Category Archives: Monthly Column

November 2023: Plant Pathology Playlist

Music IconYears ago, I participated (with three other Extension colleagues) in a weekly Saturday morning horticulture Q&A radio show in Milwaukee, WI.  One of the fun aspects of the show (other than being able to wax poetic about plant diseases on the air) was that I was allowed to select songs, snippets of which would be played as the show went in and came out of commercials.  Each month, I’d pick a theme (“celestial bodies” anyone?) and select seven or eight songs that both fit the theme and my musical tastes.  For this month’s web article, I continue this tradition by sharing some of my favorite plant-titled songs (with links to recordings) and providing commentary on diseases that might affect the referenced plants.

A Morning with the Roses

It’s hard to avoid “rose” songs in music.  They seem to be everywhere just like roses shrubs are everywhere in garden settings.  This “rose” song by Richard Dworsky is my favorite.  It’s an instrumental piece and one of the first New Age songs I ever encountered.

The most common disease of roses is black spot.  This disease affects rose leaves and canes, with classic symptoms being feathery-edged black leaf spots.  On susceptible rose varieties, the disease can be so severe that shrubs will defoliate.  For the causal rose grower, I suggest dealing with the disease by simply only growing black spot-resistant varieties.  Routine thinning of shrubs to promote better airflow and create a drier environment is another useful management strategy.  For hardcore rose growers, use of preventative fungicide treatments on particularly susceptible varieties may be needed to keep the disease under control.

Honeysuckle Rose

This Fats Waller/Andy Razaf song is part of the Great American Songbook, a compilation of “. . . the most important and influential popular songs and jazz standards from the early 20th Century. . .” (per the Great American Songbook Foundation).  The definitive version of this song for me (probably because it’s the first version I heard as a kid) is by Lena Horne (I could listen to her sing the telephone book).  I also really love versions by contemporary jazz singer Jane Monheit and the amazing and tragic Eva Cassidy (I suggest listening to her cover of another plant-themed song, Sting’s “Fields of Gold”, as well).

Although this is another “rose” song, we’re going to concentrate, disease-wise, on the honeysuckle part of the title.  Every year, I enjoy watching my parents’ vining honeysuckle develop powdery mildew, the most common disease that I see on this plant.  By the end of the summer, the plant’s leaves are powdery and white, but as with most plants, the disease is primarily a cosmetic issue and causes little actual damage.  My parents’ honeysuckle blooms profusely and attracts hummingbirds (which my parents can watch for hours on end).  The twisted vines also provide shelter for English sparrows (much to my parents’ chagrin).  Management of powdery mildews on most plants, in my mind, involves developing the ability to ignore the diseases, given their cosmetic nature.  On more susceptible plant species (e.g., phlox and beebalms), growing resistant varieties and thinning plants to increase airflow and reduce humidity (the driving environmental factor for powdery mildew development) can help manage these diseases.

Willow Song

I’m not a huge opera fan, but this aria from “The Ballad of Baby Doe” by Douglas Moore and sung by the marvelous Beverly Sills really mesmerized me when I stumbled across it years ago.  Baby Doe was one of Sills’ signature roles (although I will always remember her best for her guest appearance on “The Muppet Show”).  If opera isn’t your thing, then consider as an alternate willow song, Gordon Lightfoot’s “Pussywillows, Cat-Tails”.

Probably the most common diseases that I see on willows (usually weeping willows) are canker diseases.  There are a wide range of canker fungi that can infect and girdle willow branches, leading to branch dieback.  Often weeping willows grow rapidly and outgrow significant damage from canker diseases.  However, if management is needed, I suggest pruning four to six inches below obviously dead areas on branches.  Always be sure to prune only when it is dry, and be sure to disinfest pruning tools between cuts by dipping them in bleach diluted to a final concentration of 0.5% sodium hypochlorite (the active ingredient) 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 decide to 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 bleach use.  You can dispose of branches by burning (where allowed) or burying them.


This song was written by Pat Alger, Ralph Murphy, and Ralph Murthy, and I found it on country singer Kathy Mattea’s “Lonesome Standard Time” album.  Mattea is one of my favorite country artists from the 1980s and 1990s.  I challenge you to listen to her recording of “Where Have You Been?” and not a shed a tear.

If you talk about seeds, then from a disease standpoint, you need to discuss damping-off.  This disease has both a seed decay phase (where seeds rot before germinating) and a seedling phase (where seedlings collapse and die just after emergence).  Damping-off can be caused by several fungi and water molds, with the water mold Pythium probably the most common organism involved.  To prevent damping-off, use pasteurized potting mixes/soil, decontaminate pots, germinate seeds at warm temperatures, and keep soil moisture on the dry side as seeds germinate and seedlings emerge.

Dusty Miller

I doubt that this traditional bluegrass song is about dusty miller plants, but I had to include the song in my list because one version of it was recorded by Alison Krauss.  “Dusty Miller” showcases Krauss’ prowess with a fiddle; she’s world-class.  I encourage you to explore her other music starting with her big hit (with her band Union Station), a cover of the Paul Overstreet/Don Schlitz song “When You Say Nothing at All”.  Her voice is ethereal and angelic.  There’s a reason she’s won 26 Grammy Awards (including two album of the year awards).

I rarely see dusty miller in the clinic, but when I do, the problem is typically a root rot of some kind.  Root rots tend to be caused by the same organisms that cause damping-off (discussed above).  At least some level of root rot pathogens can be found in most garden soils, so management of these diseases tends to involve moderating soil moisture.  Root rot organisms tend to be more active in wet soils, so making sure not to over-water and over-mulch can help prevent root rots from being an issue.  Most established plants require roughly one inch of water per week during the growing season.  Mulch usage varies depending on soil type.  For heavy soils (e.g., clay), use one to two inches of a high quality mulch (I like shredded oak bark mulch and red cedar mulch).  On light soils (e.g., sand), use three to four inches of mulch.

The Wind that Shakes the Barley

This adaptation (by Robert Dwyer Joyce) of a traditional Celtic song is on the album of the same name by Canadian national treasure Loreena McKennitt.  Possessed of a haunting soprano voice and known for her harp accompaniments, I have enjoyed McKennitt’s work ever since hearing her perform “Penelope’s Song” on NPR in 2007.

