Tree work words: pests and diseases
Signs, symptoms and damage words from the Bugwood IPED glossary, plus biosecurity, notifiable and regulated-area words from Forest Research, GOV.UK, the CFIA and Tiakina Kauri.
Checked against the sources at the bottom of this page on October 8, 2026. Rules, fees and pay change: the source has the last word.
This page reports what the official source says. It is not legal advice: ask the office named here. Two kinds of words sit on this page. The first kind names what a crew can see on a tree, such as frass, flagging or a conk. The second kind comes from plant health agencies, such as notifiable, regulated area or biosecurity. The sources define the words. They do not say what any sign means in a particular tree, and neither does this page.
Every meaning is written in our own words from the page named in its row. A word that none of those pages defines is not listed. The wider A to Z list is the tree work glossary.
Words and meanings
| Term | Meaning | Source |
|---|---|---|
| Sign | In the IPED glossary, direct physical evidence of what is causing a problem. A fungal fruiting body counts as a sign. | University of Georgia Bugwood wiki, IPED glossary |
| Symptom | In the IPED glossary, how the plant itself responds to what is causing the problem. Wilting and flagging count as symptoms. | University of Georgia Bugwood wiki, IPED glossary |
| Causal factor | Anything that disrupts a plant's normal growth, in the IPED glossary. | University of Georgia Bugwood wiki, IPED glossary |
| Abiotic | Relating to non-living agents, for example the surroundings, in the QTRA glossary. | QTRA glossary of tree terms, PDF with 1999 extracts |
| Pathogen | In the QTRA glossary, a micro-organism that makes another living thing diseased. The IPED glossary describes a biological agent that gives its host a disease or illness. | QTRA glossary of tree terms, PDF with 1999 extracts; University of Georgia Bugwood wiki, IPED glossary |
| Disease | In the QTRA glossary, tissue in a living thing that stops working or is destroyed, leaving out mechanical damage, and in trees usually the work of disease-causing micro-organisms. | QTRA glossary of tree terms, PDF with 1999 extracts |
| Infection | In the QTRA glossary, a parasitic micro-organism establishing itself in the tissues of a tree or other living thing. | QTRA glossary of tree terms, PDF with 1999 extracts |
| Dieback | In the QTRA glossary, parts of a woody plant dying, beginning at the shoot tips or root tips. | QTRA glossary of tree terms, PDF with 1999 extracts |
| Flagging | In the IPED glossary, foliage on a single branch turning yellow or wilting, as happens with a number of tree diseases. | University of Georgia Bugwood wiki, IPED glossary |
| Wilt | The loss of water pressure in a leaf that makes it droop or curl or lose some of its colour, in the IPED glossary. The QTRA glossary defines a vascular wilt as a disease where water-conducting cells stop working. | University of Georgia Bugwood wiki, IPED glossary; QTRA glossary of tree terms, PDF with 1999 extracts |
| Chlorotic | Plant tissue that looks pale green to yellow, in the IPED glossary. | University of Georgia Bugwood wiki, IPED glossary |
| Canker | In the IPED glossary, a dead patch on a twig, branch or bole, often sunken. The QTRA glossary calls it a lasting lesion where bark and cambium have died after fungi or bacteria took hold. | University of Georgia Bugwood wiki, IPED glossary; QTRA glossary of tree terms, PDF with 1999 extracts |
| Conk | In the IPED glossary, the spore-producing body of certain fungi that rot wood. | University of Georgia Bugwood wiki, IPED glossary |
| Fungal fruiting body (sporocarp, sporophore) | A fungal structure that produces and releases spores. The IPED glossary uses sporocarp, and the QTRA glossary uses sporophore for the spore-bearing structure. | University of Georgia Bugwood wiki, IPED glossary; QTRA glossary of tree terms, PDF with 1999 extracts |
| Mycelium, mycelial fans | Mycelium is the body of a fungus, a mass of branching threads. Mycelial fans are flat sheets of fungal tissue, usually just under the bark. Both come from the IPED glossary. | University of Georgia Bugwood wiki, IPED glossary |
| Rhizomorph | A shoestring-like structure produced by some root disease fungi, in the IPED glossary. | University of Georgia Bugwood wiki, IPED glossary |
| Resinosis, pitch | Resinosis is an exudation of pitch on the tree, often tied to fungal infection of roots, bole or branches or to root collar weevils. Pitch is a very viscous liquid, also called resin. Both are IPED definitions. | University of Georgia Bugwood wiki, IPED glossary |
| Slime flux | An exudate of sap and bacteria associated with several kinds of bacteria, in the IPED glossary. | University of Georgia Bugwood wiki, IPED glossary |
| Frass | Solid insect excrement, usually a mixture of chewed plant fragments, in the IPED glossary. | University of Georgia Bugwood wiki, IPED glossary |
| Exit hole | A hole left by a young adult insect leaving the tree after the larva pupates and the adult hatches, in the IPED glossary. The same glossary calls tiny bark holes made by exiting beetles shot holes. | University of Georgia Bugwood wiki, IPED glossary |
| Gall | In the IPED glossary, plant tissue that grows abnormally because of insects or mites feeding or otherwise acting on it. | University of Georgia Bugwood wiki, IPED glossary |
| Honeydew | In the IPED glossary, a sticky sweet substance on which several dark-mycelium fungi can grow. | University of Georgia Bugwood wiki, IPED glossary |
| Leaf mining | In the IPED glossary, the winding track left where insects feed or live inside a leaf, beneath its surface. | University of Georgia Bugwood wiki, IPED glossary |
| Skeletonizer | An insect whose feeding leaves a lacy pattern on foliage, in the IPED glossary. | University of Georgia Bugwood wiki, IPED glossary |
