Category Archives: Fact Sheet

Plant Problems to Watch for in 2022

Boxwood Blight Boxwood Blight
Host:   Boxwood
Pathogens:   Calonectria pseudonaviculata
Signs/Symptoms:   Circular, brown leaf spots followed by leaf drop and shrub death
For more information see:   UW Plant Disease Facts D0023
Lipstick Rust Lipstick Rust
Host:   Chinese juniper, apple, crabapple
Pathogen:   Gymnosporangium yamadae
Signs/Symptoms:   Brown blobs with orange gelatinous masses (juniper), red leaf spots (apple, crabapple)
Late Blight Late Blight
Host:   Tomato, potato
Pathogen:   Phytophthora infestans
Signs/Symptoms:   Water-soaked spots on leaves, leathery areas on tomato fruits, rapid plant death
For more information see:   UW Plant Disease Facts D0068
Septoria Leaf Spot and Early Blight Septoria Leaf Spot and Early Blight
Host:   Tomato
Pathogens:   Septoria lycopersici and Alternaria solani
Signs/Symptoms:   Spotting and eventual total collapse of leaves, working from the bottom of the plant up
For more information see:   UW Plant Disease Facts D0100/46
Septoria Leaf Spot of Lilac Septoria Leaf Spot of Lilac
Host:   Lilac
Pathogen:   Septoria sp.
Signs/Symptoms:   Dead spots on leaves, potentially leading to complete leaf browning
Wood Rots Wood Rots
Hosts:   Woody trees and shrubs
Pathogens:   Miscellaneous wood rot fungi
Signs/Symptoms:   Shelf-like growths on trunks and branches
Canker Diseases Canker Diseases
Hosts:    Woody trees and shrubs
Pathogens:   Miscellaneous canker fungi
Signs/Symptoms:   Sunken areas on trunks/branches
For more information see:   UW Plant Disease Facts D0027, D0037, D0042, D0055, D0074, D0114
Virus Diseases Virus Diseases
Hosts:   All plants, particularly herbaceous ornamentals
Pathogen:   Miscellaneous plant viruses
Signs/Symptoms:   Blotchy leaf color, growth distortions
For more information see:   UW Plant Disease Facts D0036, D0063, D0067, D0115, D0116, D0130
Rhizosphaera Needle Cast Rhizosphaera Needle Cast
Hosts:   Colorado blue spruce, other spruces
Pathogen:   Rhizosphaera kalkhoffii
Signs/Symptoms:   Browning/purpling of interior needles of lower branches, followed by needle drop
For more information see:   UW Plant Disease Facts D0093
Chlorosis Chlorosis
Hosts:    Pin oak, red maple, birch, azalea, white pine, blueberry
Pathogen:   None
Signs/Symptoms:   Yellow leaves with dark green veins
For more information see:   UW Plant Disease Facts D0084
Improper Planting Improper Planting
Hosts:   Woody trees and shrubs
Pathogen:   None
Signs/Symptoms:   No root flare at the soil line, girdling roots, frost cracks, canopy thinning, early fall color, branch dieback, tree/shrub decline and death

 

Boxwood Blight – Pest Alert

What is boxwood blight?  Boxwood blight (also known as box blight and boxwood leaf drop) is a devastating disease of boxwood (Buxus spp.) that can cause leaf loss and eventual death of affected shrubs.  Boxwood shrubs are commonly grown as hedges and as individual plants in home landscapes and public gardens.  Boxwood blight can affect any type of boxwood (Buxus spp.) including European or common boxwood (Buxus sempervirens)Korean littleleaf boxwood (B. sinica var. insularis), and Japanese littleleaf boxwood (B. microphylla var. japonica).  In addition, the disease has been reported on Japanese and Allegheny pachysandra (Pachysandra terminalis and Pachysandra procumbens respectively), two common groundcovers.  Boxwood blight has been found in Europe and New Zealand, and was first confirmed in the U.S. in 2011.  The disease was first detected in Wisconsin (in Kenosha County) in 2018.  The disease has subsequently been found in Dane, Milwaukee and Ozaukee Counties.

