Category Archives: Disease – Deciduous Woody Ornamental

Disease - Deciduous Woody Ornamental, Fact Sheet

Eastern Filbert Blight

What is Eastern filbert blight?  Eastern filbert blight is a potentially serious fungal disease found throughout the United States, including Wisconsin.  It affects only Corylus species, commonly known as hazelnuts or filberts.  On hazelnuts native to Wisconsin such as American hazelnut (Corylus americana) and beaked hazelnut (Corylus cornuta), the disease causes little significant damage, but on the commonly grown European hazelnut (Corylus avellana), including Harry Lauder’s walking stick (Corylus avellana ‘Contorta’), the disease is lethal.  Turkish filbert (Corylus colurna) also appears to be highly susceptible.

Eastern filbert blight can cause small black cankers that form in rows, or deep gouges in the bark of severely infected trees/shrubs.
Eastern filbert blight can cause small black cankers that form in rows, or deep gouges in the bark of severely infected trees/shrubs.

What does Eastern filbert blight look like?  Eastern filbert blight causes cankers (i.e., dead, collapsed areas of bark) on branches or main trunks.  Easily visible within the cankers are black, football-shaped stromata (the reproductive structures of the causal fungus).  The stromata often form in rows of two.  Cankers first appear on new twigs and expand over time.  American hazelnut trees/shrubs are able to live almost indefinitely with Eastern filbert blight, forming a small number of slowly-expanding cankers (if any cankers form at all) that lead to limited branch dieback.  On European hazelnut however, cankers will expand anywhere from one inch to three feet in a year, and can eventually form long, deep gouges or grooves on severely affected trees/shrubs.  European hazelnuts typically die due to girdling from Eastern filbert blight within five to 10 years.

Where does Eastern filbert blight come from?  Eastern filbert blight is caused by the fungus Anisogramma anomala.  Stromata formed by the fungus produce spores that are spread short distances by water splash and over longer distances by wind.  Humans also can spread Anisogramma anomala on their hands and clothing, on gardening tools, and by transporting wood from infected trees/shrubs.  Unlike other canker fungi that can infect through wounds, the Eastern filbert blight fungus primarily infects through immature tissue on actively growing shoots.  Cankers appear 12 to 18 months after infection.  Eastern filbert blight does not affect hazelnut leaves, fruits or nuts.

How do I save trees/shrubs with Eastern filbert blight?  There is no cure for Eastern filbert blight.  If only a few branches on a tree/shrub are affected, prune these branches two to three feet below each canker.  Disinfest tools after each cut by dipping them for at least 30 seconds in a 10% bleach solution or (even better) a 70% alcohol solution.  Alternatively, use a spray disinfectant containing roughly 70% ethanol, spraying tools until they drip and then allowing them to air dry.

If a tree/shrub is severely affected by Eastern filbert blight (e.g., when there are so many cankers on multiple branches that the tree/shrub would look ugly if pruned, when branch pruning would require removing part of the trunk, or when trunk cankers are present), removal of the tree/shrub is the preferred management strategy.

Pruned branches and removed trees/shrubs should be burned (where allowed by local ordinance), deep-buried, or chipped (as long as the chips are allowed to dry to kill the fungus).

How do I avoid problems with Eastern filbert blight in the future?  Consider planting native species of hazelnut (e.g., American and beaked hazelnut) that are naturally resistant to the disease.  If you decide to plant European hazelnut, select cultivars that have been bred for resistance.  ‘Jefferson’, ‘Santiam’, ‘Yamhill’, and ‘Theta’ are resistant, nut-bearing cultivars.  ‘Red Dragon’ is a resistant, ornamental cultivar.  Note that these cultivars are not hardy in all hardiness zones in Wisconsin.  Hybrid hazelnuts (crosses between American and European hazelnut) are becoming increasingly available, but should be used with caution because their susceptibility to Eastern filbert blight has not been adequately tested.

Once hazelnut trees/shrubs are established in your yard, routinely inspect the plants for infection and remove infected branches as they occur.  Watch for dying branches in the summer and cankers (particularly on or near the youngest growth) in the winter.  Inspecting trees during the winter is very important, because cankers are more visible at that time.