Barley is not a plant that home gardeners typically grow, but as part of my diagnostic responsibilities, I often receive agricultural crop samples such as barley and wheat.  A common disease of these grain crops is barley yellow dwarf, a viral disease caused by Barley yellow dwarf virus (BYDV)This virus is aphid transmitted.  The virus causes yellowing of barley and wheat leaves, particularly the flag leaf (the leaf just below the developing grain head).  This leaf is incredibly important for producing the nutrients needed for proper filling of grain heads.  Thus, the disruption and yellowing caused by BYDV can lead to substantial yield losses.  Management of the disease often entails modifying planting times.  For fall-sown wheat varieties, late planting after aphid populations have declined for the growing season is recommended to limit infections.  For spring sown wheat varieties, early planting is recommended.  This allows substantial time for plants to grow before aphids arrive and infections can occur.  Late infections have a lesser impact on yield.

Moments in the Woods

This song is from “Into the Woods”, perhaps my favorite Stephen Sondheim musical (I’m a huge Sondheim fan in general).  The added bonus of the version of the song linked above is that it’s sung by one of my favorite contemporary singers, Sara Bareilles, who starred in the 2022 Broadway revival of the show.  If you like Bareilles’ voice, I suggest checking out “Gravity” (and other songs) from her “Little Voice” album.

Thinking of plant diseases that I might encounter during a “moment in the woods”, black knot immediately comes to mind.  This is the disease that I affectionately call poop-on-a-stick, because the causal fungus induces formation of feces-like galls on branches of cherry and plum trees.  At this time of the year, even with an absence of leaves, I can ID these trees in wooded settings just based on black knot symptoms.  Pruning out infected branches on trees in landscape settings can help manage the disease.  However, certain individual cherry or plum trees can be so susceptible to black knot (and have so may galls), that I recommend “basal pruning” (i.e., removal) and replacement.

Prairie Trains

The final song on my playlist is a shoutout to my friend and colleague, Extension Dane County’s Lisa Johnson.  I’ve know Lisa since high school and watched her develop as a music composer and performer over the years.  This song, from her “The Season” album, is an ode to the many trips that she and I made in our undergraduate days to a prairie remnant (now long gone) sandwiched between the stretch of Hwy. 26 and the adjacent railroad track that ran between Fort Atkinson and Jefferson, WI.  I have many fond memories of those expeditions and the prairie plants that we stumbled upon.

One of the prairie plants that Lisa mentions in her song is big blue stem, and back in 2022 I received photos of this grass suffering from culm smut.  This is a fungal disease where spores of the causal fungus infect the plant’s flowers causing the formation of a fleshy gall.  This gall eventually degrades into a powdery mass of blackish fungal spores that are blown to other big blue stem plants where they initiate additional infections.  The pathogen not only infects the seed heads, but it eventually systemically colonizes the rest of the plant.  Infected plants become stunted, and can continue to produce flower galls and fungal sporulation for a time.  Eventually the plants decline to the point where they no longer bloom and eventually die out.  Interestingly, there is speculation that this disease plays a role in the normal process of plant succession in prairies.  That said, if you love your big blue stem, removing infected plants as soon as you see them is important to prevent spread of the pathogen to other big blue stem in your planting.

I hope you’ve enjoyed this month’s musical plant disease adventure.  If you have your own favorite plant-titled or plant-themed songs, I’d love to hear about them.  Feel free to contact me at or (608) 262-2863 with your suggestions.  Happy Thanksgiving everyone!

October 2023: Poison Apples for the Halloween Season

Poison Apple IconOctober is National Apple Month and also host to my favorite holiday of the year, Halloween.  (Does the latter really surprise you given my my moniker, Dr. Death?)  So, in honor of both events, I decided that for this month’s web article, I’d talk a bit about diseases that can adversely affect apple fruits and make them less than optimal for use in making pies and seasonal treats like caramel apples.  The pathogens involved in these diseases do not produce compounds toxic to humans, so technically the infected apples are not poison per se.  However, the damage these pathogens cause often makes apple fruits unusable.

Apple Scab

Apple Scab
Apple scab. (Photo courtesy of UW-Madison PDDC)

This disease is the most common that I see causing issues on apple fruits.  The causal fungus (Venturia inaequalis) commonly infects apples leaves, often leading to defoliation in susceptible apple varieties.  Once leaf infections occur, the fungus can eventually infect fruits leading to symptoms that range from blackish surface blemishes to fruit growth distortions (if infections occur early in fruit development).  Of the apple fruit diseases, apple scab is the most cosmetic in my mind.  Fruits are often usable if peeled.  The downside to the disease is that consumers expect perfect, perfect fruit and are not accepting of fruits with apple scab lesions.  Also, scab-blemished fruits typically do not store as well as unblemished fruits.  For this reason, commercial apple growers spend a lot of time, effort, and money spraying apple trees with fungicides to prevent this disease.

Gymnosporangium Rusts

Gymnosporangium Rust
Gymnosporangium rust. (Photo courtesy of Mary Ann Hansen, Virginia Polytechnic Institute and State University,

The fungi involved in these diseases (which include cedar-apple rust, cedar-hawthorn rust, and cedar-quince rust) must infect both woody rosaceous plants (most commonly, apples and hawthorns), and junipers to complete their life cycles.  Red cedar (Juniperus virginiana) is a particularly susceptible juniper host.  I most commonly see Gymnosporangium rust symptoms on leaves, where bright yellow to orange spots (about the size of a dime or nickel) form.  But, fruit infections on hawthorn (where you will see spiny, salmon-colored fruit) are also very common.  I have seen fewer apple fruit infections, but they do occur, and the lesions tend to have a spiny appearance.  Infected fruits are often frightening and fascinating at the same time.

Fire Blight

Fire Blight
Fire blight. (Photo courtesy of University of Georgia Plant Pathology, University of Georgia,

2023 was a banner year for fire blight in my estimation.  I diagnosed more fire blight this year than any other year in my 25 years at the PDDC.  The bacterium that causes the disease (Erwinia amylovora) commonly gains entry into trees through flowers.  Honeybees pick up the bacterium as they feed on oozing sap from infected branches.  The bees then drop the pathogen off as they pollinate.  Erwinia amylovora can rapidly colonize branches leading to significant dieback, and even tree death.  Interestingly this year, I received samples of apple fruits (not full developed, but well on their way) with blotchy, rotted areas that were quite sticky.  These areas tested positive for Erwinia amylovora.  This was a first for me.  I had never seen fireblight on apple fruits before.

