Category Archives: Monthly Column

August 2020: Green Grow the Lilacs – NOT!

LilacLilacs are one of my favorite spring-flowering shrubs.  When sited properly (in full sun) and pruned/thinned regularly, they reliably produce a bounty of beautiful blooms each spring in a myriad of colors.  And oh that scent!  Is there really anything that smells better than the scent of lilacs in full bloom?

In most years, lilacs tend to be relatively disease free.  However, this year, I have seen a fair number of disease issues on lilacs that have ranged from cosmetic to lethal.  Here’s a round up of common lilac diseases to watch for.

Powdery MildewLilacs are the poster child (in my mind) for this disease.  They routinely exhibit the white, powdery growth on their leaves that is characteristic of powdery mildew, but tend to show no adverse effects from the disease.  The best management strategy for powdery mildew on lilac is to develop a healthy ability to ignore the disease during the growing season.  Then in the fall, be sure to collect up the leaf debris from your lilacs, and burn (where allowed), bury or compost the leaf debris.  Even with diligent leaf clean up, don’t expect a powdery mildew-free lilac next year.  The pathogen has a sneaky way of surviving in the overwintering buds of the plant.

Bacterial BlightThis disease tends to be more of an issue early in the growing season, often just as lilacs are beginning to leaf out.  The bacterium that causes bacterial blight (Pseudomonas syringae pv. syringae) often is part of the normal microflora that lives on lilac leaves, occurring at a low enough level not to cause any disease issues.  If the population increases however (often in response to wetter weather), the bacterium can lead to leaf tissue necrosis (i.e., death).  The dead areas (sometimes in discrete spots, other times in larger blotches) typically have yellow halos.  To complicate matters, Pseudomonas syringae pv. syringae has a protein in one of its membranes that mimics an ice crystal.  So, if the bacterium is present on lilacs in high numbers and a cold snap occurs, plants tend to be more prone to cold injury, particularly branch tip dieback.  Management of bacterial blight includes good fall clean up (as described above) and pruning in the case of branch dieback.  Prune four to six inches below obviously dead areas on branches.  Be sure to prune only when it is dry, and be sure to disinfest your pruning tools between cuts by dipping them in 10% bleach or (even better) 70% alcohol (e.g., rubbing alcohol).  Spray disinfectants can be used as a source of alcohol as well.  Just be sure to check the ingredient list of the disinfectant that you select to make sure it contains roughly 70% alcohol.  If you use bleach, be sure to thoroughly rinse your tools after you are done pruning and oil them to prevent rusting that can be caused by the use of bleach.  You can dispose of branches by burning (where allowed) or burying them.

Septoria Leaf Spot:  This has been the number one disease this season on lilac (and is towards the top of my disease list for all plants).  I have received numerous inquiries about lilacs with leaves that have partially or fully browned starting at the bottom of the shrub and working up the plant.  The culprit in this browning appears to be a species of Septoria, a fungus related to (but distinct from) the organism that causes Septoria leaf spot of tomato.  While the browning caused by this disease is quite dramatic, the disease is not lethal.  If you look carefully at the branches with symptomatic leaves, you should be able to find healthy leaf buds at the base of the petioles of this year’s leaves.  These buds are ready to sprout next spring to produce a new crop of leaves.  Good fall clean up (see above) is the place to start in managing Septoria leaf spot.  Routine pruning/thinning to open the canopy and promote rapid drying of leaves when they get wet will also help keep this disease at bay.  If we continue to see wetter summers, this disease may become a chronic, severe problem, and use of fungicides to manage the disease may become necessary.  However, I suspect we will cycle into a series of drier summers over the next couple of years, and if we do, I would expect the serverity of this disease to decrease, and no fungicide treatments will be needed.

Lilac Witches’ Broom:  This disease is caused by the same bacterium-like organism (called a phytoplasma) that causes ash yellows.  The phytoplasma is introduced into a lilac’s food-conducting tissue (i.e., phloem) by leafhoppers.  Once in the plant, the phytoplasma leads to a yellowing of foliage, stunting of the entire plant, and over-production of lateral branches (i.e., brooming).  Infected plants typically decline and die over a period of several years,.  There is no way to get rid of phytoplasmas, so removal and replacement of infected shrubs is the management strategy of choice.

Verticillium WiltVerticillium wilt is the most rapidly lethal of the lilac diseases, and the disease that I most commonly see on Japanese tree lilac.  The fungus that causes this disease (tyically Verticillium dahliae for lilac) is found in the soil and infects plants through the roots.  It colonizes the water-conducting tissue (i.e., xylem) inside the plant and blocks it off.  This prevents water movement from the roots to the branches, leading to wilting.  Typically the wilting starts in a single branches.  As the disease progresses, a localized cluster of branches wilts, and eventually, the entire tree/shrub dies.  Verticillium dahliae has a wide host range, so if you have a lilac with this disease, you need to be very careful about what you choose as a replacement.  Conifers are your best best, although a limited selection of deciduous trees and shrubs (tricolor beech anyone?) ban be used.

NEED HELP?  If you need help diagnosing any of the lilac diseases described above (or diseases of any other kind of plant for that matter), feel free to contact the PDDC.  For the PDDC’s current policy on sample submission, including submission of digital photos, check out the following link.  As always, be sure to check out the PDDC website for timely information on plant diseases.  Also, feel free to follow the clinic on Twitter or Facebook (@UWPDDC) to receive timely PDDC updates.  Or alternately, put in a request to subscribe to the clinic’s new listserv (UWPDDCLearn) by emailing

Hang in there, be safe, and stay healthy everyone!

