Category Archives: Pest Alerts

Sudden Oak Death

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.

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.

The disease can affect or has been reported in association with a wide range of woody and herbaceous plants including, but not limited to 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), and witch hazel (Hamamelis virginiana), 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), and wood rose (Rosa gymnocarpa).

Sudden oak death was first reported in the US in California and has subsequently been found in other US states, including in Wisconsin in 2019.  Sudden oak death has also been reported in Europe.

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 large 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-like water mold 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 organism 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 was introducing into Wisconsin in 2019 on nursery stock grown in the state of Washington.

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.

How do I save a plant with sudden oak death?  If you believe you have seen a plant that has sudden oak death, please IMMEDIATELY submit a sample to the Plant Disease Diagnostics Clinic (PDDC), care of the address in the box at the bottom of this page.  Double bag suspect plant tissue in sealable plastic bags and place the bagged specimen in a box or envelope for shipping.  Include contact information (complete address, phone number, email address) in a separate sealable plastic bag with the sample.  Tape over all of the edges of boxes and envelopes used for shipping to keep everything sealed inside.  Write on the box or envelope that the box or envelope contains a suspect SOD sample.  If you have questions about collecting or submitting a sample, contact PDDC staff at (608) 262-2863 or at pddc@wisc.edu.

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, other than to collect a specimen for submission for a diagnosis.  Be sure to decontaminate any tools or other items that come into contact with the plant (including those used to collect a diagnostic sample) by dipping them for at least 30 seconds in 10% bleach.  If a 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, UW-Madison Plant Disease Diagnostic Clinic, Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI  53706-1598, phone: (608) 262-2863, email: pddc@wisc.edu, see the USDA APHIS sudden oak death website https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/pests-and-diseases/phytophthora-ramorum/sod, or contact your County Extension agent.

Professional Guide to Emerald Ash Borer Insecticide Treatments

Emerald ash borer insecticide treatment considerations.  

A variety of insecticide products and application methods are available to professionals for control of the emerald ash borer (EAB).  Since the presence and infestation level of EAB is quite difficult to determine at early stages of an infestation, insecticide treatments may be merited to mitigate damage by EAB.  However, not all ash trees should be treated as some may be too extensively compromised or in poor condition to receive treatment.  Due to the expense of yearly insecticide treatments, one should consider the value of a particular ash tree in relation to insecticide treatment costs before making any treatments.  In addition, consider the health of each tree before treating.  Research suggests that insecticide treatments are significantly more effective on EAB-infested ash trees with less than 50% canopy thinning.  Insecticide treatments are not suggested for trees with greater than 50% canopy thinning.  Ash trees with greater than 50% canopy thinning should be removed and destroyed in accordance with established state and federal guidelines.  For additional information on this topic, see University of Wisconsin Garden Pest Alert XHT1215, Is My Ash Tree Worth Treating for Emerald Ash Borer.

Emerald ash borer insecticide treatment options. 

Insecticide products that are available for use by professionals, with information on appropriate application methods and application timings, are summarized in Table 1.  These products include:

  • Ace-Jet (acephate)
  • ACECAP Systemic Insecticide Tree Implants (acephate)
  • Alpine (bifenthrin)
  • ArborMectin (emamectin benzoate)
  • AzaGuard (azidirachtin)
  • Boxer Insecticide-Miticide (emamectin benzoate)
  • Brandt enTREE EB (emamectin benzoate)
  • Dinocide, Dinocide HP (dinotefuran)
  • IMA-jet, IMA-jet 10 (imidacloprid)
  • Imicide, Imicide HP (imidacloprid)
  • Inject-A-Cide B (bidrin)
  • Merit 2F, Merit 75 WP, Merit 75 WSP (imidacloprid)
  • Onyx, OnyxPro (bifenthrin)
  • Pointer (imidacloprid)
  • Safari (dinotefuran)
  • Tempo (cyfluthrin)
  • Transtect (dinotefuran)
  • Tree-äge, Tree-äge G4 (emamectin benzoate)
  • Treeazin (azadirachtin)
  • TreeMec Inject (emamectin benzoate)
  • Xytect 2F, Xytect 75 WSP, Xytect 10% infusible (imidacloprid)

University research indicates that soil drenches or injections of imidacloprid provide excellent EAB protection for small ash trees [less than six inches diameter at breast height (DBH)] in the first year following treatment.  Larger trees may require two consecutive years of treatment before they are effectively protected.  Thus, treatment of large trees should begin before the trees become infested.  While spring and/or fall applications are allowed on certain product labels, recent university research has indicated that spring applications have been more effective at controlling EAB and protecting canopy health.  Most insecticide treatments must be repeated each year.  Products containing emamectin benzoate are labeled to provide two years of protection.  Recent university research suggests that some of these products may provide more than three years of control with a single application when used at the highest labeled rate.