Black Rot

Black Rot
Black rot. (Photo courtesy of University of Georgia Plant Pathology, University of Georgia,

I don’t see this fungal fruit disease often, but I commonly see the pathogen involved (a Sphaeropsis species) cause cankers and dieback on apple branches.  Often, when clients think they have a fire blight problem, the real problem is the canker phase of black rot.  The black rot pathogen also causes frogeye leaf spot on apple leaves.  Interestingly, the pathogen does not sporulate well on leaves, but it sporulates profusely on branches and fruits.  Fruit symptoms are often large, roughly circular, dark areas of softened tissue.  If you look closely within the decayed tissue, you may notice a series of concentric rings showing how the fungus has colonized the fruit.  You may also notice tiny, pimple-like structures embedded in the rotten tissue.  These are the fruiting bodies (i.e., reproductive structures) of the pathogen, filled with relatively large, oblong, brown spores.

Bitter Rot

Bitter Pit
Bitter pit. (Photo courtesy of University of Georgia Plant Pathology, University of Georgia,

Bitter rot is caused by fungi in the genus Colletotrichum (typically Colletotrichum gloeosporioides or Colletotrichum acutatum).  This genus contains many fungi that cause anthracnose leaf diseases.  On apple, the bitter rot pathogens are primarily fruit pathogens (leaf symptoms are only rarely observed), leading to symptoms that look somewhat similar to those observed with black rot.  Bitter rot lesions are often large, roughly circular, and somewhat tannish to brown in color.  Concentric rings are typically quite obvious with the diseased tissue, and pimple-like fruiting bodies abound.  Individual spores of the bitter rot pathogens are smaller than those of the black rot pathogen, oblong and colorless.  En masse on the surfaces of fruits however, these spores can have a pink, salmon, or orange color.

Management of apple fruit diseases varies from disease to disease, but in general involves:

Cleaning up leaf debris and rotted fruits

Removal of these materials eliminates overwintering sites for many of the disease-causng organisms discussed above.  Leaf debris removal is particularly important for management of apple scab, but not particularly important for the Gymnosporangium rusts (because the spores that infect apple trees come from junipers).  Dispose of leaf and fruit debris by burning (where allowed), burying, or hot composting.

Pruning routinely

Pruning removes infected branches that can serve as a source of pathogens (e.g, those that cause fire blight, black rot, and bitter rot).  In addition, routine pruning of a healthy tree opens the canopy and promotes drier conditions that are less favorable for infections to occur.  For branches with probable fungal infections, pruning approximately four to six below obviously dead tissue will likely be adequate to remove pathogens.  If fire blight is of concern however, more aggressive pruning, 12 inches below obviously diseased branch tissue, is needed.  Be sure to prune only when it is dry, and be sure to disinfest your pruning tools between cuts by dipping them in bleach diluted to a final concentation of 0.5% sodium hypochlorite (the active ingredient) 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 and oil tools after you are done pruning to prevent rusting that can be caused by bleach use.  Dispose of branches by burning (where allowed) or burying them.

Eliminating alternate hosts

This technique is most important for managing Gymnospoangium rusts.  Removing junipers near apple trees will help break the life cycle of Gymnosporangium fungi and substantially reduce or even elminate these rust diseases.  Unfortunately removing junipers may not be practical.  I have seen some recommendations for commercial apple producers that advise removing junipers within a two mile radius of apple producing areas!  This would not be possible in a home gardening setting.  For apple scab, removing susceptible crabapple trees may be helpful in controling scab on fruit bearing trees by eliminating a potential source of fungal spores.

Planting resistant varieties

When buying new apple trees, I always recommend that home fruit growers select varieties that have resistance to both apple scab and fire blight.  These two diseases are typically the most problematic for home gardeners.

Using fungicide treatments

I recommend this option only as a last resort and only if you have had your apple disease problems formally diagnosed.  By knowing which apple diseases you commonly encounter, you can develop a fungicide treatment regime tailored to your specific situation.

Now that I’ve spent the afternoon writing about apple fruit diseases, my tummy is rumbling.  It’s time for me to track down a caramel apple.  As always, if you have questions about plant diseases, don’t hesitate to contact me at or (608) 262-2863.  Enjoy the last colorful days of autumn, everyone!

September 2023: Plant Disease Management and Organic Gardening

Organic Gardening Icon - Green Bag with Gardening Implements and SeedsSeptember is National Organic Month, so I thought I’d use this month’s PDDC web article to explore techniques for plant disease management that fall within the philosophy of organic gardening.  This philosophy tends to steer gardeners away from the use of chemicals for plant disease control.  There are many disease management techniques that are appropriate for organic gardening, and quite frankly, when I am making control recommendations for virtually any client, the primary techniques that I recommend are organic in spirit.  These include:

Practicing good garden clean up

Disease-causing organisms often survive in the remains of infected plants.  Removing and properly disposing of this debris can help reduce pathogen populations in a garden or landscape.  Whether you do this clean up in the fall after plants have gone dormant for the year or in the spring before plants begin to emerge for the new growing season is up to you.  There are pros and cons to either choice.  Disposal methods for this debris include burning (not the most environmentally friendly option), burying (a somewhat laborious task), or hot composting (probably the best technique if done properly).

Using resistant plant varieties

Individuals of a particular plant species can be highly variable in terms how they react to disease-causing organisms.  Plant enthusiasts have exploited this variability by watching for plants that develop less severe symptoms and interbreeding these healthier individuals to develop disease resistant plant varieties.  I often recommend that home gardeners plant apple trees that have been bred for resistance to apple scab and fire blight, or rose shrubs that have been bred for resistance to black spot.  Monarda, phlox, and cucumber varieties that are resistant to powdery mildew can be useful in home gardens as well.  One downside to using resistant varieties, is that these plants may not have other horticultural characteristics (e.g., flower color, size, scent, flavor) that gardeners are looking for.

Buying healthy plants and seeds

You can easily introduce disease-causing organisms into a garden via infected (or otherwise contaminated) plant materials.  Carefully inspect new plants for evidence of disease issues (e.g., leaf spotting, sunken areas on branches or trunks, fuzzy growth on upper or lower leaf surfaces, etc.), and avoid buying problematic plants.  Seeds can also be a source of disease-causing organisms but can be much more difficult to assess, as they may not exhibit obvious symptoms.  Try to purchase seeds from a reputable grower/company (although even the best of growers can occasionally have disease issues).  If you have a suspect batch of seed (particularly vegetable seed), consider using hot water treatments to help eliminate disease-causing organisms.  These treatments can be particularly effective for controlling seed-borne bacteria.

