question: How exactly do trees get sick and how do plant related sicknesses spread?
comment: There is various ways, via pathogens or insects such as earwigs,apheids, mealy bugs that eat the leaves and the bark, spreading from tree to tree. Dead rotten tissue spreads. They can spread if not contained. They are contained using a range of methods such pesticides. Chemicals that kills pests. Or pruning where the dead or infected tissue is cut way. Diseases can also be contained via biological methods that involve the use of lady-bugs to kills the pests.
passages: List of foliage plant diseases
  
  For diseases of foliage plants, see the following lists:
  
  BULLET::::- List of Croton diseases
  
  BULLET::::- List of Ficus diseases
  
  BULLET::::- List of foliage plant diseases (Acanthaceae)
  
  BULLET::::- List of foliage plant diseases (Agavaceae)
  
  BULLET::::- List of foliage plant diseases (Araceae)
  
  BULLET::::- List of foliage plant diseases (Araliaceae)
  
  BULLET::::- List of foliage plant diseases (Araucariacea)
  
  BULLET::::- List of foliage plant diseases (Asclepiadaceae)
  
  BULLET::::- List of foliage plant diseases (Bromeliaceae)
  
  BULLET::::- List of foliage plant diseases (Cactaceae)
  
  BULLET::::- List of foliage plant diseases (Commelinaceae)
  
  BULLET::::- List of foliage plant diseases (Gesneriaceae)
   List of foliage plant diseases (Commelinaceae)
  
  This is a list of diseases of foliage plants belonging to the family Commelinaceae.
  
  Section::::References.
  
  BULLET::::- Viruses Infecting Wild and Cultivated Species of the Commelinaceae
  
  BULLET::::- Characterization and Electron Microscopy of a Potyvirus Infecting Commelina diffusa. Commelina mosaic virus
  
  BULLET::::- Commelina mosaic virus
  
  BULLET::::- Characterization of a Potyvirus Causing a Leaf Distortion Disease of "Trandescantia" and "Zebrina" Species
  
  BULLET::::- Trandescantia mosaic virus
  
  BULLET::::- Brome Mosaic Virus Isolates Naturally Infecting "Commelina diffusa" and "C. communis" 
  
  BULLET::::- Mosaic Disease of Rhoeo discolor Caused by a Strain of Tobacco Mosaic Virus
   BULLET::::- List of pecan diseases
  
  BULLET::::- List of peanut diseases
  
  BULLET::::- List of peach and nectarine diseases
  
  BULLET::::- List of papaya diseases
  
  BULLET::::- List of Jerusalem cherry diseases
  
  BULLET::::- List of hop diseases
  
  BULLET::::- List of hemp diseases
  
  BULLET::::- List of grape diseases
  
  BULLET::::- List of date palm diseases
  
  BULLET::::- List of cineraria diseases
  
  BULLET::::- List of chickpea diseases
  
  BULLET::::- List of foliage plant diseases (Maranthaceae)
  
  Section::::References.
  
  BULLET::::- Alford, D.V. 2012. Chapter 4-Miscellaneous Pests. "Pests of Ornamental Trees, Shrubs, and Flowers" (2): 434-443.
   "Ceratocystis coerulescens" enters its host through wounds, especially wounds in buttress roots and lower trunk. All diseased trees have been found to have man-made wounds from tapping and/or driving and dragging logs over them. Therefore it’s believed that the trees successfully combat the pathogen when it enters wounds higher up made by animals, insects, or weather. Sapstreak disease is commonly associated with the presence of opportunistic fungi "Armillaria" and/or "Xylaria".
  
