbiotic association with the roots of a plant, generally in a way that is beneficial to the plant.


narrow-range oil

A highly refined petroleum or seed-derived oil that is manufactured specifically to manage (e.g., kill or repel) pests on plants. Also called horticultural, superior, or supreme oil.

natural enemy

An organism (e.g., a parasite, pathogen, or predator) that attacks and kills one or more pests. These organisms provide biological control.


Death of tissue accompanied by dark discoloration.


A gland that secretes nectar.


A pesticide for nematodes.


The slightly enlarged part of a stem where buds are formed and flowers, leaves, and stems originate.

nonpersistent virus

A virus that is carried on the mouthparts of its vector (e.g., an insect) and is lost after the vector feeds once or a few times. A stylet-borne virus.


The immature stage of insects (e.g., aphids and grasshoppers) that develop through incomplete metamorphosis. The juveniles that hatch from eggs and develop into adults through a series of molts without passing through a pupal stage.



Relating to or derived from living matter (as in decaying plant material in a field). For substances (e.g., pesticides or decaying plant matter), this term also means that the substance contains carbon and hydrogen atoms. For agriculture (organic agriculture), organic describes a process in which animals or plants are raised or grown without the use of synthetic fertilizers, synthetic pesticides, or genetic engineering. For animals, organic means the animals are managed without antibiotics, added growth hormones, or animal products, as well as other specifications.


The portion of the flower that contains the ovules, which later develop into seeds. The ovary later matures into the fruit.


To lay or deposit eggs.


The act of laying or depositing of eggs.


A capsule or covering that contains a group of eggs, excreted by the ovipositing female.


packing tissue

In walnut, the firm, membranous tissue lining the nut shell and separating the kernel halves.


A branching cluster of flowers held on a stem, such as the flowering parts of most grasses.


The modified calyx of flowers in the sunflower family (Asteraceae, formerly Compositae), which usually takes the form of awns, bristles, or scales.


An organism that derives its food from the body of another organism without killing the host directly. In integrated pest management, this term also encompasses parasitoids.


An insect that spends its immature stages feeding on or inside of the body of a host insect, ultimately killing its host over the course of its development.


A form of asexual reproduction. Development of an egg without fertilization.


A disease-causing organism.


The stem of an individual flower or fruit.


The covering (skin) that encloses the kernel.


A plant that can live three or more years and flower at least twice.


Several layers of corky cells located on the outside of the epidermis of a potato tuber and containing high amounts of suberin.

perithecium (plural: perithecia)

A globular to flask-shaped fruiting body with an apical pore through which spores (ascospores) are released.

persistent virus

A virus that systemically infects its vector (e.g., an insect) and generally is transmitted for the remainder of the vector's life.


An organism that interferes with the availability, quality, use, or value of a crop, other desirable plant, or managed environment or resource. An organism that creates a nuisance or otherwise is undesirable.

pest resurgence

The rapid rebound of pest abundance after the numbers were reduced by management action.


Any substance or mixture intended for destroying, killing, preventing, or repelling a pest (including fungi, insects, nematodes, rodents, or weeds) or mitigating problems pests cause. Also includes any substance or mixture intended for use as a defoliant, desiccant, or plant growth regulator.

pesticide resistance

A result of genetic selection in which a pest population is able to survive or resist the effects of a pesticide or group of pesticides that formerly controlled the pest, ultimately resulting in the pesticide being less effective or no longer effective.

pesticide rotation

The practice of alternating pesticides of different modes of action in order to prevent the development of pesticide resistance.


The stalk connecting a leaf to a stem.


A value used to express the relative acidity or alkalinity (basic) of a substance (e.g., soil or pesticide mixture). The hydrogen ion concentration of a substance as expressed in a negative logarithmic scale ranging from 0 to 14. Lower numbers indicate acidity; higher numbers indicate alkalinity.

phenoxy herbicides

A group of herbicides for broadleaf plants derived from phenoxy-acetic acid. These herbicides include 2,4-D; 2,4-DB; and MCPA.


A substance secreted by an organism to affect the behavior or development of other members of the same species. Pheromones used to monitor or manage insect pests include sex pheromones and aggregation pheromones.


The vascular tissue of a plant that transports sugars and other photosynthesis products from the leaves, such as downward to roots.


An organism that withdraws nutrients from the food-conducting tissue (phloem) of a plant's vascular system.


The products of photosynthesis, used to support plant fruit production, growth, and respiration.


The process by which plants convert sunlight, carbon dioxide, and water into sugars and other compounds needed to support development, growth, and reproduction.

physiological disorder

An unhealthy condition caused by factors other than a pathogen. An abiotic disorder.