Planting trees and shrubs (and plants in general) in the right environment

Plants that are under environmental stresses tend to be more prone to disease issues.  Before purchasing plants, make sure they are well adapted to the light, moisture, and fertility conditions at your location.  Put the right plant in the right place.  Pagoda dogwood is a tree that is often sited poorly in urban landscapes.  I see these trees in the middle of an open yard with grass growing up to the trunk where there is a lot of light, excessive heat, and limited water. Pagoda dogwood is an understory tree that prefers shady, cool, moist conditions.  When planted in a hot, dry, sunny environment, this tree tends to be more prone to developing golden canker, a serious and often lethal fungal disease.  Also, be cautious about planting pin oaks or red maples.  In much of Wisconsin, these trees are prone to chlorosis, because soil pH is so high that the trees have trouble taking up adequate iron (pin oak) or manganese (red maple).

Using proper plant spacing and thinning of trees and shrubs

Plant diseases tend to be more of an issue when plants are crowded.  Crowded plants trap humid air, which slows leaf drying.  Wetter leaves favor infection by disease-causing fungi and bacteria.  Planting herbaceous plants farther apart, routinely dividing large clump plants (e.g., peonies), and regularly pruning trees and thinning shrubs can help create a drier environment that is less favorable for disease development.  Regular pruning also removes diseased branches, thus eliminating a source of pathogens and reducing pathogen spread.

Watering properly

Avoid using sprinklers for watering your garden, as this method wets leaves and creates a favorable environment for fungal or bacterial infection.  Use of overhead watering can eliminate any benefits you might gain by properly spacing and pruning/thinning plants (as described above).  Instead of a sprinkler, water with a drip or soaker hose that applies water directly to the soil and keeps moisture off of leaves.

Keeping weeds under control

Weeds compete with garden and landscape plants for nutrients, leading to stress that can predispose plants to infection.  Weeds also crowd other plants, trapping moisture and creating an environment conducive to infection and disease development.  Finally, weeds can serve as reservoirs for disease-causing organisms that can eventually move from the weeds to your favorite ornamentals and vegetables.  So, weed, weed, weed.  Fewer weeds translates into a healthier garden.

The points that I’ve outlined above are just a few of the many techniques that you can employ to achieve a healthier and more aesthetically appealing garden or landscape.  If you have questions about these or any other plant-disease-management techniques, feel free to contact me at or (608) 262-2863.

Now, go forth and garden!!

August 2023: Bugging Out Over Plant Diseases

Insect IconThis growing season has largely been a bust when it comes to plant diseases.  Our dry weather has not been favorable for diseases (particularly leaf diseases) to development.  On the other hand, 2023 has been a banner year for insects, and PJ Liesch, the UW insect diagnostician, has been very busy identifying insect problems.  As it turns out, plant diseases and insects are not totally unrelated.  There are a fair number of disease-causing organisms that can be moved from plant to plant by insects, and it’s these insect-vectored pathogens, and the diseases that they cause, that I have been seeing a lot of this year.

Fire blight

In my June 2021 web article (Fired Up About Fire Blight), I bemoaned the fact that often when people see dying branches on apple, crabapple, and pear trees, they assume the dieback is due to fire blight.  Often it is not.  But, this year I have seen an uptick of fire blight cases.  I suspect that, in part, this is due to increased transmission of the fire blight bacterium (Erwinia amylovora) by honeybees.  In the absence of rains during flowering, which tends to discourage their activity, honeybees are out pollinating a wide range of plants, including apples, crabapples, and pears.  Honeybees also visit branches where they feed on oozing sap.  On trees suffering from fire blight, this sap often contains the fire blight bacterium.  Honeybees become contaminated with the pathogen and carry it to apple, crabapple, and pear flowers, where it can infect.  As I attempt to diagnose fire blight, I often check dying apple, crabapple, and pear branches to see if infections appear to have started near flower clusters.  If so, my fire blight radar goes off.

Among the numerous fire blight cases this year, I had two interesting/sad ones.  The first case (more in the interesting category) was fire blight on mountain-ash.  Although called an “ash”, this tree (the one with the clusters of bright orange fruits) is in the same plant family as apples, crabapples, and pears, and it is a known host for fire blight.  The sample that was submitted to my clinic was from a tree that had numerous dying branches, and it appeared that infections had occurred through flowers.  The second case (definitely in the sad category) involved an apple grower who had numerous dwarf trees that he had espaliered.  Many of them exhibited dieback, and all of the samples that he submitted tested positive for fire blight.  Unfortunately, my recommended pruning for fire blight (i.e., cut 12 inches below where there are obvious symptoms/dieback) functionally meant that the grower had to remove and destroy many of his trees.

Bacterial wilt of cucurbits

I have had a number of vine crop (e.g., cucumber, melon) samples arrive at the clinic with wilting symptoms.  Fungal diseases like Verticillium wilt and Fusarium wilt, as well as water mold diseases like Phytophthora root and crown rot, can cause wilting symptoms.  However, for many of the cucurbit samples in 2023, not only was there wilting, but there was also significant scarring on the vines from cucumber beetle feeding.  These insects can carry Erwinia tracheiphila, the bacterial wilt pathogen, in their intestinal tracts.  As they feed, cucumber beetles defecate in their feeding wounds, inoculating plants.  The bacterium colonizes the water-conducting tissue of the plants and blocks it off, leading to reduced water movement from the roots to the vines, and thus wilting results.

Diagnosis of bacterial wilt can be relatively easy on certain types of vine crops (particularly cucumber).  You cut a wilted vine off near the base of a plant, then cut a roughly six to eight inch vine segment from that severed vine, giving you two vine sections.  You then hold the two vine segments apart for about 10 seconds (allowing liquid to ooze from the severed water-conducting tissue), then rub the ends of the cut vine segments together gently for another 10 seconds, then very slowly pull the two vine sections apart.  If you see thin, spider web-like strands pull between the two vine pieces, you’re dealing with bacterial wilt.  Management of this disease primarily depends on keeping cucumber beetles under control.

Insect-transmitted viruses

There are many viruses that can adversely affect plant growth and productivity.  A fair number of these viruses are insect transmitted.  Early in the year, when many of my samples come from commercial greenhouses, I tend to see thrips-transmitted viruses.  These include Impatiens necrotic spot virus (INSV) and Tomato spotted wilt virus (TSWV)Interestingly, this year I detected TSWV in commercially grown potato plants, where the virus produced necrotic (i.e., dead) spots that were reminiscent of early blight symptoms.

