A I P DAN INTRODUCTION TO PLANT DISEASESAlan WindhamProfessor, Plant Pathology, gyUT Extension

PLANT PATHOLOGY, ANIINTRODUCTION

Introductory plant pathology is often taught as an undergraduate course at an university over a g ysemester.  This introduction to plant pathology is brief by necessity and meant to introduce Master Gardeners to the world of plant diseases.Gardeners to the world of plant diseases.

For more information on plant pathology visit our lab’s Facebook page, UT Extension publications, and the books mentioned at the end of this presentation.

SOIL, PLANT AND PESTCCENTER

For all your diagnostic needs: soil andneeds: soil and plant tissue testing, insect and disease id ifi iidentification .

http://soilplantandpest.utk.edu

FOLLOW US ON FACEBOOKwww.facebook.com/SoilPlantPestCenter

Or search for: Soil, Plant Pest Center

INFORMATION ON SPPC F PFACEBOOK PAGE

Info about new diseases and iinsect pests

Info about diseases or pests that Info about diseases or pests thatare active

I d ill t ti Images and illustrations

IMAGESIMAGESImages from past posts. Keep abreast of plant pest activity.

WHY STUDY PLANTP ?PATHOLOGY?

Plant pathology is the study of plant diseases Plant pathology is the study of plant diseases

Life on earth as we know it, would not be possible without green plantswithout green plants

Directly or indirectly plants provide all of the food on which the human population relieson which the human population relies

Plants are valuable for shelter, fiber, fuel, ornamental and landscape usesornamental and landscape uses

Plant diseases reduce the yield of principal food and cash crops by almost 20% worldwidecash crops by almost 20% worldwide

SOME INFAMOUSDDISEASES

It’s impossible to separate plants from the history and culture of humans

IRISH POTATO FAMINE1845 18601845-1860

Millions died or emigrated to other countries as a result of the famine.  The causal fungus waswas Phytophthora infestans.

POTATO FIELD DEVASTATED BYA GLATE BLIGHT

170 yrs after the  I i h t tIrish potato famine we still battle the same organism. g

CHESTNUT BLIGHTCHESTNUT BLIGHT

Discovered in 1904 in the U.S.

Devastating to the American chestnut

Research in hopes of developing resistantdeveloping resistant trees continues

Image: American Chestnut Foundation; acf.org

AMERICAN CHESTNUTS WEREKING OF THE APPALACHIANKING OF THE APPALACHIAN

FORESTSTh A iThe American chestnut made up 1 or every 4 trees in the Appalachian forests.  The wood was rot resistant andresistant and used for rail fences, poles and furniture. The nuts were invaluable to wildlife and livestocklivestock.

DUTCH ELM DISEASEDUTCH ELM DISEASE

Dutch elm disease was introduced on l lelm logs imported from Europe for furniture veneer in the 1920’s. Elm bark beetles are the vector for the fungusfor the fungus that causes Dutch Elm Disease.

DISEASE RESISTANT ELMSDISEASE RESISTANT ELMS

Princeton

Valley Forge

N HNew Harmony

* Lacebark elms are also iresistant to DED

Dogwood AnthracnoseDiscovered in TN on Flowering Dogwood in the late 1980’s

DOGWOOD ANTHRACNOSE HASBEEN DEVASTATING IN FORESTS

Dogwood Mortality in the Appalachian Region, where upRegion, where up to 75% of flower dogwood have been killed inbeen killed in forests.

NEW DOGWOODS FROMUT A RUT AGRESEARCH

Di i Disease resistant dogwoods released:

Applachian Spring – Applachian Spring anthracnose resistant

Appalachian Joy –mildew resistant

Appalachian Blush‐mildew resistantmildew resistant

Appalachian Mist –mildew resistant

Appalachian Snow –mildew resistant

CURRENT THREATSCURRENT THREATS

Citrus Greening Citrus Greening

Soybean Rust

Sudden Oak Death

Stem Rust of Wheat

Citrus Canker

Th d C k Di Thousand Cankers Disease

Boxwood Blight

Downy Mildew of Impatiens

Thousand Cankers Disease f Bl k W l tof Black Walnut

The discovery of TCD in Knox Co. in 2010in 2010 represents the first find in the native range of bl k l t iblack walnut  in the Eastern U.S. It sent shockwaves through all industries that use walnut nuts and timberand timber.