A living organism smaller than a bacterium, formerly called mycoplasma or mycoplasma-like organism. Phytoplasmas have a unit membrane but no cell wall.


Substances that are injurious to plants.


Female part of the flower, usually consisting of ovules, ovary, style, and stigma.


An organism that transfers pollen, commonly bees and other insects.


A plant that provides pollen. The variety used as a source of pollen for cross-pollination.

pome fruit

A simple fleshy fruit that has a core of several small seeds surrounded by a thin, tough layer. Examples are apples and pears.

postemergence herbicide

An herbicide applied after weeds emerge.


Any animal (including insects and mites) that attacks and kills other animals (prey) and then feeds on them, usually consuming many prey during its lifetime.

preemergence herbicide

An herbicide applied before weeds emerge.

presence/absence sampling

A sampling or monitoring method that involves recording only the presence or absence of a given organism (e.g., an insect pest) on a sample unit (e.g., a leaf), rather than counting the numbers of individuals. Also called binomial sampling.

primary bloom

The first production of flowers on a potato plant, occurring after 8 to 12 leaves have been formed on the mainstem and generally coinciding with the beginning of the tuber growth phase.

primary inoculum

The initial source of a pathogen that starts disease development in a given location.

primary roots

The central, first-formed, or main roots of a plant. In strawberry, roots that develop from the crown of the plant.


A fleshy, unsegmented, leglike appendage on the abdomen of certain insect larvae (e.g., caterpillars and sawflies).


A prominent, platelike structure that covers a portion or all of at least the upper surface (dorsum) of the first thoracic segment of an insect.


Any part of an organism from which a new organism can grow. For plants, this includes bulbs, seeds, and tubers. For fungi, this includes sclerotia and spores.

protectant fungicide

A fungicide that prevents a plant from being infected by a fungal pathogen. A fungicide that prevents the development of a fungal infection.

protective coverings

Any cloth, screen, plastic or other material placed over growing plants to prevent damage by pests or harsh weather.


The first (front) segment of the insect thorax.

pupa (plural: pupae)

The nonfeeding, relatively inactive stage between larva and adult in insects that undergo complete metamorphosis.


To develop into a pupa.


A small, blisterlike elevation of epidermis from which spores emerge.

pycnidium (plural: pycnidia)

A small, spherical or flask-shaped structure formed by certain types of fungi, inside which spores are produced.



One of four equal parts into which a field can be divided for monitoring.


A period of enforced isolation and restricted movement that is imposed to prevent the spread of pests. The legal enforcement of measures aimed to prevent a pest from spreading or establishing in new areas.


random sample

A method of sampling in which the selection of the sample area is based on chance, and in which all parts of a given area have equal chance of being selected for sampling. Locations for samples are not predetermined either by previous sampling in that field, the relationship of one sample location to another, or other patterns.

rat-tail bloom

A secondary bloom in apples or pears that results when terminal buds form and open on the current season's growth.


The apex of the flower stem that bears the organs of the flower.

regrowth bud

The buds on alfalfa crowns that become new stems.

reproductive bud

The buds on alfalfa stems that become flowers.


The site where a pest can survive in the absence of a host crop, and that can facilitate an infestation in a crop.

residue management

Management (including incorporation and decomposition) of crop or weed matter that remains in the field or other area after harvest.


In cells, the process by which nutrients are metabolized to provide energy needed for cellular activity. In animals, the production of energy, typically with the intake of oxygen and the release of carbon dioxide from the digestion of complex organic substances.


A horizontal, underground stem that forms roots at the nodes to produce new plants.


To remove weeds or damaged crop plants.


Mechanical crushing of potato vines to hasten vine death, sometimes used synonymously with vine-killing.


The lower portion of a graft that consists of the root system. The cultivar or variety used for that part of a graft.


A cluster of leaves arranged in a compact circular pattern, often on young plants, at a shoot tip, or on a shortened stem.

rosetted bloom

A flower with petals that have been tied together with silk by a pink bollworm larva.


Abnormal growth caused by certain pathogens in which new foliage is stunted and tightly bunched.

row cover

Any fabric or covering placed over rows of plants to protect them from pest damage or harsh weather.


In leaves, rough in appearance with sunken veins and raised interveinal tissue. A rough appearance generally caused by virus infection.


Any of the hoofed mammals (including cattle, deer, and sheep) that chew cud.


In strawberry, a stolon from which a daughter plant may develop. In cucurbits, a vine.


In various crops (e.g., apples, pears, red potatoes, tomatoes), damage that consists of brown discoloration and rougher texture. In russet potato varieties, thickening of the periderm on tubers that occurs after vine senescence.



Activity that reduces the spread of pathogen inoculum, especially the removal and destruction of infected plant parts and cleaning of equipment and tools. The practice of removing crop debris and weeds from growing areas.


