Parasitic Diseasesdunnam.net › triton › pathology › parasitic_diseases.pdf · 2008-12-05 · Parasitic Plants According to the American Heritage Dictionary a parasite is- An

Parasitic DiseasesParasitic Diseases

Plants killing plantsPlants killing plants

Parasitic PlantsParasitic Plants

According to the American Heritage According to the American Heritage Dictionary a parasite isDictionary a parasite is--

An organism that grows, feeds, and is sheltered on An organism that grows, feeds, and is sheltered on or in a different organism while contributing or in a different organism while contributing nothing to the survival of its hostnothing to the survival of its host

More than 2,500 species of plants are known More than 2,500 species of plants are known to be parasitic on other plantsto be parasitic on other plants

Characteristics of Parasitic PlantsCharacteristics of Parasitic Plants

Most parasitic plants have developed Most parasitic plants have developed specialized organs that penetrate the host plant specialized organs that penetrate the host plant and establish connections to that plantand establish connections to that plant’’s s vascular tissuevascular tissueParasitic plants have various degrees of Parasitic plants have various degrees of dependence on the host plantdependence on the host plant

Characteristics of Parasitic Plants Characteristics of Parasitic Plants (2)(2)

Mistletoe has chlorophyll but no roots, it is Mistletoe has chlorophyll but no roots, it is dependent on the host only for support, water dependent on the host only for support, water and basic nutrientsand basic nutrientsOther plants like dodder have little or no Other plants like dodder have little or no chlorophyll and no true roots and are chlorophyll and no true roots and are completely dependent on the host plantcompletely dependent on the host plant

Significant Parasitic PlantsSignificant Parasitic Plants

Though there are more than 2500 identified Though there are more than 2500 identified parasitic higher plants only a very few are parasitic higher plants only a very few are significant, the following occur in the U.S. and significant, the following occur in the U.S. and cause notable damagecause notable damageDodderDodderDwarf mistletoesDwarf mistletoesTrue mistletoesTrue mistletoesWitchweedsWitchweeds

DodderDodder

Widely distributed in the Americas and attacks Widely distributed in the Americas and attacks several ornamentalsseveral ornamentalsAffects the growth and yield of infected plantsAffects the growth and yield of infected plants

Losses range from slight to complete destructionLosses range from slight to complete destruction

May also serve as a bridge for transmission of May also serve as a bridge for transmission of viruses from virus infected plants to virusviruses from virus infected plants to virus--free free plants if both plants are infected by the same plants if both plants are infected by the same dodder plantdodder plant

Dodder SymptomsDodder Symptoms

Orange or yellow vine strands grow and wrap Orange or yellow vine strands grow and wrap around stems and abovearound stems and above--ground plant partsground plant partsGrowing tips reach out and attack nearby Growing tips reach out and attack nearby plants, causing infestations up to 10 feet in plants, causing infestations up to 10 feet in diameterdiameterDodder continues to enlarge during the Dodder continues to enlarge during the growing season and, if on perennial plants, growing season and, if on perennial plants, from year to yearfrom year to year

Dodder Symptoms (2)Dodder Symptoms (2)

During late spring dodder produces clusters of During late spring dodder produces clusters of white, pink or yellowish flowers which form white, pink or yellowish flowers which form seedseedInfected plants become weakened and vigor Infected plants become weakened and vigor declinesdeclinesPlants may be smothered and may be killedPlants may be smothered and may be killed



Dodder growing tips rotate counter-clockwise (viewed from top) around host plant and reach out seeking nearby plants


Dodder on impatiens

Note the swellings on the side of the dodder that contacts the host.

Dodder secretes enzymes that break down host plant surface tissue and allow structures called haustoria to enter the host and attach it its vascular system


Dodder on tomato

This dodder has just begun attacking the tomato stem.

Note the growing tip is starting to stand away from the stem. As the dodder gets larger the tip will be farther away from the host stem and more likely to contact adjacent plants


Dodder flowers

Dodder has masses of flowers in late spring which quickly produce seed that drop into the soil.

