The Bugwood Network

Disease

(Classical Definition)



Biotic = Living / Abiotic = Non-living


Lots of Big Words

  • Already defined "disease","pathogen" and "host."
  • Several are used to describe the effect of a disease on a host

  • Disease Effects

    Hyperplasia

    • Too rapid growth resulting in a gall, canker, broom or other form of excessive growth

    Hypoplasia

    • Restriction of normal growth resulting in stunting, dwarfing or chlorosis

    Necrosis

    • Tissue death resulting in scorch, shot hole or other symptom of dead tissue

    Disease Control

    • Protection
    • Exclusion
    • Eradication
    • Therapy

    Protection

    Surface

    • Precludes a pathogen from contacting a potential host

    Systemic

    • Introduce a chemical into the host to kill pathogens attempting to colonize them at some later time

    Silvicultural

    • Maintain vigorous stands of trees which are better able to biologically exclude infection from occurring

    Exclusion

    Vector Control

    • Prevent vectors from attacking potential hosts

    Quarantine

    • Prevent tne spread of disease by not allowing movement of infected host material into or out of specific areas

    Chemical/biological Treatment

    • Fungicidal treatment of potential hosts or habitats, genetic manipulation of hosts or pathogens, culling of diseased stock prior to planting, and "escape."

    Eradication

    Removal of diseased parts or individuals

    Pesticidal (chemical or biological) treatment

    • Similar to exclusion – kills pest organism

    Habitat modification

    • Removal of bark to kill vectors or dessicate pests,fumigation of soil or plant parts, dormant sprays of trees, destruction of infected host material by fire or other treatment, etc

    Therapy

    Selective Chemicals

    • Generally involves the use of systemic chemicals which are pest selective and host neutral or beneficial

    Physical or Environmental Methods

    • Removal of an environmental element which is leading to disease or damage

    Biotic Diseases – Fusiform Rust

    Caused by a fungus, Cronartium fusiforme,
    it primarily affects loblolly and slash pines.
    This rust causes characteristic cigar-
    shaped (fusiform) cankers on branches
    or stems of the host tree.

    In the spring, spores
    formed at the canker cause it
    to appear as if the tree is rusting –
    thus the name of the disease.

    What you really need to
    know is that the fungus
    alternates between oak
    and pine hosts.

    The life cycle of the fungus is
    complex, having 5 stages - BUT....

    There is some direct mortality, but,
    significant cankering, deformation
    and structural weakening occurs in
    the survivors.

    Stem breakage at the canker
    is a common occurrence.


    Little Effect on Pulpwood Production. Significant Loss in Sawlogs Due to Butt Log Degrade. Significant Risk of Mechanical Failure of Tree at Canker - Poses Significant Risk in Recreational or High Visitor Use Settings.



    Genetic, chemical and silvicultural treatments are available to combat fusiform rust.
    Fusiform rust hazard to loblolly pine
    in the South has been mapped.

    As has hazard posed by fusiform
    rust to slash pine in the South.


    Control

    A variety of control tactics are available to combat fusiform rust. They include:

    • gentic screening
    • preplant seedling treatment
    • chemical treatment in the field
    • and silvicultural manipulation

    Annosus Root Rot

    Annosus root rot (or root disease) is
    caused by a fungus, Heterobasidion
    annosum (formerly Fomes annosus).
    The first symptom of this
    disease is thinning of the
    crowns of affected trees.

    The real damage is in the roots
    which initially show resin soaking…


    Later are stringy, white and rotten
    with no mechanical strength.

    Which leads to the last symptom
    of annosus root rot -- windthrow.


    Hazard mapping using soil characteristics can be done at a variety of levels to give a warning of potential problems. High hazard for annosus root rot caused mortality results when there is 12 or more inches of sand or sandy loam with good drainage and little clay in the mix.



    Generalized Southwide hazard map
    for annosus root rot – Red is areas of
    high hazard for mortality, - Blue is
    areas of probable growth loss.
    Bee Branch, Alabama quad sheet
    (USGS 1:24000 scale), Bankhead
    NF showing areas of high (red),
    moderate (yellow), and low (green)
    hazard for annosus root rot.