Fungicides can be used for management, but should only be used as a last resort.  Not all fungicides that are approved for Eastern filbert blight control are particularly effective, but chlorothalonil has been shown to be an effective preventative treatment, although it will not cure existing infections.  Note that not all formulations of chlorothalonil are approved for use on nut-bearing hazelnuts; many formulations can only be used on ornamental hazelnuts.  Therefore, if you decide to use chlorothalonil, be sure to select the appropriate formulation for your particular situation.  Apply the first treatment at bud break (i.e., when half the buds show a separation of leaves) and additional treatments (up to three) every two weeks thereafter.  If you plan to eat nuts from your hazelnut tree, make sure that your last fungicide treatment is applied at least 120 days before anticipated nut harvest.  For further details about recommended fungicides, spray rate recommendations, and diagrams of bud stages, see “Pest Management Guide for Hazelnuts in the Willamette Valley”, Oregon State University Extension Bulletin EM8328 available at https://catalog.extension.oregonstate.edu/em8328.

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

Disease - Deciduous Woody Ornamental, Fact Sheet

Volutella Blight

What is Volutella blight? Volutella blight is a common and potentially lethal disease of Japanese pachysandra (Pachysandra terminalis), an evergreen, semi-woody groundcover that is grown in shade gardens throughout hardiness zones 4 and 5 in Wisconsin. Volutella blight can severely limit the aesthetic appeal of pachysandra wherever it is grown.

Volutella blight often starts as lesions on individual leaves, but can eventually kill groups of pachysandra plants.
Volutella blight often starts as lesions on individual leaves, but can eventually kill groups of pachysandra plants.

What does Volutella blight look like? Volutella blight begins as discrete, water-soaked areas (lesions) on pachysandra leaves and stems that eventually turn black/brown and become necrotic (i.e., die). Lesions can be circular, oval or irregular in shape, and may have darker margins. Distinct concentric rings also may be visible in the lesions. Lesions on a single leaf can merge and cause the collapse of the entire leaf, while stem lesions can lead to the collapse of an entire pachysandra plant. When severe, Volutella blight can kill large patches of a pachysandra planting.

Where does Volutella blight come from? Volutella blight is caused by the fungus Volutella pachysandricola which survives in infected plants, as well as on and in pachysandra plant debris. During wet weather, this fungus produces masses of light-orange to pink fungal spores and hyphae (i.e., fungal threads) that may be visible to the naked eye.

How do I save a plant with Volutella blight? Remove diseased leaves, as well as any leaf debris, and prune back or dig up plants with stem infections. Be sure to prune only when plants are dry to minimize the spread of the causal fungus. When disease is severe, remove diseased plants, then follow with one or more applications of a broad-spectrum fungicide (e.g., one containing chlorothalonil). Select a product that is labeled for use on pachysandra, and follow all label instructions to ensure that you apply the product in the safest and most effective way possible.

How do I avoid problems with Volutella blight in the future? V. pachysandricola is a somewhat opportunistic pathogen, most often causing problems on pachysandra that is weakened or under stress. Therefore, reduce any stresses where possible. Reduce stress due to overexposure to sun by always planting pachysandra in a shady area. Do not overcrowd new plantings, and thin existing beds to not only reduce stress from competition, but also to promote good air flow and rapid drying of plants. Dry plants are less likely to become infected than plants that stay wet for extended periods. To prevent water stress during the summer and reduce winter injury over the winter, established pachysandra should receive approximately one inch of water per week during the growing season up until the point where there is snowfall or the ground freezes. Newly planted pachysandra should receive approximately two inches of water per week. Minimize salt usage on sidewalks or driveways near pachysandra beds to limit salt injury. Control insect pests and avoid over-pruning of pachysandra to limit wounds that might serve as entry points for V. pachysandricola.

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

Disease - Deciduous Woody Ornamental, Fact Sheet

Verticillium Wilt of Trees and Shrubs

What is Verticillium wilt? Verticillium wilt is a typically fatal disease that affects a wide range of deciduous woody ornamentals in Wisconsin. Trees most commonly and severely affected are maple and ash. Other trees and shrubs such as barberry, catalpa, elm, lilac, linden, smoke-tree and redbud susceptible. In addition, many herbaceous ornamentals, as well as vegetable crops (see University of Wisconsin Garden Facts XHT1146 “Vertcillium Wilt of Vegetables”), can be affected by this disease.

Sudden yellowing, wilting and death of leaves and branches, particularly starting in one section of a tree or shrub, is a typical symptom of Verticillium wilt.
Sudden yellowing, wilting and death of leaves and branches, particularly starting in one section of a tree or shrub, is a typical symptom of Verticillium wilt.