Dodder seeds may germinate immediately or remain dormant until next season

Seeds germinate producing a stem but no root, the stem immediately begins rotating, apparently searching for a nearby host plant

Dodder Symptoms (8)Dodder Symptoms (8)Dodder flowers

Note the difference in color from the previous flower. Flower color can range from white to pink to yellowish

Dodder Disease CycleDodder Disease Cycle

Dodder Dodder overwintersoverwinters either as seed or in some either as seed or in some cases on perennial plantscases on perennial plantsSeeds germinate in spring and produce a shoot Seeds germinate in spring and produce a shoot but no rootbut no rootThe shoot begins rotating, apparently The shoot begins rotating, apparently searching for a nearby host plant, if no host is searching for a nearby host plant, if no host is found the shoot drops to the ground and lays found the shoot drops to the ground and lays dormant for a few weeks then diesdormant for a few weeks then dies

Dodder Disease Cycle (2)Dodder Disease Cycle (2)

If a host plant is found the dodder emits If a host plant is found the dodder emits enzymes which break down surface tissue of enzymes which break down surface tissue of the host and sends the host and sends haustoriahaustoria into the hostinto the hostDodder then climbs the host, wrapping in a Dodder then climbs the host, wrapping in a countercounter--clockwise direction (viewed from clockwise direction (viewed from above) as it growsabove) as it growsThe growing tip stands away from the host The growing tip stands away from the host apparently searching for adjacent host plantsapparently searching for adjacent host plants


The The haustoriahaustoria make a connection to the hostmake a connection to the host’’s s vascular tissue from which it takes water and vascular tissue from which it takes water and nutrients (dodder has no chlorophyll and nutrients (dodder has no chlorophyll and cannot make its own food)cannot make its own food)The base of the dodder shrivels and dies and The base of the dodder shrivels and dies and the dodder loses all contact with the soil and is the dodder loses all contact with the soil and is completely dependent on the host plant for all completely dependent on the host plant for all water and foodwater and food


The host plantThe host plant’’s growth is suppressed as the s growth is suppressed as the dodder takes its water and nutrientsdodder takes its water and nutrientsThe host may eventually die either from loss of The host may eventually die either from loss of food, loss of light from being covered by food, loss of light from being covered by dodder or bothdodder or bothIf a host plant is infected with a virus, the virus If a host plant is infected with a virus, the virus may travel through the dodder to adjacent host may travel through the dodder to adjacent host plantsplants


The dodder plant develops flowers and seedsThe dodder plant develops flowers and seedsThe seeds drop to the ground and may be The seeds drop to the ground and may be spread by water, animals and equipmentspread by water, animals and equipmentSeeds can be spread over very long distances Seeds can be spread over very long distances by contaminated crop seedby contaminated crop seed

Dodder Cultural ControlDodder Cultural Control

The best control is to prevent dodder from The best control is to prevent dodder from invading growing areas byinvading growing areas by

Using dodderUsing dodder--free seed or plantsfree seed or plantsCleaning equipment before moving it from Cleaning equipment before moving it from infested fields to clean fieldsinfested fields to clean fields

Dodder Chemical ControlDodder Chemical Control

Dodder can be controlled using contact Dodder can be controlled using contact herbicides such as herbicides such as paraquatparaquat or or diquatdiquat early in early in the seasonthe seasonHerbicides kill the host plants as well so Herbicides kill the host plants as well so prevention by cultural control is preferredprevention by cultural control is preferredNote that Note that translocatedtranslocated herbicides such as herbicides such as Roundup wonRoundup won’’t kill dodder since it has no t kill dodder since it has no roots to destroyroots to destroy