Aphids also commonly transmit plant viruses.  In herbaceous ornamentals and vegetables, Cucumber mosaic virus (CMV) is the aphid-transmitted virus that I most commonly see.  This virus causes blotchy color (i.e., mosaic) or line patterns on leaves, as well as growth distortions.  In recent correspondence with Damon Smith, the UW-Madison field and forage crop pathologist, I learned that he has been seeing another aphid-transmitted virus, Barley yellow dwarf virus (BYDV), in many wheat fields this year.  In wheat, BYDV causes yellowing of the upper leaves of the plant, particularly the flag leaf (i.e, the leaf just under the developing grain head).  Infection by the virus can lead to significantly reduced yields.  BYDV can also infect other “grass” crops including barley, oats, and corn.  I had a suspicious corn sample arrive at the clinic in late July, and I suggested the client submit a sample to another lab for BYDV testing (I do not test for this virus at the PDDC).

The diseases described above just scratch the surface of plant diseases where there is a potential insect connection.  If you would like read more, check out the UW Plant Disease Facts on ash yellows, aster yellows, Dutch elm disease, ergot, oak wilt, plum pox, soybean vein necrosis disease and thousand cankers disease.  After reading, if you if you have questions about these or any other plant diseases, feel free to contact me at or (608) 262-2863.  I am always here to help.

July 2023: 25 Years. . . 25 Cool Diseases

Twenty-fifth Anniversary IconJuly 1 marked my 25th anniversary as director of the University of Wisconsin Plant Disease Diagnostics Clinic.  In celebration of that milestone, this month’s web article highlights 25 diseases, disorders, and oddities that look like diseases, but aren’t.  All of these tickle my fancy as a geeky plant pathologist.  I am emphasizing diseases/disorders/oddities that can be identified by eye.  Where I have a UW Plant Disease Facts fact sheet on the disease/disorder/oddity, I provide a link.  Where I don’t, I provide more extensive comments and a link to a photo.  For several of the entries, I wax nostalgic about unusual encounters I’ve had with the diseases/disorders/oddities over the years.


Leaf/Fruit Diseases

The diseases in this section are all fungal and very common.  I’ve made a fair amount of money diagnosing these diseases in my 25 years in the clinic.

Powdery Mildews

Powdery mildews are one of my favorite types of fungal diseases due to the very ornate microscopic structures that they produce.  Powdery mildews are mostly cosmetic diseases but can be the bane of cucurbit, phlox, beebalm, and ‘Diablo’ ninebark growers.

Tar Spot

These incredibly visual diseases often pop up on maples, most commonly silver and Norway maple.  When I first started in the PDDC, I tended to see these diseases primarily in counties that bordered Lake Michigan.  Nowadays, I can find them anywhere in the state.

Taphrina Diseases

The most common of these diseases is peach leaf curl, which gives peach leaves a colorful, seersucker sort of look.  The more bizarre versions of these diseases cause fruits to swell and become spongy.  Plum pockets and what I have dubbed chokecherry pockets are examples.  I encountered this latter disease for the first time in 2023.  I love seeing new diseases!!

Gall Diseases

Gall diseases lead to the overgrowth of affected plant parts.  Some are fungal, some are bacterial.  All are quite cool!

 Black Knot

This is the fungal disease that I affectionately call “poop-on-a-stick”.  I can’t tell you how many of my former students have told me that they remember this disease because of my use of this rather risqué name.

Common Corn Smut

Is this disease bad or good?  It all depends on your point of view.  If you’re a sweet corn grower, you really don’t want to see this disease at all.  If spores of the fungus get into canned corn, they give the corn an off flavor.  If you run a restaurant however, you may be quite pleased to find this fungus on your sweet corn, so that you can harvest it and include it on your menu as huitlacoche.

Crown Gall

This is the classic bacterial disease that kick-started today’s industry of genetically modifying/engineering plants.  This industry was first gaining traction back when I was in graduate school (i.e., the Jurassic Period).

Leafy Gall

Think of this disease as crown gall on steroids.  You get the tumorous growth of crown gall but with the added bonus of tons of tiny leaves and shoots.  After reading about this disease for years, I finally received a sample for the first time in 2022.

Rust Diseases

Rust diseases are a large of group of diseases caused by closely related fungi that are very host specific.  Some rust fungi complete their life cycles on a single type of plant.  Others require two, often very different, plants to complete their life cycles.  I think rusts are very interesting and tend to get a smile on my face when these diseases arrive at the clinic.

Gymnosporangium Rusts

I find this group of rusts, which includes cedar-apple rust, cedar-hawthorn rust, and cedar-quince rust, very attractive, particularly given that many of the diseases that I see routinely are rotting, slimy, and rather (ahem) odiferous.  Gymnosporangium rusts are always suitable for inclusion in a plant disease bouquet to be used at a summer field day.  Other diseases. . . not so much.

Fir Broom Rust

This is an alternating rust that infects both fir trees and chickweed.  I have never seen the disease on chickweed, but the symptoms and signs on fir are very distinctive.  Infection leads to production of a massive cluster of branches (i.e., a broom) with pale, wimpy needles that produce masses of yellow, powdery spores.  Optimally, you would try to eradicate any chickweed near your fir trees to control this disease.  Unfortunately, this weed is so common and inconspicuous that eradication is difficult.  Management of fir broom rust more typically involves pruning out the branch masses in fir trees as they form.  The first time I encountered this disease was when a client sent me photos of his fir trees.  The photos were of such high resolution that I could zoom in and see sporulation on the needles!  My client could tell I was very excited about seeing this disease for the first time, and, kind soul that he was, he dropped off the sample on one of his trips through Madison from the Eau Claire area.

Elderberry Rust

The symptoms of this disease remind me of a huge, yellow banana slug hugging an elderberry branch for dear life.  This disease is definitely in the running for my #1, favorite plant disease.

White Pine Blister Rust

This disease is potentially lethal in white pine as the causal fungus can girdle the main trunks of white pine trees.  In the spring, the fungus produces the blister-like reproductive structures on white pine that gives the disease its name.  Many years ago, I had a VERY long phone conversation with a client who wanted to start a currant farm in northern Wisconsin in the middle of white pine forest.  That’s a really bad idea given that currants (along with gooseberries) are the alternate host for the white pine blister rust fungus.  I don’t think I convinced my client to abandon this idea, and I’ve often wondered over the years if she ever started her currant farm and if so, what the consequences were.

 Canker Diseases

 These diseases girdle branches and cause branch dieback.  I have seen a lot of these diseases over the years.

 Golden Canker

This disease is specific to pagoda dogwood, particularly those trees improperly sited in hot, dry, full-sun locations.  This is another disease that is “attractive” in my rather warped worldview.  Like with Gymnosporangium rusts, I often include this disease in festive disease bouquets.