What does Verticillium wilt look like? The first signs of Verticillium wilt that you may notice are individual branches that suddenly wilt and die. Affected branches may occur on one side of the tree or may be scattered throughout the tree. If you carefully peel away the bark of these branches, you may see brown or green streaking in the sapwood just under the bark. Streaking is common in trees such as maple or redbud, but often is not visible in ash and lilac.

Where does Verticillium wilt come from? Verticillium wilt is caused primarily by two fungi, Verticillium dahliae and Verticillium albo-atrum. These fungi are commonly found in Wisconsin soils and in roots, branches and leaves of infected plants. These fungi enter trees and shrubs through their roots and grow in the xylem (i.e., the water-conducting tissue) of plants where they lead to blockage of water movement. This lack of water movement is what eventually leads to wilting.

How do I save a tree or shrub with Verticillium wilt? Trees and shrubs infected with Verticillium cannot be cured and will likely eventually die. However, you can extend the life of your plants by making sure that you water and fertilize properly. Make sure established trees and shrubs receive approximately one inch of water per week. If rainfall is insufficient, use a drip or soaker hose to apply supplemental water. Fertilize trees as needed, but be sure to base any fertilization on a soil nutrient test. To prevent competition for water and nutrients, remove lawn grass within the drip line of your trees and shrubs (i.e., the edge of where the branches extend) and replace it with shredded hardwood, pine or cedar mulch. On heavy clay soils, use three inches of mulch. On other soils, use three to four inches of mulch. Be sure to keep mulch two inches from the main trunks and crowns of trees and shrubs. In addition, prune out dead branches as they occur. Dispose of these branches by burning (where allowed by local ordinance) or landfilling them. DO NOT bury or compost these branches. Be sure to clean your pruning tools between cuts by dipping them for at least 30 seconds in a 10% bleach solution or (preferably due its less corrosive properties) 70% alcohol. Rubbing alcohol and many spray disinfectants contain approximately this alcohol concentration. Decontaminating your tools will help prevent spread of Verticillium from branch to branch, or more importantly from tree to tree, as you prune.

Internal streaking in the sapwood of a branch is typical of Verticillium wilt.
Internal streaking in the sapwood of a branch is typical of Verticillium wilt.

How do I avoid problems with Verticillium wilt in the future? The best way to avoid Verticillium wilt is to plant trees and shrubs that are immune or resistant. Resistant deciduous trees and shrubs (as adapted from “Diseases of Trees and Shrubs, Second Edition” by W. Sinclair and H. H. Lyon (Comstock Publishing Associates, 2005)) include apple, aspen, azalea, beech, birch, butternut, crabapple, dogwood, flowering quince, ginkgo, hackberry, hawthorn, hickory, holly, honeylocust, katsura tree, mountain-ash, oak, pear, poplar, sweetgum, sycamore, walnut, and willow. Conifers (e.g., pines, spruces and firs) appear to be immune to the disease. Also, DO NOT use mulches that may have been produced from infected trees or that are of unknown composition. Finally, immediately collect and discard leaves that have fallen from symptomatic trees. Both mulch and leaves are potential sources of Verticillium.

For more information on Verticillium wilt: See UW-Extension Bulletin A2537, “Maple and Other Tree Disorder: Verticillium Wilt” (available at http://learningstore.uwex.edu); University of Wisconsin Garden Facts XHT1146, “Verticillium Wilt of Vegetables” (available at http://hort.uwex.edu); or contact your county Extension agent.

Thanks to Jean Ferdinandsen, Patti Nagai and Scott Reuss for reviewing this document.

Disease - Deciduous Woody Ornamental, Fact Sheet

Tubakia (Actinopelte) Leaf Spot

What is Tubakia (Actinopelte) leaf spot? Tubakia leaf spot, formerly known as Actinopelte leaf spot, is a common late-season leaf disease of oaks. All species of oak appear to be susceptible to the disease, but oaks in the red oak group (such as black, red and pin oak) appear to be most susceptible.

Symptoms of Tubakia (Actinopelte) leaf spot on oak.
Symptoms of Tubakia (Actinopelte) leaf spot on oak.

What does Tubakia (Actinopelte) leaf spot look like? People often confuse symptoms of Tubakia leaf spot with those of oak anthracnose (see University of Wisconsin Garden Facts XHT1001). However anthracnose tends to develop earlier, in the cooler part of the growing season (May and June), while Tubakia leaf spot tends to develop later, during the warmer summer months (July and August). Initial symptoms of Tubakia leaf spot include small to large dark brown or reddish-brown spots on leaves. Spotting can occur on leaf veins, and death of the veins leads to collapse of leaf tissue beyond the point of infection. Small twig cankers may also form. When the disease is severe, Tubakia leaf spot can cause early defoliation of oaks. However disease usually develops late enough in the growing season that no long-term adverse effects on tree health occur.