THOUSAND CANKERD /WDISEASE/WALNUT

The TNThe TN Department of Agriculture has restricted movement of black walnut lumber and firewood fromfirewood from quarantine areas.

THOUSAND CANKERS DISEASES VSYMPTOMS AND VECTOR

The walnut  twig beetle is the vector of the

1.5mm

vector of the fungus that causes TCD.

UT AGRESEARCHUT AgResearch advances science in agriculture and food systems, natural resource management, and family and community sciences.

PLANT DISEASES- THE BASICS

HOW DO WE DIAGNOSEP D ?PLANT DISEASES?

What is the host?

Imagine a healthy plant

What plant functions are being disrupted?

What plant parts are affected?

What are the signs and symptoms of disease?

WHAT PLANT PART ISAFFECTED? FUNCTIONSAFFECTED? FUNCTIONS

DISRUPTED?

Root knot nematode injury on begoniabegonia.  Deformed roots are inefficient at transporting water and nutrients.

COMPARE A HEALTHY ANDPDISEASED PLANT

Hosta ‘August Moon’ infected with  hosta virus X

SIGNS AND SYMPTOMS OFDDISEASE

Symptom – damage to the plant e g leafto the plant e.g. leaf spots

Signs – can we seeSigns  can we see the pathogen? Brown structures in th l f tthe leaf spot

Anthracnose on switchgrass

SIGNS OF DISEASESIGNS OF DISEASE

Fungal structures and spores of Colletotrichum the causal agent ofFungal structures and spores of Colletotrichum the  causal agent of anthracnose on switchgrass

SIGNS AND SYMPTOMS OFP MPOWDERY MILDEW ON CRAPE MYRTLE

Sign‐white fungal growth on leaves andon leaves and flowers

Symptoms‐di t t d ldistorted leaves and flowers

THE PLANT DISEASE STOOLTHE PLANT DISEASE STOOL

DiDiseaseManage by:

ent

•Disrupting the pathogen•Modifying the environment

nmeenvironment

•Altering the physiology or genetics of the h

nviro

host

En

PLANT DISEASEMMANAGEMENT

Avoidance

Exclusion

Eradication

Protection

AVOIDANCEAVOIDANCE

Choosing a planting location where the 

h iThis landscape pathogen is not present

This landscape bed was modified by incorporating  4 

Choosing a planting site not conducive to di

inches of pine bark into the soil prior to planting azaleas as a diseaseazaleas as a means to avoid phytophthoraroot rot.

EXCLUSIONEXCLUSION

Legal restrictions and quarantinesand quarantines

Propagation of disease free cuttingsdisease free cuttings

Production of disease free seed indisease free seed in areas not favorable for disease 

ERADICATIONERADICATION

Removal of pathogens from infested soil  and toolstools

Removal of pathogens from infected seed orfrom infected seed or plant parts

Removal of infectedRemoval of infected plants

Steaming soil to eradicate root knot nematode

PROTECTIONPROTECTION

Cultural control

i l i l lBiological control

Chemical control

Genetic resistance

Knockout rose is resistant to black spot and cercospora leaf spot

DISEASE CONTROL WITHFUNGICIDES

Fungicides protect healthy  plants

Fungicides protect new Fungicides protect new, flushes of shoots or roots

Fungicides do not cure sick plants!plants!

CONTROL OF POWDERYM DMILDEW ON DOGWOOD

Dogwood on the right was  sprayed once a week for six weeks prior to the onset of powdery mildewpowdery mildew with copper octanoate(copper soap).

UntreatedCopper Soap

HOW DO WE KNOW WHATD ?ORGANISMS CAUSE DISEASE?

A i t th ith di d

Koch’s Postulates

Associate a pathogen with a diseased plant

Robert Koch was 

Isolate the pathogen in culture

Inoculate a healthy plant and 

a German scientist that conducted breakthrough y p

reproduce symptoms

Isolate the pathogen again

breakthrough research on anthrax and cholera.

Isolate the pathogen again

KOCH’S POSTULATES FORD ADOGWOOD ANTHRACNOSE

WHAT ARE THE CAUSES OFD ?DISEASE?

Fungi

Bacteria

N t d Nematodes

Viruses

Parasitic plants

Abiotic Factors