Common Garden Disease Diagnosis
Transcript of Common Garden Disease Diagnosis
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Common Plant Diseases and Disorders
Inga Meadows, Extension Plant Pathologist, Vegetables & Herbaceous Ornamentals
Mountain Horticultural Crops Research & Extension CenterTransylvania & Buncombe County – Master Gardeners
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Introduction
• What is disease?• Abiotic vs. biotic diseases• Disease Triangle• Disease resistance• Most common diseases• Resources
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Definition of Disease
Disease • abnormal growth• undesirable appearance• disfunction in plant• reduced yieldDepends on who you are!• Commercial grower, homeowner• Natural forest, ornamental, timber
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Abiotic vs Biotic Disease
Abiotic – caused by non-living factor• Nutritional deficiency• Drought• Genetic variation• Soil conditions (compaction, root-bound)• Lightning strike• High / low temperature• SunscaldBiotic – caused by living organism• Fungi• Bacteria• Nematodes• (Viruses)• Insects
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Disease Triangle
Envir
onm
ent
Disease
Host
PathogenSoil moistureSoil typeHumidityLeaf wetness
ProtectantsPreventionAvoidance
Resistance, Crop rotation
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What is disease resistance?
In the presence of the pathogen:
Susceptible – disease will occurResistant – no diseaseTolerant – less disease than susc.;
not resistant
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What is disease resistance?
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Signs vs. Symptoms
SymptomsYellowingDiebackStuntingWiltingSpottingRoot knottingRoot discoloration
SignsSpores
MyceliumFruiting body
Bacterial oozingNematode
Virus
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Signs vs. Symptoms
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Abiotic vs. Biotic Diseases
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Abiotic vs. Biotic Diseases
• Abiotic– caused by non-living factor
• herbicide damage, • nutrition deficiency/excess • heat/humidity• salts in media
• Biotic– caused by living organism
• fungi• bacteria• nematode• viruses, viroids• phytoplasmas
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How can you tell biotic or abiotic?
• Examine the pattern– Entire field? Or in patches?– One variety? Or all?– One side of field/garden? (i.e., drift)– Has the plant grown out of it?
• Are there signs present?• Are they pathogenic?
– saprophytes quickly colonize blossom end rot
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Edema
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Herbicide damage
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Nitrogen Deficiency
Haifa-group.com
Add standard fertilizer – 20-20-20Add bone meal, fish meal, etc.
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Phosphorous Deficiency
Haifa-group.com
Add standard fertilizer – e.g., 0-46-0Add manure, compost
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Blossom end rot
librariangreens.files.wordpress.com
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Blossom end rot
www.ces.ncsu.edu
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Biotic Diseases
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Leaf spots
• Fungi or bacteria• e.g., anthracnose, bacterial leaf spot, blight• May be able to see spores or bacterial streaming• Be aware:
– common names of diseases– saprophytic fungi or bacteria
• Moist chamber– moist paper towel in a ziploc bag, 1-2 nights– examine for spores– warning: saprophytes will also sporulate!
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Leaf spots
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Leaf spots
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Moist chamber
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Rusts, Smuts, and Bunts
• Basidiomycetes • Rusts: Multiple stages of
life cycle• Rusts: Alternate hosts
– cedar/apple rust– daylily/(Patrinia) rust– wheat/barberry rust
• Smuts & bunts: commonly attack seeds of grasses– corn smut
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Rusts, Smuts, and Bunts
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Rusts, Smuts, and Bunts
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Corn Smut - Huitlacoche
APS
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Powdery Mildews
Sally Miller
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Powdery Mildew
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Powdery Mildew
• Different host = Different PM species– wide host range: cucurbits, oaks, tomatoes,
peppers, dogwood, ornamentals• Susceptibility to other diseases• Mostly occurs on upper surface, but can be found on
underside• Management
– Resistant variety– Increase spacing – increase air flow– full sun, overhead water– Sulfur
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Downy Mildew
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Downy Mildew
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Basil Downy Mildew
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Basil Downy Mildew
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Downy Mildews
• Cucurbits, basil, crucifers, grapes, hops, impatiens, soybeans, sunflowers
• Most, if not all, do not survive winter in NC• Shows up in late July, August• Management
– Tolerant (or resistant?) variety– Coppers or chlorothalonil
• Preventative only– Serenade Max may provide some control?
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Phytophthora blight, crown/root rot
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Phytophthora blight, crown/root rot
PDIC
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Phytophthora blight, crown/root rot
PDIC
• Over 100 species• Wide host range: vegetables, ornamentals, fruit
trees, grapes, you name it • Brought in by transplants, soil
– few oddballs travel via wind• Survives in soil for many years• Extended periods of heavy rain, humidity• Temps: 75-85°F• Water-logged soils• Management: Resistant varieties, rotate beds, use
raised beds
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Damping-off fungi(Rhizoctonia, Pythium, Fusarium)
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Damping-off fungi(Rhizoctonia, Pythium)
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Damping-off fungi(Rhizoctonia, Pythium)
Many hosts!Caused by Rhizoctonia, Pythium, FusariumCan be managed:• Avoid cool & wet conditions• Older seedlings not affected• Cull diseased immediately• Avoid saturated soil & high nitrogen
– (fertilize after first true leaves emerge)• Use new soil, trays
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Botrytis gray mold
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Botrytis gray mold
Many hosts!The fungus is ubiquitous – it’s everywhere!Caused by humid, cool conditions
-often in the greenhouse, can be outdoorsCan be managed:• Increase air circulation, even if cloudy and
humid outdoors• Dead tissue is colonized first; remove it• Cull any diseased tissues
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Viruses, viroids, phytoplasmas
APSnet.org
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Viruses, viroids, phytoplasmas
• Technically not living organisms; require host DNA to replicate
• Usually don’t kill plant• Can look like abiotic disorder• Usually patterns
– mosaics, speckling, streaking, ringspots• Transmitted by insects, equipment/humans,
nematodes, fungi
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Viruses, viroids, phytoplasmas
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Nematodes
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Nematodes
• Microscopic worms• Cause stunting, plant death
– root knotting• Many genera and species• Wide host range
– soybeans, peanuts, vegetables, ornamentals, tobacco, etc.
• Mostly soilborne, but some foliar• Equipped with stylet to puncture plant tissue
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• Google: NCSU PDIC• New users – create login• Images are free!
– (But may need sample, in some cases)– Can help you determine what to sample
• Samples:– $20 through agent or MG– $30 direct
• Collect:– Multiple plants, capture range of disease– Bag soil/roots separate from foliage– If you don’t know, send it in!
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Resources
• 2017 SE US Vegetable Crop Handbook• 2017 NC Agricultural Chemicals Manual• NC Department of Agriculture
– Soil testing• NCSU Plant Pathology Extension Portal
– Late blight, downy mildew, disease updates– Disease notes
• University Extension Publications & Websites• American Phytopathological Society: APSnet.org
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Thank you!