Where does Tubakia (Actinopelte) leaf spot come from? Tubakia leaf spot is caused by the fungus Tubakia dryina (formerly Actinopelte dryina), a fungus that is most likely a fungus “complex” (i.e., a group of several distinct, but closely related fungi). Tubakia overwinters in infected twigs, and in dead leaves that hang from the tree or are scattered on the ground. Spores of the fungus are easily spread by wind and rain splash.  

How do I save a tree with Tubakia (Actinopelte) leaf spot? DO NOT panic! In most cases Tubakia leaf spot is a cosmetic disease. The disease will make a tree look a little ragged, but will not kill the tree. DO NOT attempt to use fungicide sprays to control this disease.

How do I avoid problems with Tubakia (Actinopelte) leaf spot in the future? You can reduce the number of spores that cause Tubakia leaf spot by removing and disposing of fallen, infected leaves. Leaves can be buried, burned (where allowed) or composted. When composting, make sure that your compost pile reaches high temperature (approximately 140°F). Also, make sure that your compost pile is routinely turned so that leaves on the outside of the pile eventually end up in the center of the pile. The combination of high temperature and decay of leaf tissue in a compost pile helps eliminate the Tubakia leaf spot fungus. Also, maintain good tree vigor by watering and fertilizing trees appropriately. Check with your local county Extension agent for details on how to properly care for trees.

For more information on Tubakia (Actinopelte) leaf spot: Contact your county Extension agent.

Disease - Deciduous Woody Ornamental, Fact Sheet, Pest Alerts

Thousand Cankers Disease

What is thousand cankers disease? Thousand cankers disease (TCD) is a serious, potentially fatal disease of black walnut (Juglans nigra), a tree native to Wisconsin. TCD has not yet been reported in Wisconsin, but has been found in the western United States where it was first described in 2008. TCD more recently has been reported in the eastern U.S. in Tennessee, Ohio, Pennsylvania, Virginia, and North Carolina. TCD has been fatal to black walnut in all known cases. Other walnut species found in the western U.S. (e.g., California walnut (Juglans californica) and Arizona walnut (Juglans major)) appear to be much less susceptible. Butternut (Juglans cinerea), another tree native to Wisconsin, is also known to be susceptible.

Discoloration and tunneling under the bark of a walnut branch associated with thousand cankers disease leads to disruption of water and nutrient movement and eventual tree death. (Photo courtesy of Karen Snover-Clift, Cornell University, Bugwood.org)
Discoloration and tunneling under the bark of a walnut branch associated with thousand cankers disease leads to disruption of water and nutrient movement and eventual tree death. (Photo courtesy of Karen Snover-Clift, Cornell University, Bugwood.org)

What does thousand cankers disease look like? The first symptom of TCD is a yellowing of the leaves starting at the top of a walnut tree. Eventually lower leaves yellow and branches die. Death of the entire tree soon follows. Branches on trees with TCD have tiny holes (about the size of a pencil tip) made by a small beetle that is involved in the disease. Beneath the bark of symptomatic branches, well-defined dark black or brown cankers (i.e., diseased areas) form. Cankers eventually merge, disrupting movement of water and nutrients in the tree, leading to tree death.

Where does thousand cankers disease come from? Thousand cankers disease is caused by a combination of a fungus (Geosmithia morbida) and the walnut twig beetle (Pityophthorus juglandis). The insect carries the fungus on its body and introduces the fungus into a walnut tree as it tunnels into the bark to feed. Walnut twig beetles spread the fungus locally as they move from tree to tree to feed. The fungus does not appear to spread by root grafts. Longer distance dispersal of the insect and fungus is possible when walnut seedlings, walnut firewood, and walnut wood products are moved by human activities. Walnut fruits have not been reported as a source of the insect or fungus.

How can I save a tree with thousand cankers disease? At this time, there are no formal recommendations for managing TCD. Researchers are attempting to develop treatment methods, including use of insecticides, fungicides and nutrient management, to help prolong the life of infected trees. Because TCD has not yet been reported in Wisconsin, the most important management strategy at this time is prevention.

