Category Archives: Monthly Column

August 2024: Brian’s Bucket List Bonanza

Earlier thiBucket List Icons year, one of my colleagues called me “giddy” as I was happily expounding about all of the diseases that I was seeing this year due to our wet weather.  The pinnacle of my euphoria came this month when I received a sample of one of my all-time favorite diseases, zonate leaf spot.  This disease is caused by several species of the fungus Cristulariella/Grovesinia, and occurs on a wide range of plants.

My first encounter with zonate leaf spot was back in 2018.  Interestingly, I received two samples of the disease on the same day that year, from two different Wisconsin counties (Marathon and Buffalo), and on different hosts (maple and grape).  I subsequently saw the disease in 2019 on industrial hemp from Langlade County, and the sample I received this year was another maple leaf sample originating in Dunn County. 

Symptoms of zonate leaf spot on a maple leaf
Symptoms of zonate leaf spot on a maple leaf

In my initial encounter with zonate leaf spot in 2018, a UW-Extension county educator sent me photos of maple leaves with symptoms (roughly round spots with a pattern of concentric rings) that were typical of what I had seen in online photos of the disease.  I REALLY wanted to see a physical sample (and offered to do the diagnosis for free), as zonate leaf spot had been on my plant disease “bucket list” ever since I first saw drawings of the reproductive structures of Cristulariella/Grovesnia (called conidiomata) in one of my reference books.  The Extension educator was quite accommodating. 

Conidiomata of the zonate leaf spot fungus
Conidiomata of the zonate leaf spot fungus look like tiny, tan Christmas trees popping up from the surface of a leaf.

Once the physical sample arrived, I again noted typical zonate leaf spot lesions.  I scanned the lesions under my dissecting microscope and relatively quickly found conidiomata of the pathogen.  These structures are HUGE, are multicellular, and are tannish and pyramidal in shape.  Quite frankly, they look like tiny, tan Christmas trees popping up from the leaf surface.  If you saw these (and they are readily visible using a 20X hand lens), you might think they are insect droppings of some kind.  I ended up incubating the maple leaves in a moist chamber for several days, hoping to stimulate additional sporulation.  Interestingly, the fungus eventually formed black sclerotia (resting structures) that were readily visible to the naked eye.  In the recent maple sample that I received, I immediately found both conidiomata and sclerotia as soon as I pulled the sample from the bag. 

Sclerotia of the zonate leaf spot fungus on a maple leaf
Sclerotia (resting structures) of the zonate leaf spot fungus on a maple leaf. The sclerotia are a mass of fungal tissue that initially are white but eventually turn black.

When I encountered zonate leaf spot in 2019 on hemp, I decided to go a step further in the identification of the fungus, as I was not able to find any reports of zonate leaf spot occurring on this host plant.  I plucked one of the conidiomata from the leaf surface and placed it on the center of a petri-plate filled with a potato-based growth medium.  The grew quite quickly on this medium.  Sue Lueloff, the molecular diagnostician in my clinic at the time, was able to able obtain a DNA sequence for the fungus, which matched sequences from known isolates of Grovesinia moricola. 

While I tend to get very excited when I see zonate leaf spot, as a home gardener, there’s not much to worry about.  This disease is similar to most other, more common leaf diseases in terms of management.  You begin by making sure to collect up and dispose of any leaves from infected trees after they drop in the fall.  The leaves can be burned (where allowed), buried, or hot composted.  Maintenance pruning of susceptible woody species can help with control of the disease as well.  This pruning opens up the plant canopy and improves airflow, which helps speed drying when leaves get wet.  This drier environment is less favorable for Cristulariella/Grovesnia to infect.  To be honest, zonate leaf spot does not appear to be a serious disease in most instances, so don’t panic if you think you see the disease.  Just let me know if you do, as you will make my day!  

