Good Class4 Ornamental Diseases

Ornamental Plant Diseases Commercial Pesticide Applicator Exam Preparation Laura Pottorff, Colorado State University Adams County

Diseases Caused by Fungi • If the cause affects leaves/flowers only – Fungi • Powdery mildew • Botrytis • Rust • Anthracnose • Marsonnina • Apple scab • Septoria leaf spot

Common characteristics of fungi that affect leaves/flowers • Live above ground • Spread via wind, water, insects • Often require a water film on leaf surface to germinate and penetrate plant tissue. • Often overwinter on plant debris.

Powdery mildew on poinsettia

Powdery mildews • Produces talcum powder-like growth on leaf surface. (Sign) • Many, many plants are susceptible (even weeds).

Powdery mildew • Example: – Western sand cherry

Powdery mildew • Fungus overwinters on leaf debris • Favored by – shade, poor air circulation

Powdery mildew management • Clean up leaf debris. • Improve air circulation with selective pruning. • Fungicides – Potassium bicarbonates, Oils, Sulfur, Neem – Cleary’s 3336, Eagle, Bayleton

Botrytis (Gray mold) • Fungus produces gray mold on surface of flowers, fruit, leaves, and stems.

Botrytis • Favored by • Management – high humidity – Clean up debris – Poor air circulation – Good plant culture – Wounded or weakened – Avoid over watering tissue – Avoid over fertilization – Many of the same fungicides as for powdery mildew control *follow label directions.

Rust diseases • Two types – single host • sunflower rust • snapdragon rust • rose rust – two hosts • Juniper - Hawthorn rust

Juniper - Hawthorn Rust • Rocky Mt. Juniper – Galls

Juniper - Hawthorn Rust • Hawthorn – Leaf spots

Cedar/apple rust leaf Cedar/apple rust “spores” on leaf spots on crabapple underside of crabapple June-August August - April April - June Cedar/apple rust gall on juniper Cedar/apple rust “spore horns” on juniper

Juniper Hawthorn Rust Management • Separate hosts • Prune out galls on juniper • Clean up leaves in autumn on hawthorn • Fungicides – Juniper • Bordeaux mixture – Hawthorn • Bayleton, Cleary’s 3336

Day Lily Rust • Native to China, • Main way of spread Japan, Korea, Taiwan, – Airborne spores Russia • Be on the look out – Not yet in Colorado • Heteroecious rust – Day lily – Patrinia (lily family) – Hosta? (lily family) Diagram: M. Hahn and K. Mendgen, Konstanz University

Day Lily Rust • First found in U.S. in December 2000 • Due to nature in which plants are moved about there is concern • We do not know how serious this disease will be

Day Lily Rust

Daylily rust • Symptoms

Day Lily Rust • Not Daylily rust

Day Lily Rust • Signs

Day lily Rust management • Fungicides known to be affective against rust and labeled for day lily – Banner Maxx (propiconazole) • home owner version – Fertilome liquid systemic fungicide – Contrast (flutalonil) – Heritage (azoxystrobin) – Systhane (myclobutanil) – Daconil – Mancozeb

Apple Scab (Venturia inequalis) • Hosts: Apple, Crabpple, Malus spp. • Symptoms

Apple Scab • Favored by • Management – Wet spring – Clean up leaf debris in fall – Poor air circulation – Fungicides normally – Certain varieties more not needed. susceptible • Radiant crabapples

Anthracnose Anthracnose

Anthracnose • Anthracnose is a term • Hosts: oak, sycamore, for a type of leaf spot ash, and many other disease. ornamentals • Blotchy, necrotic lesions. • Normally not serious. • Outbreaks dependent on spring weather conditions.

Anthracnose • Life cycle: – fungus overwinters on leaves that fall to the ground in autumn. – Spores become active in spring and blow up to newly emerging leaves. – Favored by spring moisture.

Anthracnose • Management: – clean up leaf debris – allow for better air movement – fungicides are normally not needed

Marsonnina leaf spot on aspen

Marsonnina leaf spot • Host: Aspen • Damage: Yearly infestations may weaken tree. Causes premature leaf drop. • Normally not a concern in native areas (except for ruining fall color) • In landscaped areas may detract from look of tree.

Marsonnina leaf spot • Symptoms – dark black spots on leaves

Marsonnina leaf spot • Life cycle: – Fungus overwinters on leaf debris – Will spread to newly emerging leaves in the spring. – Symptoms visible in late summer - fall.

Marsonnina leaf spot management • When symptoms are visible (late summer): – Clean up leaf debris – IT IS TOO LATE TO SPRAY • If a fungicide application is warranted – Apply in the spring during bud break • Cleary’s 3336 • 26GT

Septoria leaf spot Photos:Government of British • Hosts: Cottonwood, Columbia- Forest Services maple and dogwood • Round leaf spots with dark margin • Fruiting structures within tan interior of leaf spot Fruiting structures

Integrated Pest Management of Fungal Leaf Spots • Clean up leaf debris (sanitation) • Avoid moisture on leaf surface • Decrease relative humidity • Improve air circulation • Is the plant located in the “right place” • Optional – Funigicides

Examples of Alternative Fungicides Labeled for Most** Leaf Spots • **READ THE LABEL!!! – Copper sulfate (anthracnose, powdery mildew, juniper tip blights) – Neem oil (Triact, Rose Defense) for powdery mildew – Potassium bicarbonate (Kaligreen, First Step) for powdery mildew – Sulfur (powdery mildew, black spot)

