=caterpillars =caterpillars
All factors present disease can result Methods of control can modify the triangle Susceptible Host Disease No Disease Host PathogenEnvironment
Biotic factors (biological in origin) Fungi Bacteria Viruses Nematodes Phytoplasmas Abiotic factors (non-biological) Weather Environmental pollutants
Largest pathogen group Over 200,000 known species of fungi More than 8,000 cause plant diseases Reproduce by asexual and sexual means Spores are like seeds
Powdery Mildew White coating on plant sprinkled with powdered sugar Group of diseases Host specific Environmental conditions correct (high humidity)
Rust Rusty-orange powdery pustules Easily removed by rubbing leaf Can produce 4 types of different spores Alternate hosts (Cedar-apple rust fungus)
Symptom Abnormalities in a plant Give us a sense if fungus or other pathogen Spots Roughly circular NECROTIC (dead area) Lesions Irregular shaped spots Lesions can have yellow halos Blight Spots or lesions enlarge and merge
Black Spot of Elm, Gnomonia ulmea
Lesions Often delimited (bordered) by veins Angular appearance Fungal lesions more irregular shape
Alternaria leaf blight caused by Alternaria solani (left) and Septoria leaf blight caused by Septoria lycopersici (right)
Cankers Lesions on stems, branches or trunks Sunken and discolored Outer bark fallen away
Rots Destruction and disintegration of a large portion of the plant Affected areas are discolored and soft Crown rots Root rots Southern blight Sclerotium rolfsii
Fruit Rots Start as dry rots Secondary microorganisms (bacteria) begin and lead to soft, slimy rots Pytophthora fruit rot of pumpkin
Wilts Indicate plant is not getting water Plants have a droopy appearance Root rots Root system decayed, no longer absorb water Cineraria with root rot Pythium
Wilts Vascular wilt invades the xylem (water conducting tissue) Vascular discoloration or browning Xylem changes from whitish color to brown, green or gray color Verticillium Bacterial Wilt of Cucumber carried by Cucumber Beetle
Second most important group of plant pathogens Spots Lesions Blight Rots Vascular wilts Galls
Galls Bacterial infections can cause galls to form Bacterium induces gall formation by injecting it’s own DNA into a plant cell Crown gall
Reproduce by taking over host reproductive machinery Often associated with insect vectors Reproduction can take place in vector Can be transmitted mechanically Grower handling issues Plants rubbing together
Mosaic Mottling Leaf and Fruit Distortions Ringspot
Mosaic Classic symptom Blotchy light and dark green coloring on leaves Poinsettia mosaic virus
Rose Mosaic Virus Interesting lines and patterns
Mottle Blotchy coloring occurs on flowers of other colored flower parts
Some cases of viral infections can be highly desirable Tulips
Leaf and Fruit Distortions Leaves are narrow or “strappy”, thicker then normal Leaves are curled and twisted Fruit has warts (yellow raised bumps) Zucchini
Ringspot Concentric ring patterns on fruit or leaves Papaya ringspot
Odd bacteria like organisms Much smaller than bacteria, need an electron microscope Transmitted by insects usually leafhoppers Leafhoppers are phloem feeders
Virescence Brooming Fasciation Twisting and Distortion
Virescense Normally colored plant parts are green Brooming Plant parts become overly branched and bushy
Brooming - Ash Yellows
Fasciation Flattening of plant parts Maple branch
Twisting, Distortion and Virescence Cosmos with Aster Yellows
Parasitic worms Very complex compared to other pathogens Usually seen only with a light microscope Reproduce by eggs
Nematodes Identified by extracting from soil or infected plant material Non-pathogenic vs. pathogenic nematodes Pathogenic have a stylet Modified tooth that punctures and feeds on plant tissue
Gall formation by nematodes Nematode tunnels into the root It’s saliva stimulates plant root cells to divide
Nutritional abnormalities Pesticide exposure Environmental pollutants Adverse weather conditions
Abnormalities are called INJURIES Discolortion Yellowing Chlorosis Reddening
Yellowing at margins of leaf lack of molybdenum General yellowing lack of nitrogen Leaf veins remain green and leaf blades turn yellow lack of iron or manganese Reddening of foliage lack of phosphorus
Molybdenum deficiency on poinsettia Yellowing at margins
Pesticide exposure Curling and cupping Geranium exposed to the herbicide 2,4-D
Pesticide exposure Twisting Tomatoes exposed to the herbicide 2,4-D
Pesticide exposure Distortion Rose exposed to a phenoxy-type herbicide Symptoms similar to viruses and phytoplasmas Gather information
Pesticide exposure Fungicide use can cause marginal burning Follow the label directions
Environmental Pollutants Contaminants in water or the air Marginal bronzing on Shefflera due to exposure to sulfur dioxide
Environmental Pollutants Lesions on Dracena from high levels of fluoride in water or fluoride gas Paper thin lesions, concentrated at margins
Environmental Pollutants Browning of arborvitae due to dog urine
Environmental Pollutants Cold injury Candles starting to grow and cold weather comes Gather information
Environmental Pollutants Heat injury High temps can cause tissue damage
Environmental Pollutants Adverse weather conditions Winter injury Air temps rise but soil temps are cold Plant begins growing but the roots can’t get water to the foliage Plant desiccates and dies
Environmental Pollutants Adverse weather conditions Drought stress, reddening of branches
Plant Disease Diagnostics Clinic Soil and Plant Analysis Lab Nutritional disorders
Slides in power point are copy write: 1999 by the Board of Regents of the University of Wisconsin System doing business as the division of Cooperative Extension of the University of Wisconsin Extension