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Garden Saturday, February 2, 2008 Kasia Kinzer Plant Diagnostician NDSU Plant Diagnostic Lab


NDSU Plant Diagnostic Lab stats What i Disease? Wh t is Di ?

Definition of disease

What are biotic causes of disease? What are abiotic causes of disease? Tips on distinguishing between biotic and abiotic causes in general

Spruce Diseases

What causes symptoms on spruce?

Tips on how to differentiate possible diseases caused by plant pathogenic fungi from chemical injury or other abiotic causes of symptoms



Lab Trivia: Tree diagnoses

NDSU Plant Diagnostic Lab 2007

Total tree diagnoses in 2007: 150

Deciduous: 88 Evergreen: 62

Total spruce diagnoses: 55

Blue (Colorado Blue): 12 Black hills spruce (white): 2 Species not specified: 41

More Lab Trivia

Abiotic: Abi ti 36

NDSU Plant Diagnostic Lab 2007

Most common spruce problems:

Winter injury (8) Mechanical injury (5) Chemical injury (4) `Environmental stress' (19)

Biotic: 23

Stigmina needle cast (5) g ( ) Cytospora canker (2) Rhizosphaera needle cast (1) Spider mites (6) Aphid, needleminer, borer, or sawfly (5)



What is Disease?

Any malfunctioning of host cells and tissues resulting from continuous irritation by a pathogenic agent or

environmental factor leading to development of symptoms

­ Agrios







Causes of Diseases

Infectious ( (Biotic) )

Fungi Arthropods Viruses Bacteria Nematodes And so on (arthropods, too)

Non-Infectious (Abiotic)

Nutrient deficiency or toxicity Moisture Temperature Light pH Mechanical Herbicide injury Other Chemical injury

What are symptoms and signs?


response of plant (what the plant looks like)

Examples: wilting, needle discoloration, dead branches


physical presence of organism (or its parts) that causes disease

Examples: insect bodies, castings, frass; fungal vegetative or fruiting bodies



Examples of Symptoms

brown inner needles

Yellow tips on needles

wilted new growth

canker, excessive sap

Examples of Signs

fungal fruiting bodies

actual pest

fungal fruiting bodies



Herbicide Symptoms or Not?

Characteristics of Biotic Causes C

Symptoms AND signs typically present; may need lab work to induce signs Can spread from one plant to another Can worsen over time Pattern within a tree may be nonuniform

Characteristics of Abiotic Causes C

Symptoms only

Can spread within a plant over time Usually do not spread within a plant Usually do not spread from one plant to another (some exceptions) Usually do not worsen over time Pattern within a tree or among trees may be uniform, sided, discrete

Symptoms usually appear gradually Symptoms may appear all at once

Herbicide Symptoms or Not?

Many symptoms can understandably be confused with possible herbicide injury f d ith ibl h bi id i j

Symptoms from different causes look similar

Look for mechanical injury Look for root disturbances Look for evidence of arthropod feeding Look for environmental stressors

Look for BOTH symptoms and signs to confirm a diagnosis of a BIOTIC disease



Diseases of Spruce

Common biotic diseases:

Needle cast diseases

Rhizosphaera needle cast Stigmina needle cast

Cytospora canker

Common abiotic problems:

"Environmentall stress" "E i t t " Winter injury Mechanical injury Chemical injury

Needle Cast Diseases

Rhizosphaera needle cast

Caused by Rhizosphaera kalkhofii

Confirmed in North Dakota in early 1990s

Stigmina needle cast

Caused by Stigmina lautii

First diagnosed in North Dakota in 2006 Probably present prior to 2006



Needle Cast Diseases

Symptoms are similar:

Discoloration of inner needles (not current growth) Needle loss (inner needles; not current growth) Lower portions of tree affected first; can progress upward Does not normally kill buds

Severe cases can kill buds of lower branches

Needle Cast Diseases

Signs are superficially similar

Signs of Stigmina lautii

Signs of Rhizosphaera kalkhoffi



Needle Cast Diseases

Management of Rhizosphaera needle cast

May be M b warranted f hi h value t d for high l trees Fungicides (e.g. chlorothalonil; Bordeaux mixture):

First application: when new needles are 50% normal length Second application: 3-4 weeks later when needles are fully elongated Must be applied for at least two consecutive years

No recommendations available for Stigmina needle cast

What else can cause browning of inner needles?

Biotic causes, such as

Feeding by arthropods in a previous year (e.g. aphids, mites)

Abiotic causes, such as

Exposure to a toxin in a previous year Drought stress in a previous year Nutrient deficiency in a previous year



Cytospora canker

Caused by a fungus: Cytospora sp. Symptoms

Brown and dying needles on a branch (usually lower branches first) Branch dies (bud is dead) Excessive bluish-white sap


Fruiting bodies just under bark at canker


Prune out infected branches in late winter or during dry periods

Cytospora Canker - Symptoms

Note individual dead branches here and there Buds of dead branches are dead d d



What else can kill buds?

Abiotic diseases, such as

Severe winter injury Girdling by mechanical injury Herbicide injury Shading out of lower branches

Biotic diseases, in addition to Cytospora diseases canker

Boring insects

Abiotic diseases of Spruce

Winter dessication Frost injury Herbicide injury

Look for patterns



Winter Desiccation

Can be confused with herbicide injury Note brown needles at top half of trees, above the snow line Affected branches not necessarily dead (depends on severity)

Spring Freeze Injury

Can be confused with herbicide injury Background information needed



Herbicide injury

Note spiral pattern of dead branches Note very `clean' lawn (no weed to be found!)

Herbicide injury ­ suspected

Note sided nature, fairly uniform distribution throughout tree, including upper canopy Too young for needle cast di t disease or Cytospora canker No evidence of mechanical injury



What damaged these trees?

More information is needed ...

Look at the Big Picture

Note healthy trees in background Note healthy weeds in foreground Note cultivation (spruce have shallow root systems) Root disturbance seems more likely than chemical injury in this scenario



Herbicide injury or not?

Provide or obtain as much information as possible, such as

When and how was tree planted How often is tree watered What surrounds the tree (fields, lawn, etc) How old is the tree Are different species affected similarly Chemical history of lawn and nearby fields

When Wh did symptoms first appear, and are they t fi t d th spreading or getting worse Note pattern of symptoms in tree Look for any other cause of symptoms

Herbicide injury or not?

Usually based on visual evaluation

Can sometimes narrow possibilities into a few chemical families Not always definitive!

Chemical analysis sometimes warranted

But this can be costly! Helpful to have an idea of chemical family Private and public chemical testing labs available



If you want help, or if you suspect chemical injury:

Take lots of good quality pictures g q yp Document as much as possible (handout) Consult local experts Consult county extension agents Bring sample to a diagnostic lab, such as lab

NDSU Plant Diagnostic Lab 206 Waldron Hall 701-231-7854

Thank You!

NDSU Plant Diagnostic Lab Website: (contains info on services available and fees, and has a partial list of chemical analysis labs in the Midwest)



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