Trunk injections and implants require physically drilling or coring into a tree during the application of the insecticide.  Thus, use of these application methods has the potential to cause injury to trees (especially smaller trees), and may provide entry points for certain disease-causing fungi [e.g., Nectria, the cause of Nectria canker (see University of Wisconsin Garden Facts XHT1094 Nectria Canker)].

Table 1.  EAB insecticide treatments available to professionals

Table 1.  EAB insecticide treatments available to professionals*
Active Ingredient Product(s) Timing Application Method
Acephate ACE-Jet Mid-May to mid-June Trunk Injection
Acecap Implants Trunk Implant
Azadirachtin AzaGuard, Treeazin Early/mid-April to
early September
Trunk Injection
Bidrin Inject-A-Cide B Inject when infestation is evident Trunk injection
Bifenthrin Alpine, Onyx,

OnyxPro

Apply prior to or just at the time of adult emerge. Multiple applications may be needed Preventative bark and foliage cover sprays
Cyfluthrin Tempo
Dinotefuran Dinocide, Dinocide HP Late-April to late-May Trunk injection
Safari, Transtect, Zylam Soil drench, trunk spray
Emamectin benzoate ArborMectin, Boxer, Brandt enTREE EB, Tree-äge, Tree-äge G4, Tree-äge R10, TreeMec April to September Trunk injection
Imidacloprid Merit 75 WP, Merit 75 WSP, Merit 2F, Xytect 2F, Xytect 75WSP, and others Mid-April to late-May

and/or

Early-Sept. to mid-October

Soil injection or drench
IMA-jet, IMA-jet 10, Imicide, Imicide HP, Pointer, Xytect 10% Mid-April to mid-May Trunk injection

The University of Wisconsin does not endorse any one specific commercially available insecticide.  Products discussed in this fact sheet have been evaluated in a variety of university research tests on EAB (www.emeraldashborer.info).  No matter which insecticide you use, always read and follow all label instructions.  Avoid skin contact with insecticides and safely store insecticides out of the reach of children.

For more information on controlling emerald ash borer:

For more information on controlling emerald ash borer:  See
http://labs.russell.wisc.edu/eab/
www.emeraldashborer.wi.gov or www.emeraldashborer.info,
University of Wisconsin Pest Alerts XHT1181 (Homeowner Guide to Emerald Ash Borer Insecticide Treatments) and XHT1215 (Is My Ash Tree Worth Treating for Emerald Ash Borer).

Is My Ash Tree Worth Treating for Emerald Ash Borer?

This factsheet addresses some of the most frequently asked questions regarding the treatment of ash trees for emerald ash borer (EAB), and the removal and disposal of infested trees.

High value ash trees are candidates for treatment for emerald ash borer.
High value ash trees are candidates for treatment for emerald ash borer.

When should I consider treating my ash tree for EAB?Based on current research, EAB treatments are suggested only for ash trees located within 15 miles of a confirmed EAB site, or for trees located within a quarantined area.  Insecticide treatments are not necessary for ash trees located outside of these areas.  Even within the 15-mile radius, not all trees should be treated.  Due to the expense of insecticide treatments for EAB, consider the value of a particular ash tree in relation to insecticide treatment costs before making any treatments.  Proper use of EAB insecticides can help maintain the health of high value ash trees over time.  Lower value ash trees are not ideal candidates for EAB insecticide treatments.

How do I know if my ash tree has value?  Ash trees can be a valuable part of the landscape.  A properly cared for ash tree can increase property value, provide environmental benefits such as runoff and erosion mitigation, and reduce electricity costs by shading a home.  Determining tree value can be subjective.  Qualities to consider when assessing value include (but are not limited to) a tree’s overall health, shape, location with respect to landscape design, and appearance through the seasons, as well as whether or not a tree provides shade.  A healthy ash that is properly located in the landscape, has a nice shape and good fall color, and provides shade has value.  An ash tree that is not healthy due to disease or insects, has poor shape or structural damage, is otherwise unattractive, or is in a bad location (e.g., near a power line) is of lower value.

How do I know if there are ash trees in my area that are infested with EAB?  The Wisconsin Department of Agriculture Trade and Consumer Protection (DATCP) keeps track of EAB infestations in the state.  Visit the Wisconsin DATCP Emerald Ash Borer Resource Guide website (http://datcpservices.wisconsin.gov/eab/) and view the interactive map.  You can also contact your local county UW-Extension office to see if EAB has been found in your area.