WitchweedWitchweed

WitchweedWitchweed is a serious parasitic plant in is a serious parasitic plant in Africa, Asia and AustraliaAfrica, Asia and AustraliaIt was discovered in the U.S. in 1956 in the It was discovered in the U.S. in 1956 in the CarolinasCarolinasEffective state and federal quarantines have so Effective state and federal quarantines have so far contained the parasite to the original far contained the parasite to the original infection sitesinfection sitesWitchweedWitchweed is a small (6is a small (6”” to 12to 12””) plant that is ) plant that is attractive with pink, red or orange flowersattractive with pink, red or orange flowers

WitchweedWitchweed SymptomsSymptoms

Affected plants are stunted, wilt and turn Affected plants are stunted, wilt and turn yellowish. They may die if heavily parasitizedyellowish. They may die if heavily parasitizedOne to several One to several witchweedwitchweed plants may be plants may be growing above ground next to the infected growing above ground next to the infected plantsplantsRoots of host plants contain many Roots of host plants contain many haustoriahaustoriafrom from witchweedwitchweed roots where the connection to roots where the connection to the host is madethe host is made

WitchweedWitchweed Symptoms (2)Symptoms (2)Witchweed plant at base of corn plant

Witchweed has small, elongated leaves and red or orange flowers

Attachment to the host plant is made by roots, not the above-ground parts

WitchweedWitchweed Symptoms (3)Symptoms (3)

Witchweed in corn field

WitchweedWitchweed Symptoms (4)Symptoms (4)

Witchweed flower and bud

WitchweedWitchweed Symptoms (5)Symptoms (5)Witchweed attachment

The larger white structure is witchweedwhich can grow underground and make its attachment to the host plant

Some witchweed plants never grow through the surface of the soil, those plants will eventually die

WitchweedWitchweed Disease CycleDisease Cycle

WitchweedWitchweed overwintersoverwinters as seed in the soilas seed in the soilMost seeds require a dormant period of 15 to Most seeds require a dormant period of 15 to 18 months before germination though some 18 months before germination though some can germinate immediately without any can germinate immediately without any dormant perioddormant periodSeeds close to host roots germinate and grow Seeds close to host roots germinate and grow toward those roots attracted by exudates of the toward those roots attracted by exudates of the host rootshost roots

WitchweedWitchweed Disease Cycle (2)Disease Cycle (2)

As soon as the As soon as the witchweedwitchweed root contacts the root contacts the host root its tip develops a bulbhost root its tip develops a bulb--shaped shaped haustoriumhaustoriumThe The haustoriumhaustorium dissolves and penetrates the dissolves and penetrates the host roots within 8 to 24 hourshost roots within 8 to 24 hoursLeading cells of the Leading cells of the haustoriumhaustorium force their force their way into the vascular tissue of the host rootsway into the vascular tissue of the host roots


WitchweedWitchweed develops xylem which connects to develops xylem which connects to the host xylemthe host xylemIt does not develop typical phloem cells but It does not develop typical phloem cells but connects to the host phloem as wellconnects to the host phloem as wellThe chlorophyll of The chlorophyll of witchweedwitchweed is functional but is functional but it still takes manufactured food from the hostit still takes manufactured food from the hostOften several hundred Often several hundred witchweedwitchweed plants will plants will infect the roots of a hostinfect the roots of a host


Most of the Most of the witchweedwitchweed plants do not survive to plants do not survive to reach the surface because the host plant cannot reach the surface because the host plant cannot support so manysupport so manyThe elapsed time from seed germination to The elapsed time from seed germination to producing new seeds can be 60 to 120 daysproducing new seeds can be 60 to 120 days

WitchweedWitchweed Cultural ControlCultural Control

WitchweedWitchweed is difficult to control so infestation is difficult to control so infestation should be avoided at all costsshould be avoided at all costsCatch crops of susceptible host plants force the Catch crops of susceptible host plants force the germination of germination of witchweedwitchweed which can then be which can then be plowed under or killed by herbicidesplowed under or killed by herbicidesTrap crops of nonTrap crops of non--susceptible host plants cause susceptible host plants cause witchweedwitchweed to germinate but since the hosts are to germinate but since the hosts are nonnon--susceptible the susceptible the witchweedwitchweed starves and diesstarves and dies