How can I avoid problems with thousand cankers disease in the future? The best way to prevent the spread of TCD (as well as other tree pests and diseases)s to not move firewood! For information about the restrictions on moving firewood in Wisconsin visit the Wisconsin Department of Natural Resources website at http://dnr.wi.gov/topic/invasives/firewood.html. Also be cautious about moving walnut transplants or other walnut products (especially those with the bark still attached), particularly if they are coming from an area where TCD has been reported.

For more information on thousand cankers disease or if you suspect you have seen this disease: Contact your county Extension agent or the Plant Disease Diagnostics Clinic (http://pddc.wisc.edu).

* Completed as partial fulfillment of the requirements for Plant Pathology 558 at the University of Wisconsin Madison.

Thanks to Diana Alfuth, Cory Bender, Laura Jull, Phil Pellitteri, Katie Schlichter and Wendy Kramper for reviewing this document.

 

Disease - Deciduous Woody Ornamental, Fact Sheet

Tatters

What is tatters? Tatters is a leaf disorder affecting primarily members of the white oak group of oaks (i.e., oaks with leaves with rounded lobes) including bur, white and swamp white oaks. Members of the red oak group of oaks (i.e., oaks with leaves with pointed lobes), including red, black, pin and shingle oaks, as well as other types of trees, rarely display the disorder. Tatters was first documented in Iowa, Indiana and Ohio in the 1980’s, and since then has been documented throughout much of the Midwest.

Leaves with tatters appear shredded, or as if damaged by leaf-feeding insects.
Leaves with tatters appear shredded, or as if damaged by leaf-feeding insects.

What does tatters look like? Trees with tatters have leaves that are lacy and shredded. Some leaves may appear as though the tissue between veins has been neatly ripped out, while other leaves have an irregular pattern of damage. The amount of damage may vary from leaf to leaf and branch to branch. Adjacent oak trees may show different amounts of damage due to genetic variability, variation in environmental conditions, or other external factors. Tatters is commonly confused with anthracnose (see University of Wisconsin Garden Facts XHT1001), or damage by leaf-feeding insects.

Where does tatters come from? The cause of tatters has not been precisely determined. Tatters is thought to be a physiological disorder caused by damage to leaf tissue in the bud-stage, or during the opening of buds in the spring. Suggested causes of tatters include cold or herbicide injury or, much more rarely, injury due to insect feeding or egg-laying.

How do I save a tree with tatters? DO NOT panic. Trees affected with tatters often produce replacement leaves within two to three weeks after tattered leaves appear. However, producing new leaves weakens trees and may make them more susceptible to other diseases and drought stress. If your trees suffer from tatters, make sure they receive sufficient water (approximately one inch per week for established trees). If rainfall is insufficient, use a drip hose or soaker hose to apply supplemental water. To prevent competition for water and nutrients, remove lawn grass within the drip line of your trees and replace it with shredded hardwood, pine or cedar mulch. On heavy clay soils, use three inches of mulch. On other soils, use three to four inches of mulch. Be sure to keep mulch two inches from the main trunks of the trees. Fertilize trees as needed, but be sure to base any fertilization on a soil nutrient test.

How do I avoid problems with tatters in the future? There is no known method for preventing tatters. However, the occurrence of tatters one year does not guarantee that the same trees will suffer from tatters in subsequent years.

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

Disease - Deciduous Woody Ornamental, Fact Sheet

Tar Spot

What is tar spot? Tar spot is a common, visually distinctive and primarily cosmetic fungal leaf spot disease. While tar spot can affect many species of maple including big leaf, mountain, red, Rocky mountain, sugar, and sycamore maple, in Wisconsin, this disease most commonly affects silver maple. Boxelder (also known as ash-leaved maple), willow, holly and tulip-tree can also be affected by tar spot.

Symptoms of tar spot on silver maple leaves.
Symptoms of tar spot on silver maple leaves.

What does tar spot look like? Initial symptoms of tar spot are small (approximately 1∕8 inch) yellowish spots that form on infected leaves. These spots may remain relatively small, or may enlarge over the growing season to roughly 3∕4 inch in diameter. As tar spot progresses, the center of the infected area becomes raised and turns black. This black area resembles a blob of tar on the leaf surface. Careful examination of the tar-like areas reveals convoluted line patterns that resemble fingerprints.

Where does tar spot come from? Several fungi in the genus Rhytisma (most commonly Rhytisma acerinum and Rhytisma punctatum) cause tar spot. These fungi commonly survive in leaf litter where they produce spores that lead to leaf infections.