P.S.:  Bonus points if you recognize where this month’s article title comes from.

July 2020: Elderberry Whine – Rust, Rust Everywhere!

Rust Fungi2020 has been a banner year for rust diseases.  I can’t remember a year where I have seen so many rusts on so many different plants:  apple, ash, buckhorn, crabapple, elderberry, hawthorn, Jack-in-the-pulpit, juniper (including red cedar), mayapple, raspberry, spinach, spruce, violet and white pine.  Rust diseases are caused by a closely related group of fungi, with each fungus in the group highly adapted to causing disease on specific plants.  These fungi are incredibly complex.  They can produce from two to five different types of spores depending on the particular rust fungus, and their life cycles fall into two major categories:  autoecious and heteroecious.

Autoecious rust fungi are able to complete their entire life cycles on a single plant host.  A classic rust disease that falls into this category is rose rust.  This rust produces one of my favorite spores, a teliospore (i.e., a resting spore) that looks like a corndog.  While I have yet to see rose rust in 2020, I have seen several other autoecious rusts including mayapple rust, Jack-in-the-pulpit rust and orange rust of black raspberry.  Orange rust is particularly destructive.  Infected plants become stunted and spindly, and they do not produce flowers or fruit.  Removal and destruction of infected plants is the only effective management strategy for this disease.

Heteroecious rust fungi require two different plants in order to complete their life cycles.  The most common heteroecious rusts that I see every year are the Gymnosporangium rusts.  These rusts spend part of their life cycles on junipers (particularly red cedar) and the remainders of their life cycles on certain woody rosaceous plants such as apple, crabapple and hawthorn.  I actually think the symptoms that these diseases cause (i.e., bright yellow leaf spots on rosaceous hosts) are quite pretty, giving the trees some additional aesthetic appeal after their flowers have faded and fallen for the year.  Other heteroecious rusts that I have seen this year include white pine blister rust (hosts:  white pine and gooseberries/currants) and crown rust (hosts:  buckthorn and turfgrass).

I have to give a special shout out to elderberry rust, a heteroecious rust that alternates between elderberry and sedges.  Symptoms on elderberry are some of the most awesome that I get to see of any disease.  Infection by the rust fungus causes formation of a swollen areas (called galls), as well as growth distortions.  The galls eventually produce a bright yellow spores (these are the spores that infect the alternate sedge host), making the galls look like banana slugs.  TOTALLY COOL!!

I really can’t wait to see how many more rusts I can check off my plant disease bucket list this summer.  If you see any rust diseases (or any cool diseases in general), feel free to email me photos.

NEED HELP?  If you need help diagnosing plant diseases, feel free to contact the PDDC.  For the PDDC’s current policy on sample submission, including submission of digital photos, check out the following link.  As always, be sure to check out the PDDC website for timely information on plant diseases.  Also, feel free to follow the clinic on Twitter or Facebook (@UWPDDC) to receive timely PDDC updates.  Or alternately, put in a request to subscribe to the clinic’s new listserv (UWPDDCLearn) by emailing

Hang in there, be safe, and stay healthy everyone!

June 2020: Cherries and Peaches and Plums, Oh My!

FruitThese days, digital photos of diseased plants are arriving fast and furious in the Plant Disease Diagnostics Clinic (PDDC) email inbox.  While clients have been having problems with many different types of plants, I have been receiving a large number of photos of stone fruits.  Ornamental and fruit-bearing varieties of cherries, plums and peaches seem to be having a rather tough year this year.  Several of the diseases that adversely affect stone fruits are fairly straightforward to diagnose by photo.  Below are the common diseases of cherries, plums, and peaches that I have been seeing thus far this season.

Peach Leaf curlPEACH LEAF CURLThe name of this fungal disease is quite descriptive.  Infected peach leaves become curled and puckered, and often have a combination of a green, creamy-white and fuchsia color.  Peach leaf curl seems relatively cosmetic, but repeated occurrences of the disease over time can reduce the quantity and quality of fruit.  Typically with leaf diseases, I recommend good fall clean up of leaves for management.  Unfortunately, this strategy does not work for pearch leaf curl, as the pathogen (Taphrina deformans) overwinters on peach branches.  Management of the disease relies of use of fungicides (e.g., copper-containing products) applied either after leaf drop in the fall or prior to bud swell in the spring.

Peach Leaf curlBLACK KNOTThis disease, which is specific to plants in the genus Prunus (e.g., cherries and plums), is what I affectionately refer to as “poop-on-a-stick”.  It really does look as though some pesky animal has defecated on the branches of affected trees and shrubs.  The fungal pathogen involved (Apiosporina morbosa) induces formation of black, gnarly swollen areas (called galls or knots) on infected branches.

Unfortunately, once the knots form, the only method of management is to remove the growths by pruning.  For fungal diseases, I typically recommend pruning roughly four to six inches below the diseased area.  When pruning, be sure to decontaminate tools between cuts by treating them for at least 30 seconds with 70% alcohol (e.g., straight rubbing alcohol), a commercial disinfectant or 10% bleach.  Spray disinfectants work as well (as long as they contain roughly 70% active ingredient).  Just spray tools until they drip and then allow them to air dry.  When using bleach, be sure to rinse tools completely after pruning and then oil them to prevent rusting.  Dispose of black knot galls by burning (where allowed) or burying them.  In some situations, there will be so many galls in a tree that my recommendation is what I call “basal pruning” or “a single pruning cut at the ground level”.  You remove the affected trees and replace it with non-susceptible plants.