  Importance
   BULLET::::- List of foliage plant diseases (Araceae)
  
  BULLET::::- List of foliage plant diseases (Acanthaceae)
  
  BULLET::::- List of foliage plant diseases (Agavaceae)
  
  BULLET::::- List of foliage plant diseases (Araliaceae)
  
  BULLET::::- List of foliage plant diseases (Asclepiadaceae)
  
  BULLET::::- List of foliage plant diseases (Gesneriaceae)
  
  BULLET::::- List of Ficus diseases
  
  BULLET::::- List of foliage plant diseases (Polypodiaceae)
  
  BULLET::::- List of foliage plant diseases (Vitaceae)
  
  BULLET::::- List of rhododendron diseases
  
  Section::::Biology.
   "Phytophthora cactorum" has an extremely wide host range, and can infect over 200 species or 160 genera of trees, ornamentals, and fruit crops. In general, "P. cactorum" is capable of infecting both young and old plants, and causes root rots and crown rots of the many genera it infects. Although the symptoms this pathogen produces varies between the types of organisms it infects, in general disease occurs during periods that are both wet and warm. Furthermore, most infections are caused by zoospores entering the plant through wounds.
   Section::::Disease cycle.
   Lists of plant diseases
  
  This is a list of articles that are lists of plant diseases.
  
  Section::::A.
  
  BULLET::::- List of foliage plant diseases (Acanthaceae)
  
  BULLET::::- List of African daisy diseases
  
  BULLET::::- List of African violet diseases
  
  BULLET::::- List of foliage plant diseases (Agavaceae)
  
  BULLET::::- List of alfalfa diseases
  
  BULLET::::- List of almond diseases
  
  BULLET::::- List of anemone diseases
  
  BULLET::::- List of apple diseases
  
  BULLET::::- List of apricot diseases
  
  BULLET::::- List of foliage plant diseases (Araceae)
  
  BULLET::::- List of foliage plant diseases (Araliaceae)
  
  BULLET::::- List of foliage plant diseases (Araucariaceae)
  
  BULLET::::- List of foliage plant diseases (Asclepiadaceae)
   Mango wilt is known only in Brazil, even though mango trees ("Mangifera indica") are grown in other areas where "C. fimbriata" is common on other plants. Infection typically occurs through fresh wounds on trees although root infections also occur. Infection is often accompanied by secondary attack by various ambrosia beetles.
  
  Section::::Diseases.:Ficus wilt.
  
  Ficus wilt is a severe disease found in fig trees ("Ficus carica") in Brazil. There is also an Asian form of Ficus wilt caused by "C. fimbriata" found in southern Japan.
  
  Section::::Diseases.:Rapid 'Ohi'a Death.
   Crown rot or root rot of strawberries is a common example of diseases of fruit crops caused by "P. cactorum". On strawberries, "P. cactorum" infects the roots and the base of the plant causing stunting and reduced leaf size, with possible complete plant collapse later in the season. Similarly to apple trees, crown rots of strawberries caused by "P. cactorum" can be partially diagnosed by cutting the crown of the plant and observing brown vascular tissues, and root rots by brown or black stunted roots.
  
  Section::::Life cycle.
   Section::::Elements of an epidemic.:Types of epidemics.
  
  Pathogens cause monocyclic epidemics with a low birth rate and death rate, meaning they only have one infection cycle per season. They are typical of soil-borne diseases such as Fusarium wilt of flax. Polycyclic epidemics are caused by pathogens capable of several infection cycles a season. They are most often caused by airborne diseases such as powdery mildew. Bimodal polycyclic epidemics can also occur. For example, in brown rot of stone fruits the blossoms and the fruits are infected at different times.
   Section::::Disease Cycle.
  
  Section::::Disease Cycle.:Factors that give rise to infection.
   BULLET::::- Rickettsia which causes possibly this citrus greening disease
  
  BULLET::::- Spiroplasma
  
  BULLET::::- Dutch elm disease
  
  BULLET::::- Ink disease
  
  BULLET::::- Emerald ash borer
  
  BULLET::::- Olive tree pathology
  
  BULLET::::- Witch's broom
  
  BULLET::::- White Pine Blister Rust
  
  BULLET::::- Phytophthora cinnamomi which causes root rot
  
  BULLET::::- Phytophthora ramorum which causes sudden oak death
  
  BULLET::::- Polypore or bracket fungus
  
  BULLET::::- Tinder conk
  
  Section::::Signs and symptoms.
  