| Witches' broom | In the IPED glossary, a dense cluster of twigs like a broom, formed when weak apical dominance lets side shoots lengthen. | University of Georgia Bugwood wiki, IPED glossary |
| Epicormic sprouts | In the IPED glossary, a shoot from a latent or adventitious bud on a stem or branch, or a sucker from the base of the tree. | University of Georgia Bugwood wiki, IPED glossary |
| Frost crack | In the IPED glossary, a crack in woody stem tissue from uneven expansion and contraction in extreme cold. | University of Georgia Bugwood wiki, IPED glossary |
| Biosecurity | A set of precautions that aim to prevent the introduction and spread of harmful organisms, including non-native pests such as insects and disease-causing pathogens such as some bacteria and fungi, in Forest Research's and GOV.UK's wording. | Forest Research page on biosecurity; GOV.UK guidance on tree pest biosecurity |
| Pathway (of spread) | GOV.UK lists ways tree pests and diseases move between or within countries: live plants and tree products, timber and wood packaging, dirty tools, kit, machinery and vehicles, soil and organic material, and natural means such as wind and water. | GOV.UK guidance on tree pest biosecurity |
| Wood packaging material (WPM) | GOV.UK's term for packaging such as shipping crates and pallets, listed as a pathway for tree pests and diseases. | GOV.UK guidance on tree pest biosecurity |
| Notifiable pest or disease | A pest or disease an authority lists as notifiable. Forest Research says a land owner may be issued a Statutory Plant Health Notice for one, and that a list of notifiable pests is on the UK Plant Health Information Portal. See report a pest: United Kingdom. | Forest Research page on biosecurity |
| Statutory Plant Health Notice (SPHN) | A notice a statutory plant health authority such as the Forestry Commission may issue for a notifiable pest or disease. Forest Research says it requires the recipient to eradicate or contain the pest, that receiving one is not an offence, and that not following it can bring enforcement action. | Forest Research page on biosecurity |
| TreeAlert, TreeCheck | TreeAlert is Forest Research's online tool for reporting suspect findings of tree pests and diseases in Britain. TreeCheck is the equivalent in Northern Ireland. | Forest Research page on TreeAlert; Forest Research page on biosecurity |
| Plant passport | Forest Research's biosecurity page tells professionals to check plant passport and registration requirements with the Animal and Plant Health Agency before importing or moving plants. | Forest Research page on biosecurity |
| Phytosanitary | Forest Research's biosecurity page glosses it as plant health, as in phytosanitary measures and treatments when importing certain materials or packaging. | Forest Research page on biosecurity |
| Management zone | In England, Forest Research says zones set up for oak processionary moth (OPM) carry movement restrictions on large oak trees. See regulated: oak processionary moth. | Forest Research page on the OPM |
| Caterpillar hairs (OPM) | OPM is oak processionary moth. Forest Research says older caterpillars have tiny hairs with an irritating protein, that contact can cause skin rashes, eye irritation and breathing problems, and that the hairs can stick to ropes used by tree surgeons. | Forest Research page on the OPM |
| Regulated area | A mapped area where the Canadian Food Inspection Agency sets rules on moving potentially infested material. For emerald ash borer the agency says a Movement Prohibition Notice stops the movement of affected materials from a property where the beetle is found. See regulated: emerald ash borer. | CFIA page on regulated areas and items |
| Kauri hygiene zone | In New Zealand's kauri dieback rules, the area three times the radius of the dripline of a kauri canopy, in which earthworks need a risk management plan from August 2, 2023. | Tiakina Kauri page on National Plan rules |
Reading these sources
The sign and symptom words come from the IPED glossary, written by the University of Georgia Center for Invasive Species and Ecosystem Health for forest pest identification. The QTRA glossary supplies a few disease terms. Forest Research says signs on a tree can have many causes, and its reporting tool asks for photographs of the whole tree, the symptom in context and the symptom close up.
Agencies ask for suspected regulated pests to be reported to the office for the country. Those offices and tools are on the report-a-pest pages for the United Kingdom, the United States, Canada, Ireland, Australia and New Zealand. Pages on single regulated pests include emerald ash borer, ash dieback and oak processionary moth. For who may apply pesticides, see pesticide licences by country.
Management and treatment of a named pest are not covered here. Each agency page for the pest lists what that agency says about it.
Contains public sector information published by the Health and Safety Executive and the Forestry Commission and licensed under the Open Government Licence v3.0. The wording above is ours.
Sources
- University of Georgia Center for Invasive Species and Ecosystem Health, IPED glossary, read October 8, 2026
- QTRA, Glossary of Arboricultural Terms (incorporating extracts from Lonsdale 1999, HMSO), PDF uploaded June 2023, read October 8, 2026
- Forest Research, Biosecurity, read October 8, 2026
- Forestry Commission and APHA via GOV.UK, How biosecurity can prevent the introduction and spread of tree pests and diseases, read October 8, 2026
- Forest Research, TreeAlert, read October 8, 2026
- Forest Research, Oak processionary moth, read October 8, 2026
- Canadian Food Inspection Agency, Regulated areas and items: emerald ash borer, read October 8, 2026
- Tiakina Kauri, National Plan rules, read October 8, 2026