Bacterial CankerBACTERIAL CANKERProbably the most serious of the diseases that I have seen on stone fruits this year is this one.  The pathogens involved (two variants, called pathovars, of the bacterium Pseudomonas syrinage) infect branches causing branch dieback.  From infected areas, sap emerges and gelatinizes on branch surfaces.  For bacterial canker, timely pruning of diseased branches is critical for management, as the pathogens can rapidly colonize infected branches and move into the main trunks of trees where they can girdle the trunks, killing the trees.

Prune at least 12 inches below visible dieback on affected branches and again dispose of branches by burning (where allowed) or burying them.  Decontaminate tools as described above for black knot.  When bacterial canker occurs in main trunks, tree removal and replacement is the only real option.


If you need help diagnosing plant diseases, feel free to contact the PDDC.  For the PDDC’s current policy on sample submission, including submission of digital photos, check out the following link.  As always, be sure to check out the PDDC website for timely information on plant diseases.  Also, feel free to follow the clinic on Twitter or Facebook (@UWPDDC) to receive timely PDDC updates.  Or alternately, put in a request to subscribe to the clinic’s new listserv (UWPDDCLearn) by emailing

Hang in there, be safe, and stay healthy everyone!

May 2020: Toxic Plant Disease Olympics

Toxic Plant OlympicsMost days, I really love my job.  I am well-known for my love of plant disesaes and I tend to get giddy when plant samples arrive at the PDDC.  There is always the possibility with each new package that I will become reacquainted with an old disease friend (e.g., cedar-apple rust) or that I will be introduced to new disease friend that I’ve been wanting to meet for years (e.g., zonate leaf spot).

Others days, I open a package and my shoulders sag, and I let out sigh.  This most often occurs when the sample potentially has a disease/pathogen that is regulated by either the state or federal government.  These diseases are often fascinating in and of themselves, but the paperwork involved with their diagnosis can be soul crushing.  Right now in Wisconsin, there are three diseases on my radar that fall into this dreaded category.  This month’s web article is devoted to these medal-winning diseases that keep me up at night.

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

In the scheme of things, boxwood blight is not bad as regulated diseases go.  Boxwood blight was introduced into Wisconsin in 2018 through contaminated nursery stock and is regulated at the state level.  The Wisconsin Department of Agriculture, Trade and Consumer Protection (WI DATCP) monitors boxwood blight’s spread and is currently attempting to eradicate the disease as it rears its ugly head, particularly in nurseries.  I first encountered boxwood blight last summer when a landscape maintenance professional submitted a sample from a boxwood shrub planted at a Madison area residence.  Once I made my diagnosis, I immediately contacted WI DATCP so that they could follow up with the homeowner regarding containment and eradication.

Boxwood blight typically first shows up as distinct spots appearing on leaves in the lower canopy of boxwood shrubs.  Most boxwood varieties are very susceptible to the disease and rapidly defoliate and die.  Pachysandra, a common ground cover, is also susceptible.  If you want to see how devastating this disease can be, do an internet search on “boxwood blight” and your favorite state along the eastern seaboard (e.g., North Carolina, Virginia, Maryland).  You will find photos of landscapes where every boxwood has been wiped out.  For additional details on this disease, check out our boxwood blight pest alert.

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.

Sudden oak death (I prefer the name Ramorum blight) was first described in California in the 1990’s and has killed millions of oaks in that state.  Because of its destructive potential, the disease/pathogen is regulated at the federal level by the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS).  There has been movement of the disease/pathogen over the years into other states (again through movement of nursery materials), and in 2019, WI DATCP inspectors found the disease on an azalea in a nursery in Wausau.  Unfortunately, azaleas from the same supplier were distributed to nurseries around Wisconsin, and many were sold to homeowners before WI DATCP became aware of potential problems.  Another possible introduction of the disease/pathogen on red ‘Double Knockout’ roses also occurred in 2019.  I have not yet had this disease arrive in my lab, but I did prescreen several samples for the disease last summer.  Based on my preliminary testing, I forwarded two suspicious samples to a second lab for another round of testing.  If those samples had tested positive at this second lab (luckily they didn’t), they would have been sent to yet another lab (a USDA APHIS facility) for a final round of testing.

Unfortunately the symptoms of sudden oak death/Ramorum blight are not readily distinguishable from other diseases.  Branch dieback, nondescript leaf browning and eventually plant death can be typical symptoms.  See our sudden oak death pest alert for additional details on this diease.

