SPRUCE DISEASES: HERBICIDE SYMPTOMS OR NOT?

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1 SPRUCE DISEASES: HERBICIDE SYMPTOMS OR NOT? Garden Saturday, February 2, 2008 Kasia Kinzer Plant Diagnostician NDSU Plant Diagnostic Lab Overview NDSU Plant Diagnostic Lab stats What is Disease? 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 1

2 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 NDSU Plant Diagnostic Lab 2007 Most common spruce problems: Abiotic: 36 Winter injury (8) Mechanical injury (5) Chemical injury (4) Environmental stress (19) Biotic: 23 Stigmina needle cast (5) Cytospora canker (2) Rhizosphaera needle cast (1) Spider mites (6) Aphid, needleminer, borer, or sawfly (5) 2

3 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 Host Pathogen Disease Environment 3

4 Causes of Diseases Infectious Non-Infectious (Biotic) (Abiotic) Fungi Arthropods Viruses Bacteria Nematodes And so on (arthropods, too) Nutrient deficiency or toxicity Moisture Temperature Light ph Mechanical Herbicide injury Other Chemical injury What are symptoms and signs? Symptoms response of plant (what the plant looks like) Examples: wilting, needle discoloration, dead branches Signs physical presence of organism (or its parts) that causes disease Examples: insect bodies, castings, frass; fungal vegetative or fruiting bodies 4

5 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 5

6 Herbicide Symptoms or Not? Characteristics of Biotic Causes Symptoms AND signs typically present; may need lab work to induce signs Can spread within a plant over time Can spread from one plant to another Can worsen over time Pattern within a tree may be nonuniform Symptoms usually appear gradually Characteristics of Abiotic Causes Symptoms only 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 may appear all at once Herbicide Symptoms or Not? Many symptoms can understandably be confused with possible herbicide id injury 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 6

7 Diseases of Spruce Common biotic diseases: Needle cast diseases Rhizosphaera needle cast Stigmina needle cast Cytospora canker Common abiotic problems: Environmental stress 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

8 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 8

9 Needle Cast Diseases Management of Rhizosphaera needle cast May be warranted for high h value 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 9

10 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 Signs Fruiting bodies just under bark at canker Management 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 10

11 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 canker Boring insects Abiotic diseases of Spruce Winter dessication Frost injury Herbicide injury Look for patterns 11

12 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 12

13 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 disease or Cytospora canker No evidence of mechanical injury 13

14 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 14

15 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 did symptoms first appear, and are they 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 15

16 If you want help, or if you suspect chemical injury: Take lots of good quality pictures Document as much as possible (handout) Consult local experts Consult county extension agents Bring sample to a diagnostic lab, such as NDSU Plant Diagnostic Lab 206 Waldron Hall 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) 16