How do I know if my ash tree has EAB?  Symptoms of an EAB infestation can include canopy thinning starting in the upper portion of the tree, epicormic sprouting (i.e., formation of sprouts) along the trunk, bark splitting, and woodpecker damage.  These symptoms indicate general tree stress, and can be due to EAB.  However, they also can be caused by diseases or insects other than EAB.  Specific signs of EAB include D-shaped exit holes (~3/16 inch wide) in the bark of the tree, S-shaped larval tunnels and/or larvae (cream colored, up to 1½ inches long) beneath the bark, and adults (metallic green, ~3/8 inch long).  Visit the UW-Madison Emerald Ash Borer in Wisconsin website (http://labs.russell.wisc.edu/eab/) for additional information on the symptoms and signs of EAB.

If I decide to treat my ash tree, will I have to treat every year?  In most cases, yes.  Most insecticides registered for EAB management require yearly applications to effectively protect a tree.  Products containing the active ingredient emamectin benzoate, are labelled for two years of protection.  Products containing emamectin benzoate are trunk-injected insecticides intended for use by professional insecticide applicators (e.g., certified arborists).  Such products can effectively protect an ash trees if the tree is treated every other year.

Can I treat an ash myself or do I have to call an arborist?  If your ash is smaller than 47 inches around the trunk at chest height [i.e., 15″ diameter at breast height (DBH)], you may be able to treat your ash tree yourself.  University of Wisconsin Pest Alert XHT1181 (“Homeowner Guide to Emerald Ash Borer Insecticide Treatments”) provides a list of products currently available for homeowner use.  If you decide to treat your own trees, be sure to read and follow all label instructions of the insecticide that you select to ensure that you use the product in the safest and most effective manner possible.

In some situations, hiring a certified arborist to treat your ash tree may be more desirable.  Professionals have access to specialized application equipment and additional insecticides not available to homeowners.  They are also trained to measure trees accurately, and assess the overall health of trees.  The Wisconsin Arborists Association website (http://www.waa-isa.org) has a list of certified arborists in the state.

Note that the University of Wisconsin does not endorse any insecticide products, and does not recommend any professional products over those available directly to homeowners.

Am I allowed to treat an ash tree in my yard between the sidewalk and street?   The answer to this question varies from municipality to municipality.  In many cases, municipalities have treatment or removal and replacement plans already in place.  Contact your local town, village or city to determine an appropriate strategy for protecting your sidewalk trees.

How much does it cost to treat an ash tree for EAB?  A single tree that is 32 inches around at chest height (approximately 10″ DBH) can be treated with a granular or liquid soil drench homeowner product for about $20-35/year.  Larger trees will require a larger amount of product and costs will be higher.  Arborist treatment costs vary depending on tree size and location, the insecticide selected, and the application method.  Other arborist-specific site visit charges may apply as well.  Consult at least two arborists in your area to discuss treatment options and costs.  To make an accurate comparison among service providers, make sure you know what insecticide will be used, the method of application, and how often treatments will be made.  An arborist will not be able to determine the exact cost of treatment for your specific ash tree without a site visit, but an arborist should be able to provide you with a cost estimate for a typical ash tree.

Do I have to remove my ash tree if it is infested with EAB?  Applying protective insecticide treatments to a healthy ash tree to prevent an EAB infestation is the best strategy for managing EAB.  However, if a tree becomes infested and the infestation is detected early, you may be able to treat your ash tree to prevent further damage, and help the tree recover.  Research suggests that insecticide treatments are significantly more effective on EAB-infested ash trees with less than 50% canopy thinning.  Insecticide treatments are not recommended for trees with greater than 50% canopy thinning; these trees should be removed.  Trees that become infested with EAB and are not treated will ultimately die and will need to be removed.

How much does it cost to remove an ash tree?  Typically, a small (less than 25 feet in height) ash tree may cost a few hundred dollars to be removed by an arborist.  Larger trees may cost $1,000 or more to be removed.  Individual factors (e.g., the proximity of the tree to structures, power lines, or other hazards) can significantly increase the cost of removal.  Tree removal costs also may vary from location to location in Wisconsin.  Ultimately, removing recently killed trees while they are structurally sound, rather than allowing them to deteriorate, may be safer and more cost effective.

How do I dispose of wood from an infested ash tree?  If you choose to remove an infested ash tree, check with your municipality to see if a wood disposal or utilization program is in place.  If you have a tree removed by a tree care service, the service may be able to handle the disposal of wood from the infested tree.  If you decide to use wood from an ash tree for firewood or other purposes, use it locally.  Transporting infested wood risks spreading EAB elsewhere in the state, and may be in violation of Wisconsin’s quarantine laws.  Information about Wisconsin’s firewood regulations can be found on the Wisconsin DATCP Emerald Ash Borer website (http://datcpservices.wisconsin.gov/eab/).