Eastern Filbert Blight

This disease is the bane of European hazelnut, and I often see it on Harry Lauder’s walking stick.  I really like how the fruiting bodies (i.e., reproductive structures) of the causal fungus pop out of the dead branches.  It looks like an insect marched along the length of the branch leaving tiny footprints in its wake.

Blister Canker (Nailhead Canker)

This disease tends to be an issue on stressed apples and crabapples (although I have also seen it on serviceberry).  The causal fungus infects larger branches and tree trunks, and eventually forms clusters of large, round, black pads (technically called stromata) in amongst the bark.  Embedded in the stromata are fungal reproductive structures that contain elongate sacks with eight dark-colored spores.  This disease is awesome as a teaching tool because if preserves nicely at room temperature with little fuss.

Miscellaneous Diseases

 Not all diseases are easily categorizable!


This disease has had a significant impact on human history, due to the toxic compounds that the causal fungus produces.  Check out “St. Anthony’s fire” or “ergotism” online if you’d like to read more on this.  In a very personally satisfying PDDC moment, I diagnosed this disease and helped a horse owner save her horses.  The horses were in declining health because they had been grazing in their paddock on grasses that had this disease.  The fix was any easy one.  The client just had to mow the grass to remove the infected seed heads and then had to be sure to mow again anytime the grass began to flower.

Dead Man’s Fingers

This is a root rot pathogen that I most commonly see on stressed trees and shrubs.  The most hysterical photo of dead man’s fingers that I’ve seen looked like someone’s toes were sticking out from under a log.

White Mold

This is one of the more destructive fungal diseases that I see, causing problems across a wide range of herbaceous plants.  Look for the mouse-dropping-like resting structures of the causal fungus on (and inside) infected plant tissue.  If you see these, they are a dead giveaway that you’re dealing with white mold.

Fertility Issues

 Not all plant health problems are true diseases where a pathogen (i.e., a disease-causing organism) is involved.


This is a classic disease of pin oak and birch where the trees are suffering from an iron deficiency.  In red maple, a manganese deficiency is typically the problem.  Lack of these nutrients in the soil is often not the issue, but overly high soil pH (which makes these nutrients less available for plant uptake) is.

Blossom End Rot

People tend to tend to think of tomatoes when they think of blossom end rot, but any vegetables that’s botanically a fruit (e.g., peppers, eggplant, cucumbers, squash) can suffer from this disorder.  A calcium deficiency in the fruits is the problem.  A lack of calcium in soils is typically not the issue but a lack of water (e.g., from drought or uneven watering) more commonly is.


 Sometimes what I see are not diseases, but some other sort of amazing oddity. . .


This is a parasitic plant that grows prolifically, covering parasitized plants in what looks like a mass of yellow or orange spaghetti.  The most awesome example of dodder I’ve ever seen was back in my undergraduate days when I found an entire lot next to the Fort Atkinson, WI sewage treatment plant covered with the plant.  You could make out shapes of shrubs under the growth.  Mind boggling!

Fairy Rings

Fairy rings can cause aesthetic issues on golf courses and in home lawns but are relatively cosmetic issues.  Their most classic form is a ring of mushrooms growing in a grassy area.  If you believe in ancient lore, you may want to stake out these rings when you find them to watch for dancing fairies on a moonlit night.

Slime Molds

Slime molds come in many shapes and forms.  The most common slime mold gardeners encounter looks like a neighborhood dog upchucked on newly spread mulch.  My personal favorites are a) one that looks like a cluster of tiny cattails and b) one that looks like a spherical birdcage under the microscope.  I have to give a shout out to Marilyn Hanson, my high school biology teacher, who introduced me to slime molds (and fungi as well) and was instrumental in setting me on the path that led to me becoming a plant pathologist.


I have had a number of somewhat awkward conversations with clients about these common garden fungi, some of which look like a certain part of the male anatomy (thus the awkwardness).  In addition to their odd form, stinkhorns (as the name implies) have a rather unpleasant odor.

Bird’s Nest Fungi

“Super cute” are the best words to describe these fungi.  Their reproductive structures look like tiny bird’s nests complete with eggs!  Watch for these in clusters in mulched flowerbeds.


These fantastic organisms are a symbiotic combination of a filamentous fungus, an alga (often a blue-green alga, more accurately referred to as a cyanobacterium), and in certain instances a yeast (a non-filamentous type of fungus).  Please don’t bemoan seeing lichens growing on the trunks of your trees (or anywhere else).  If you see lots of different types of lichens in your area, that’s an indication of good air quality.

I hope you’ve enjoyed this list and my trip down memory lane.  If you have questions, feel free to contact me at or (608) 262-2863.  Enjoy the rest of your summer!!

June 2023: Weeding is Fundamental!

Weeding Tools IconMark your calendar. June 13th is National Weed Your Garden Day. It’s time to get out into your garden to remove those unwanted plants growing in amongst your prized herbaceous ornamentals and tasty vegetables. Not only will weeding make your garden look more tidy and beautiful, it will also help make your favorite garden plants healthier. How do weeds negatively impact your garden plants’ health? Let’s look at some ways.

Weeds compete for nutrients and water

All plants in a garden use and compete for available soil nutrients and water to grow, flower, and set fruit and seed. Nutrients and water used by weed plants are not available to be used by ornamentals and vegetables that we are attempting to grow. This leads to smaller plants, fewer flowers, and reduced vegetable yields. In addition, plants stressed for nutrients and water because of competition from weeds are less likely to be able to produce compounds that they can use to fend off infections by the myriad of plant pathogens in the environment. This can contribute to an increase in infections and disease, leading to a further reduction in plant quality and yield.

Weeds create an environment that is more favorable for infections to occur

Weeds, like all garden plants, produce foliage. Thus, high weed pressure in a garden will lead to a denser plant canopy that will reduce airflow. When leaves get wet (e.g., when it rains), this lack of air movement will increase the length of time that it will take for the leaves to dry. Longer periods of leaf wetness will provide more time for spores of fungal plant pathogens to germinate and infect, thus increasing the likelihood that many types of leaf diseases will develop.

In addition, plants (including weeds) transpire. Transpiration is a natural loss of water from leaves as they take in carbon dioxide and release oxygen during photosynthesis. Dense plant canopies trap this released moisture, creating humid conditions around leaves. High humidity tends to promote sporulation of many disease-causing fungi, which can lead to an increase in additional infections. For some disease-causing fungi (e.g., powdery mildew fungi), high humidity (rather than leaf wetness) is the environmental factor that promotes spore germination and infection.

