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Managing Diseases in the Landscape

Kevin Korus

Coordinator - Plant and Pest Diagnostic Clinic

DPH Student

448 Plant Science Hall

What are plant diseases?

Anything that prevents a plant from

performing to its maximum

potential.

Types of diseases

Abiotic Disease caused by a non-

living agent Sun scorch, nutrient

deficiencies, chemical burn

Biotic

Disease caused by a

living agent.

Fungi, bacteria,

nematodes, viruses

(pathogens)

What size are plant pathogens?

Common plant

pathogens and

their size relative

to each other and

to a plant cell

Nematode

head

bacterium

Plant

cell

Plant

cell

nucleus

viruses

fungus

Viruses

Too small to be seen with

light microscope

Transmitted by aphids,

mites, other insects,

nematodes, and fungi

Virus acquired by insects

through feeding on infected

plant tissue

Hosta Virus X

Tulip Virus X

Tulip Breaking

Virus

•Destroyed the Dutch

economy in th1600’s.

•13,000 florins

• Spread by

contaminated bulbs or

vectored by aphids.

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Bacteria

Single-celled organisms

An opening is required

for infection to occur.

Favored by humid

conditions.

Can survive in soil and

in/on plant debris.

Fungi

Hyphae – small thread-like

filaments

Mycelium – mass of hyphae

Spores – reproductive

structures

Most fungi require free

moisture to cause infection of

plants

Can survive in soil or on plant

debris

Potato Blight

(Phytophothora infestans)

Irish Potato

Famine

1845-1852

1 million

starved

2 million

emigrated

Spread by contaminated seed and previously infected debris

Nematodes

Microscopic worm-like animals

Feed on roots and above ground plant parts.

Roots become distorted or galled after feeding occurs.

Some are vectored by insects.

Can survive in soil, in plants, and in insect vectors.

Similar to viral infections

Stunting

Chlorosis

Epinasty (abnormal growth)

Phytoplasmas Confirmation of Diagnosis -

Phytoplasmas

Electron Microscopy Serological Tests

Molecular Tests

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Terms: Pathogen vs. Disease

Disease: Any malfunctioning of host cells and tissues that results from continuous irritation by a pathogenic agent or environmental factor and leads to the development of symptoms

Pathogen: An entity, usually a microorganism, that can incite disease

◦ The Disease Pine Wilt is caused by the

Pathogen Bursaphelenchus xylophilus.

Terms

Sign ◦ Visible evidence of the presence of the pathogen.

Symptom ◦ Various changes in function and appearance of the infected plant.

Pop Quiz

Sign or symptom?

Abiotic Diseases

www.fao.org

Frost Crack

Maple

Root Girdling

hort.ufl.edu

hort.ufl.edu

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Salt Damage Winter Injury

Lawn Mower Blight Herbicide Drift

Biotic Diseases Diplodia / Sphaeropsis Tip Blight

ppdl.purdue.edu

5

Sphaeropsis Tip Blight (Diplodia)

Austrian, Scotch, red,

ponderosa and mugo

pine

Spores overwinter on

infected needles, needle

sheaths and cones

Rain and high humidity

are required for spore

germination

Images courtesy of University of Nebraska

Sphaeropsis Tip Blight (Diplodia)

Control

Avoid overcrowding

Protective fungicide

sprays

◦ Two applications

◦ Third week of April -

first week of May

◦ Bordeaux mixture

Image courtesy of University of Nebraska

Dothistroma Needle Blight

Austrian & ponderosa

pine

Needles infected by

fungal spores as they

emerge in spring

Brown to reddish

brown spots begin to

appear in early fall

Image courtesy of University of Nebraska

Dothistroma

Dothistroma Needle Blight Control

Plant resistant evergreen varieties

Avoid overcrowding trees

Maintain good air circulation

Protective fungicide sprays

◦ Bordeaux mixture ppdl.purdue.edu

Rhizosphaera Needle Cast

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Rhizosphaera Needle Cast

Colorado blue spruce –

susceptible; Norway

spruce – somewhat

resistant

Purple brown needles

with black fruiting

bodies of fungus

associated with stomata

in rows on needles

Rhizosphaera Needle Cast Control

Plant resistant varieties

Reduce stress on trees

◦ Water and mulch during dry

weather

Preventative fungicides when

new growth is ½ - 2 inches

◦ Repeat in 3-4 weeks

Cytospora Canker of Spruce Cytospora Canker

hort.uwex.edu plantdoctor.pbworks.com

hyg.ipm.illinois.edu

Cytospora Canker of Pine Cytospora Canker of Pine

Stroma

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Cytospora Pitch Cytospora Canker of Concolor Fir

Cytospora Canker of Concolor Fir

Image courtesy of Sarah Browning, University of Nebraska

Cooperative Extension

Pine Wilt

Scotch pine

Also Austrian and

sometimes white pine

Older tree, at least 10 yrs

Rapid decline of tree

Causal organism

◦ Pinewood nematode

Vector

◦ Pine Sawyer beetle

nfs.unl.edu

Nematodes

enter

feeding

wounds

Susceptible host

Pine sawyer beetles

lay eggs in bark of

dying trees.

