All posts by ddlang

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!

Vegetable Varieties for Containers

Growing plants in containers (referred to as container gardening) is an easy way to grow and maintain vegetables.  Vegetables grown in containers can easily fit on a window sill, balcony, deck, door step or any other place where space is limited but where environmental conditions are suitable for vegetable production.

The list below contains recommendations on varieties of popular vegetables that are well-suited for growing in containers.

Click the vegetable names to expand the panel and view the variety info. The panel expands downward.

To close the expanded panel, click the vegetable name below it.

In addition to the vegetables listed above, most varieties of herbs and salad greens are perfectly suitable for containers.

For more information on vegetable varieties for containers and container gardening in general:  See Extension Bulletin A3382, Container Gardening, or contact your county Extension agent.

Lily Leaf Beetle – Pest Alert

The lily leaf beetle (LLB), Lilioceris lilii, also known as the red or scarlet lily beetle, is an invasive insect of Eurasian origin.  This insect was first reported in North America in eastern Canada during World War II and was most likely introduced in shipments of plant materials from Europe.  LLB spread to New England in the 1990’s and has been moving westward since that time.  LLB made its first appearance in Wisconsin in 2014 and as of the end of 2019 has been found in 12 counties including Dane, Door, Langlade, Lincoln, Marathon, Oneida, Pierce, Portage, Price, Shawano, Taylor and Wood Counties.

Severe feeding damage from lily leaf beetles on a lily plant (left) and an adult lily leaf beetle (right). Photos courtesy of Leslie J. Mehrhoff, University of Connecticut,
Severe feeding damage from lily leaf beetles on a lily plant (left) and an adult lily leaf beetle (right). Photos courtesy of Leslie J. Mehrhoff, University of Connecticut,

LLB can cause significant damage to true lilies (Lilium spp.), including both native and cultivated types, as well as fritllaries (Fritillaria spp.).  LLB can also cause damage, but to a lesser extent, to lily of the valley (Convallaria majalis) and Solomon’s seal (Polygonatum spp.).  LLB does not cause damage to daylilies (Hemerocallis spp.), canna lilies (Canna spp.) or calla lilies (Calla palustris).

Appearance:  LLB adults are bright red and approximately 1/4 inch long, with black legs, head, antennae, and undersides.  When disturbed, LLBs tumble from plants and land upside down on the ground, where they play dead.  Their dark-colored undersides make them hard to spot.  To potentially deter predators, adults squeak if squeezed.

LLB larvae have plump, squishy bodies and are slug-like in appearance.  They tend to be orange or yellowish in color with black heads.  At maturity, larvae can be almost 1/2 inch long.  As a defensive tactic, larvae typically camouflage themselves with their own excrement and can resemble slimy greenish-brown slugs or a mobile pile of animal droppings.

LLB eggs are tiny (less than 1/10 inch long) and reddish in color.  Female LLBs lay the eggs (typically in a batch of a dozen or less) on the underside of leaves in a row parallel to a vein.

Symptoms and Effects:  Both LLB adults and larvae chew irregular holes and notches in lily leaves, stems, and developing buds.  Larvae are the more damaging stage of the insect.  When feeding damage is severe, LLBs can completely defoliate plants and destroy flowers.

Life Cycle:  There is a single generation of LLBs each year, but adults can live for several years.  LLBs overwinter as adults in sheltered places, soil, and plant debris in gardens and wooded areas.

These overwintering sites are not necessarily near lilies or other host plants.  Early in the spring, LLB adults emerge to feed, mate and lay eggs.  Because they are strong fliers, LLBs can disperse over long distances to locate host plants.  Eventually, females lay between 250 and 450 eggs.  Eggs hatch within four to eight days.  Emerging larvae feed for two to three weeks during the spring and early summer.  Engorged larvae eventually drop to the soil to pupate (i.e., transform into adults).  Pupae are bright orange and encased in a white cocoon with black spots.  Adults emerge 16 to 22 days later and feed throughout the rest of the growing season and into the fall.

Lily leaf beetle eggs (left) and a lily leaf beetle larva camouflaged with its own feces. Photos courtesy of Gail Hampshire (left) and Kenneth R. Law, USDA APHIS PPQ,
Lily leaf beetle eggs (left) and a lily leaf beetle larva camouflaged with its own feces. Photos courtesy of Gail Hampshire (left) and Kenneth R. Law, USDA APHIS PPQ,

Control:  If you have a small number of lilies, consider hand-picking and crushing adults and larvae or knocking them into a container of soapy water.  Also, crush eggs by hand if you see them.  Repeat this process regularly throughout the growing season.  If LLB becomes a chronic and severe problem, consider replacing your lilies with plants that are not attacked by the insect.

You can also use conventional and organic insecticides to help protect plants from the LLB.  Conventional insecticides containing carbaryl, cyfluthrin, cypermethrin, deltamethrin, lambda-cyhalothrin, permethrin, and zeta-cypermethrin control a broad range of pests, including LLB.  Organic insecticides containing azadirachtin, pyrethrins, or spinosad can also be used, as well as horticultural oils and insecticidal soap.  Make sure that the product that you select is labelled for use on landscape flowers.  Be aware that conventional and organic insecticides can pose risks to pollinators, so follow all directions on the label to minimize risks to bees and other pollinators.