Yellowing and wilting characteristic of Ralstonia wilt. Photo courtesy of WI DATCP
Yellowing and wilting characteristic of Ralstonia wilt. Photo courtesy of WI DATCP

This is the granddaddy of regulated diseases that I have encountered over the years.  One variant of the bacterium that causes this disease (Ralstonia solanacearum race 3, biovar 2) causes a devastating disease of potatoes (called brown rot) and was classified in the early 2000’s as a select agent by the federal government.  This means that the pathogen is recognized as having the potential to be weaponized and used in bioterrorism attacks against US agriculture.  Ralstonia wilt was first detected on geraniums in Wisconsin (on a plant submitted to the PDDC) in 1999 with additional introductions on this crop through 2004.  In March of 2020, the disease/pathogen was detected after a 16 year absence, this time on Fantasia® ‘Pink Flare’ geraniums in Michigan.  This variety of geranium was also distributed to greenhouses in 38 other states including Wisconsin.  USDA APHIS is currently leading efforts to eradicate potentially contaminated plants and to decontaminate affected greenhouses.  The PDDC has the capacity to detect the bacterial species involved in the disease (but not the specific race and biovar) using the plant disease equivalent of a home pregnancy test.  Suspect samples must be forwarded to USDA APHIS labs for a final confirmation of race/biovar.

A major problem with Ralstonia wilt is that plants can be contaminated with the bacterium without showing symptoms.  Eventually, in susceptible hosts like geranium, the bacterium colonizes the plant’s water-conducting tissue and blocks water movement, leading to leaf wilting and yellowing.  Sometimes, only part of the plant will wilt at first, but eventually the disease is lethal.  For more on this disease, check out our Ralstonia wilt pest alert.

If you believe you are seeing ANY of the diseases described in this article, please contact me IMMEDIATELY at (608) 262-2863 or  We will need to make arrangements for appropriate testing.  And also, as always, feel free to follow me on Twitter or Facebook (@UWPDDC) to receive updates on these and other diseases.

Hang in there, be safe, and stay healthy everyone!

April 2020: What Do I Have to Do to Get My Picture Took?

Camera IconThe impact of COVID-19 on the Plant Disease Diagnostics Clinic (PDDC) and the services that the clinic provides has continued to evolve.  As of March 28, 2020, and until further notice, the PDDC is no longer accepting physical samples for diagnoses, and clinic staff members are restricted to working from home.  Nonetheless, I and the other staff at the PDDC are committed to the providing the best possible services that we can to our clients given these restrictions.

While submitting physical samples is not possible, the PDDC is still accpting digital photos for diagnosis.  In this month’s PDDC web article, I would like to provide pointers on what sorts of pictures you should take to optimze the possibility I will be able to make as accurate a diagnosis as possible, options for getting the photos to the PDDC and what you can expect after your submission.


  • Take LOTS of pictures. Err on the side of taking too many photos.  The more photos you send me, the more likely I will see something that will lead me to an accurate diagnosis.
  • Take a variety of pictures. These should include:
    • Landscape shots. These sorts of photos show how your diseased plant is situated in your yard relative to other plants, buildings, driveways, sidewalks, etc.  They can often provide clues on environmental factors that may be contributing to the disease problem you are seeing.
    • Whole plant shots. These photos will show the distribution of symptoms on the plant.  Are the symptoms in just one area?  Are they scattered throughout the plant?  Is the entire plant affected?
    • Close up shots. Take pictures of affected leaves (both tops and bottoms), branches, roots, fruits or any other affected plant part.  I need to look for symptoms (e.g., leaf spots, cankers, discolorations, growth distortions, etc.), as well as signs of pathogens (e.g., fungal sporulation) that can help me with my diagnosis.
  • Take high quality pictures. This means taking:
    • High resolution photos. The higher the resolution, the better I will be able to increase the size of the picture and still see lots of detail.  The more detail I can see, the more likely I will be able to figure out what’s going on.
    • Crisp, non-fuzzy photos. If a picture is fuzzy, I won’t be able to see much or tell you much.


  • This is typically the easiest way to submit photos.  Use for emailing.
  • The PDDC website. You will now find links on the PPDC website (on the main page, “Sample Collection and Submission” page and “Service and Fees” page) to a “Digital Diagnosis” form.  Fill out the form, upload your photos and click on “Submit”.
  • Text message. If email or submission via the PDDC website are not options for you, feel free to call me at (608) 262-2863.  After we talk, if you need to submit photos, I can provide you a cell phone number where you can send your photos via text message.


  • A prompt response. I try to respond to phone and email inquiries within 24 hours.
  • The best diagnosis that I can provide. I have always maintained that looking at photos is not the best way to diagnose plant diseases.  That said, I will provide you with my best interpretation of what may be happening to your plants based on photos that you provide.
  • Management recommendations. Where possible, I will provide suggestions on how you can mitigate the problem that you are seeing and prevent it from happening in the future.
  • Any follow-up you may need. My door (well, actually my email and phone at this point) is always open if you need additional consultations after I provide my diagnosis.

It is my commitment to provide you with the best possible service under our current circumstances.  Please do not hesitate to contact me at (608) 262-2863 or if you think I might be able to help you.  Also check out the PPDC website for online resources (e.g., University of Wisconsin Garden Facts, Wisconsin Disease Almanac, monthly web articles).  And feel free to follow my clinic updates on Twitter or Facebook (@UWPDDC).

Be safe and stay healthy everyone! 

P.S.:  Bonus points if you know the origin of the title of this month’s article.

March 2020: Plant Disease Diagnostics in the Time of COVID-19

LAST UPDATE:  June 18, 2021

Over the past week, reports of COVID-19 in Wisconsin have increased dramatically.
To help keep PDDC customers and staff safe, I am making changes to the way the PDDC delivers services.
Below is a list of what will change, and what will remain the same.
I will update this list as UW-Madison and PDDC policies change.

