Plant Diseases
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Transcript of Plant Diseases
Plant DiseasesPresented by Terry Ferriss, PhD
University of Wisconsin—River Falls
Causes or Agents of Plant Diseases
• Abiotic – non-pathogenic / physiological• EX: environmental, cultural, air
pollution, etc.
• Biotic --- caused by living organisms (pathogens)– Ex: Primarily: Bacteria, Virus, Fungi
Ozone damaged potatoPhoto by Gerald Holms
Plant Disease TriangleSusceptible Host Plant
Pathogen Favorable environment
Disease
Identifying Diseases• Symptoms: – Reaction of host plant to the organism or agent• Ex: Leaf spots, wilting, chlorosis, galls
Crown Gall on PeachPhoto: Turner Sutton
Alternaria blotch on applePhoto: Turner Sutton
Identifying Diseases (cont.)• Signs:– Physical evidence of the presence of the disease
• Ex: Bacterial ooze, fungal spores, fungal hyphae
Bacterial ooze on apple (fire blight) Green mold on orange (Penicillium)Photos: Turner Sutton
Bacteria• Microscopic / Single cell organism• Reproduces by dividing• Signs/symptoms
– Water soaked spots – papery as ages– Chlorotic spots with “HALOS”– Angular spots & chlorosis are between veins– Soft rots– Discoloration of vascular system– Fasciation / Galls
Wildfire bacterium of tobacco (Pseudomonas tabaci) Photo: NCSU Plant Path Dept.
Close-up of Xanthomonas leaf spot of croton shows vein-delimited spots with irregular water-soaked margin. DPI Photo Credit: Jeffrey W. Lotz; Univ FL
Spread of Bacteria• Spread: – Physical spread by humans -
hands / tools, etc– Splashing contaminated water– Contaminated irrigation water– Insects / birds
Foliar symptoms of bacterial leaf disease of aglaonema include hydrosis of infected tissue and leaf spots and blight caused by the bacterial plant pathogen Dickeya chrysanthemi.. (Photo: S. Nelson) Univ of Hawaii
Control of Bacteria“DIFFICULT”
Therefore Prevention is BESTSanitation
Rogue infected plantsInsect control
Clean stock/ seed
Common Bacteria:Xanthomonas;
Pseudomonas (Ralstonia) Erwinia
Viruses
Scanning electron micrograph of Tobacco mosaic virus
Photo: NCSU Plant Path Dept.
•Very small•similar in size and chemistry to DNA
•Spread:• Insects / fungi / nematodes from one infected plant to another
•Control: •Clean stock •Insect control•Rogue out infected plants
NO CHEMICAL CONTROLS !!!!!NO CHEMICAL CONTROLS !!!!!
Viruses• Symptoms: (many and varied)– Stunting– Mottling / blotches / spots– White – yellow – brown rings on lvs– Deformed plant parts– Breaking of the flower color
UGA Plt Path Dpt Archive Photo
Cucumber mosaic virusPhoto: Div. Plt Industry Archives
FL Dept of Ag
VirusNotable Examples: TSWV: Tomato spotted wilt virusINSV: Impatiens necrotic spot virus
TMV: Tobacco mosaic virus TMV can be transmitted via cigarettes Ring spot virus on tropical foliage plants
Fungal Diseases1 = Fungus 2+ = fungi
Hyphae = single thread
Mycelium = mass of hyphae
Spores = fruiting or reproductive structures asexual and sexual spores possible
Root Rot DiseasesWater Mold Fungi
Pythium PhytophoraCharacteristics:• soil born• Favored by cool, wet soil• Encouraged by: low O2, hi NH4
+, hi SS• Low O2 root exudate = stimulates spore germination
Non-water Mold FungiRhizoctonia : drier, brown rot intermediate moistureFusarium: Dk brown - black favored by dry-interm.H2O collapsed roots, stunted pltThielaviopsis: drier, BLACK rot likes hi pH (6.5 +)Stunted plt; excessive lf dropOlder plts / pansy / poinsettia
Root Rot Symptoms/Signs
Pythium on cuttings and pltsChase Horticultural Service
1. Attacks at soil line ( Pythium) 2. Lack of root hairs3. Dark roots / outer root cortex sloughs off4. Lower lvs – chlorosis + abscise 5. Decline in vigor / stunted growth6. When severe = wilt
Control of root rots1. Sanitation2. Well aerated medium3. Avoid excessive moisture in medium4. Biological: Protective fungi (ex: Trichoderma sp in RootShield / PlantShield & others)
5. Chemical: Water molds: Subdue; Benlate, Aliette, etc Non-water molds: Truban, Chipco, Medallion, Daconil, Cleary 3336, Heritage,etc
Botrytis cinerea = “Grey Mold”
Signs/ symptoms:1.Grey “fuzz” 2.Black sunken-lesions3.Tissue blackening/ collapse / rotDevelopment favored by :1.Dead & stressed plant parts2.Poor air circulation3.Any temp 33-850 F
Plant Disease Clinic; Cornell Univ.
Botrytis on PoinsettiaBrian Whipker; NCSU
Controlling Botrytis1. Air circulation
2. Watch stressed plants
3. Chemical : Termil (fumigant) Chipco , Daconil, Medallion, etc
Powdery Mildew1. Mycelia feed via haustoria2.Spread: • spores fly in low RH (day)• Spores germinate in high
relative humidity (RH) + free water at night
Univ. of IL Extension, PM on lilac
PM spores on lower epidermis; NCSU
Controlling Powdery Mildew1. Reduce RH2. Sanitation3. Increase air circulation4. Biological: Horticultural oil potassium bicarbonate (baking soda) Neem oil Bacillis subtilis sulfur 5. Chemical: Copper based fungicides, also: Banner, Eagle, Heritage, Pipron, Strike Terraguard, Compass O
Other Fungal Leaf Spot Diseases
1. Alternaria2. Anthracnose3. Cercospera4. Septoria5. Fusarium6. Many others
Alternaria; Cornell Dept of Plant Path.
Anthracnose leaf spot and twig blight on maple; Iowa State University Extension
Fusarium :U
CDavis
Fungal Leaf Spots• Round spots / sometimes elongated• Not limited by veins• Bulls-eye effect is common
University of Wisconsin—River Falls
Thank you
Terry Ferriss, PhD