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

Poison Ivy

What is poison ivy?   Poison Ivy (Toxicodendron radicans), is a perennial woody plant that grows as either a low shrub or a climbing vine.  Poison ivy is native to North America and is common in Wisconsin, growing in pastures, roadside ditches, fence rows, wooded forests, beaches and parks.  CONTACT WITH POISON IVY CAN LEAD TO SKIN RASHES, SKIN BLISTERS OR OTHER ALLERGIC REACTIONS.

Young poison ivy leaves (left) can have smooth margins, while mature poison ivy leaves (right) often have serrated or lobed leaf margins.
Young poison ivy leaves (left) can have smooth margins, while mature poison ivy leaves (right) often have serrated or lobed leaf margins.

What does poison ivy look like?  Poison ivy has alternate leaves, and each leaf has three leaflets.  The middle leaflet has a short stalk and is larger than the two other leaflets.  Leaflets are variable in shape but are typically oval with pointed tips.  The margins (edges) of leaflets can be smooth, serrated (i.e., resemble a saw blade) or lobed.  In late summer, poison ivy produces clusters of whitish berries.  These berries are eaten by birds, and the seeds inside are spread through bird droppings.

Other common plants can be confused with poison ivy.  These plants and the characteristics that distinguish them from poison ivy are outlined in the table below.

Look Alike Species How to Distinguish from Poison Ivy
Boxelder (seedlings) Opposite branching; 3+ leaflets per leaf
Ash (seedlings) Opposite branching; 3+ leaflets per leaf
Virginia creeper 5 leaflets per leaf (newly emerged leaves may have fewer)
Wild sarsaparilla 3 leaves at the top of stem; each leaf with 3-7 leaflets
Raspberry/blackberry 3+ leaflets per leaf; spiny stems
Clematis/virgin’s bower Opposite branching; side leaflets with obvious stalks
Hog peanut Leaves without teeth or lobes; weak stemmed
Jack-in-the pulpit Leaves with 3 leaflets; leaflets all stalkless
Wild strawberry Leaves with 3 leaflets; leaflets all stalkless

Why is poison ivy a problem?  All parts of poison ivy plants (including leaves, stems and roots) produce a resinous oil called urushiol that can cause severe itching, inflammation and blistering.  The oil can be spread by anything that comes in contact with poison ivy including garden tools, clothing, boots or pets.  Urushiol is present not only in living poison ivy plants but can remain active in dead plants for up to two years.  Skin sensitivity to poison ivy can vary from person to person.  If you burn poison ivy, the vaporized oil that is released can cause severe systemic allergic reactions if inhaled.

How do I avoid or reduce problems associated with poison ivy?  LEARN HOW TO IDENTIFY POISON IVY AND AVOID CONTACT WITH THE PLANT WHENEVER POSSIBLE.  If you will be working in an area where poison ivy is likely to grow, wear long pants with boots, a long-sleeved shirt and gloves to help reduce exposure.  In addition, you may want to use a poison ivy preventative lotion that can provide additional protection.  After working in a poison ivy-infested area, carefully remove and wash your clothing with hot, soapy water.  Use sanitary wipes to clean gardening tools or other items that may have come in contact with poison ivy plants.

If you believe you have come in contact with poison ivy, immediately wash any potentially exposed skin with regular soap under cold, running water.  Avoid using complexion soaps as these types of soaps tend to spread urushiol on the skin and can make the problem worse.  Poison ivy cleansing products (e.g., Tecnu skin cleanser) can help remove urushiol from skin if used within four to eight hours of exposure.  Magnesium sulfate containing skin products (e.g., Dr. West’s Poison Ivy Wash) can also help to detoxify urushiol and ease itching.  If you believe you have inhaled urushiol vapor, IMMEDIATELY contact a physician for advice.

If you believe your pet has been exposed to poison ivy, immediately bathe them using a pet-safe shampoo to remove urushiol residues.

How can I control poison ivy?

Herbicides containing the active ingredients glyphosate and triclopyr are effective in controlling poison ivy if used according to the label directions.  Use foliar sprays to spot treat shrub-form poison ivy plants or vining poison ivy growing on inert objects (e.g., fences), but only apply treatments after leaves are fully expanded and plants are actively growing (i.e., summer and early fall).  DO NOT apply foliar sprays to poison ivy growing on trees and shrubs, as the herbicide may damage these supporting plants.  Alternatively, at any time of the year, cut poison ivy stems near the soil surface and paint the stumps with a more concentrated herbicide formulation.  Be sure to read the instructions on the label of whichever herbicide you select for details on how to use the product in the safest and most effective manner possible.

When removing poison ivy plants, collect all of the above ground plant parts.  Also, be sure to rake the ground to collect any leftover poison ivy berries, leaves, stems and roots.  DO NOT burn or compost any of these materials.  Instead, bag and dispose of them in your municipal garbage.  After you remove plants and debris, spread four to six inches of clean wood chip mulch over the site to prevent possible exposures to urushiol that may remain on or in the soil.