How do I save a tree with tar spot? DO NOT panic. For most maples and other susceptible plants, tar spot is not a serious disease. It is primarily a cosmetic disease that makes the tree look a little ragged, but does not kill the tree or shrub, nor even cause serious defoliation. Fungicides containing copper and mancozeb are labeled for tar spot control in Wisconsin. However, fungicide treatments for this disease are rarely, if ever, warranted. Consult with your county UW-Extension horticulture professional to determine if your tree warrants treatment. If warranted, three fungicide applications will be necessary for control: one at bud break, one when leaves are half expanded, and one when leaves are fully expanded. Be sure to read and follow all label instructions of the fungicide that you select to ensure that you use the fungicide in the safest and most effective manner possible.

How do I avoid problems with tar spot in the future? You can reduce or even eliminate tar spot (and thus the need for fungicide treatments), by simply removing fallen, infected leaves from around your trees each fall. Infected leaves should be buried or composted.

For more information on tar spot: Contact your county Extension agent.

Thanks to Lis Friemoth, Ann Joy and Mike Maddox for reviewing this document.

Disease - Conifer, Disease - Deciduous Woody Ornamental, Disease - Herbaceous Ornamental, Fact Sheet, Pest Alerts

Sudden Oak Death

Rapid wilting and die back of branch tips can be a symptom of ramorum dieback.
Rapid wilting and die back of branch tips can be a symptom of ramorum dieback.

What is sudden oak death? Sudden oak death (also called ramorum leaf blight or ramorum dieback) is an oftentimes lethal disease that has caused widespread death of tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), California black oak (Quercus kelloggii), and Shreve oak (Quercus parvula var. shrevei) in California. The disease has also been reported in Oregon, as well as in Europe. Currently 60 species of plants have been reported to be susceptible to the disease. Twenty-eight of these plants are confirmed hosts. In addition to the trees listed above, the following trees fall into this group:

  • bigleaf maple (Acer macrophyllum)
  • Bodnant viburnum (Viburnum X bodnantense)
  • ‘Brouwer’s Beauty’ pieris (Pieris floribunda X japonica)
  • California bay laurel (Umbellularia californica)
  • California buckeye (Aesculus californica)
  • California coffeeberry (Rhamnus californica)
  • California honeysuckle (Lonicera hispidula)
  • canyon live oak (Quercus chrysolepis)
  • coast redwood (Sequoia sempervirens)
  • doublefile viburnum (Viburnum plicatum var. tomentosum)
  • douglas-fir (Pseudotsuga menziesii var. menziesii)
  • evergreen huckleberry (Vaccinium ovatum)
  • Formosa firethorn (Pyracantha koidsumii)
  • ‘Forest Flame’ pieris (Pieris formosa X japonica)
  • Himalaya pieris (Pieris formosa)
  • Japanese camellia (Camellia japonica)
  • Japanese pieris (Pieris japonica)
  • laurustinus (Viburnum tinus)
  • madrone (Arbutus menziesii)
  • manzanita (Arctostaphylos manzanita)
  • rhododendron (Rhododendron spp.)
  • Sasanqua camellia (Camellia sasanqua)
  • toyon (Heteromeles arbutifolia)
  • western starflower (Trientalis latifolia)
  • witch hazel (Hamamelis virginiana)

An additional 31 species including the following are suspected hosts, although tests to verify their susceptibility have not yet been completed:

  • Burkwood viburnum (Viburnum X burkwoodii)
  • California hazelnut (Corylus cornuta)
  • Camellia X williamsii
  • cascara (Rhamnus purshiana)
  • Chinese pieris (Pieris formosa var. forrestii)
  • common lilac (Syringa vulgaris)
  • David viburnum (Viburnum davidii)
  • drooping leucothoe (Leucothoe fontanesiana)
  • European beech (Fagus sylvatica)
  • European cranberrybush viburnum (Viburnum opulus)
  • European turkey oak (Quercus cerris)
  • European yew (Taxus baccata)
  • fragrant viburnum (Viburnum farreri)
  • grand fir (Abies grandis)
  • Holm oak (Quercus ilex)
  • horse-chestnut (Aesculus hippocastanum)
  • lingonberry (Vaccinium vitis-ideae)
  • mountain laurel (Kalmia latifolia)
  • Northern red oak (Quercus rubra)
  • Pieris formosa var. forrestii X Pieris japonica
  • poison oak (Toxicodendron diversiloba)
  • Prague viburnum (Viburnum X pragense)
  • reticulate camellia (Camellia reticulata)
  • salmonberry (Rubus spectabilis)
  • Southern red oak (Quercus falcata)
  • strawberry tree (Arbutus unedo)
  • sweet chestnut (Castanea sativa)
  • Viburnum X carlcephalum X Viburnum utile
  • Victorian box (Pittosporum undulatum)
  • wayfaringtree viburnum (Viburnum lantana)
  • wood rose (Rosa gymnocarpa)