Pine Wilt Disease Cycle

Resistant host:

Transmitted

nematodes die

Nematodes feed

on blue stain fungi

Nematodes attach

to pupae before

they emerge

Bark beetle galleries

Pine Wilt

Currently no chemicals are recommended to control either the beetle vector or the nematode

Diseased trees should be removed by end of April, which is before the beetles become active and could move the nematode from infested to non-infested trees

Trees should be burned or buried

Diseases of Hardwoods /

Deciduous Trees

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Anthracnose

Sycamore, ash, oak, maple, walnut

Also poplar

Host specific fungi

Causes leaf spot or leaf blight (typically along leaf veins)

Twig and shoot dieback ornamentaldiagnostics.blogspot.com

Oak Anthracnose

Ash Anthracnose Anthracnose

Fungi overwinter on

infected twigs or small

branches

Symptoms appear

following cool, wet

weather in spring

Leaf or shoot blight

may appear suddenly

after a rain

Anthracnose Control

Plant resistant species

Rake & destroy fallen leaves

Prune out dead or infected branches

Mulch & water during dry periods

Protective fungicide spray

Apple Scab

Favored by wet, humid

weather

Olive to greenish-black

lesions on leaves,

petioles and fruits

Fruit lesions enlarge

and become cracked &

scabby Image courtesy of University of Nebraska

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Apple Scab Apple Scab Control

Plant resistant varieties

Rake & remove infected

leaves

Protective fungicide

spray

Image courtesy of University of Nebraska

Upper leaf surface Lower leaf surface

Aecial spores

Telial spores

Cedar-apple rust Cedar-Apple Rust

Apple, crabapple,

hawthorn

Spore production &

release favored by wet

weather

Spores blown from

juniper host to apple

host flickrhivemind.net

Cedar-Apple Rust

Fruit lesions similar to

leaf spots

Infected at blossom end

Decrease fruit size

Fruit distortion

Premature fruit drop

Images courtesy of University of Nebraska

Fire Blight

Apple, crabapple, pear,

cotoneaster, hawthorn,

firethorn, mountain ash,

rose, quince, spirea,

viburnum (limited)

Bacterial disease

Erwinia amylovora

Courtesy Iowa State University

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Fire Blight

Bacteria overwinters at

edge of cankers

Milky ooze from

cankers contain

hundreds of bacteria

Bacterial ooze spread

by rain, wind and

insects to the flowers

Courtesy University of Nebraska

Fire Blight

Blossoms wilt, shrivel

and turn brown

Twigs form shepard’s

crook at tip

Leaves wilt, then turn

dark brown or black

and remain attached to

the tree

Fire Blight

Sunken, smooth cankers develop on main

branches and trunk

Cankers eventually become cracked

Fire Blight Control

Plant resistant varieties

Prune and discard infected branches

Prune only during the dormant season

◦ Cut 6-12 inches below the visible canker

Apply fertilizers sparingly in spring

Protective sprays

◦ Streptomycin or copper-based beginning at pink stage

Dutch Elm Disease

American elm

Fungal disease transmitted

by insect vector

◦ Native bark elm beetle

◦ European elm bark beetle

Image courtesy North Dakota State University

Dutch Elm Disease

Also can be spread

through natural root

grafts

Image courtesy Colorado State University

Streaking of vascular

tissue, characteristic

symptom

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Dutch Elm Disease

Management

◦ Remove dead trees

◦ Prevent root grafts

◦ Plant resistant elms

◦ Injection of chemical

fungicides to protect

high value trees

Sudden Oak Death

Leaf lesions due to P. ramorum on Camellia japonica

variety Kramer’s Supreme. Sporangium of P. ramorum

Spread of Phytophthora ramorum

www.sciencedirect.com

Verticillium Wilt

Affects over 300 kinds of plants

◦ Annuals & perennials

◦ Trees & shrubs

◦ Food & fiber plants

Caused by a soil-borne fungus

Attacks the plants vascular system

Image courtesy Ned Tisserat, Kansas State University Research &

Extension

Verticillium Wilt

Microsclerotia

◦ Resting structure

◦ Survives in soil for several years

Fungal spores invade the plant though root wounds

Cool temperatures favor fungal development Image courtesy Ned Tisserat, Kansas State University Research &

Extension

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Verticillium Wilt Control

Avoid planting

susceptible plants in

locations with a history

of verticillium wilt

Remove infected

branches

Burn infected wood

debris Image courtesy Ned Tisserat, Kansas State University Research &

Extension

Thousand Canker of Walnut Walnut twig beetle (Pityophthorus juglandis)