The portion of a graft that consists of the top part of the plant, such as the branches, trunk, and tree top. The cultivar or variety used for the top part of a graft.

sclerotium (plural: sclerotia)

A compact mass of hardened mycelia that serves as a dormant stage in some fungi. A fungal survival structure.

secondary bloom

A second production of flowers on a potato plant that occurs at the end of the main stem of an indeterminate cultivar or at the leaf axils along the main stem of a determinate cultivar.

secondary infection

An additional infection facilitated or enabled either by a previous infection caused by another pathogen or a previous injury.

secondary pest outbreak

An increase in or infestation of a pest (the secondary pest) following a management action (generally a pesticide application) taken to control a different pest, caused either by the destruction of natural enemies that normally control the secondary pest or elimination of the secondary pest’s competitors.

secondary roots

The network of fine roots that develops from the primary roots of a plant. Roots that branch off of one or more primary roots.

secondary spread

The spread of a pathogen within a field after the initial or primary infection.


A grasslike, herbaceous plant that, unlike grasses, has unjointed stems. Sedge stems are commonly solid and triangular in cross-section.

seed leaf

A leaf formed in a seed and present on a seedling at germination. Also called a cotyledon.

seed piece

Portion of a potato tuber containing at least one eye that is planted to produce a new potato plant.

seed cotton

Raw, harvested cotton that is still attached to seeds before ginning.

selective pesticide

A pesticide that is toxic to a relatively small number of species, including the target pest and closely related species.


The ability to set fruit with pollen from the same flower or plant.


The condition or gradual process of deterioration with age.


One of the outermost structures of the flower that make up the calyx, commonly arranged in a whorl, which usually encloses the other flower parts.

sequential sampling

A sampling method in which the number of samples is not fixed in advance; the number of samples taken depends on the results of the previously taken samples.


Permanently attached. Incapable of moving from place to place. On plants (e.g., flowers), attached directly at the base, not raised on a stalk or stem.

seta (plural: setae)

A bristle or hair.

sex pheromone

A substance secreted by an individual to attract individuals of the same species for mating. Sex pheromones are commonly emitted by female insects to attract males.


The part of a grass leaf that encloses the stem below the collar region.


In strawberry (a subset of June-bearing cultivars), requiring a period of time with day length shorter than a minimum (about 14 hours) to induce flower buds.


Fertilizer or other material added to the soil around a growing crop. The most common use is sidedressing nitrogen to induce nutrient uptake and rapid growth.

sieve tubes

The elongated living cells of the phloem, which are the conduits of sugars produced during photosynthesis.


Physical evidence of a pest’s presence that can be seen on a host or its surroundings. For example in plant pathogens, signs can include fruiting bodies and spores.


To remove leaf tissue between the veins, leaving the network of veins intact.

soil profile

The characteristics and differences of soil at different depths. The arrangement of soil into layers.


The practice of heating soil to levels lethal to pests using solar energy by laying clear plastic on soil surfaces for 4 to 6 weeks during warm, sunny weather.

sooty mold

Fungi that form a dark coating on foliage, fruit, or other surfaces on which honeydew has been deposited by phloem-sucking insects (e.g., aphids and whiteflies).


The abbreviation for a single species.

species (abbreviation: sp. if singular, spp. if plural)

A group of individual organisms consisting of similar individuals that can interbreed in nature to produce fertile offspring.

specific gravity

The ratio of the density of a substance to the density of pure water. In potato, often used to quantify the dry matter content of potato tubers.


An elongated, relatively tall inflorescence in which individual flowers are attached tightly against the main stem. Commonly the flower arrangement is unbranched and the newest flowers are at the tip.


An external opening in the body of an insect or other arthropod that allows air to enter the respiratory system.

sporangium (plural: sporangia)

A structure in which asexual spores are contained.


A reproductive structure produced by fungi and other organisms that develops into a new individual under proper conditions.


The production of spores.


Abbreviation for multiple species.


A young, germinated seedling. A new stem formed from the eye of a potato tuber.

sprout inhibitor

A substance applied to potato vines or stored tubers to prevent sprouting.


On fruit trees, a short, woody shoot on which flowers and fruit develop.


A cotton flower bud.


Abbreviation for subspecies.


A male flower structure comprised of the pollen-bearing anther and a stalk or filament.

stand decline

The gradual (over a period of 3 to 5 years) debilitation of an alfalfa field due to the combined effects of pests and unfavorable environmental conditions.


The central cylinder inside the cortex of the roots and stems of vascular plants, which contains the conducting or vascular tissue.


A stalk or stem, especially of a fungus but may also pertain to plants.