For more information on controlling emerald ash borer: 

Homeowner Guide to Emerald Ash Borer Insecticide Treatments

Emerald ash borer insecticide treatment considerations.  Several insecticide products are available to homeowners for control of emerald ash borer (EAB).  Since the presence and infestation level of EAB is quite difficult to determine at early stages of an infestation, insecticide treatments may be merited to mitigate damage by EAB.  However, not all ash trees should be treated as some may be too extensively compromised or in poor condition to receive treatment.  Tree location, value, and health, as well as the cost of treatment are all factors to consider.  Due to the expense of yearly insecticide treatments, one should consider the value of a particular ash tree in relation to insecticide treatment costs before making any treatments.  In addition, consider the health of each tree before treating.  Research suggests that insecticide treatments are significantly more effective on EAB-infested ash trees with less than 50% canopy thinning.  Insecticide treatments are not suggested for trees with greater than 50% canopy thinning.  Trees with greater than 50% canopy thinning should be removed and handled in accordance with local guidelines.  For a more detailed discussion on this topic, see University of Wisconsin Garden Facts XHT1215, Is My Ash Tree Worth Treating for Emerald Ash Borer.

Emerald ash borer insecticide treatment options.  Insecticide products available for use by homeowners are summarized in Table 1.  They include:

  • ACECAP 97 Systemic Insecticide Tree Implants (acephate)
  • Bayer Advanced 12 Month Tree and Shrub Insect Control II (imidacloprid)
  • Bayer Advanced 12 Month Tree and Shrub Protect & Feed (imidacloprid)
  • Bayer Advanced 12 Month Tree and Shrub Protect & Feed II (imidacloprid + clothianidin)
  • Bonide Annual Tree & Shrub Insect Control with SYSTEMAXX (imidacloprid)
  • Compare N Save Systemic Tree & Shrub Insect Drench (imidacloprid)
  • Ferti-lome Tree and Shrub Systemic Drench (imidacloprid)
  • Monterey Once a Year Insect Control II (imidacloprid)
  • Optrol (imidacloprid)
  • Ortho Tree & Shrub Insect Control Granules (dinotefuran)
  • Several other products containing imidacloprid are also currently available

Most of the products available to homeowners are systemic insecticides containing imidacloprid and are applied as soil drenches around the base of an ash tree.  A few granular products are also available.  Recent university research suggests that applications of imidacloprid should be made in spring to be most effective.  Research also has demonstrated that soil applications of imidacloprid-containing homeowner products provide excellent EAB protection for ash trees that are less than about 47 inches in circumference [i.e., 15 inches in diameter at breast height (DBH)].  Due to differences in application rates and label restrictions, treatment by a tree care professional (e.g., arborist) may be the best option for larger trees.  For best results, treatment of trees should begin before trees become infested.  Lastly, insecticide treatments must be repeated each year to maintain the health of ash trees.

Be aware that many insecticide products available at hardware stores and garden centers look alike.  Carefully check all product labels before purchase to make sure that you have selected the correct product/active ingredient.  ALWAYS read and follow the pesticide label directions on the product that you select!

Finally, note that although ACECAP 97 Systemic Insecticide Tree Implants are available to homeowners, we do NOT recommend that homeowners use these because they require physically drilling into a tree during their application.

Table 1

Emerald ash borer insecticide treatments available to homeowners

Product Active Ingredient Timing Type of application
Ortho Tree & Shrub Insect Control Granules (G) Dinotefuran Early-June to mid-June Granule (G)
Bayer Advanced 12 Month Tree & Shrub Insect Control II (D)

 

Bayer Advanced 12 Month Tree & Shrub Protect & Feed (D or G)

 

Bonide Annual Tree & Shrub Insect Control with SYSTEMAXX (D)

 

Compare N Save Systemic Tree & Shrub Systemic Insect Drench (D)

 

Ferti-lome Tree & Shrub Systemic Drench (D)

 

Monterey Once a Year Insect Control II (D)

Imidacloprid Mid-April to mid-May Soil Drench (D)

or

Granular (G)

Optrol (D) Imidacloprid Mid-April to mid-May

and/or

Early-Sept. to mid-Oct.

Soil drench (D)
Bayer Advanced 12 Month Tree & Shrub Protect & Feed II (D) Imidacloprid

+

Clothianidin

Mid-April to mid-May Soil Drench (D)
ACECAP 97 Systemic Insecticide Tree Implants Acephate Mid-May to mid-June Trunk Implant

Other emerald ash borer treatment options.

Homeowners may also contact a certified arborist or certified pesticide applicator to treat their trees.  See http://www.waa-isa.org for a list of certified arborists in Wisconsin.  Professionals have access to some products that are not available to homeowners.

The University of Wisconsin does not endorse commercially available insecticide products over those available directly to homeowners.  Products discussed in this fact sheet have been evaluated in university research tests on EAB.