Boxwood blight can cause severe leaf loss and eventual death of boxwood shrubs. (Photo courtesy of David Clement, University of Maryland Extension)
Boxwood blight can cause severe leaf loss and eventual death of boxwood shrubs. (Photo courtesy of David Clement, University of Maryland Extension)

What does boxwood blight look like?  Initially, brown spots appear on the leaves.  The spots eventually enlarge and merge together.  Infected leaves turn brown and fall off.  Boxwood blight can cause total leaf loss on a shrub within days of the first onset of symptoms.  Dark brown to black sunken areas can also form anywhere on the stems, leading to branch dieback  Boxwood blight often kills plants shortly after all of the leaves drop.  Damage from winter burn (see UW Plant Disease Facts D0127, Winter Burn), dog urine and other diseases such as Volutella blight may look superficially similar to symptoms of boxwood blight.

Where does boxwood blight come from?  Boxwood blight is caused by the fungus Calonectria pseudonaviculata (sometimes referred to as Cylindrocladium pseudonaviculatum or Cylindrocladium buxicola) which thrives in humid, warm conditions.  The fungus is typically introduced into any area on nursery plants that are infected, but not showing symptoms.  Holiday wreaths containing boxwood sprigs have also been documented as a source of the boxwood blight fungus.  Once the fungus has been introduced into the landscape, spores can be easily spread by splashing water (e.g., rain or sprinklers), wind or contaminated gardening tools (e.g., pruners, shovels, gloves).  The boxwood blight fungus can survive and produce spores in dead boxwood leaves and branches (including those that have fallen onto the ground) for several years.

How can I save a plant with boxwood blight?  Because boxwood blight is new to Wisconsin and relatively rare, eradicating the causal fungus may be possible.  Therefore, if you find boxwood blight, remove and destroy any affected shrubs.  Currently, free testing for boxwood blight is available through the UW-Madison Plant Disease Diagnostics Clinic (https://pddc.wisc.edu/).  Plants (roots and all) confirmed to have boxwood blight, as well as any leaves or branches that have fallen from these plants, should be removed and destroyed by burning (where allowed by local ordinance), deep burying (at least two feet deep) or double bagging (in plastic garbage bags), then landfilling.  DO NOT compost any parts of infected shrubs.  Thoroughly decontaminate any tools used in the removal process by treating them for at least 30 seconds in 70% alcohol (e.g., rubbing alcohol or certain spray disinfectants) or (as a last resort) in 10% bleach.  If you use bleach, be sure to thoroughly rinse and oil tools after pruning to prevent rusting.

How can I avoid problems with boxwood blight in the future?  

Consider using shrubs other than boxwood in your landscape.  If you decide to use boxwood, choose boxwood blight resistant varieties where possible.  In Wisconsin, hybrid boxwoods ‘Green Gem’ and ‘Karzgreen (Green Ice®), Japanese littleleaf boxwood varieties ‘Jim Stauffer’, ‘Little Missy’ and ‘Winter Gem’, and Korean littleleaf boxwood varieties ‘Eseles’ (Wedding Ring®), ‘Franklin’s Gem’, ‘Pincushion’, ‘Wee Willie’, ‘Winter Beauty’ and ‘Wintergreen’ are hardy to at least USDA hardiness zone 5 and have been documented to be resistant to boxwood blight.  Always buy boxwood shrubs from local, reputable suppliers who have thoroughly inspected boxwood plants for evidence of boxwood blight.

Leaf spots typical of boxwood blight on boxwood sprigs in a holiday wreath. (Photo courtesy Purdue PPDL)
Leaf spots typical of boxwood blight on boxwood sprigs in a holiday wreath. (Photo courtesy Purdue PPDL)

Isolate new boxwood shrubs from established boxwoods for several weeks before planting, as boxwood blight symptoms not become apparent until weeks after purchase.  DO NOT plant boxwoods in areas where boxwood blight has been a problem in the past, as the fungus can survive in boxwood debris (e.g., leaves and branches) for several years.  When planting, space boxwood plants far enough apart from each other, as well as other shrubs, so that branches on adjacent shrubs do not overlap.  This will increase air flow between plants and promote a drier environment that will be less favorable for boxwood blight development.  Avoid watering plants with sprinklers or overhead with hoses; instead use a soaker or drip hose.  This will limit splash of spores from plant to plant and also promote a drier environment that is less favorable for disease.