Update 6/18/2021


The PDDC continues to accept walk-in samples delivered to the shelving unit in the hallway outside the clinic (Rm. 183 Russell Labs).  However, clinic staff will not be available to interact with clients.  Anyone entering Russell Labs who has not been vaccinated for COVID-19 is required to wear a mask and practice social distancing (6 ft. between people).  For additional details on the procedure for submitting digital samples online and physical samples (either in-person or via mail), please see the 12/28/20 update below.

Update 4/30/2021


Starting May 10, 2021, the PDDC will once again be accepting walk-in samples delivered to the shelving unit in the hallway outside the clinic (Rm. 183 Russell Labs).  However, due to continued concerns about COVID-19, clinic staff will not be available to interact with clients.  Also, anyone entering Russell Labs is required to wear a mask and practice social distancing (6 ft. between people).  For additional details on the procedure for submitting digital samples online and physical samples (either in-person or via mail), please see the 12/28/20 update below.

Update 12/28/2020


As we enter into 2021, COVID-19 continues to be of concern.  Therefore, physical sample submissions to the PDDC will continue to follow the same protocol and prioritization as outlined in my update of April 24, 2020 (see below).   The only changes for the new year are that the PDDC will now charge a $20 fee for digital diagnostics, and there will be a $5 increase in the base fee for physical samples.  For a complete fee schedule, click here.  To submit photos for a digital diagnosis, click here.  To access the PDDC submission form to be included with physical samples, click here.  

Update 4/24/2020


The PDDC has been authorized to begin accepting physical samples  again.  However, clinic staffing and hours will be limited, and the number of samples that the clinic will be able to accommodate will be severely restricted. 

Before submitting a sample, you must contact the PDDC using the form on this page , by emailing or by calling (608) 262-2863.  If you use the clinic online form or email the clinic, please include photos whenever possible.  Based on this initial contact, clinic staff will determine if a digital diagnosis is possible or if a physical sample submission is needed.

Even with prescreening, the PDDC will likely not be able to accommodate all samples that would normally require submission of a physical samples.  As needed, physical sample submissions will be prioritized as follows:

  • Commercial production food and agriculture-related samples (e.g., vegetables, fruits, field and forage crops);
  • Commercial/homeowner samples of regulatory importance (e.g., late blight, boxwood blight);
  • Commercial production, non-food samples (e.g., nursery, greenhouse samples);
  • Homeowner food samples (e.g., vegetables, fruits);
  • Commercial/homeowner non-production, non-food samples (e.g., trees, shrubs, herbaceous ornamentals).

Certain regulatory samples (e.g., sudden oak death/Ramorum blight) will be redirected to the Plant Industry Lab at WI DATCP.

Digital diagnoses will continue to be provided free of charge.   Normal clinic fees will apply to any physical samples submitted to the PDDC.

Update 3/28/2020
Until further notice, the PDDC will not be accepting any physical samples for diagnosis.  Customers are welcome to continue submitting questions and/or digital photos to the PDDC by submitting the form on this page.   

Update 3/18/2020

CALS administration has closed the Russell Labs building to visitors. PDDC customers may only submit samples by mail.

Plant Disease Diagnostics:

  • We will still accept samples for diagnosis.
  • You can still submit your diseased plants by mail.
  • The building is locked, so you can no longer drop off samples in person.
  • I am discontinuing in-person consultations about samples.
  • I will continue to mail out hard copies of reports and invoices.  If you prefer I email your results, please note this on your submission form.


  • All in-person PDDC presentations are cancelled until further notice.
  • Instead, I can provide presentations on a number of topics via remote learning.
    • Click here to learn more about the topics offered.
    • Call me (608-262-2863) or email me ( to learn more about possible remote learning options (e.g. teleconferencing/ videoconferencing, etc.).

Online Resources:


  • In-person consultations are discontinued until further notice.
  • Phone (608-262-2863) and email ( channels are still open.  Digital photos showing the disease problems are welcome, please attach them to your email.  I may not be able to make a formal diagnosis from your photos, but I will do my best.

Most of All…

Stay safe everyone!  I wish you well in the challenging days ahead!!

February 2020: Yacking It Up About Plant Diseases

Yacking It UpLast month in my summary of my activities for 2019, I mentioned that I had given 111 talks/presentations/workshops during the course of the year.  This month I’d like to elaborate a bit on the types of outreach presentations that I provide.


Quite frankly, I’m willing to talk about plant diseases on any crop/plant other than turf (there are other Extension specialists who handle this crop).  I truly think that plant diseases are INCREDIBLY COOL.  I give talks to both commercial (i.e., agricultural/horticultural grower and consultant) and consumer (i.e., general public) audiences.

Most typically though, I provide education for the general public, often concentrating on teaching about diseases of herbaceous ornamentals, woody ornamentals and vegetables.  I often partner with county Extension staff, Master Gardener Volunteer groups, technical college instructors, professional organizations, public libraries and garden clubs to reach as wide a range of home gardeners (and horticulture professionals) as possible.

Types of Talks

To learn more about the specifics on the types of talks that I do, check out a couple of sections of the Plant Diseases Diagnostics Clinic (PDDC) website:

2020 Events Calendar

On my events calendar, I try to list every talk/presentation/workshop that I give during the year.  The calendar changes constantly as I book new presentations.

The calendar entries includes the titles of my talks, as well as the dates, times and towns where I will be.  If you ever see a presentation in a town near you and are interested in additional details on the program, feel free to contact me and I can provide those details.

