Diseases of Woody and Herbaceous Plants

David L. ClementDavid L. Clement

University of Maryland Cooperative Extension

Anthracnose diseases of trees

� Early to late spring

� Spotting followed by lesions running along veinsveins

� May cause defoliation

� Overwinter on twigs and buds

� Most require no treatment

Oak anthracnose

� Very common

� No treatments necessarynecessary

Sycamore anthracnose

� Causes defoliation

� Some resistance in London PlaneLondon Plane

� Can cause disfigured shape in canopy

Discula anthracnose

� Initial spots enlarge and form lesions along the veins

Lesions can � Lesions can appear ragged

� Check lower leaf surfaces for small black dots

Discula anthracnose

� Spotting on bracts is rare

� Compare with Botrytis which is slimeywhich is slimey

Discula anthracnose

� Water sprouts on trunk are especially susceptible

� Remove promptly to prevent stem infectionsRemove promptly to prevent stem infections

Anthracnose Diseases of Trees

Tree Name Latin Name

Sexual Stage of anthracnose

Asexual Stage of anthracnose

Ash Fraxinus Gnomoniella fraxini Discula fraxini

Birch Betula Apiognomonia sp. Cryptocline betularumBirch Betula Apiognomonia sp. Cryptocline betularum

Elm Ulmus Stegophora ulmea unknown

Filbert Corylus Monostichella coryli unknown

Dogwood Cornus unknown Discula destructiva

Hickory Carya Gnomonia caryae Asteroma caryae

Anthracnose Diseases of Trees

Tree Name Latin Name

Sexual Stage of Anthracnose

Asexual Stage of Anthracnose

Hornbeam Carpinus Apiosporopsis carpinea Monostichella sp.

Maple Acer Aureobasidium apocryptum

Unknown

Discula campestrisMaple Acer

apocryptum Discula campestris

Discula umbrinella

Colletotrichum gloeosprioides

Oak Quercus Apiognomonia quercina Discula querrcina

Redbud Cercis Aureobasidium sp. unknown

Sycamore Platanus Apiognomonia veneta unknown

Fungal Leaf Spots of TreesTree Name Latin

Name

Sexual Stage of Leaf Spot Fungus

Asexual Stage of Leaf Spot Fungus

Ash Fraxinus Mycosphaerella effigurata

M. fraxinicola

Pseudocercosporella fraxini

unknown

Crabapple Malus Venturia inaequalis Fusicladium pomi

Dogwood Cornus Elsinoe corni

unknown

unknown

Septoria floridae

Hawthorn Crataegus Diplocarpon mespili Entomosporium mespili

Horse Chestnut

Aesculus Rhytisma spp.

unknown

unknown

Phyllosticta minima

Leaf spots

� Tar spot on maple

Leaf Spots

� Oak leaf blister

Leaf Spots

� Tulip poplar eyespot gall

Leaf Spots

� Eyespot gall on maple

Powdery mildew

� Symptoms on dogwood

Powdery mildew

� Early fall color symptoms

Powdery mildew

� Symptoms on sycamore

Powdery mildew

� Symptoms on oak

Powdery mildew

� Symptoms on pansies

Powdery mildew

� Symptoms on zinnia flowers

Rust Diseases

� Symptoms on cedar

Rust Diseases

� Symptoms on hawthorn fruit

Rust Diseases

� Symptoms on hawthorn twigs

Rust diseases

� Symptoms on ash

� Alternate host is cord grass along the salt marshesmarshes

Wilt diseases

� Dutch elm disease

Wilt diseases

� Dutch elm disease

Wilt diseases

� Verticillium wilt

Wilt diseases

� Mimosa wilt

Fireblight

� Caused by bacterium

� Only attacks plants in the rose family

� Characteristic � Characteristic shepherds crook

� Leaves remain attached

� On pears the leaves turn black

Fireblight

� In wet weather bacterial ooze can be spread by insects or rain

Bacterial leaf scorch

� Caused by a bacterium

� Thins the canopy

� Causes dieback

� Starts from the lower � Starts from the lower branches and interior of the canopy

� Has killed street trees especially in NJ

Bacterial leaf scorch

� Symptoms on elm

Bacterial leaf scorch

� Symptoms on maple

Bacterial diseases

� Symptoms on zinnia

Virus diseases

� Relatively rare

� Cause various symptoms that might be confused with nutritional disorders or be confused with nutritional disorders or chemical damage

Virus diseases

� INSV on impatiens

Air pollution

� Ozone damage

Phytotoxicity

� Chemical damage is more uniform than disease symptoms

� Symptoms appear on many plants at the Symptoms appear on many plants at the same time in the landscape

Phytotoxicity

� Chemicals applied during extreme heat or incompatible mixtures

Herbicide damage

� Dicamba injury

Herbicide damage

� Symptoms on maple

Sooty mold

� Black coating grows on honey dew

� Usually indicates a scale or aphid problemscale or aphid problem

Drought damage

� Leaf curling

Leaf Distortion

� Aphid feeding damage

Freeze damage

� Symptoms on iris

Phytotoxicity

� Wood alcohol damage form mulch

Drought Damage

� Scorch on trycirtis