Be cautious when buying holiday wreaths or other garlands.  Avoid holiday decorations that contain boxwood, whenever possible.  If you are unsure whether a wreath that you have purchased contains boxwood, assume that it does, and dispose of it appropriately by burning, deep burying or double bagging and landfilling as described above.  Be careful to collect and dispose of any leaves or branches that may have fallen from wreaths as well.  Make sure that no potentially contaminated materials end up near boxwood shrubs in your yard.  Under NO circumstances should you attempt to compost any suspected boxwood materials.

Once boxwood blight has been reported near your location, you may want to consider using preventative fungicide treatments for management.  Fungicides containing chlorothalonil (alone or in combination with thiophanate-methyl or tebuconazole), fludioxonil, metconazole, and tebuconazole (as a stand-alone product) have been shown to provide good control of boxwood blight if applied prior to the development of any symptoms.  These fungicides will not cure existing disease.  If you decide to use fungicides, you will need to treat every seven to 14 days throughout the growing season.  DO NOT use fludioxonil, metconazole, or tebuconazole as the sole active ingredient for all treatments.  If you decide to use one of these active ingredients, alternate its use with at least one of the other active ingredients listed above (except DO NOT alternate metconazole and tebuconazole as these products are chemically related).  Alternating active ingredients will help minimize problems with fungicide-resistant strains of the boxwood blight fungus.  Be sure to read and follow all label instructions of the fungicide(s) that you select to ensure that you use the product(s) in the safest and most effective manner possible.

Finally, routinely (e.g., weekly) check boxwood plants for boxwood blight.  Immediately remove any symptomatic plants and fallen leaves and branches, and dispose of them as described above.

For more information on boxwood blight:  Contact your county Extension agent.

Thyronectria Canker

What is Thyronectria canker?  Thyronectria canker is a common fungal disease of honeylocust (Gleditsia triacanthos), occurring wherever this tree is grown.  Black locust (Robinia pseudoacacia) and Kentucky coffeetree (Gymnocladus dioicus) have also been reported to be susceptible to the disease.  Thyronectria canker is non-lethal and typically causes relatively minor damage to affected trees.

Thyronectria canker leads to sunken areas on honeylocust branches that are peppered with black spots.
Thyronectria canker leads to sunken areas on honeylocust branches that are peppered with black spots.

What does Thyronectria canker look like?  Thyronectria canker causes branch dieback.  Affected branches are typically relatively small in diameter (approximately one inch or less), although larger branches can become infected.  On smaller branches, distinct sunken areas (cankers) form at the point of infection.  Within the sunken area, small dark-brown to black spots are typically visible.

Where does Thyronectria come from?  Thyronectria canker is caused by the fungus Thyronectria austoamericana (sometimes written Thyronectria austo-americana).  The spots visible within the sunken areas on infected branches are clusters of fruiting bodies (i.e., reproductive structures) of the fungus.  These structures produce multicelled, light- to medium-brown spores that, when released, can blow to susceptible trees, leading to new infections.  Long periods of wet weather are favorable for infection to occur.

How do I save a tree with Thryronectria canker?  Remove infected branches by pruning four to six inches below obviously infected areas on branches.  Be sure to prune only when it is dry, and be sure to disinfest pruning tools between cuts by treating them for at least 30 seconds with 70% alcohol (e.g., rubbing alcohol straight out of the bottle), spray disinfectants (as long as they contain 60 to 70% alcohol) or 10% bleach.  If you use bleach, be sure to thoroughly rinse and oil tools after you are done pruning to prevent rusting.  Dispose of branches by burning (where allowed) or burying them.  DO NOT use fungicides for control of this disease.

