Common Garden Disease Diagnosis

Common Plant Diseases and Disorders

Inga Meadows, Extension Plant Pathologist, Vegetables & Herbaceous Ornamentals

Mountain Horticultural Crops Research & Extension CenterTransylvania & Buncombe County – Master Gardeners

Introduction

• What is disease?• Abiotic vs. biotic diseases• Disease Triangle• Disease resistance• Most common diseases• Resources

Definition of Disease

Disease • abnormal growth• undesirable appearance• disfunction in plant• reduced yieldDepends on who you are!• Commercial grower, homeowner• Natural forest, ornamental, timber

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

Disease Triangle

Envir

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Disease

Host

PathogenSoil moistureSoil typeHumidityLeaf wetness

ProtectantsPreventionAvoidance

Resistance, Crop rotation

What is disease resistance?

In the presence of the pathogen:

Susceptible – disease will occurResistant – no diseaseTolerant – less disease than susc.;

not resistant

What is disease resistance?

Signs vs. Symptoms

SymptomsYellowingDiebackStuntingWiltingSpottingRoot knottingRoot discoloration

SignsSpores

MyceliumFruiting body

Bacterial oozingNematode

Virus

Signs vs. Symptoms

Abiotic vs. Biotic Diseases

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

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

Herbicide damage

Nitrogen Deficiency

Haifa-group.com

Add standard fertilizer – 20-20-20Add bone meal, fish meal, etc.

Phosphorous Deficiency

Haifa-group.com

Add standard fertilizer – e.g., 0-46-0Add manure, compost

Blossom end rot

librariangreens.files.wordpress.com

Blossom end rot

www.ces.ncsu.edu

Biotic Diseases

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!

Leaf spots

Moist chamber

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

Rusts, Smuts, and Bunts

Corn Smut - Huitlacoche

APS

Powdery Mildews

Sally Miller

Powdery Mildew

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

Downy Mildew

Basil Downy Mildew

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?

Phytophthora blight, crown/root rot


PDIC


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

Damping-off fungi(Rhizoctonia, Pythium, Fusarium)

Damping-off fungi(Rhizoctonia, Pythium)

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

Botrytis gray mold

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

Viruses, viroids, phytoplasmas

APSnet.org


• 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

Nematodes

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

• 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!

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

Thank you!

Common Garden Disease Diagnosis

Education

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