For more information on controlling emerald ash borer:   See:
http://labs.russell.wisc.edu/eab/
http://www.emeraldashborer.wi.gov or
http://www.emeraldashborer.info or contact your county Extension agent.  For a video demonstration of treating your ash trees using a systemic drench, see
http://labs.russell.wisc.edu/eab/2014/07/12/protecting-your-tree-from-the-emerald-ash-borer/.

Viburnum Leaf Beetle

The viburnum leaf beetle (VLB), Pyrrhalta viburni, is an invasive insect that feeds exclusively on and can significantly damage Viburnum species.  VLB is native to Europe and was detected in Canada in 1947.  The first report of VLB in the United States was in New York State in 1996.  VLB is now found scattered across much of the northeastern US.  In Wisconsin, an isolated infestation of VLB was discovered in Dane County in 2009, but was successfully eradicated.  In 2014, VLB was detected on a mature viburnum bush in northern Milwaukee County and other nearby infestations were detected in June 2015.  At present, VLB infestations are known from Kenosha, Milwaukee, Ozaukee, Washington, Waukesha, and Winnebago Counties.

Viburnum leaf beetles adults (left) and larvae (right). (Photos courtesy of Paul Weston, Cornell University, Bugwood.org)
Viburnum leaf beetles adults (left) and larvae (right). (Photos courtesy of Paul Weston, Cornell University, Bugwood.org)

Appearance: Adult VLB’s are approximately ¼ inch long and yellowish-brown in color. VLB larvae can be up to ⅓ inch long and range in color from yellowish-green to light brown with a series of black spots and dashes on their bodies.

Symptoms and Effects: VLB larvae chew holes in viburnum leaves in the spring creating a lace-like (i.e., skeletonized) pattern.  VLB larvae feed individually or in small groups and can cause significant damage to viburnum shrubs.  This damage can resemble the feeding damage of Japanese beetles (see University of Wisconsin Garden Facts XHT1062 “Japanese Beetle”).  In late June and early July, VLB adults begin to feed, chewing oblong holes in leaves.  Severe VLB infestations can cause complete defoliation of a viburnum shrub, which weakens the plant over time and can eventually lead to death.

Life Cycle: There is only one generation of VLB per year.  VLB’s overwinter as eggs and development from eggs to adults takes approximately eight weeks.  Larvae typically appear in early to mid-May and feed for several weeks, passing through three stages (instars) as they grow.  In early to mid-June, larvae pupate in the soil and adults emerge by late June or early July.  VLB females lay eggs during the summer and into October.  They chew small pits in twigs, deposit five to eight eggs into each pit, and then cover the pits with tiny pieces of chewed wood to protect the eggs.  Each female can deposit up to 500 eggs.  Eggs remain in place through the winter until they hatch the following spring.

Control:

Cultural:  When selecting viburnum plants for the landscape, DO NOT use arrowwood viburnum (Viburnum dentatum), European cranberrybush viburnum (Viburnum opulus), or American cranberrybush viburnum (Viburnum opulus var. americanum) as these types of viburnums are strongly preferred by VLB.  Instead use resistant viburnums such as doublefile viburnum (Viburnum plicatum f. tomentosum), Judd viburnum (Viburnum x juddii), or Koreanspice viburnum (Viburnum carlesii).  In addition, between October and the following spring, examine viburnums for twigs where VLB’s have laid their eggs.  Prune and destroy these twigs to reduce VLB numbers.  During the growing season encourage natural VLB predators in your area (e.g., lady beetles, spined soldier bugs, assassin bugs, green lacewings) that can reduce VLB numbers.

Adult viburnum leaf beetle feeding damage (left) and egg-laying sites (right). (Photos courtesy of Paul Weston, Cornell University, and Bruce Watt, University of Maine; Bugwood.org)
Adult viburnum leaf beetle feeding damage (left) and egg-laying sites (right). (Photos courtesy of Paul Weston, Cornell University, and Bruce Watt, University of Maine; Bugwood.org)

Chemical:  Prior to bud break, apply horticultural oil to twigs where VLB eggs have been laid.  This will significantly reduce the number of eggs that will hatch.  Control any surviving larvae with contact insecticides such as acephate, bifenthrin, carbaryl, cyfluthrin, deltamethrin, lambda-cyhalothrin, and permethrin.  Horticultural oil, insecticidal soap, pyrethrins and spinosad can also be effective.  To achieve the best results, apply insecticides when larvae are small and before they have caused significant damage.  VLB adults can be managed with contact insecticides, if needed, but are mobile and more challenging to control.  Systemic products (e.g., clothianidin and imidacloprid) applied as soil drenches can also be effective, but apply these products after flowering (to minimize any risks to pollinators), but before VLB damage occurs to achieve the best protection.