How do I avoid problems with Thyronectria canker in the future?  Make sure your honeylocust tree is properly fertilized and watered to reduce stress and promote vigorous growth.  Fertilize your honeylocust only if you have soil and foliage nutrient tests that indicate nutrient deficiencies that need to be corrected.  The UW Soil and Forage Lab (https://uwlab.soils.wisc.edu/) can assist with testing.  An established honeylocust tree (i.e., a tree that has been planted for three or more years) requires approximately one inch of water per week from the time it buds out in the spring, through the summer and into the fall up until it starts to turn its normal fall color.  When there is insufficient rain, water at the drip line of the tree (i.e., the edge of where the branches extend), or more extensively in the root zone if possible, using a drip or soaker hose.  Remove grass out to the drip line of the tree, and mulch this area with a high quality mulch (e.g., shredded oak bark mulch, one of the cedar mulches).  Use one to two inches of mulch if you have a heavier (e.g., clay) soil and three to four inches if you have a lighter (e.g., sandy) soil.  Keep mulch four inches from the trunk of the tree.  Finally, consider routine maintenance pruning by a certified arborist (see https://www.waa-isa.org/) to thin the canopy of your honeylocust tree.  Thinning will provide better airflow through the tree, promoting more rapid drying of branches and leaves, thus leading to a less favorable environment for infections to occur.

For more information on Thyronectria canker:  Contact your county Extension agent.

Iris Severe Mosaic

What is iris severe mosaic?  Iris severe mosaic (also called yellow latent disease or gray disease) is a potentially severe viral disease that can adversely affect both bulb and rhizome-forming irises, as well as crocuses.  German bearded irises are particularly susceptible to the disease.  Commercially produced irises and crocuses affected by iris severe mosaic cannot be sold.  Thus, iris severe mosaic can have potentially significant economic consequences for iris and crocus producers.

Pale green and yellow stripes on iris leaves are typical symptoms of iris severe mosaic.

What does iris severe mosaic look like?  Symptoms of iris severe mosaic can occur on any plant part.  Leaves, particularly middle or outermost leaves, may have pale green to yellow stripes.  Younger, interior leaves often do not exhibit symptoms.  Flowers may develop blotchy color (a symptom known as color break).  Overall, affected plants may be stunted, producing smaller than normal flowers, and smaller bulbs, rhizomes or corms.  Symptoms tend to be more severe when temperatures are cooler.  At higher temperatures, symptoms are less obvious.  Similarly, iris and crocus plants grown indoors tend to develop more severe symptoms than those grown outdoors.  In some situations, plants with iris severe mosaic may not show any symptoms.

Where does iris severe mosaic come from?  Iris severe mosaic is caused by Iris severe mosaic virus (ISMV), a virus transmitted primarily by aphids, specifically the potato aphid (Macrosiphum euphorbiae) and the green peach or peach-potato aphid (Myzus persicae).  These aphids acquire the virus from infected plants and subsequently transmit the virus to non-infected plants as they feed.  ISMV can also be spread as infected plants are divided to produce additional plants.

Tools (e.g., pruning tools, knives, etc.) used when working with infected plants can become contaminated with sap containing ISMV and can serve as another means of spreading the virus to healthy plants.

How do I save plants with severe iris mosaic?  Most types of iris can tolerate low levels of ISMV.  However, infected plants remain infected indefinitely and cannot be treated in any way to eliminate the virus.  Therefore, you should dig up and either bury or burn affected plants as soon as you observe symptoms.  This will help limit the spread of the virus.

How do I avoid problems with iris severe mosaic in the future?  When possible, plant Siberian iris (Iris sibirica) as this species is resistant to ISMV.  Take care when planting German bearded iris (Iris germanica).  This type of iris is very popular (and incredibly beautiful) but tends to show more severe symptoms of iris severe mosaic.  When purchasing iris plants, buy only from reputable producers who have an ISMV management plan.  Such a plan should include careful monitoring of stock plants for iris severe mosaic symptoms, diligent removal and destruction of infected plants, routine removal of weeds in production areas to eliminate plants that can serve as reservoirs for aphids, and applications of insecticides to control aphid populations.

When dividing iris plants, decontaminate tools routinely by treating them for a minimum of one minute with:

  • 75 tablespoons Alconox® (a lab detergent) plus 2.5 tablespoons sodium lauryl sulfate (SLS), also known as sodium dodecyl sulfate (SDS), in one gallon of water, or
  • 14 dry ounces of trisodium phosphate (where allowed by state or local ordinance) in one gallon of water.

These ingredients can be ordered on the internet.  If you decide to use SLS (SDS), be sure to wear gloves, safety goggles and a dust mask, and mix the solution in a well-ventilated area as SLS (SDS) is a known skin and eye irritant.  Once treated, rinse items with sufficient water to remove any residues.