Weeds can serve as a reservoir for disease-causing organisms

Many disease-causing organisms are very host specific, in that they can infect only a single type of plant or only a small group of very closely related plants. Other pathogens have broad host ranges and can infect many types of plants. Weeds (particularly perennial weeds) can serve as reservoirs where these broad-host-range pathogens can overwinter and subsequently spread to garden plants. In particular, I worry about weeds harboring viral pathogens such as Tobacco mosaic virus (TMV), Cucumber mosaic virus (CMV), Impatiens necrotic spot virus (INSV), and Tomato spotted wilt virus (TSWV). These viruses can survive in weed hosts and can subsequently be moved be moved from plant to plant by insects, on gardening tools, or even by just handling plants. Weed species can also serve are reservoirs for the phytoplasma that causes aster yellows, and they can help keep fungal pathogens such as Verticillium (the cause of Verticillium wilt) at elevated levels in garden soils. By weeding, you can eliminate sources many disease-causing organisms and help prevent pathogen survival and spread.


So, as you get some spare time in the coming weeks, be sure to spend a few minutes in your garden removing those pesky, unwanted plant species. You will not only end up with a more beautiful garden, but ultimately a healthier garden as well.


If you have questions about weeds and how they can impact diseases in your yard, feel free to give me a shout. As always, you can reach me at or (608) 262-2863. Go forth and weed!!

May 2023: Jewels in the Crown

Crown IconThere was a fair amount of pomp and circumstance earlier this month surrounding the coronation of King Charles III of England. As I was reading the news articles, I began to imagine how plant diseases might fit into a coronation ceremony. I doubt that British royals would find any of the diseases that I deal with particularly appealing. However, in typcal Dr. Death fashion, I found three diseases that, in my eccentric world view, could fit into a ceremony to crown a plant pathologist king or queen. I hope you enjoy my selections.

Crown Rots

The most destructive of the “crown” diseases are crown rots. The fungi and fungi-like water molds involved in these diseases often infect though a plant’s roots and eventually destroy a plant’s crown (i.e., the part of the plant where the roots and above-ground plant parts converge). Plant death is a common result. Crown rot pathogens prefer wet conditions; thus, crown rots tend to be more prevalent in heavier (e.g., clay) soils, in low areas, and in wet growing seasons. Management of crown rots involves improving soil drainage by adding organic matter (e.g., compost, leaf litter) to heavier soils and/or creating raised beds. Proper mulching (not more than two inches on heavier soils) can help prevent these diseases as well. Finally, for plants of high economic or sentimental value, fungicide treatments are a possibility. For treatments to be effective however, proper identification of crown rot pathogen(s) is critical, as some crown rot fungicides target fungi, others water molds.

Crown Gall

I got excited recently when I was removing leaf litter from my parents’ wintercreeper and caught sight of greenish-white, tumor-like blobs (galls) on the main trunk of the shrub. These blobs are typical of crown gall, a disease caused by the soil-borne bacterium Agrobacterium tumefaciens. This bacterium has a very wide host range; I commonly see crown gall on wintercreeper, rose shrubs, and apple trees. Often tumors form in the crowns of affected plants, but root galls are also common. Management of crown gall involves removing and destroying infected plants and avoiding planting susceptible plant species in areas where the disease has been observed.

Interestingly, when Agrobacterium tumefaciens infects a plant, it injects a small piece of its DNA (i.e., genetic material) into plant cells, where this DNA inserts into plant chromosomes. This bacterial DNA codes for enzymes that produce a variety of interesting chemical compounds. These compounds hijack plant cell growth and cause cells to grow fast and divide like crazy, leading to characteristic crown gall tumors. Other enzymes make opines, a class of chemicals that are a favorite food of the bacterium. Scientists eventually discovered that they could manipulate Agrobacterium tumefaciens DNA and incorporate plant genes into it. With these plant genes in place, the bacterium then could be used to infect a different type of plant, thus moving plant genes from one plant to another. Via this process, genetically engineered/modified plants were first produced.

Crown Rust

This is perhaps the most fitting plant disease for this month’s article, as the name of the causal fungus is Puccinia coronata. The species designation (coronata) refers to projections on the fungus’ club-shaped reproductive structures that give the clubs a crown-like appearance. Home gardeners most commonly see crown rust on turf; if you have ever walked through your lawn and ended up with orange shoes, you’ve encountered this disease. The orange powder is sporulation that allows the fungus to reinfect turfgrass. Interestingly, Puccinia coronata needs two host plants to complete its life cycle. The second host plant for Puccinia coronata is buckthorn, the invasive tree that takes over understories of wooded areas. Puccinia coronata produces a second type of spore in the spring that drifts from turfgrass to buckthorn, infecting leaves and green branch tissue of the tree. These infections lead to yellow leaf spots and yellow, distorted branch growth. These yellow areas produce yet another spore that drifts back to turfgrass, completing the fungus’ life cycle. Management of crown rust involves eradicating buckthorn, as well as regular mowing and optimal nitrogen fertilization of lawns to help remove the fungus and help turfgrass outgrow the disease.


Can you think of any other plant diseases that are fit for a plant disease king or queen? If so, let me know. Also, if you have questions about the diseases discussed above and/or how to submit samples to the clinic, feel free to give me a shout. As always, you can reach me at or (608) 262-2863. Long live plant diseases!!

April 2023: The Best Things in Life Are Free!

Free IconThe Plant Disease Diagnostics Clinic (PDDC) typically charges a small fee for providing diagnoses of plant diseases and disorders.  However, there are certain instances where the PDDC waives fees.  In particular, if there are plant diseases that are new to the state and/or potentially have severe negative economic impacts to Wisconsin agriculture, the PDDC does not charge to provide a diagnosis.  Early detection of new diseases can help in limiting and slowing spread, and may even provide opportunities to eradicate a disease.  Early detection of established, but economically important, diseases can help provide growers critical information for disease management.

The following are diseases that the PDDC will be providing free diagnoses for in 2023.

Late Blight

This disease can have a huge impact on the commercial potato industry in Wisconsin (the third largest potato-producing state in the US).  Identifying this disease as early as possible and determining which variant(s) of the pathogen (and there are many) has(have) arrived in the state are critical for providing timely and appropriate control recommendations to commercial potato producers.  Because the disease can affect tomatoes as well as potatoes, I encourage home gardeners to watch for this disease in their vegetable gardens.  If you see any suspicious leaf spotting on tomato or potato leaves or on tomato fruits, submit a sample for free testing.  Just indicate when you submit that you are concerned about late blight.

