Glossary

peridermthe outer layers of tissue of woody roots and terns consisting of the cork cambium and the tissues produced by it. such as bark.

permanent branches

in structural pruning of young trees branches that will be left in place often forming tbe initial scaffold framework of a tree (contrast with temporary branches).

permanent wilting pointpoint at which a plant cannot pull any more water from the soil and suffers permanent damage (compare to available water. field capacity. gravitational water. and saturation point).

permeableallowing liquids or gases to pass through. as with a membrane or material.

permitwritten order granting permission to conduct a specified task or action.

personal protective equipment(PPE) personal safety gear such as hard hat. safety glasses. hearing protection. and leg protection. including chaps.

personal protective equipment (PPE)personal safety gear such as helmet. safety glasses. hearing protection. gloves. and leg protection. including chaps.

perviouspenetrable; allowing passage through; often used to describe surfaces.

pestorganism (including. but not limited to. weeds. insects. or fungi) that is damaging. noxious. or a nuisance.

pest preventionan approach to pest management that encourages favorable plant development conditions and discourages favorable pest development conditions.

pest resistancein plants. the tendency to withstand or to not develop certain pest problems.

pest resurgenceincrease in the population of a pest following a reduction in the population of natural predators or parasites of that pest. Usually the result of a nonspecific pesticide or unfavorable environmental condition.

pest suppressionan approach to pest management that reduces the pest

pesticideany chemical used to control or kill unwanted pests such as weeds. insects. or fungi.

pesticide resistanceability to withstand certain pesticides; survival ofjust a few genetically resistant pests that reproduce can lead to populations that are resistant.

petiolestalk ofa leaf or portion ofa leaf between the stem and the blade.

petiolulestalk of a leaflet.

PGRplant growth regulator

pHunit of measure that describes the alkalinity or acidity of a solution. Negative log of the hydrogen ion concentration. Measured on a scale from 0 to 14. Greater than 7 is alkaline. less than 7 is acid. and 7 is neutral (pure water) (see acidity and alkalinity).

phasein an electric utility system. a single primary line affixed to a pole or cross arm. Technically. phase refers to the synchronized movement of electrical energy and pertains to common designs of electric supply lines such as single phase (one primary conductor). two phase (two primary(...)

phase-to-groundin an electric utility system. the electrical potential between an energized conductor and the ground.

phase-to-neutralin an electric utility system. the electrical potential between an energized conductor and the neutral wire.

phase-to-phasein an electric utility system. the electrical potential between two energized conductors or between an energized conductor and a neutral conductor.

PHCPlant Health Care

phellemthe outer portion of the bark that often exfoliates in plates or peels as it sheds from the tree.

Phellinus noxiusPhellinus noxius (??????) is a white simultaneous rot fungus that causes Brown Root Rot(BRR) disease (???), which could result in rapid health and structural deterioration of trees and may lead to tree failure.

phellodermthe inner portion of the outer bark generated by the cork cambium that stores energy and may photosynthesize.

phellogenmeristematic tissue located in the bark and that generates the phelloderm on the inside and the phellem on the outside. Cork cambium.

phenological stagea biological stage of development of an organism that may be associated with other biological events such as insect hatching.

phenologyrelationship between the climate and biological events. such as flowering or leafing out in plants.

phenology calendara calendar that correlates pest activity or development with readily observable. seasonal events such as plant budding. flowering. or fruiting.

phenolsnaturally produced organic alcohols. One of several chemical defense compounds in trees.

pheromonechemical substance produced by an animal (usually in reference to insects) that serves as a method of communication with other individuals of the same species.

photoperiodlength of daylight and/or darkness required for certain developmental processes and growth in plants.

photosynthategeneral term for the sugars and other carbohydrates produced during photosynthesis.

photosynthesisprocess in green plants (and in algae and some bacteria) by hitch light energy is used to fom1 glucose (chemical energy) from water and carbon dioxide. "

photosynthesizeto form sugar (glucose) from water and carbon dioxide using the energy of light (see photosynthesis).

phototropisminfluence of light on the direction of plant growth. Tendency of plants to grow toward light.

phylum (pl. phyla)primary taxonomic group within kingdom.

physiological disorderin plants. a disorder not directly caused by an insect. pathogen. or injury.

physiologyin arboriculture. the study of the life function of a tree (contrast with anatomy. morphology. and taxonomy).

phytochromeplant pigment that is sensitive to certain wavelengths of light. Plays a role in plant responses to light.

phytotoxictend to describe a compound that is poisonous to plants.

phytotoxicityquality of being phytotoxic.

pigmentsubstance that appears colored as a result of the reflection of certain light wavelengths.

pin locksee notch gate.

pinchingthe equivalent of heading performed on a very young tree or plant (see heading).

pinnatetype of compound leaf. with leaflets along each side of a common axis (contrast with bipinnate and palmate).

pitch tubestubular structures created by insects on the bark around entrance holes; can be made of resin. boring dust. and/or frass. Usually associated with conifers.

piththe central core of a stem. Often is a lighter color than surrounding tissue.