For more information on poison ivy:  Contact your county Extension agent.

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:  April 24, 2020

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 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!!

Using Wood Ash in the Home Garden

Using wood ash in home gardens can increase soil fertility and raise soil pH.
Using wood ash in home gardens can increase soil fertility and raise soil pH.

Home gardeners often ask if wood ash can be used as a fertilizer in vegetable gardens and flowerbeds, around landscape trees and shrubs, and on lawns.  Wood ash can be a valuable source of certain nutrients and can also be used to modify soil pH.  However, it needs to come from an appropriate source and its use should be based on recommendations from soil fertility testing provided by a professional lab such as the UW Soil and Forage Lab (

What are the potential benefits of using wood ash?  Wood ash contains nutrients that can be beneficial for plant growth.  Calcium is the plant nutrient most commonly found in wood ash and may comprise 20% or more of its content.  Potassium (also called potash) is another common component of wood ash, occurring at concentrations of up to 5%.  Magnesium, phosphorus and sulfur are also typically found in wood ash at concentrations of up to 2%.  Finally, wood ash can contain trace amounts of iron, aluminum, manganese, zinc, boron and other nutrients needed by plants.

In addition to its nutrient content, wood ash can help in neutralizing soil acidity.  When wood is burned, high amounts of carbonates are produced.  Carbonates react with and neutralize acid in the soil, causing the soil pH to increase.  The levels of carbonates present in wood ash (and thus its acid-neutralizing properties) will vary depending on the type of wood burned and how the wood was burned.  In general, wood ash has about 50% less acid-neutralizing capacity than commercially available acid neutralizers such as pelletized lime or aglime.  Approximately four cups of wood ash can be substituted for one pound of aglime.

What are potential downsides of using wood ash?  On occasion, even the best wood ash may contain heavy metals such as cadmium and lead, but the levels of these metals can be minimized by carefully selecting the wood that is burned to produce the ash (see below for details).  In addition, the increase in soil pH associated with using wood ash tends to decrease the likelihood of plants taking up heavy metals.  If wood ash is used at recommended rates, concentrations of heavy metals should be low enough not to pose a threat to plants, or to animals or humans who eat plants grown in treated areas.  If you are concerned about heavy metals in your wood ash, consider testing for these elements prior to use.  The UW Soil and Forage Lab (mentioned above) does not test for heavy metals at this time; however staff can help answer questions about heavy metal contaminants.

Because using wood ash tends to increase soil pH, applying it where acid-loving plants (e.g., blueberries, azaleas/rhododendrons, birch trees, red maples, pin oaks) are growing will likely not be beneficial.  Using wood ash may actually be detrimental and contribute to problems with chlorosis [see University of Wisconsin Gardens Facts XHT1002 (Chlorosis),, for details].  In addition, many vegetables and other landscape plants prefer slightly acidic soils, so wood ash should be used judiciously when growing these plants.  Finally, in some cases, increased pH due to use of wood ash may promote certain diseases.  As an example, potatoes grown at higher pH tend to be more prone to potato scab [see University of Wisconsin Gardens Facts XHT1117 (Potato Scab), available at, for details].

In order to use wood ash in the best manner possible, always make applications to garden soils based on the plants that are to be grown and based on recommendations from a certified soil testing lab.

What type of wood ash should I use?  If you decide that using wood ash is appropriate for your gardening needs, only use wood ash that has come from trees grown in natural areas.  DO NOT use wood ash produced from trees grown near industrial sites, in soils that may be contaminated with toxins or heavy metals, or if you have no knowledge of the origin of the wood that you are burning.  Also, DO NOT use ash produced by burning treated wood, waste oil, plastics or garbage.

How do I apply wood ash?  Prior to use, sift wood ash to remove large charcoal pieces, as well as any active embers.  Apply only the amount of wood ash recommended based on a soil fertility test and based on the nutrient needs of the plants that you intend to grow in the treated area.  Applying excessive amounts can lead to nutrient toxicity and/or nutrient deficiency issues in plants.  Applications of wood ash are generally limited to a maximum of 15 to 20 pounds (approximately a five gallon pail) per 1000 sq. ft., per year.  Spread wood ash evenly over the area to be treated (e.g., vegetable garden bed, established perennial flowerbed, lawn or other landscape area) during the winter.  Because wood ash particles are very fine and can easily be blown by the wind, avoid making applications when it is windy.  Whenever possible, apply wood ash to moist soil.  Where feasible (e.g., in a vegetable garden), work the ash into the soil using a rototiller, spade or rake in early spring.

Due to its alkalinity, wood ash can potentially pose a human health risk.  Therefore, when working with it, be sure to wear appropriate protective clothing (e.g., long pants, long sleeve shirt, gloves, eye goggles, dust mask) to limit exposures that might lead to skin, eye or respiratory irritation.

For more information on using wood ash in the home garden, as well as soil fertility testing:  Contact your county Extension agent.

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