    Infection of living trees is generally
    caused by spores landing, germinating
    and growing into freshly cut stumps.
    From there the fungus grows into the root
    systems of healthy trees via root grafts.

    Control – Uninfected Strands –
    Powdered borax is used to prevent germination of spores when protecting
    trees in uninfected sands.

    Sprinkled onto freshly cut stumps, it
    forms a barrier which prevents germination
    of the spores of the fungus.


    Control - Already Infected Stands

    The preferred treatment is currently unavailable. Phlebia gigantea, a fungus, excludes H. annosum by rapidly colonizing the stump and precluding annosus root rot.

    Even though the process here is to enhance a natural population of fungi, this biocontrol tool is not currently registered by the EPA. Borax stump treatment is not recommended if the stand is infected already.


    Littleleaf Disease

    Littleleaf disease is caused by
    a primary fungus, Phytophthora
    cinnamomi, plus site factors and
    other fungi. It primarily affects
    shortleaf pine and, to a lesser
    extent, loblolly pine.
    Shortly before the death of infected
    trees, they produce a heavy ‘stress
    crop’ of small, mostly sterile cones.

    Early symptoms include shortened
    and off-color (yellow green) needles.


    Littleleaf Disease is a Root Disease

    • Hazard is site related
    • Highest risk on soils with - High clay content
    • Poor internal drainage (often showing gleying of the soil), and,
    • Low nitrogen content


    Using this information we find that much of
    the commercial range of shortleaf pine is potentially high hazard for littleleaf disease.


    Control

    Recommendations for controlling this disease are primarily silvicultural and mechanical.
    Sanitizing the stands on about a six year cycle beginning with the onset of disease symptoms will minimize economic loss.
    Breaking up any existing plow-pan can return an affected site to productivity. Fertilizing may be used to gain a log grade – but this is a one-shot, short-term remediation.



    Integrated pest management
    scheme for managing fusiform
    rust, annosus root rot, and
    littleleaf disease.


    Vascular Wilts

    Damage is caused by the formation
    of tyloses in the vascular system of
    the host plant which restricts the
    flow of needed water and nutrients.
    Gallery of the European elm bark
    beetle, one vector of the Dutch elm
    disease fungus, on the inner bark of an elm.

    American elm showing the primary
    symptom of Dutch elm disease, caused
    by the fungus, Ceratocystis ulmi.

    Streaking of the xylem is a common
    symptom of vascular wilt diseases;
    here seen in a winged elm.

    Oak wilt (Texas style) is
    another serious vascular wilt.

    Control – While there has
    been some limited success
    with fungicides, sanitation is
    the best control strategy
    available to control this disease.

    The fruiting structures of C. ulmi on a
    branch segment cultured in a laboratory;
    barely visible to the naked eye.


    Oak wilt (Texas style) is another
    serious vascular wilt.


    Control

    While there has been some limited success with fungicides, sanitation is the best control strategy available to control this disease.

    Both the oak wilt and Dutch elm disease fungi pass through root grafts to infect new hosts. Trenching to sever root contacts followed by fumigation (Vapam) has been successfully used to contain the spread of these diseases.


    Cankers






    Most perennial cankers, despite being unsightly, are not treated. However...

    Pitch canker, caused by the fungus
    Fusarium moniliforme var. subglutinans,
    is of special concern when it occurs.

    Primary symptoms are dead
    needles and an extremely heavy
    resin flow on the terminal leader(s).

    Chief hosts of this disease are
    slash and Virginia pines.

    Resin soaking of the internal
    canker on a terminal leader.

    Results in heavy pitch flow on
    the terminal leader, and, also, to
    the name of this disease.

    Cross section of an infected stem
    showing the typical triangular
    extension of the canker into the stem.

    Severe infection can result in almost
    100% of the stems in a stand being
    infected. Sanitation is the only
    forestry control measure.


    Leaf (or Needle) Diseases

    In general, leaf spots are caused by fungi or bacteria which overwinter on fallen leaves in the duff.
    Oak leaf blister – Gets homeowners attention, but not serious.