How do we get rid of it? (Integrated Pest Management) • If the cause affects leaves/flowers (and stems) only – Bacteria • Fire blight

Spring - Summer Fire blight cycle Shepherd’s crook Canker

Fire blight cycle Summer - Winter

Integrated Pest Management of Fire blight • Prevention • Control – Resistant varieties – Removal of • Crabapples symptomatic branches – Centurion (disinfect tools – David between each cut) – Indian Summer – Molten Lava – Pesticides – Profusion • Streptomycin sulfate – Robinson (for agricultural use – Biological control only) • Blight Ban (Pseudomonas • Copper flourescens)

Bacterial blight (Pseudomonas) • Hosts: Lilac, • Symptoms: blackened stems, petioles, and Cotoneaster leaves. Shepherds crook. • Occurs in spring • Commonly confused with frost injury Photos from Cornell University

Bacterial Blight • Management – Dry spring weather is a natural control – Prune out diseased branches, disinfecting pruning tools between each cut. – Results from chemical control are often unsatisfactory

Bacterial Wetwood • Hosts: Cottonwood, • Callus formation Siberian Elm, Willow retarded • Smelly, ooze running down trunk

Bacterial wetwood • No effective methods exist to eliminate wetwood disease. Preventing damage and stress to a tree's roots and stem is the best way to avoid a serious wetwood problem. Drought conditions increase wetwood problems, so it is important that the tree receives adequate water, especially during spring and summer months.

Crown Gall Agrobacterium tumefaciens • Hosts: Stone and pome fruits, roses, cottonwood, junipers, grapes. • Symptoms: wilting, gall at crown line or on roots.

Crown gall management • Bacterium is soilborne • Remove plant • Replant with nonsusceptible species • Avoid root wounding

How do we get rid of it? (Integrated Pest Management) • If cause (who) only affects stems – Fungi • Cankers Canker caused by bacteria Canker caused by fungus

Dieback caused by?

So What??? Cytospora? Fruiting structures = fungus Thyronectria?

Dieback caused by?

Girdling

Integrated Pest Management for Canker diseases • Remove affected branch. • Remove entire plant if on main stem. • Optional – Improve health of plant • Fungicides are not effective

Vascular wilts • If the cause (who) only affects internal plant tissues – Fungi • Dutch Elm Disease (Vectored) • Verticillium wilt (soilborne)

Vascular wilt disease – Can also move • Dutch elm disease between trees through – Vectored by the elm root graphs bark beetle

Integrated Pest Management for Dutch Elm Disease • Prevention • Control – Resistant varieties – Remove tree – Fungicide injection – Trench potential root graphs • Arbotect (benzimadazole) – Control vector • Alamo (propioconazole) Fungicide injection Photo by Lise Mahnke

Vascular Wilt Disease • Verticillium wilt • Gray to olive brown vascular streaking – Soilborne fungus – Many types of plant hosts • Woody • Herbaceous

Integrated Pest Management of Verticillium Wilt • Prevention • Control – Rotation of host plants – Removal of tree (not mandated) – Resistant tree varieties – Fungicides not • Hawthorn effective • Honey locust • All conifers • Apple/Crabapple/Pear • Sycamore • Oak • Willow • Mt Ash • Linden

• Dieback caused by?

Girdling root

Problems affecting roots • If cause (who) only affects roots • Biotic – Fungi (Pythium, Rhizoctonia) • Abiotic – Root girdling – Oxygen starvation – Etc.

Symptoms of root rot • Soft brown mushy roots – Sloughing of cortex

Integrated Pest Management for Fungal Root Rots • Biotic – Avoid over watering/improve soil drainage – Destroy severely affected plants – Optional • Fungicides

Fungicides Labeled for Most** Root Rot Fungi • **READ LABEL DIRECTIONS – Rhizoctonia or Fusarium • Iprodione (Chipco 26019) • azoxystrobin (Heritage) • Thiophanate methyl (Cleary’s 3336) • Trifloxystrobin (Compass) • Gliocladium virens (Soilguard) - Biological

Fungicides Labeled for Most** Root Rot Fungi • **READ LABEL DIRECTIONS – Pythium or Phytophthora • Metalaxyl (Subdue or Chipco Signature) • azoxystrobin (Heritage)

Abiotic Diseases • environmentally induced disease • the precursors or primary plant problems – lead to plant stress/weakness – lead to invasion of insects and disease

Affecting Roots • Soil condition and drainage is the primary problem

Affecting roots (and leaves) • Abiotic- 80% of all landscape plant problems fall this category

Affecting Roots (and leaves) • oxygen starved roots

Colorado Blue spruce located on south facing slope in urban landscape.

Plant siting • Natives and adapted non natives can be Ginnala maple planted together. – Watch that moisture regimes are similar Yucca

Affecting Roots (leaves symptomatic) • Nutrient deficiency – brought on by • soil condition • excess moisture – oxygen starvation

Affecting roots (leaves symptomatic) • Leaf scorch – an imbalance between water uptake and loss.

Affecting Leaves External “pressures” typically “blow” in.

Leaves affected – Freeze

Affecting leaves • 2,4-D herbicide injury to Ginnala maple

Is a Chemical Necessary? – Is the host plant valuable? – Is the pest/disease properly identified? – Is the disease life- or health-threatening? – Does this plant have a history of disease? – Are effective, legal treatments available? – Will one or two applications suffice? – Have cultural control practices been used?

Good Class4 Ornamental Diseases

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