Cankers (Geosmithia sp and Fusarium solani)

http://www.ppdl.purdue.edu/PPDL/pubs/walnutthousandcankersdisease.pdf

http://entomology.ucdavis.edu/news/images/walnuttwigbeetlepencil.jpg

Thousand Canker of Walnut

Initial symptoms involve a

yellowing and thinning of the

upper crown

Progresses to include death

of larger branches

Final stages – large areas of

foliage may rapidly wilt

Trees often killed within 3

years after initial symptoms

http://www.ppdl.purdue.edu/PPDL/pubs/walnutthousandcankersdisease.pdf

Open Cankers Do Not Form

May see bark cracking

around entrance holes, star

shaped wounds at leaf scars,

and staining on trunk, but

these are not diagnostic

Dr. Ned Tisserat

Distribution of Black Walnut

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Management

Do not move fire wood

Currently no chemical control

Canker

Cankers

Nearly all canker pathogens are wound parasites

Death of bark and underlying cambium tissue is associated with a dead bud, branch stub, or twig, or with some type of mechanical injury

Cankers

Most cankers

produce fruiting

structures on newly

killed wood.

Tendrils of

Cytospora canker.

Conditions Favoring Cankers

Environmental stresses

favor the development of

most canker diseases.

Mechanical wounding

provides entry sites for

canker-causing pathogens.

Moisture after wounding

(within one week) creates

an environment favorable

for infection.

Thyronectria Canker of Honeylocust

Image courtesy of Michigan State University

Extension

Canker Management

Fungus readily infects wounded tissue but remains latent in the tree without causing symptoms – fungicide sprays cannot be effectively timed.

Wound dressings are not recommended.

Select the planting site carefully, avoiding drought prone sites. (Anticipate the future needs of the mature tree)

Cytospora Canker of Douglas Fir

Image courtesy of Sarah Browning, University of

Nebraska Cooperative Extension

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Canker Management

Remove dead trees and

prune diseased

branches. Disinfect

tools after each cut.

Prune in late winter or

during dry periods to

reduce the potential

spread of the

pathogen.

Image courtesy Michigan State University Extension

Diseases of Landscape Perennials

Impatiens Downy Mildew

Host

◦ Impatiens walleriana

Pathogen

◦ Plasmopara obducens

Powdery Mildew

Superficial white or gray growth over the surface of leaves, stems, fruits & flowers

Host specific fungi

Favored by

◦ Moderate temperatures

◦ High humidity

◦ Poor air circulation www.missouribotanicalgarden.org

Powdery Mildew

Spaherotheca pannosa var.

rosae fungi develop wind-

borne spores

Low rainfall plus 70°–80°

Low daytime humidity, high

nighttime humidity

Depletes nutrients

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Powdery Mildew Control

Plant resistant varieties

Rake & remove infected leaves

Improve air circulation

Increase sun exposure

Avoid overcrowding plants

Improve soil drainage

Protective fungicide sprays

www.missouribotanicalgarden.org

Black Spot

Fungal—Diplocaron rosae

High humidity and wet foliage

Spores overwinter on infected tissue

Circular black spots with fringed margins, yellow around spots

Poor quality flowers; plant may die

Black Spot Rose Rosette

Viral—maybe

Affects plants with R.

multiflora in parentage

Wild, reddish growth

Spread by insect vector

Remove all infected plants

Rose Rust

sperlingnursery.com

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Rose Rust

Yellow/brown spots on upper leaf surfaces, starting on lower leaves

Blotchy undersides

Plants lack vigor

Fungi (Phragmidium spp.) develop wind-borne spores

Moisture/moderate temperatures (55°-75°)

www.microbeworld.org

www.flickr.com

Crown Gall

Crown Gall

Bacterium (Agrobacterium tumefaciens) in soil;

often imported on tools

Enters through wounds and secretes a

compound causing rapid cell growth—galls

Disrupts flow of nutrients and water

Prune out galls and canes and disinfect Plant

resistant varieties

Black Knot

Crown, Root and Stem Rots

Most landscape

perennials/annuals

susceptible

aggie-horticulture.tamu.edu

Crown, Root and Stem Rots

Many plants

susceptible to crown,

root and stem rots

Caused by many

different types of

Fungi and Bacteria

franoiswirthensohn.girlshopes.com

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Crown, Root and Stem Rots

Symptoms:

◦ Discoloration of stem,

crown, roots

◦ Plants are wilted,

flaccid

◦ Dark brown/black

water soaked tissues

◦ Foul odor

franoiswirthensohn.girlshopes.com

Crown, Root and Stem Rots

Management:

◦ Plant resistant

varieties

◦ Improve soil drainage

◦ Remove infected

plants

◦ Chemical treatments

involve soil drenches

which are costly and

need repeat

applications

Plant Health Management

Choose right, place right

◦ Environment and spacing

◦ Diversity

Be observant

◦ Do you look or do you see?

◦ Catch problems early

Minimize stress to maximize health

The Disease Triangle

Host Pathogen

Environment

Host Pathogen

Environment

The Disease Triangle

Host Pathogen

Environment

Host Pathogen

Environment

Disease Management Strategy

• Ability to influence or manipulate

most

least

pathogen

host

environment

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QUESTIONS?