For more information on severe iris mosaic:  Contact your county Extension agent.

Vegetable Disease Quick Reference

Septoria Leaf Spot Septoria Leaf Spot and Early Blight
Host:   Tomato
Pathogens:   Septoria lycopersicia and Alternaria solani
Signs/Symptoms:  Spotting and eventual total collapse of leaves working from the bottom of the plant up
For more information see:        UW Garden Facts D0100/D0046
Late Blight Late Blight
Hosts:   Tomato, potato
Pathogen:   Phytophthora infestans
Signs/Symptoms:  Water-soaked spots on leaves, leathery areas on tomato fruits, rapid plant death
For more information see:        UW Garden Facts D0068
Blossom End Rot Blossom End Rot
Host:   Tomato, pepper, eggplant, cucumber, squash
Cause:   Calcium deficiency
Signs/Symptoms:  Decayed areas on the bottom sides of vegetable fruits
For more information see:        UW Garden Facts D0022
Powdery Mildew Powdery Mildew
Hosts:    Any vegetable, particularly vine crops, peas
Pathogens:    Miscellaneous powdery mildew fungi
Signs/Symptoms:  Powdery white growth on leaves
For more information see:        UW Garden Facts D0086
Common Corn Smut Common Corn Smut
Hosts:   Corn
Pathogen:   Ustilago maydis
Signs/Symptoms:  Pasty white masses on corn ears eventually decomposing into a brown powder
For more information see:        UW Garden Facts D0031
Black Rot Black Rot
Hosts:   Crucifers (e.g., cabbage, broccoli, cauliflower)
Pathogen:   Xanthomonas campestris pv. campetris
Signs/Symptoms:  V-shaped yellow/dead areas on leaves progressing into plant deterioration and death
For more information see:        UW Garden Facts D0019
Potato Scab Potato Scab
Hosts:    Potato, carrot, beet, other root crops
Pathogen:  Streptomyces scabies
Signs/Symptoms:  Brown, rough, scab-like areas on tubers and roots
For more information see:        UW Garden Facts D0083
Verticillium Wilt Verticillium Wilt
Host:   Tomato, pepper, eggplant, potato, vine crops
Pathogen:  Verticillium spp.
Signs/Symptoms:  Leaf yellowing and wilting of plants followed by eventual plant death
For more information see:        UW Garden Facts D0122
Aster Yellows Aster Yellows
Hosts:    Carrot
Pathogens:    Aster yellows phytoplasma
Signs/Symptoms:  Yellow/orange/purple leaves, stunted roots with tufts of white hairy roots
For more information see:        UW Garden Facts D0007
Bacterial Wilt Bacterial Wilt
Hosts:   Vine crops
Pathogen:   Erwinia tracheiphila
Signs/Symptoms:  Sectional wilting and eventual death of plants after cucumber beetle feeding
For more information see:        UW Garden Facts D0014
Basil Downy Mildew Basil Downy Mildew
Host:   Basil
Pathogen:   Peronospora belbahrii
Signs/Symptoms:  Downward-cupped, yellow leaves with purple-gray fuzz on leaf undersurfaces
For more information see:        UW Garden Facts D0015

For more information on conifer diseases:  See https://pddc.wisc.edu/ or contact your county Extension agent.

Root Rots on Houseplants

Wilting of poinsettia associated with Pythium root rot.
Wilting of poinsettia associated with Pythium root rot.

What is root rot? Root rot is a general term that describes any disease where the pathogen (causal organism) causes the deterioration of a plant’s root system. Most plants are susceptible to root rots, including both woody and herbaceous ornamentals. Root rots can be chronic diseases or, more commonly, are acute and can lead to the death of the plant.

How do you know if your plant has a root rot? Homeowners often become aware of root rots when they note that a plant is wilted, even though the soil is wet. Plants with root rots are also often stunted, and may have leaves with a yellow or red color, symptoms that suggest a nutrient deficiency. Careful examination of the root systems of these plants reveals roots that are soft and brown. These roots may have a bad odor.