For more information on viburnum leaf beetle: Contact your county Extension agent.

Blueberry Maggot

Blueberry maggot was first detected in Wisconsin in the summer of 2016 in Adams and Sauk Counties.  This pest feeds inside blueberry fruit and caused damage in commercial blueberry production in the eastern and southern United States, as well as in eastern Canada.  This insect is expected to eventually have a significant impact on blueberry production in Wisconsin.

Blueberry maggot adult with characteristic wing patterns (left) and larva (right). (Photos courtesy of Rufus Isaacs, Michigan State University)
Blueberry maggot adult with characteristic wing patterns (left) and larva (right). (Photos courtesy of Rufus Isaacs, Michigan State University)

Appearance:  The adult blueberry maggot is a fly that is approximately 3/16 inch long and resembles a small housefly, but with dark bands on its wings.  Larvae (or maggots) are legless and can grow up to 5/16 inch in length.  Each larva has a single hook-like tooth at its mouth end.  Blueberry maggots are very similar in appearance to the closely related apple maggot, with adults of both being virtually identical in size and appearance (including wing patterns).  However, apple maggot does not feed on blueberries.

Host Range:  Blueberry (Vaccinium corymbosum) is the only commercially-grown fruit crop affected by blueberry maggot.  Wild hosts include plant species in the genera Vaccinium and Gaylussacia including wild blueberries, lingonberry, dangleberry, deerberry and huckleberry.

Symptoms and Effects:  A single larva feeds inside each fruit causing the berry to become soft as it develops.  Damage may go unnoticed until after harvest, when maggots crawl out of fruit and become visible among fresh fruit or in processed blueberry products (e.g., jams, preserves, pie fillings).

Life Cycle:  Adult blueberry maggots begin to fly in June or July, and continue to fly through August.  Females feed and mate for at least one week before they move to blueberry plants to begin laying eggs.  Females lay a single egg under the skin of a nearly ripe blueberry fruit and can lay up to 100 eggs during their approximately one month-long life span.  Eggs hatch within one week and damage from larvae generally first appears in mid-July, continuing until blueberries have been harvested.  Each maggot feeds in a single blueberry during its two- to three-week development.  After completing their development, larvae drop to the ground and overwinter as pupae in the upper few inches of soil.  A distinctive characteristic of the blueberry maggot is that, although most pupae develop to form adults by the following spring (completing one generation of the insect in a year), some pupae remain underground and do not mature for two or three years.

Monitoring:  Monitor for blueberry maggot adults several weeks before blueberries begin to ripen (usually in early June) using yellow sticky cards impregnated with a feeding attractant (ammonium acetate or ammonium carbonate).  You can buy cards that are pretreated with the attractant, or buy the cards and attractant separately and apply the attractant yourself.  Fold the sticky cards in a V-shape with the yellow side facing down and put up two traps for every five acres.  Because blueberry maggot is currently not widespread in Wisconsin, you can check cards weekly until you find the first adult.  After this initial find, check cards every few days.  Once you find an average of greater than one adult per trap for several days in a row, begin chemical treatments (see below).  Note that the feeding attractant is not specific for blueberry maggot, so you may find other types of flies on the cards – use a hand-lens or magnifying glass to positively identify any blueberry maggot adults.  Remember that blueberry maggot and apple maggot look very similar, but that apple maggot does not feed on blueberries, so flies trapped in blueberry fields/patches are most likely to be blueberry maggot.

Once you have detected adults, you can also test fruit for the presence of larvae.  Collect 100 berries from throughout your planting.  Then break the skins of the berries and mix the berries with a salt-water solution (1 part salt to 4 parts water).  Larvae will float to the surface.  The number of larvae you find represents the percentage of fruit infested.

Control:  Cultural control methods can be useful in preventing blueberry maggot infestations.  Remove weeds to eliminate habitat for blueberry maggot.  Remove wild blueberry and huckleberry plants as these can serve as alternate hosts for the insect.  Harvest fruits thoroughly and heat (to at least 120°F) or freeze any damaged or unusable fruits to kill blueberry maggot larvae.  This is particularly important if you compost fruit, because blueberry maggot pupae can readily survive in compost and serve as a source of an infestation in future years.  Clean soil thoroughly from equipment or beehives that might be moved between blueberry patches.  Blueberry maggot pupae can easily be moved in soil.

