Disease

Biotic = Living / Abiotic = Non-living

Lots of Big Words

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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