Where does root rot come from? A large number of soil-borne fungi cause root rots. Pythium spp., Phytophthora spp., Rhizoctonia solani, and Fusarium spp. are the most common root rot fungi. These fungi have wide host ranges, and thus can cause root rots on a wide variety of plants. Most root rot fungi prefer wet soil conditions and some, such as Pythium and Phytophthora produce spores that can survive for long periods in soil or plant debris.

How do I save a plant with root rot? Often the best and most cost effective way of dealing with a plant with root rot is to throw it out. If you decide to keep a plant with root rot, REDUCE SOIL MOISTURE! Provide enough water to fulfill the plant’s growth needs and prevent drought stress, but DO NOT over-water.

Throw out plastic pots if plants grown in them have suffered from a root rot.
Throw out plastic pots if plants grown in them have suffered from a root rot.

We DO NOT recommend use of chemical fungicides for control of root rots on houseplants because of the limited availability of products for use by homeowners, and because those products that are available tend to be expensive.

How do I avoid problems with root rots? First, buy plants from a reputable source and make sure they are root rot-free prior to purchase. Second, replant your houseplants properly. Use a pot with drainage holes, but DO NOT put rocks or gravel at the bottom of the pot. The presence of rocks or gravel can actually inhibit drainage. Use a pasteurized commercial potting mix, NOT soil from your garden. Garden soils often contain root rot fungi. Add organic material (e.g., peat moss) to heavy potting mixes to increase drainage. Third, minimize potential contamination of your plants with root rot fungi. DO NOT reuse potting mix from your houseplants, or water that has drained from your plants, as both potentially can contain root rot fungi. After working with plants with root rot problems, disinfest tools, working surfaces and clay pots with a 10% bleach or detergent solution, or alcohol. DO NOT reuse plastic pots as they are often difficult to disinfest adequately. Finally and most importantly, moderate plant moisture. Provide enough water to fulfill your plants’ needs for growth and prevent drought stress, but DO NOT over-water. In particular, DO NOT allow plants to sit in drainage water. REMEMBER, root rot fungi grow and reproduce best in wet soils.

For more information on root rots: Contact your county Extension agent.

Lichens

There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.
There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.

What are lichens? Lichens are organisms that arise from mutually beneficial interactions between certain fungi and algae. The fungi provide the physical structures of the lichens, as well as protection for the algae. The algae, in turn, produce food for the fungi via photosynthesis.

What do lichens look like? Lichens come in four basic growth forms. Crustose lichens are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens are leaf-like and composed of flat sheets of tissue that are not tightly bound together. Squamulose lichens are composed of scale-like parts. Fruticose lichens are composed of free-standing branching tubes.

Where do lichens come from? Lichens are everywhere. There are an estimated 13,500 to 17,000 species of lichens, and lichens can be found growing in tropical, temperate and polar regions throughout the world. Lichens will grow on almost any surface that is stable and reasonably well-lit. In temperate regions, lichens can often be found growing on the bark of trees or old fence posts. Others lichens grow in less hospitable places, such as bare rock surfaces or old headstones in graveyards, where they aid in the breakdown of rocks and the formation of soil.

There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.
There are many types of lichens. Crustose lichens (left) are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens (right) are leaf-like and composed of flat sheets of tissue that are not tightly bound.

How do I save a tree with lichens? DO NOT PANIC! Lichens do not harm trees; they are not pathogens or parasites, and do not cause disease. Lichens are self-reliant, with the algal component of the lichen producing food for the organism via photosynthesis. Lichens absorb water and minerals from rainwater and the atmosphere, and because of this, they are extremely sensitive to air pollution. As a result, the presence or absence of certain lichen species can be used as an indicator of levels of atmospheric pollutants. Information on the abundance and species of lichens growing in an area can give a good indication of the local air quality.

For more information on lichens: Contact your county Extension agent.