  Symptoms are a result of a pathogen:
  
  BULLET::::- Blight
  
  BULLET::::- Burl
  
  BULLET::::- Canker
  
  BULLET::::- Chlorosis
  
  BULLET::::- Drunken trees
  
  BULLET::::- Forest dieback
  
  BULLET::::- Gall
  
  BULLET::::- Girdling
  
  BULLET::::- Leaf scorch
  
  BULLET::::- Root rot
  
  BULLET::::- Virescence
  
  BULLET::::- Wilt disease
   Back to top
  
  Section::::O.
  
  BULLET::::- List of oats diseases
  
  Back to top
  
  Section::::P.
  
  BULLET::::- List of foliage plant diseases (Palmae)
  
  BULLET::::- List of papaya diseases
  
  BULLET::::- List of pea diseases
  
  BULLET::::- List of peach and nectarine diseases
  
  BULLET::::- List of peanut diseases
  
  BULLET::::- List of pear diseases
  
  BULLET::::- List of pearl millet diseases
  
  BULLET::::- List of pecan diseases
  
  BULLET::::- List of pepper diseases
  
  BULLET::::- List of Persian violet diseases
  
  BULLET::::- List of pigeonpea diseases
  
  BULLET::::- List of pineapple diseases
  
  BULLET::::- List of foliage plant diseases (Piperaceae)
  
  BULLET::::- List of pistachio diseases
  
  BULLET::::- List of pocketbook plant diseases
   "H. occidentale" can also spread directly between the adjacent trees through root contact with an infected tree. This phenomenon can devastate forests creating ‘circles of death’ that can be difficult to remove from a stand. However compared to other root rot pathogens the genets of disease circles are not as large or as old as those found from "Armillaria" or "Phellinus".
  
  Section::::Control.
   BULLET::::- "Phytophthora citricola"—causes root rot and stem cankers in citrus trees
  
  BULLET::::- "Phytophthora fragariae"—causes red root rot affecting strawberries
  
  BULLET::::- "Phytophthora infestans" causes the serious disease known potato (late) blight: responsible for the Irish potato famine.
  
  BULLET::::- "Phytophthora kernoviae"—pathogen of beech and rhododendron, also occurring on other trees and shrubs including oak, and holm oak. First seen in Cornwall, UK, in 2003.
  
  BULLET::::- "Phytophthora lateralis"—causes cedar root disease in Port Orford cedar trees
  
  BULLET::::- "Phytophthora megakarya"—one of the cocoa black pod disease species, is invasive and probably responsible for the greatest cocoa crop loss in Africa
   BULLET::::- List of durian diseases and pests
  
  Back to top
  
  Section::::E.
  
  BULLET::::- List of elm diseases
  
  BULLET::::- List of English walnut diseases
  
  BULLET::::- List of foliage plant diseases (Euphobiaceae)
  
  Back to top
  
  Section::::F.
  
  BULLET::::- List of flax diseases
  
  BULLET::::- List of fuchsia diseases
  
  Back to top
  
  Section::::G.
  
  BULLET::::- List of foliage plant diseases (Gentianaceae)
  
  BULLET::::- List of geranium diseases
  
  BULLET::::- List of foliage plant diseases (Gesneriaceae)
  
  BULLET::::- List of grape diseases
  
  Back to top
  
  Section::::H.
  
  BULLET::::- List of hazelnut diseases
  
  BULLET::::- List of hemp diseases
  
  BULLET::::- List of holiday cacti diseases
  
  BULLET::::- List of hop diseases
   Section::::Ecology.:Plant disease interactions.
  
  One of their most harmful roles is as the agent of many plant diseases. For instance:
  
  BULLET::::- Dutch Elm Disease, caused by the closely related species "Ophiostoma ulmi" and "Ophiostoma novo-ulmi", has led to the death of many elms in Europe and North America.
  
  BULLET::::- The originally Asian "Cryphonectria parasitica" is responsible for attacking Sweet Chestnuts ("Castanea sativa"), and virtually eliminated the once-widespread American Chestnut ("Castanea dentata"),
  
  BULLET::::- A disease of maize ("Zea mays"), which is especially prevalent in North America, is brought about by "Cochliobolus heterostrophus".
  