    Needlecasts – Often extensive but cause only limited damage – No control attempted.

    Needle rusts – Unsightly but not serious.

    Poplar leaf rust – More of the same.


    Control

    In the forestry setting generally nothing is done except for a couple of specific diseases. However, there is generally lots of homeowner interest, so we have presented a few examples. Homeowner control – Rake, and remove or burn leaves in the fall.



    Brown spot of longleaf pine, caused by the fungus Scirrhia acicola, is a management problem.
    The disease primarily affects longleaf pine seedlings causing them to remain in the grass stage of development for extra years.

    Typical spotting and banding of
    the needles which gives brown
    spot disease its name.


    Control

    Systemic fungicide application (generally in a root slurry at the nursery) can confer 1 to 2 seasons of protection from this disease after outplanting. Prescribed fire is used to reduce grass competition and the humidity held by grasses which favors the fungus. Over-the-top fungicide sprays are sometimes used in the field.



    Sycamore anthracnose is a significant urban/suburban problem requiring more
    than the rake-and-burn solution.


    Decay

    In forest trees, decay is
    generally caused by fungi,
    although there are a few
    bacterial decays associated
    with trees.
    The presence of tree decay is often
    first recognized when the fungal
    plant, which is microscopic, fruits.
    Conks on the side of a tree or on wood
    are sure signs of decay in progress.

    In the discussion of annosus root rot I
    showed a white rot – above is a brown rot.


    Control

    No therapeutic treatments for rotting exist at the present time. Avoid wounding trees and remove over-age susceptible trees from the stand. Primary concern is in recreation areas and other areas where you invite the public. Remember, however, that though it poses risks, decay is a necessary recycling process in the forest – it is not all bad!


    Mycorrhizae

    A beneficial fungus – root relationship.
    Fungus colonizes, but does not damage,
    plant roots Yields better water and nutrient uptake for the tree, and Provides a food source (sugars and starches) for the fungus.
    Pisolithus tinctorius is a common
    mycorrhizal fungus which is being
    used to custom tailor seedlings
    for outplanting in harsh
    environments.

    Mycorrhizal roots have greater surface
    area available to absorb water and nutrients.


    Nematodes

    Nematodes are a group of microscopic roundworms. They use a stylet to pierce
    roots or other plant parts and suck nutrients from the plant. They cause a variety of problems including the galling and outright killing of plants.
    Pinewood nematode caused mortality of Japanese black pine – suspected that the nematode had been imported into the US
    in the late 1970s – actually it had been
    exported to Japan from the US.

    Diagnostic shape of the
    tail of a pinewood nematode.


    Mistletoe

    Parasitic vascular plant which
    embeds its “root” into branches of trees.
    Winter appearance of a
    mistletoe infested tree.

    Leaves of a true mistletoe (vs. dwarf
    mistletoe which is a serious management problem in western conifers).

    Rooting of a mistletoe plant in an oak
    branch. Control is generally not done
    since damage is not serious


    Nursery Disease

    Damping off, pitch canker,
    fusiform rust, needle blights and
    other diseases are commonly
    chemically treated in the forest
    tree nursery setting.


    Abiotic Damage

    Lightning Damage - Often a
    preconditioning agent for insect
    or disease attack No therapy available.
    Ice Damage - Weight of ice on
    branches causes them to break –
    often also damaging the main stem
    of the tree. No therapy is available.

    Hurricane caused wind breakage –
    salvage or leave in place are the
    only options for this damage type.

    Hurricane caused salt spray
    damage – no therapy available.

    Air Pollution Damage - Control (scrub) emissions at the stack or tailpipe –
    no therapy once damage is caused.

    Drought Kill - Nothing possible except irrigation which is obviously not
    practical at the forest level.

    Misleading Sign of Disease -
    The fungus shown here on the side
    of an oak is a common last straw.
    It is found on many dead trees,
    but didn’t cause the original damage –
    just took advantage of an already
    bad situation.

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    The University of Georgia - Warnell School of Forestry and Natural Resources and
    College of Agricultural and Environmental Sciences - Dept. of Entomology
    Last updated on Tuesday, February 25, 2003 at 12:56 PM
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