At this time, sudden oak death has not been reported in Wisconsin. However, the disease was recently found at a large nursery near Los Angeles, CA that ships plants throughout much of the United States, including Wisconsin. Thus, the disease may be present in Wisconsin, but not yet detected.

Ramorum leaf blight symptoms can mimic those of other leaf spots and blights.
Ramorum leaf blight symptoms can mimic those of other leaf spots and blights.

What does sudden oak death look like? Symptoms of sudden oak death vary depending upon the plant species infected. On some hosts, infections occur primarily on leaves leading to light brown leaf spots and blotches. These leaf symptoms may be indistinguishable from other, more common, leaf spots and blights, or may mimic sunburn or leaf scorch symptoms. Twigs and branches that become infected often wilt, forming a “shepherd’s-crook”, and subsequently die back. Infection of tree trunks leads to cankers (i.e., sore-like areas) that produce copious amounts of an amber to black colored ooze. This ooze can dry to form a stained area on the bark. Removing the bark over the affected area will reveal discolored wood beneath that sometimes (but not always) has a black border. Cankers can eventually expand to girdle trunks, thus resulting in the death of the tree or shrub. Trunk infections appear not to extend into the root system of the plant. Once sudden oak death cankers develop, other pathogens may invade the infected areas, accelerating tree or shrub death and complicating the diagnosis of the disease.

Where does sudden oak death come from? Sudden oak death is caused by the fungus Phytophthora ramorum, which was first recognized as a pathogen in 1995. Phytophthora ramorum can be spread over long distances through movement of infected plants or infested plant parts. The fungus can also be moved with contaminated soil (e.g., on vehicle tires, tools, or shoes), or in contaminated water. Once established on plants in a given location, the fungus produces reproductive structures (called sporangia) that can be moved from plant to plant by rain splash, or wind. Phytophthora ramorum has currently been documented as occurring in California, Oregon and Europe, but the recent discovery of the pathogen in a large nursery in California that ships plants throughout the United States raises the possibility that this pathogen may have been spread to other areas.

How do I save a plant with sudden oak death? If you believe you have seen a plant that has sudden oak death, IMMEDIATELY call the Plant Disease Diagnostics Clinic (PDDC) at (608) 262-2863 to make arrangements for an appropriate diagnosis. Because Phytophthora ramorum is a regulated, quarantined pathogen, DO NOT remove the affected plant (or parts thereof) or take the plant from the site where it is located. PDDC staff will make arrangements for sample collection and testing. If your plant tests positive for Phytophthora ramorum, it will be removed and destroyed to help prevent further spread of the pathogen.

How do I avoid problems with sudden oak death in the future? Carefully inspect any new nursery stock upon delivery (or prior to purchase, if possible) for symptoms of sudden oak death. Keep new stock isolated from older stock as long as possible, to minimize possible movement of the pathogen should the disease develop after plants have arrived. If you see any suspect symptoms, alert the PDDC so that arrangements can be made for proper testing for Phytophthora ramorum.

For more information or help in diagnosing sudden oak death: Contact Brian Hudelson, Plant Disease Diagnostic Clinic, Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI 53706-1598, phone: (608) 262-2863, fax: (608) 263-2626, email: bdh@plantpath.wisc.edu, see the USDA APHIS sudden oak death website http://www.aphis.usda.gov/ppq/ispm/sod, or contact your County Extension agent.

Disease - Deciduous Woody Ornamental, Disease - Fruit Crop, Disease - Herbaceous Ornamental, Disease - Vegetable, Fact Sheet

Southern Blight

What is Southern blight? Southern blight is a serious, and typically lethal, fungal disease that is most common in the tropics and subtropics. This disease also can cause damage in the southern U.S., and can even become a problem in temperate states like Wisconsin during periods of warm, moist weather. Southern blight has a wide host range, affecting over 500 plant species. Vegetable and fruit hosts include tomato, pepper, onion, beet, rhubarb, strawberry, lettuce, cucumber, melon, carrot, asparagus and parsley. Ornamental hosts include aster, dahlia, daylily, gladiolus, hosta, impatiens, peony, petunia, rose, rudbeckia, salvia, sedum and viola. Small woody ornamentals can be susceptible as well.

