Plant Diseases. Presented 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.
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Plant Diseases Presented 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 potato Photo by Gerald Holms
Plant Disease Triangle Susceptible Host Plant Disease Favorable environment Pathogen
Identifying Diseases • Symptoms: • Reaction of host plant to the organism or agent • Ex: Leaf spots, wilting, chlorosis, galls Crown Gall on Peach Photo: Turner Sutton Alternaria blotch on apple Photo: 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 BEST Sanitation Rogue infected plants Insect control Clean stock/ seed Common Bacteria: Xanthomonas; Pseudomonas (Ralstonia) Erwinia
Viruses • Very small • similar in size and chemistry to DNA • Spread: • Insects / fungi / nematodesfrom one infected plant to another • Control: • Clean stock • Insect control • Rogue out infected plants • NO CHEMICAL CONTROLS !!!!! Scanning electron micrograph of Tobacco mosaic virus Photo: NCSU Plant Path Dept.
Viruses • Symptoms: (many and varied) • Stunting • Mottling / blotches / spots • White – yellow – brown rings on lvs • Deformed plant parts • Breaking of the flower color Cucumber mosaic virus Photo: Div. Plt Industry Archives FL Dept of Ag UGA Plt Path Dpt Archive Photo
Virus Notable Examples: TSWV: Tomato spotted wilt virus INSV: Impatiens necrotic spot virus TMV: Tobacco mosaic virus TMV can be transmitted via cigarettes Ring spot virus on tropical foliage plants
Fungal Diseases 1 = Fungus 2+ = fungi Hyphae = single thread Mycelium = mass of hyphae Spores = fruiting or reproductive structures asexual and sexual spores possible
Root Rot Diseases Water Mold Fungi Pythium Phytophora Characteristics: • 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 Fungi Rhizoctonia: drier, brown rot intermediate moisture Fusarium: Dk brown - black favored by dry-interm.H2O collapsed roots, stunted plt Thielaviopsis: drier, BLACK rot likes hi pH (6.5 +) Stunted plt; excessive lf drop Older plts / pansy / poinsettia
Root Rot Symptoms/Signs 1. Attacks at soil line ( Pythium) 2. Lack of root hairs 3. Dark roots / outer root cortex sloughs off 4. Lower lvs – chlorosis + abscise 5. Decline in vigor / stunted growth 6. When severe = wilt Pythium on cuttings and plts Chase Horticultural Service
Control of root rots 1. Sanitation 2. Well aerated medium 3. Avoid excessive moisture in medium 4. 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: • Grey “fuzz” • Black sunken-lesions • Tissue blackening/ collapse / rot Development favored by : • Dead & stressed plant parts • Poor air circulation • Any temp 33-850 F Botrytis on Poinsettia Brian Whipker; NCSU Plant Disease Clinic; Cornell Univ.
Controlling Botrytis • Air circulation • Watch stressed plants • Chemical : Termil (fumigant) Chipco , Daconil, Medallion, etc
Powdery Mildew 1. Mycelia feed via haustoria • 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 Mildew 1. Reduce RH • Sanitation • Increase air circulation • Biological: Horticultural oil potassium bicarbonate (baking soda) Neem oil Bacillissubtilis sulfur • Chemical: Copper based fungicides, also: Banner, Eagle, Heritage, Pipron, Strike Terraguard, Compass O
Other Fungal Leaf Spot Diseases • Alternaria • Anthracnose • Cercospera • Septoria • Fusarium • Many others Alternaria; Cornell Dept of Plant Path. Fusarium :UCDavis Anthracnose leaf spot and twig blight on maple; Iowa State University Extension
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