WitchweedWitchweed Chemical ControlChemical Control

WitchweedWitchweed can be killed by contact herbicides can be killed by contact herbicides or by or by translocatedtranslocated herbicides both of which herbicides both of which also kill the host plantsalso kill the host plantsSeeds may remain in the soil so treatment may Seeds may remain in the soil so treatment may be necessary for several yearsbe necessary for several years

Dwarf MistletoesDwarf Mistletoes

Dwarf mistletoes infect conifers and occur Dwarf mistletoes infect conifers and occur wherever conifer trees growwherever conifer trees growIn the U.S. they are more severe in the western In the U.S. they are more severe in the western half of the countryhalf of the countryDamage in conifer forests is extensiveDamage in conifer forests is extensiveTrees become stunted, deformed or killedTrees become stunted, deformed or killedSize may be reduced 50% to 80%Size may be reduced 50% to 80%Infected wood has large knots and spongy Infected wood has large knots and spongy abnormal grainabnormal grain

Dwarf Mistletoe SymptomsDwarf Mistletoe Symptoms

Dwarf mistletoe occurs as tufts along the Dwarf mistletoe occurs as tufts along the twigs, branches and trunkstwigs, branches and trunksInfected twigs and branches develop swellings Infected twigs and branches develop swellings and cankers on the infected areasand cankers on the infected areasThe swellings contain The swellings contain haustoriahaustoria of the parasite of the parasite which grow into bark, cambium and xylemwhich grow into bark, cambium and xylemInfected branches often produce witchInfected branches often produce witch’’s s broomsbrooms

Dwarf Mistletoe Symptoms (2)Dwarf Mistletoe Symptoms (2)

Young dwarf mistletoe plant on pine


Dwarf mistletoe on pine

Note the swellings on branches at infection sites


Dwarf mistletoe on hemlock

Note swelling on stem


Damage from dwarf mistletoe on trunk

The damage resembles a burl but the wood quality is very poor

The damaged area reduces the transfer of water and minerals up to the needles and of manufactured food down to the area below the damage

Dwarf Mistletoe Symptoms (6)Dwarf Mistletoe Symptoms (6)Dwarf mistletoe fruit

Dwarf mistletoe has separate male and female plants. The plants can flower after 4 to 6 years. After flowering the male shoots die. The female shoots die after discharging seeds from fruit.

When disturbed, ripe fruit “explodes”expelling seeds forcefully up to 15 meters

The sticky seed adheres to whatever it comes in contact with

Dwarf Mistletoe Disease CycleDwarf Mistletoe Disease Cycle

When disturbed a ripe fruit forcefully expels When disturbed a ripe fruit forcefully expels seeds up to 15 metersseeds up to 15 metersThe seeds are covered with a sticky substance The seeds are covered with a sticky substance and adhere to whatever they come in contact and adhere to whatever they come in contact withwithIf on a susceptible host it germinates and If on a susceptible host it germinates and produces a produces a radicleradicle which grows along the bark which grows along the bark surface until it meets a bud or surface until it meets a bud or leafbaseleafbase

Dwarf Mistletoe Disease Cycle (2)Dwarf Mistletoe Disease Cycle (2)

At a bud or At a bud or leafbaseleafbase the the radicleradicle produces a produces a haustoriumhaustorium that penetrates the bark directly that penetrates the bark directly and reaches the phloem and the cambiumand reaches the phloem and the cambiumFrom the From the haustoriumhaustorium the plant develops the plant develops strands of radial sinkers which absorb nutrientsstrands of radial sinkers which absorb nutrientsOnce established inside the host the parasite Once established inside the host the parasite produces buds that develop shoots the produces buds that develop shoots the following year or several years laterfollowing year or several years later


The shoots emerge first from the original point The shoots emerge first from the original point of infectionof infectionLater shoots emerge in increasing concentric Later shoots emerge in increasing concentric zoneszonesThe center of infection usually decays and is The center of infection usually decays and is attacked by decayattacked by decay--producing fungiproducing fungiIf witchesIf witches’’ brooms are produced on the brooms are produced on the affected area affected area haustoriahaustoria pervade all the pervade all the branchesbranches