Watch the entries as the date approaches.  I typically create handouts for my talks and link to the handouts on my calendar.  You are welcome to view these handouts online or download them to see what I’m talking about and hopefully learn a thing or two, even if you can’t attend the presentation.

Master Gardener Resources

The presentations/programs described on this page are a series of talks and hands-on opportunities that I have put together specifically to address the continuing education needs of Master Gardener Volunteers.  That said, virtually all of these presentations could be of interest to a general public audience.

Many of the talks fall into the “Diseases of” category, where I discuss diseases of broad plant groups such as vegetables, herbaceous ornamentals, evergreens and deciduous trees and shrubs.  Other of these talks cover more specific plants such as hostas and orchids.

Also included on this page are talks that are more conceptual in nature including my The Science (and Art) of Plant Disease Diagnosis and Growing Healthy Plants:  Basics in Plant Disease Management talks.

Some of the talks are just fun topics that I like to get geeky about, such as my Plant Diseases in History presentation.  The newest addition in this latter category is Confessions of a Black Thumb:  Plants That I Have Killed (or at Least Seriously Maimed), a cautionary tale of my personal gardening disasters (and there have been many).

If you are interested in getting down and dirty about plant diseases, I offer my Signs and Symptoms Workshop.  In this hands-on activity, participants have the opportunity to see and work with actual diseased plant specimens.

Finally, I offer tours of the PDDC (located on the UW-Madison campus), and typically combine this tour with tours of the Insect Diagnostic Lab, the Wisconsin Insect Research Collection and/or the Allen Centennial Garden.


If you have a group that might be interested in learning more about plant diseases, don’t be bashful about contacting me to explore the possibility.  You can contact me at  Book early as my calendar often fills up quickly.  And for addition information on the PDDC, its activities and resources, check out other sections of the PDDC website, or follow the clinic on Twitter or Facebook (@UWPDDC).

Keep warm!  And don’t worry because spring gardening season (with all those uber-cool plant diseases) is coming soon!!

January 2020: 2019 in Review

Jan 2020 Column Icon

Wow!  It’s 2020 already and I can’t say that I’ve recovered yet from the avalanche that was 2019.


Sample Processing

Clinic staff processed 1506 samples, up roughly 17.5% from 2018.  Samples came from 64 of Wisconsin’s 72 counties, as well as FL, IA, IL, IN, MA, ME, MI, MN, and NY.  Sample numbers were up sharply (despite the PDDC having increased fees in 2019) most likely in part due to having had two seasons back to back that were incredibly wet and thus favorable for disease development.

Quick Stats:

  • 1506 samples processed
  • 1500+ email and phone consults
  • 111 talks/presentations in 22 WI counties
  • 224,000 people interacted with at outreach events
  • 3,435 Garden Facts fact sheets distributed at Garden Expo alone

Molecular Diagnostics

I also believe that the PDDC’s expanding molecular (i.e., DNA-based) diagnostic offerings have helped drive higher clinic sample numbers.  Many of the molecular tests that the PDDC offers are particularly popular and useful for commercial vegetable producers.  Once again, kudos to Sue Lueloff, the PDDC’s Assistant Diagnostician, for stepping up and handling all of the molecular samples.  Sue tested numerous samples for bacterial soft rot pathogens, the oak wilt pathogen and phytoplasmas.  In addition to processing routine samples (included in the total mentioned above), Sue also worked on a survey with the Wisconsin Department of Natural Resources (WI DNR), testing ~100 tree samples from around the state for phytoplasmas.  Testing from this survey will be completed in early 2020.

Sample Highlights

As always, while Sue handled the molecular side of things at the PDDC, I handled the more classical side of the diagnostic process that involved culturing (i.e., growing pathogens from plant tissue) and microscopy.  My highlight, sample-wise, for the year was confirming my first case of boxwood blight.  This disease had been first reported in nurseries in Wisconsin by the Wisconsin Department of Agriculture, Trade and Consumer Protection (WI DATCP) in 2018, but the sample I received at the PDDC was the first instance of the disease popping up in a landscape setting (i.e., in a home garden).  I also spent a fair amount of time dealing with samples suspected of having sudden oak death/Ramorum blight.  This disease has caused wide-spread death of oak trees (as well as other trees, shrubs and herbaceous plants) in California and Oregon.  The first Wisconsin case was confirmed by WI DATCP in 2019.  Thus far, none of the putative sudden oak death samples submitted to the PDDC has tested positive for the disease.

Disease Consulting by Email and Phone

In addition to coordinating efforts with live samples in the PDDC, I continued to provide digital disease diagnostics via email, through the UW-Madison Division of Extension PlantDOC online diagnostic website, and through the Association of Specialty Cut Flower Growers Facebook page.  I also spent a lot of time on the phone answering plant disease-related questions.  All told, I likely had 1500+ exchanges in the process of handling online plant disease inquiries and phone calls.


PDDC outreach activities, once again, hit an all-time high in 2019.  I did 111 talks/presentations/workshops in 22 Wisconsin counties (many of these in-person).  My biggest outreach event was again Wisconsin Public Television’s Garden Expo.  I spent three days at the event, gave three talks (two on diseases of trees and shrubs, one on plant disease management) and helped answer questions with Lisa Johnson of Extension Dane County at Larry Meiller’s Garden Talk session.  As always, I had a steady stream of visitors to the PDDC booth, talking with and answering questions for folks the entire time.  I distributed 3,435 University of Wisconsin Garden Facts fact sheets, brochures/informational materials and other written materials.  Across all outreach programs in 2019, I interacted with almost 224,000 people.  As always, a big thanks goes out to Larry Meiller for having me on his radio show with its awesome listenership.