Plant Diseases to Watch For in 2021

Septoria Leaf Spot Septoria Leaf Spot and Early Blight
Host:  Tomato
Pathogens:   Septoria lycopersici and Alternaria solani
Signs/Symptoms:  Spotting and eventual total collapse of leaves working from the bottom of the plant up
For more information see:       UW Plant Disease Facts D0100/46
Late Blight Late Blight
Hosts:  Tomato, potato
Pathogen:   Phytophthora infestans
Signs/Symptoms:  Water-soaked spots on leaves, leathery areas on tomato fruits, rapid plant death
For more information see:       UW Plant Disease Facts D0068
Septoria Leaf Spot of Lilac Septoria Leaf Spot of Lilac
Host:  Lilac
Pathogen:   Septoria sp.
Signs/Symptoms:  Dead spots on leaves, potentially leading to complete leaf browning
Rhizosphaera Needle Cast Rhizosphaera Needle Cast
Hosts:  Colorado blue spruce, other spruces
Pathogen:   Rhizosphaera kalkhoffii
Signs/Symptoms:  Browning/purpling of interior needles of lower branches, followed by needle drop
For more information see:       UW Plant Disease Facts D0093
Gymnosporangium Rusts
Hosts:  Juniper, apple, crabapple, hawthorn, quince
Pathogen:   Gymnosporangium spp.
Signs/Symptoms:  Brown blobs with orange gelatinous masses (juniper); yellow/orange leaf spots (other hosts)
For more information see:       UW Plant Disease Facts D0058
Elderberry Rust
Hosts:  Elderberry
Pathogen:   Puccinia sambuci
Signs/Symptoms:  Light yellow, powdery growths on branches
For more information see:       UW Plant Disease Facts D0049
Scab Scab (Apple and Pear)
Hosts:   Apple, crabapple, pear, mountain-ash
Pathogens:   Venturia inaequalis, Venturia pirina
Signs/Symptoms:  Feathery-edged spots on leaves and fruits often leading to leaf loss and tree defoliation
For more information see:       UW Plant Disease Facts D0004
Bur Oak Blight
Host:   Bur oak
Pathogen:   Tubakia iowensis
Signs/Symptoms:  Wedge-shaped dead areas on leaves leading to dead leaves that stay attached to trees
Powdery Mildew
Hosts:   Herbaceous and woody ornamentals, fruits, vegetables, turf
Pathogens:   Miscellaneous powdery mildew fungi
Signs/Symptoms:  Powdery white growth on leaves
For more information see:       UW Plant Disease Facts D0084/86/87
Diplodia Shoot Blight and Canker
Hosts:  Austrian pine, other pines
Pathogen:   Diplodia spp.
Signs/Symptoms:  Dieback of branch tips with dead needles showing uneven lengths
For more information see:       UW Plant Disease Facts D0042
Boxwood Blight
Host:  Boxwood
Pathogen:   Calonectria pseudonaviculata
Signs/Symptoms:  Circular, brown leaf spots followed by leaf drop and shrub death
For more information see:       UW Plant Disease Facts D0023

For more information on plant diseases to watch for:  See https://pddc.wisc.edu/ or contact your county Extension agent.

Ten Common Plant Diseases/Disorders You Can Diagnose by Eye

Powdery Mildew Powdery Mildew
Hosts:   Herbaceous and woody ornamentals, fruits, vegetables, turf
Pathogens:   Miscellaneous powdery mildew fungi
Signs/Symptoms:  Powdery white growth on leaves
For more information see:       UW Plant Disease Facts D0084/86/87
Tar Spot - Ten Common Plant Diseases Tar Spot
Hosts:  Maples
Pathogen:   Rhytisma spp.
Signs/Symptoms:  Tarry areas (either solid spots or clusters of small spots) on leaves
For more information see:       UW Plant Disease Facts D0110
Peach Leaf Curl Peach Leaf Curl
Hosts:  Peach
Pathogen:   Taphrina deformans
Signs/Symptoms:  Light-green, yellow or purplish-red puckered areas on leaves
For more information see:       UW Plant Disease Facts D0076
Sooty Mold Sooty Mold
Hosts:  Any plant
Pathogen:   Miscellaneous sooty mold fungi
Signs/Symptoms:  Powdery black growth on leaves or needles
For more information see:       UW Bulletin A2637
Chlorosis Chlorosis
Hosts:  Oak, red maple
Cause:   Iron or manganese deficiency, often induced by high soil pH
Signs/Symptoms:  Yellow leaves with dark green veins
For more information see:       UW Plant Disease Facts D0030
Gymnosporangium Rusts Gymnosporangium Rusts
Hosts:  Juniper, apple, crabapple, hawthorn, quince
Pathogen:   Gymnosporangium spp.
Signs/Symptoms:  Brown blobs with orange gelatinous masses (juniper); yellow/orange leaf spots (other hosts)
For more information see:       UW Plant Disease Facts D0058
Black Knot Black Knot
Hosts:  Prunus spp. (plum and cherry)
Pathogen:   Apiosporina morbosa
Signs/Symptoms:  Black poop-like growths on branches
For more information see:       UW Plant Disease Facts D0018
Elderberry Rust Elderberry Rust
Hosts:  Elderberry
Pathogen:   Puccinia sambuci
Signs/Symptoms:  Light yellow, powdery growths on branches
For more information see:       UW Plant Disease Facts D0049
Golden Canker Golden Canker
Hosts:  Pagoda dogwood
Pathogen:   Cryptodiaporthe corni
Signs/Symptoms:  Gold-colored branches with orange spots
For more information see:       UW Plant Disease Facts D0055
Dog Vomit Slime Mold Dog Vomit Slime Mold
Hosts:  Any plant and on mulch
Cause:   Fuligo septica
Signs/Symptoms:  Scrambled egg-like masses on mulch or at the base of plants
For more information see:       UW Plant Disease Facts D0102