  BULLET::::- "Taphrina deformans" causes leaf curl of peach.
   Section::::Disease Cycle.:Stages of infection.
   Some plants growing on durian trees can be problematic or even parasitic.
  
  BULLET::::- dragon scales ("Drymoglossum piloselloides")
  
  BULLET::::- mistletoe ("Elytranthe barnesii")
  
  BULLET::::- mistletoe ("Loranthus pentandrus")
  
  Section::::Non-pathogenic epiphytes and symbiotes.
  
  These species live on or in durian trees as epiphytes but typically do not harm the tree or fruit. However, "Trentepohlia" species can grow thick enough to block lenticels and inhibit ramiflorous flowering.
  
  BULLET::::- "Aschersonia placentae" (teleomorph: "Hypocrella raciborskii")
  
  BULLET::::- "Diploicia canescens" (formerly "Buellia canescens"
  
  BULLET::::- oakleaf fern ("Drynaria quercifolia") Anderson (1966)
  
  BULLET::::- strangling fig ("Ficus benjamina") Anderson (1966)
  
  BULLET::::- "Hypocrella raciborskii" (syn. "Aschersonia placentae")
  
  BULLET::::- "Parmelia" sp.
  
  BULLET::::- "Phycopeltis"
   BULLET::::- Tomato ("Solanum lycopersicum" cv. Horis): necrosis of leaves. Symptoms appear on wounded tissue.
  
  BULLET::::- Pepper ("Capsicum annuum" cv. California Wonder): root infection, and fruit rot of wounded fruit. Necrosis of leaves appear on wounded tissue.
  
  Section::::Disease cycle.
   Section::::Disease Cycle.:Stages of infection.:Asexual (anamorph) stage.
   BULLET::::- leaf mould "Passalora fulva" (syn. "Cladosporium fulvum"
  
  BULLET::::- secondary/opportunistic fruit rot ("Penicillium" sp.)
  
  BULLET::::- seedling dieback ("Perisporium" sp.)
  
  BULLET::::- leaf spot ("Pestalotia" sp.)
  
  BULLET::::- pink disease/ ("Phanerochaete salmonicolor" syn. "Botryobasidium salmonicolor", "Corticium salmonicolor", "Erythricium salmonicolor")
  
  BULLET::::- leaf spot ("Phomopsis" sp.)
  
  BULLET::::- "Phomopsis" leaf spot, "Phomopsis" fruit rot, branch and stem necrosis, leaf spot of seedlings ("Phomopsis durionis")
  
  BULLET::::- sooty mould of fruits, twigs, and leaves ("Phragmocapnias betle")
  
  BULLET::::- "Phyllachora makrospora"
  
  BULLET::::- seedling rim blight, leaf spot, postharvest fruit rot ("Phyllosticta" sp.)
  
  BULLET::::- rim blight, leaf spot ("Phyllosticta durionis")
  
  BULLET::::- leaf parasite ("Placosphaeria durionis")
  
  BULLET::::- "Plokamidomyces colensoi"
   There are a number of plants that can be infected by the telial stage. Therefore, the telial stage is considered a pathogen to those plants. A few specific plant pathogenic species are listed here with their hosts.
  
  BULLET::::1. "Puccinia graminis" or known commonly as black stem rust. It infects many different cereal crops.
  
  BULLET::::2. "Gymnosporangium juniperi-virginianae". It infects the eastern red cedar (Volk, 1999). This is shown to the right.
  
  BULLET::::3. "Gymnosporangium sabinae". It infects pear trees.
  
  Section::::Spore stages.
   The pathogenicity of "Armillaria ostoyae" appears to be more common in interior stands, but its virulence is seen to be greater in coastal conifers. Although conifers along the coastal regions show a lower rate of mortality against the root disease, infections can be much worse. Despite differences in how infections occur between these two regions, infections are generally established by rhizomorph strands, and pathogenicity is correlated to rhizomorph production.
  
  Section::::Geography.
  