The parasite takes water, minerals and The parasite takes water, minerals and photosynthatesphotosynthates (manufactured food) from the (manufactured food) from the host which starves and kills the branch beyond host which starves and kills the branch beyond the infectionthe infectionIt affects the vitality of the rest of the branchIt affects the vitality of the rest of the branchIt also upsets the hormonal balance in the It also upsets the hormonal balance in the affected area which causes excess cell affected area which causes excess cell enlargement and division resulting in swellingsenlargement and division resulting in swellings

Dwarf Mistletoe Cultural ControlDwarf Mistletoe Cultural Control

The only method of control is by physical The only method of control is by physical removal of the parasiteremoval of the parasiteThis can be done by pruning infected branches This can be done by pruning infected branches or by removing entire treesor by removing entire treesUninfected trees can be protected by Uninfected trees can be protected by maintaining a protective zone around themmaintaining a protective zone around them

True MistletoesTrue Mistletoes

Evergreen parasitic plantsEvergreen parasitic plantsFound throughout the world, particularly in Found throughout the world, particularly in warmer climateswarmer climatesAttack mainly hardwood forest and shade trees Attack mainly hardwood forest and shade trees but also common fruit trees such as apple and but also common fruit trees such as apple and even some gymnosperms such as juniper and even some gymnosperms such as juniper and cypresscypressEconomic losses are generally much lower Economic losses are generally much lower than those caused by dwarf mistletoethan those caused by dwarf mistletoe

True Mistletoe SymptomsTrue Mistletoe Symptoms

The symptoms are very similar to those caused The symptoms are very similar to those caused by the dwarf mistletoesby the dwarf mistletoes

Infected areas become swollenInfected areas become swollenPlants produce witchesPlants produce witches’’ broomsbrooms

Sometimes so numerous that they account for Sometimes so numerous that they account for more than 50% of green foliage in infected more than 50% of green foliage in infected treestreesIn winter they can make deciduous trees In winter they can make deciduous trees appear evergreenappear evergreen

True Mistletoe Symptoms (2)True Mistletoe Symptoms (2)

Infected trees may live for years but growth is Infected trees may live for years but growth is affected and trees can be stunted and distortedaffected and trees can be stunted and distortedPortions beyond the infected site can be Portions beyond the infected site can be starved and killedstarved and killedMistletoes have well developed stems and Mistletoes have well developed stems and leaves and can be up to a meter highleaves and can be up to a meter high

True Mistletoe Symptoms (3)True Mistletoe Symptoms (3)

True Mistletoe Symptoms (4)True Mistletoe Symptoms (4)Mistletoe in winter

Typical mistletoe “ball” is several years old

Mistletoe is easier to see in winter as it is evergreen while most of its hosts are deciduous

True Mistletoe Symptoms (5)True Mistletoe Symptoms (5)Mistletoe detail

The stems and leaves are green and are capable of photosynthesis

Mistletoe manufactures much of its own food taking less manufactured food from the host plant than many other parasites but still causes significant damage to the host

Each of the white berries contains a single sticky seed. The berries are consumed by birds which deposit the seeds on other branches or other trees

Mistletoe ControlMistletoe Control

Control of true mistletoe is virtually the same Control of true mistletoe is virtually the same as for dwarf mistletoe, removal of infected as for dwarf mistletoe, removal of infected branches or entire plantsbranches or entire plantsA major difference is the method of spreading A major difference is the method of spreading seed, since true mistletoe seeds are spread by seed, since true mistletoe seeds are spread by birds establishing a protective zone around birds establishing a protective zone around uninfected plants is generally not effectiveuninfected plants is generally not effective

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Parasitic Diseasesdunnam.net › triton › pathology › parasitic_diseases.pdf · 2008-12-05 · Parasitic Plants According to the American Heritage Dictionary a parasite is- An