For more information on common plant diseases:  See https://pddc.wisc.edu/ or contact your county Extension agent.

Deciduous Tree Leaf Disease Quick Reference

Anthracnose for Quick Guide Anthracnose
Hosts:  Most trees, commonly ash, maple and oak
Pathogens:  Gloeosporium spp. as well as other fungi
Signs/Symptoms:  Blotchy dead areas on leaves
For more information see:  UW Plant Disease Facts D0002
Purple-bordered leaf spot Purple-Bordered Leaf Spot
Host:  Amur, Japanese, red, silver and sugar maple
Pathogen:  Phyllosticta minima
Signs/Symptoms:  Discrete, circular leaf spots with purple borders
For more information see:  UW Plant Disease Facts D0089
 Tubakia leaf spot Tubakia (Actinopelte) Leaf Spot
Hosts:  Oak
Pathogen:  Tubakia spp. (Actinopelte spp.)
Signs/Symptoms:  Discrete circular, or irregular blotchy dead areas on leaves
For more information see:  UW Plant Disease Facts D0118
 Scab Apple Scab
Hosts:  Apple, crabapple, pear, mountain-ash
Pathogen:  Venturia inaequalis, V. pirina
Signs/Symptoms:  Circular, black leaf spots with feathery edges; eventual leaf loss
For more information see:  UW Plant Disease Facts D0004
 Cedar-Apple Rust Gymnosporangium Rusts
Hosts:  Apple, crabapple, hawthorn
Pathogens:  Gymnosporangium spp.
Signs/Symptoms:  Bright yellow-orange, circular leaf spots
For more information see:  UW Plant Disease Facts D0058
 Powdery Mildew Powdery Mildew
Hosts:  Most deciduous trees
Pathogens:  Several genera of powdery mildew fungi
Signs/Symptoms:  Uniform/blotchy powdery white areas on upper and lower leaf surfaces
For more information see:  UW Plant Disease Facts D0087
 Downy Leaf Spot Downy Leaf Spot
Hosts:  Hickory, walnut
Pathogen:  Microstroma juglandis
Signs/Symptoms:  Discrete powdery white areas on lower leaf surfaces
 Clorosis Chlorosis
Hosts:  Oak, red maple
Cause:   Iron or manganese deficiency, often induced by high soil pH
Signs/Symptoms:  Yellow leaves with dark green veins
For more information see:  UW Plant Disease Facts D0030
 Scorch Scorch
Hosts:  Most deciduous trees
Cause:   Water stress induced by drought, high soil salt content, or other water-limiting factors
Signs/Symptoms:  Dead tissue on leaf margins
 Tatters Tatters
Hosts:  Most deciduous trees, but commonly oak
Cause:  Possible early season cold injury
Signs/Symptoms:  Lacy, tattered-looking leaves
For more information see:  UW Plant Disease Facts D0111

For more information on deciduous tree leaf diseases:  See https://pddc.wisc.edu/ or contact your County Extension agent.