Team Effort

What happens at the PDDC is not a solo effort.  I have LOTS of help.  I have already mentioned Sue Lueloff (molecular diagnostician extraordinaire) above.  Also part of my team are Ann Joy (who does data entry that is instrumental in keeping federal funds through the National Plant Diagnostics Network flowing into the clinic), Dixie Lang (who makes the PDDC website look beautiful and keeps the PDDC billing database running and up to snuff), Laurie Ballentine of the Russell Labs support staff (who prints and folds and otherwise produces all of the written handouts I use for my outreach efforts), and finally Alex Mikus (an undergraduate here at the UW-Madison) and Gisele Guzman (a participant in the TOPS program at East High School), my hard-working student hourlies who helped process the bulk of PDDC samples and kept me on my toes.

Onward Ho!

Now, 2020 has arrived and it’s time to gear back up!  “It’s showtime, folks!”  (Brownie points if you can identify the film that quote comes from.)

For addition information on the PDDC and its activities, check out the PDDC website, follow the clinic on Twitter or Facebook (@UWPDDC) or contact the clinic at

July: Cool Fungal Friends for a Hot and Muggy July

MushroomOver the past two weeks, I have received a number of photos of incredibly cool microorganisms that have popped up in people’s gardens or around their homes.  These organisms have all turned out to be non-pathogens (i.e., they don’t cause plant diseases), but they are some of the more extraordinary organisms that I encounter in my job.

Bird’s Nest FungiIf you’ve recently spread new mulch, you may eventually notice small (maybe ¼ to ½ inch in diameter) cup-like structures forming in groups on the mulch surface.  Closer examination of the cups will reveal egg-shaped structures inside.  Looking at these tiny structures as a whole, you’d swear that some sort of miniature bird has built a series of nests in your flowerbed.  But these mini-“nests” are actually reproductive structures of one of the bird’s nest fungi.  The “eggs” are packets of fungal spores attached to the interior of the cup by a cord-like structure.  When a raindrop hits the nest, the momentum of the falling water catapults an “egg” into the air.  The attached “cord” stretches and eventually breaks.  The broken end is sticky and eventually adheres to some object (e.g., a branch or leaf) as the “egg” flies through the air.  The attached “egg” swings around on the cord (think of a bola) and eventually gloms onto something as well.  As the walls of the catapulted “egg” degrades, the spores inside are released.  Being elevated, the spores are more likely to be picked up in air currents.  What an amazing adaptation that increases the likelihood that the spores are spread over a large distance!

Bird's Nest Fungi on Mulch in a Flowerbed
Bird’s Nest Fungi on Mulch in a Flowerbed

StinkhornsSometimes when people dig in their gardens they encounter large (an inch or larger in diameter), soft, egg-like structures in the soil.  Folks often think these are actual bird or reptile eggs.  However, if you cut the “eggs” through the center along the long axis, you discover inside a mushroom-like structure with a stalk and an oftentimes honeycomb-like cap.  These mushrooms enlarge (eventually causing the “eggs” to “hatch”) and poke up above the soil surface.  These emerging mushrooms often resemble a certain, uh-hem, part of the male anatomy.  I have had a number of amusing conversations over the years as clients have attempted to describe stinkhorns without naming the offending body part.  The name stinkhorn comes from the fact that as they produce spores, these fungi tend to smell pretty rank.  The foul small (akin to rotten meat) attracts certain insects (e.g., flies) that pick up the spores and move them long distances.  Again, this is another amazing dispersal mechanism.

Stinkhorn "Eggs"
Stinkhorn “Eggs”
Inside the Stinkhorn "Eggs"
Inside the Stinkhorn “Eggs”

Slime MoldsSlime molds are not true fungi, but members of a unique group of organisms called the myxomycetes.  These organisms spend part of the lives in an amoeba-like stage (so in a sense are animal like), but when they reproduce, form spores the way true fungi do.

The most common slime mold I encounter is one I affectionately call dog vomit slime mold, but is more commonly called scrambled egg slime mold.  This slime mold really looks like someone’s dog upchucked in your flowerbed.  Watch for this slime mold (usually in the genus Fuligo) after you’ve spread a new layer of mulch on your flowerbeds.

Dog Vomit Slime Mold on Mulch in a Flowerbed

Another slime mold you may encounter is Physarum which is often found on turfgrass.  I remember seeing this slime mold in a lawn walking home from work one day.  I thought that someone had been out on their lawn spray painting some furniture and left gray paint residue on their grass.  On closer inspection however, the gray turned out to be thousands of small, spherical fruiting bodies (i.e., reproductive structures) of the slime mold.  I have also seen this slime mold crawl over and fruit on other plants such as ginseng and tomato.

Physarum Slime Mold on a Tomato Leaf
Physarum Slime Mold on a Tomato Leaf

Perhaps the most dramatic slime mold I see is the chocolate tube slime mold (Stemonitis), which often fruits on the walls of houses.  It can form HUGE masses of what appear to be clusters of miniature cattails.  One of my friends saw this slime mold and claimed it was straight out of Stranger Things (the horror television series I’ve been binge-watching of late).  There’s no accounting for taste!  Sigh.  Slime molds will ever remain cool in my book.