Boxwood Blight

This disease was first detected in Wisconsin in 2018 but has been devastating boxwood plantings in the eastern US since 2011.  The PDDC is continuing to map the movement of boxwood blight in the state and added Door County to the official boxwood blight county map in 2022.  If you see dark leaf spots, followed by leaf collapse and branch dieback on boxwood shrubs, get a sample to the clinic for a free diagnosis.  The problem may just be winter burn, but if it is boxwood blight, I’d like to know.

Japanese Apple Rust

I more commonly call this disease lipstick rust, and there is a move afoot to change the official name to red star rust (a literal translation of the original Japanese name of the disease).  This disease is a new Gymnosporangium rust for Wisconsin, having first been reported in the state by WI DATCP in 2021.  To date, lipstick rust has been confirmed in Dane, Kenosha, Milwaukee, Outagamie, Ozaukee, Portage, Racine, Sheboygan, and Waukesha Counties.  Watch for the red or fuchsia-colored spots on apple and crabapple leaves characteristic of lipstick rust.  If you see spots of this type, I suggest first submitting digital photos to the PDDC.  If the symptoms look consistent with lipstick rust, and there has been an official confirmation of the disease in your county, I’ll make a diagnosis from the photos.  If the symptoms look consistent, and there has not been an official confirmation of lipstick rust in your county, I’ll request that you submit a physical sample for DNA sequencing (the method of choice for confirming new cases of the disease).  Either way, the diagnosis is free.


If you have questions about these diseases and/or how to submit your samples, feel free to give me a shout.  You can reach me at or (608) 262-2863.

March 2023: UW Plant Disease Facts Medallions – Collect Them All!!

Medallion Project IconI absolutely loathe exercising.  That said, I try to force myself to do at least some sort of cardiovascular workout every day in an attempt to fend off the weight gain that seems to come with age (and my inability to stop eating everything bad for me in sight).  One thing that (sort of) makes my workouts tolerable is a fitness app that I have downloaded onto my cell phone that allows me to track my steps, minutes of exercise, calories burned, and other sundry exercise-related statistics.  As I achieve goals that I have set for myself, the app plies me with cool-looking electronic medallions (and other bright and shiny visuals) to reward me for my efforts.

How on earth does this have anything to do with plant diseases?  Well, about a year ago, I was contemplating how to entice people to learn more about plant diseases, and how to make it more fun in the process.  I already had plenty of plant disease-related materials to learn from in the form of the UW Plant Disease Facts fact sheets.  There are 130 titles in that series waiting to be consumed and digested.  But, what might encourage people to partake and learn?  My fitness app, with its rewards system, came to mind.

Thus was born the UW Plant Disease Facts Medallion Project.  For each of the 130 facts sheets in the UW Plant Disease Facts series, I have created a unique electronic medallion.  In addition, for each of the 130 fact sheets, I have written a brief quiz.  Earning the medallions is really simple.  Read a fact sheet.  Then, pick the corresponding quiz, and answer the questions.  If you get all of the answers right, you are rewarded the corresponding medallion.  The medallions are automatically emailed to you, and you can save them to your computer or other electronic device.  I am hoping that earning the medallions will make learning about diseases not only educational but fun as well.

The medallions will be rolled out in stages, just to make sure the launch runs smoothly and to efficiently manage any bumps that come up along the way.  The first set of medallions will be those (roughly 30) that have to do with fruit crop diseases.  These will launch this month.  Additional sets will be made available throughout 2023.  Hopefully all 130 medallions will be available by the end of the year.  And then, who will be the first person to earn them all?

Go to the UW Plant Disease Facts Medallion Project overview page to get started earning your medallions.

I want to give a HUGE shout out to Dixie Lang, who does IT and web support for my clinic, for all of her efforts in making this project possible.  She’s the person who figured out how to set up the quizzes online and automate the delivery of the medallions.  Also, many thanks to subscribers to my clinic listserv (UWPDDCLearn).  Late last year, I sent out a request through the listserv for help in proofing the quizzes, and many subscribers helped with this.  In particular, my colleagues Diana Alfuth (Extension Pierce and St. Croix Counties) and Lisa Johnson (Extension Dane County) spent a lot of time reviewing quizzes.

If you have any questions about the Medallion Project, don’t hesitate to contact me.  You can reach me at or (608) 262-2863.  Happy learning!!

March 2023: Reading is Fun(gi)damental

Book IconI have spent a substantial portion of my career writing about plant diseases. When I started at the UW-Plant Disease Diagnostics Clinic in 1998, one of the first things articulated by county Extension educators was their need for short, concise, and to-the-point fact sheets on a variety of horticulture topics. This need led to the development of what are now known as the UW Plant Disease Facts, a series of one page fact sheets (targeted toward an adult, home-gardener audience) that cover a range of plant disease topics. I serve as the editor of this series and have authored or co-authored roughly two-thirds of the 130 titles.

When the COVID-19 pandemic hit in 2020, and I was stuck at home, writing was an increasingly important activity that I could use to fill my time.  I began to think about how I might engage a younger audience and get grade, middle and high school students interested in plant diseases. My thoughts drifted to a limerick that my coworkers (Ann Joy and Nancy Kurtzweil) and I had written back in my days with the UW Ginseng Research Program (waaaaaaaaaaaaaaay back in the Jurassic Period). The limerick:

There once was a farmer Ontarian,
The bane of his life Alternarian.
Its cure was a smash,
And brought lots cash,
And made him a wealthy agrarian.

had been taped to a refrigerator in my clinic for decades. That bit of verse made me wonder if limericks, with all of their fun and silliness, might be a way to capture the attention of a younger audience and get them immersed in the wondrous world of plant diseases.

Limerickettsia CoverThus was born Limerickettsia: A Plant Pathologist’s Book of Verse. This book, just published this year, contains 52 plant disease-themed limericks with accompanying prose descriptions, and full-color photographs and original artwork. The book includes limericks about diseases caused by all of the major types of pathogens (i.e., fungi, bacteria, viruses, nematodes, phytoplasmas and even parasitic plants), as well as limericks about things that look like plant diseases (e.g., bird’s nest fungi, slime molds, stink horns) but are not. With each limerick, you get to learn about what the plant disease looks like, how the organism that causes the disease does its thing, and tips on plant disease control. For some of the diseases (e.g., grain rusts, late blight of potato, Dutch elm disease), there are also tidbits about how the diseases have impacted human history. If you are intrigued, check out the Limerickettsia page on the UW-PDDC website.

If you have any questions about Limerickettsia: A Plant Pathologist’s Book of Verse or any of the other educational resources available through the UW Plant Disease Diagnostics Clinic, don’t hesitate to contact me. You can reach me at or (608) 262-2863.

Happy reading!!