A trailing, aboveground stem or shoot, often rooting at the nodes and forming new plants.

stoma (plural: stomata)

A natural opening in a leaf surface that allows for gas exchange and water evaporation and that opens or closes in response to environmental conditions.


A compact structure formed from fungal mycelium on the surface of a host, which generally is spore-producing.

stub cotton

A cotton crop in which the stalks are cut down after harvest, but the crown and rootstock are left in the ground to regrow the following season.

stylet-borne virus

A virus that is carried on the mouthparts of its insect vector and is lost after the vector feeds once or a few times. A nonpersistent virus.


A waxy substance that is resistant to microbial attack and is formed in the corky cells of periderm layers, such as in potatoes.


The formation of periderm layers on the cut surfaces or wounds (e.g., of potato tubers).


A shoot arising from the roots or lower part of the stem or trunk of a plant.

sun checking

Breaking or cracking of whole kernels of grain due to alternating conditions of dew, sun, and water stress.


The visible seam on a nut hull.


An outward expression or change in appearance indicating that an organism is unhealthy. In plants, symptoms include chlorosis, necrosis, and wilting.


Capable of moving throughout a plant or other organism, usually via the vascular system.



Irrigation water that has drained from a field.


A large primary root that grows vertically downward, with small lateral roots growing from it.

target pest

The pest that a management action (e.g., a pesticide application) is intended to destroy or manage.


A thick-walled, dark spore of rust and smut fungi that is able to survive adverse conditions.


A device for measuring soil moisture, such as that consisting of a buried tube of water that develops a partial vacuum as surrounding soil dries out.

terminal spikelet stage

The stage in the development of the wheat spike when the primordia (cells that will develop into florets or spikelets) of the terminal are formed.


The second of three major body divisions of an insect. The segments bearing the legs and wings (if present).


A stem or shoot of grass that grows after the initial shoot has grown from the seed.


In pests, the ability to endure a pesticide without experiencing adverse effects. In crops, the ability of a plant to grow in spite of a pest infestation. In pesticide regulation, the maximum amount of pesticide residue that is permitted on a given agricultural product. In seed certification, the maximum percentage of the crop infested with a pathogen or other pest that is allowed during field inspections for certification of a seed lot.

top crop

Fruit produced in the second fruiting cycle of cotton, mainly on upper branches.


To change the cultivar of an established tree by pruning off part or all of the existing scion and subsequently budding or grafting a new scion onto either the rootstock or the remaining scion.


A poisonous substance produced by an organism, commonly through metabolic processes.

translocated pesticide

A pesticide that is able to move throughout a plant, such as to roots after being applied to leaf surfaces. A systemic pesticide.


The evaporation of water from plants, commonly through tiny leaf openings (stomata).

trap crop

A crop or portion of a crop intended to attract pests so they can be destroyed by treating a relatively small area or by destroying the trap crop and the pests together.

treatment threshold

The point at which a given pest is numerous enough that a management action (e.g., a pesticide application) is necessary to prevent economic loss or unacceptable damage. May also be called action threshold and economic threshold.

true leaf

Any leaf produced after the cotyledons.


An enlarged, fleshy, underground stem with buds capable of producing new plants.


The formation of tubers at the ends of stolons. Tuber production.



Spore produced by a rust fungus that can spread the fungus to infect other hosts.



In plants, an identifiable variant or strain within a species, generally occurring naturally as opposed to a cultivar, which is specifically bred for particular properties. Sometimes used synonymously with cultivar.

vascular system

The system of plant tissues consisting of the phloem and xylem that transports nutrients, photosynthesis products, and water through the plant.

vascular tissue

Plant tissue that transports nutrients, photosynthesis products, and water throughout the plant.


An organism that transports and transmits a pathogen to a host.

vegetative growth

The growth of leaves, roots, and stems. Does not include the growth of reproductive structures (e.g., flowers and fruits).


In viticulture, the beginning of fruit ripening, characterized by the softening of the berries and beginning of pigmentation in black or red varieties.


Plant health or hardiness. The capacity of a plant to grow.


A tiny, infectious particle that is smaller than a virus, consisting of single-stranded, ribonucleic acid and not enclosed in a protein coat.


Capable of causing a severe disease. Strongly pathogenic.


A tiny, infectious particle consisting of nucleic acid and a protein coat, which can reproduce only within the cells of a living host.


A self-seeded, previously planted crop that has emerged at a time when it is not desired.



A type of plant damage in which the epidermal (green) tissue is removed while the leaf cuticle is left intact, leaving small segments of clear tissue.


An extension of the nut shell at the suture line.



The vascular tissue that transports nutrients and water from the roots upward through the plant.




Marked with zones or bands. Striped.


A motile spore.