A blueberry maggot trap. (Photos courtesy of Rufus Isaacs, Michigan State University)
A blueberry maggot trap. (Photos courtesy of Rufus Isaacs, Michigan State University)

As noted above, start chemical control once you find an average of greater than one adult blueberry maggot per trap for several days in a row.  Alternatively, if you have had a serious problem in the past, you may want to start sprays one week after you trap your first blueberry maggot fly.  Continue sprays every seven to 10 days through harvest.  Some reduced risk active ingredients, such as novaluron, spinetoram, and spinosad are most effective when used as soon as flies are found in traps.  In addition, consider choosing a product that also provides control of spotted wing drosophila, another serious blueberry pest (see University of Wisconsin Garden Facts XHT1237 for details).  Spinosyn, spinetoram, diamide, carbamate, pyrethroid, and organophosphate-containing insecticides are effective against both insects.  Be sure to rotate use of at least two active ingredients with different modes of action to help delay development of insecticide resistance (see http://www.irac-online.org/modes-of-action/ for details), and be sure consider the effects of sprays on non-target (e.g., beneficial insects).  Finally, because you will be spraying ripe berries, pay particular attention to the pre-harvest interval when choosing insecticides.  Check the most recent Midwest Fruit Pest Management Guide (see https://learningstore.extension.wisc.edu/products/midwest-fruit-pest-management-guide20192020-p1785?_pos=1&_sid=1521576f7&_ss=r) for complete product recommendations.

For more information on or help diagnosing blueberry maggot:  Contact your county Extension agent.

Spotted Lanternfly

Spotted lanternfly (SLF) is an invasive planthopper native to China, India, and Vietnam.  It was first detected in the U.S. in Pennsylvania in 2014, most likely arriving up to two years earlier as egg masses on materials imported from China.  As of February 2016, SLF has been confirmed in five Pennsylvania counties, but due to its highly invasive nature, it appears to be spreading rapidly.  SLF has a large host range (in Korea, over 70 plant species have been reported as hosts) and potentially could greatly impact the grape, tree fruit, plant nursery and timber industries in the U.S.

Spotted lanternfly adult (left) and nymph (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)
Spotted lanternfly adult (left) and nymph (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)

Appearance:  Adult SLFs are approximately 1 inch long and ½ inch wide when resting.  The insects’ forewings are light brown to grey with black spots at the base and have a grey net-like pattern at the tips.  The hindwings are red with black spots at the base, have white bands near the center, and have a black net-like pattern at the tips.  The heads and legs of SLF adults are black, while their abdomens are yellow with broad black bands.  When resting, adults fold their wings over their bodies and appear light brown to grey with black spots.  Adult female SLFs have a red spot at the tip of their abdomens.  SLF egg masses are 1 to 1½ inches long and ½ to ¾ inches wide, greyish-brown, covered with a grey, waxy coating, and contain 30 to 50 eggs.  First stage immature SLFs (i.e., nymphs) are wingless and black with white spots.  As nymphs mature, they eventually develop red patches, but retain their white spots.

Host Range:  SLF has a wide host range and nymphs appear to feed on leaves and branches of virtually any plant they encounter, often gathering in large numbers.  In the fall, adult SLFs gather in large numbers on tree of heaven/paradise tree, willow, maple, birch, poplar, tulip poplar, ash, oak, grape, apple and stone fruit trees (e.g., cherries and plums).  Tree of heaven/paradise tree (Ailanthus altissima) is a preferred fall feeding host for SLF adults, as well as a preferred mating and egg laying site.  This plant is an invasive species native to China that grows in disturbed sites and along roadsides.  SLF damage on grape, apple and stone fruit trees is of particular concern because these plants are important agricultural crops.

Symptoms and Effects:  SLF adults and nymphs feed on a plant’s phloem (i.e., food conducting tissue), sucking the sap from young stems and leaves, and reducing the plant’s ability to photosynthesize.  Affected plants often have weeping/oozing wounds on their trunks that eventually result in greyish-black discolorations.  Damage can lead to weakened, withered plants, and potentially even plant death.  In addition, SLFs excrete large amounts of honeydew (i.e., sugar-rich feces) which can cover stems and leaves and build up on the ground at the base of plants.  Honeydew can become colonized by sooty mold fungi (see University of Wisconsin-Extension bulletin A2637, “Sooty Mold”, available at http://learningstore.uwex.edu) giving leaves and branches a blackish coating that can further reduce photosynthesis and contribute to plant decline and death.  Oozing sap and honeydew also attract other insects such as wasps, hornets, bees, and ants.

Life Cycle:  SLF has only one generation per year and overwinters as eggs in egg masses.  In the spring and early summer, eggs hatch and SLFs go through four nymphal stages (called instars).  Adults begin to appear in July and August.  Males and females mate multiple times and females can produce one or two egg masses between September through November (or until they die from the onset of winter).  Female SLFs lay egg masses on smooth-barked trunks, branches, and limb bases of medium to large-sized trees, as well as on smooth stone and other natural surfaces, and on man-made items such as yard furniture, cars, trucks, and farm equipment.