Chocolate Tube Slime Mold on a House Soffit
Chocolate Tube Slime Mold on a House Soffit

For addition information on the PDDC and its activities and the cool disease samples I get to see, check out the PDDC website, follow the clinic on Twitter or Facebook (@UWPDDC) or contact the clinic at

June: June is Bustin’ Out All Over (With Plant Health Problems)

SunWith the arrival of June, the plant disease floodgates have burst and the PDDC has been deluged with plant specimens with a wide range of plant health issues.

Probably the most striking samples showing up at the clinic right now are those that are showing symptoms of winter/cold injury.  I continue see samples from trees and shrubs where the entire plant has died over the winter with no signs of life this spring.  In particular, I have seen (and have also heard about) burning bushes that did not survive the winter.  While my clients have been distraught over this death and destruction, I have been trying to offer a silver lining (shocking, I know for Dr. Death!).  I point out that burning bush is classified as invasive plant in Wisconsin and that the death of these plants provides an opportunity to replace the shrubs with something more exciting and environmentally friendly.

When entire trees and shrubs have not died over the winter, in many cases parts of them have.  In particular, I have seen boxwoods, arborvitaes and other evergreens where branch tips have died and bleached over the winter.  This is a fairly classic symptom of winter burn/winter injury that I see every year.  This symptom might be a consequence of direct cold injury to tissue (a distinct possibility due to the extreme cold temperatures that we experienced in late January) or due to loss of moisture (from lack of sufficient water in the fall and/or exposure to dehydrating winds over the winter).  Slightly more subtle winter injury comes in the form of deciduous trees that leaf out, typically producing small leaves that then collapse and dry up.  I have been seeing this a lot on fruit trees (e.g., apples, pears, plums, cherries).  In these situations, there was likely sufficient internally stored water in the trees to initiate bud break and start leaf expansion, but also enough cold injury to the vascular (i.e., water-conducting) tissue to limit subsequent water movement into the leaves to further expand them and keep them alive.  I expect to see this collapse of leaves continue throughout the summer.  Many folks see this dieback on apples and pears and assume the problem is fire blight, but I have yet to diagnose this disease so far this year (and I’ve been trying very hard to find it).  Management for this type of dieback is simple pruning.  I suggest pruning four to six inches below obviously dead areas on branches.  The best time to prune for most trees and shrubs tends to be in the winter, but if you need to prune during the summer, be sure to prune only when it is dry.  Even though I don’t believe the dieback that I have described above is disease related, just to be safe, I still recommend that you disinfest pruning tools between cuts by dipping them in 10% bleach or (even better) 70% alcohol (e.g., rubbing alcohol).  Spray disinfectants can be used as a source of alcohol as well.  I do not recommend using pruning paints except if you are forced to prune an oak tree during the growing season (to prevent transmission of the oak wilt fungus via sap beetles).  You can dispose of branches by taking them to your municipal yard waste recycling center (if you have one available), burning them (where allowed by local ordinance) or burying them.

Another variation on leafing out that I have seen this year that I am attributing to cold injury is where trees leaf out completely, but have smaller than normal leaf size.  In these situation, I am suspicious that there is minor damage to the vascular tissue the trees, but not sufficient to totally prevent water from reaching branch tips.  I have a redbud tree in front of my home showing this symptomology.  The tree typically has large, lush foliage that provides a privacy screen for my front door.  This year the leaves are quite small and I can easily see through the thin canopy.  This tree also had much reduced flowering this year compared to previous years.  I have also seen smaller leaves on a lot of maples (particularly silver maples) this year, but these trees have shown excessive seed production compared to other years.  I call this overflowering/seeding phenomenon the “Oh my gosh, I’m going to die, I’d better reproduce” syndrome.  Over-flowering/seeding is typical for stressed trees.  However, because this year’s flower buds were formed last summer, the underlying stress that led to over-flowering/seeding was not our winter weather, but other stresses that occurred during the growing season of 2018.  For trees with smaller leaves, I suggest making sure they are adequately watered.  I typically recommend that trees and shrubs receive approximately one inch of water per week.  If Mother Nature doesn’t cooperate, then I suggest setting up a soaker or drip hose at the drip line of the tree (i.e., the edge of where the branches extend) and applying whatever additional water is needed.  Affected trees should continue to receive water until they start to turn their normal fall color in the autumn.

And if all of the environmental stress-related issues aren’t enough, I’ve been getting inquiries about (and finally receiving samples of) what appears to be anthracnose on maples.  I expect to eventually see this disease on other trees as well.  Typical symptoms of the disease are brown to black, necrotic (i.e., dead), blotchy areas on leaves.  Our wet spring weather has been very favorable for this disease to develop.  Luckily, anthracnose tends to be a very cosmetic disease and typically causes little long-term damage to trees.  Cultivating the ability to ignore anthracnose symptoms and doing good fall clean-up of the leaves and removing them from your property typically are the best ways to handle this disease.

Phew, what a June!  Now, onward to July.  I have a feeling the deluge is going to continue!

For addition information on the PDDC and its activities, check out the PDDC website, follow the clinic on Twitter or Facebook (@UWPDDC) or contact the clinic at

P.S.:  Brownie points for those of you who recognize the origin of the title of this month’s article.