The Southern blight fungus produces large numbers of spherical, light tan to dark red resting structures called sclerotia (red arrow).
The Southern blight fungus produces large numbers of spherical, light tan to dark red resting structures called sclerotia (red arrow).

What does Southern blight look like? Southern blight initially leads to a water-soaked appearance on lower leaves, or a water-soaked lesion (spot) on lower stems. Any plant part that is near, or in contact with, the soil may become infected. Infected plants yellow and wilt, often within days of infection, particularly when the weather is moist and warm (80 to 95°F). Fruit rots, crown rots and root rots are also typical symptoms of the disease. Thick mats of white fungal threads (called mycelia) may grow from infected tissue, and typically radiate from the plant onto the soil surface. Sclerotia (small spherical structures that are about the size of mustard seeds) develop on infected tissue and on the soil surface. Sclerotia range in color from light tan to dark reddish-brown.

Where does Southern blight come from? Southern blight is caused by the fungus Sclerotium rolfsii, which lives in soil, on plant debris and on weed hosts. The fungus can be spread through movement of infested soil, infected plants and contaminated irrigation water, and by use of contaminated tools. In Wisconsin, S. rolfsii most likely enters gardens on infected nursery stock or infested mulch. Freezing temperatures will kill S. rolfsii mycelia, while sclerotia can survive at temperatures above approximately 14ºF.

How can I save a plant with Southern blight? Infected plants, as well as soil from six inches beyond an infested area, should be removed. Bury any remaining sclerotia eight to 12 inches to reduce the length of time that they will survive in the soil. Grow non-susceptible plants (e.g., larger woody ornamentals) in the affected area for two to three years following an infestation to allow time for sclerotia to die naturally. Fungicides containing triadimefon may be effective for control of Southern blight. However, these products will likely be more effective if applied as preventive treatments rather than in an attempt to “cure” existing disease.

How can I prevent Southern blight in the future? Inspect new plants prior to transplanting for sclerotia and mycelia, and throw away diseased plants. Avoid mulches that might be contaminated with S. rolfsii. S. rolfsii thrives in moist conditions. Therefore, thin existing gardens or space plants farther apart in new gardens to improve airflow and promote rapid drying of foliage.

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

Disease - Deciduous Woody Ornamental, Disease - Fruit Crop, Fact Sheet

Scab – Leaf

What is scab? Scab is a potentially serious fungal disease of ornamental and fruit trees in the rose family. Trees that are most commonly and severely affected include crabapple, hawthorn, mountain ash, apple and pear. This disease is most severe in years with cool, wet weather.

Leaf spots typical of apple scab on apple. Similar lesions occur on fruits.
Leaf spots typical of apple scab on apple. Similar lesions occur on fruits.

What does scab look like? Scab lesions (diseased areas) are often first noticed on leaves, where they most commonly occur on the upper leaf surface. Fruits are also very susceptible to infection. Lesions on both leaves and fruits are roughly circular with feathery edges, and have an olive green to black color. They can be as small as the size of a pinhead or as large a 1∕2 inch in diameter. When disease is severe, lesions can merge and cover a large portion of the leaf or fruit surface. Defoliation of the tree often follows.

Where does scab come from? Scab is caused primarily by the fungus Venturia inaequalis. Other species of Venturia can be involved as well. These fungi survive the winter in leaf litter from infected trees.

How do I save a tree or shrub with scab? If your tree is lightly affected with little or no defoliation and dry weather conditions prevail, then no treatment is necessary. If your tree has a history of severe scab and the weather is cool and wet, then consider applying fungicide treatments. Mancozeb, chlorothalonil, myclobutanil, propiconazole, or thiophanate methyl, are available for scab control. For most products, you will need to treat every seven to 14 days from bud break until wet weather subsides. Be sure to read and follow all label instructions of the fungicide that you select to insure that you use the fungicide in the safest and most effective manner possible.

How do I avoid problems with scab in the future? Remove and discard fallen, infected leaves that are a major source of spores that cause scab infections. Most importantly, consider replacing susceptible crabapples, apples and pears with resistant varieties available at your local garden center.

For more information on scab: See UW-Extension Bulletins A2173, A2594 and A8NYDS01, or contact your county Extension agent.