A cluster of adult spotted lanternflies on tree of heaven (left), and egg masses of spotted lanternfly covered by waxy deposits (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)
A cluster of adult spotted lanternflies on tree of heaven (left), and egg masses of spotted lanternfly covered by waxy deposits (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)

Scouting Suggestions:  SLF adults are poor fliers, but strong jumpers, and prefer to walk.  Nymphs and adults gather in large numbers on host plants and are easy to find at dusk or at night when they migrate up and down tree trunks.  SLFs are harder to find during the day as they tend to stay near the base of the host plants.  Beginning in late April to mid-May, watch for nymphs on smaller plants and vines, and on any new growth on trees and shrubs.  Watch for adult SLFs in late August through September, when they can be found in large numbers.  Sticky tree bands can be helpful for monitoring for young SLFs, but less useful in detecting later stage immature and adult SLFs.  From October through spring, watch for SLF egg masses (which can be very inconspicuous), particularly on tree of heaven.

Control:  To date, SLF has not been found in Wisconsin, and has been found in only five counties in eastern Pennsylvania.  These counties are under quarantine and there is an active monitoring and eradication program underway to prevent the spread of SLF.  Because SLF has great potential to adversely affect the grape, tree fruit, plant nursery, and timber industries, preventing introduction of SLF into Wisconsin is very important.  Accidental movement of egg masses poses the greatest risk for introduction.  Therefore, be sure to watch for egg masses (as well as adults and nymphs) on any item that has come from areas where SLF is established.  If you suspect that you have found SLF, please contact the University of Wisconsin-Madison/Extension Insect Diagnostic Lab at (608) 262-6510, idl@entomology.wisc.edu or http://labs.russell.wisc.edu/insectlab/contact-us/.

For more information on spotted lanternfly:  Contact your county Extension agent or see http://www.agriculture.pa.gov/Plants_Land_Water/PlantIndustry/Entomology/spotted_lanternfly/Pages/default.aspx.

Weir’s Cushion Rust of Spruces

What is Weir’s cushion rust? Weir’s cushion rust is a needle disease that disfigures and reduces growth of spruce trees (Picea spp.) of all ages. This disease has been known in both eastern and western regions of the United States, but was recognized in Wisconsin for the first time in 2002.

Yellow spots and bands in winter on spruce shoots affected by Weir's cushion rust.
Yellow spots and bands in winter on spruce shoots affected by Weir’s cushion rust.

What does Weir’s cushion rust look like? Needles on current year’s shoots affected by Weir’s cushion rust may develop yellow spots or bands in summer and fall. These spots and bands may intensify to give needles a bright “green and gold” appearance during the following spring, when tiny blister-like pustules also may develop in the yellow areas. Microscopic examination of these pustules is required for diagnosis of this disease. Affected one-year-old needles continue to yellow, turn brown, and fall off as spring and summer progress. Trees badly damaged by Weir’s cushion rust will have thin crowns due to repeated loss of the previous year’s needles.

Where does Weir’s cushion rust come from? Weir’s cushion rust results from colonization of spruce needles by the fungus Chrysomyxa weirii. This fungus overwinters in needles infected during the previous growing season. In late summer, or more typically the next spring, Chrysomyxa weirii produces spores in tiny, blister-like pustules that develop on these needles. These spores can be blown by wind or splashed by rain to newly emerging needles on the same tree or other trees. Spore germination is followed by infection of young needles.

Can I save a tree affected by Weir’s cushion rust? Fungicides containing chlorothalonil may be applied to trees affected by Weir’s cushion rust to prevent new needle infections. The first application should be made when 10% of the buds have broken and two additional applications should be made at seven to 10 day intervals thereafter. Fungicide applications do not kill the fungus in needles that are already infected, so it is important to begin applications promptly and to complete the spray program, to ensure thorough coverage of foliage. Please be sure to read and follow all fungicide label instructions to ensure that the fungicide is used in the safest and most effective manner. Needles infected by Chrysomyxa weirii the previous year will die, and the fungus will not continue to live or produce spores on dead needles. Therefore, destruction of dead needles is not necessary.

How do I avoid Weir’s cushion rust in the future? Growers and homeowners should be careful not to accept nursery stock affected by Weir’s cushion rust, which may be present in wholesale or retail nurseries. Spruces in nurseries and the landscape should be carefully inspected in late summer and fall for yellow spots and bands on current year’s needles and in spring for these symptoms and pustules on the previous year’s needles. Affected trees should not be moved to areas where the disease is not already present. Preventative application of fungicides may prevent establishment of the fungus on new trees or in previously unaffected nurseries.

For more information on Weir’s cushion rust: Contact your county Extension agent.

 

 

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.

 

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.