If you have questions about zonate leaf spot (or any other plant disease) feel free to contact me at (608) 262-2863 or pddc@wisc.edu.  As always, for more information on plant diseases and their management, be sure to check out the UW-Madison PDDC website (https://pddc.wisc.edu/).  To keep up to date on clinic activities and resources, follow the PDDC on Facebook or Twitter (@UWPDDC), or subscribe to the clinic’s listserv, UWPDDCLearn (by emailing or phoning the clinic to subscribe). 

Go forth and look for supercool, bizarre diseases.  They are out there waiting for you to discover!

July 2024: Villainous Vegetable Violations

Vegetable IconIn last month’s web article, I talked about the myriad of fruit diseases that I’ve been seeing at the clinic.  This month, I thought I’d provide a summary of the vegetable diseases that I’ve been seeing.  Many of the vegetable samples that I’ve received have been from commercial growers, but diseases don’t discriminate and can affect both commercial- and home-grown vegetables alike. 

Root/Crown rots

Given our regular (and often plentiful) rains this year (it’s pouring as I write this article), it’s not surprising that vegetable root and crown rots have been an issue.  I have seen these diseases on peas, snap beans, and vine crops thus far this season.  Typical symptoms of root/crown rots can include stunted growth, leaf yellowing and browning (caused by inhibited water and nutrient uptake), and discolored and mushy roots.  The menagerie of organisms that I’ve recovered from root/crown rotted plants has been quite impressive.  I’ve seen pathogens such as Phytophthora, Aphanomyces, and Pythium (all fungi-like water molds), as well as Rhizoctonia and Fusarium (two true fungi).  Management of root rots in home gardens relies heavily on proper crop rotation, [i.e., making sure not to grow the same vegetable (or even vegetables in the same plant family) in the same area of your garden year after year after year].  This technique helps prevent the buildup of root/crown rot pathogens in the soil (where they tend to survive quite happily).  In particular, water molds produce thick-walled, long-lived resting spores (called oospores) that can survive for years in the soil.  For details on how to use crop rotation effectively in your home vegetable garden, check out the fact sheet here

Black rot

This disease of cruciferous crops (e.g., cabbage, broccoli, cauliflower, kale) seems to have exploded.  I have had four cabbage samples with this disease show up at the clinic in the past week.  Symptoms of black root often start at the edges of leaves with yellowing that progresses into wedge-shaped necrotic (i.e., dead) areas with yellow borders.  The points of the wedge-shaped diseased areas usually follow veins.  This disease can be very destructive and lead to substantial losses in commercial vegetable production.  The bacterium that causes this disease (Xanthomonas campestris pv. campestris) is typically introduced into a garden on contaminated seed or transplants.  Once the disease has occurred in a garden, the bacterium can survive in small bits of debris from infected plants that filter into the soil.  Crop rotation is a useful technique for managing this disease.  In addition, make sure you plant high-quality seeds that are less likely to harbor the bacterium.  If you have seed that you suspect may carry this pathogen, there are hot-water treatments that you can use to decontaminate the seed. 

Interestingly, in 2024, I have seen a large number of Xanthomonas diseases (aside from black rot) on a wide range of plants including lettuce, tomato, pepper, begonia, zinnia, hydrangea, amur honeysuckle, peach, and winter wheat.  This bacterial genus contains many common and destructive plant pathogens. 

Verticillium wilt

I have only seen a single vegetable example of this disease so far this season (on melon), but Verticillium wilt affects a wide range of vegetable crops including tomato, potato, pepper, eggplant, and vine crops such as cucumber, melon, squash, and pumpkin.  The fungus involved (typically Verticillium dahliae) survives readily in soil or associated with other plants (e.g., broad-leafed weeds) and infects susceptible vegetable plants through roots.  It then colonizes the xylem (i.e., the water-conducting tissue) in the plants and blocks it, preventing water flow from the roots to the aboveground plant parts.  This results in wilting and eventual plant death.  Use of nonsusceptible vegetables (e.g., corn, peas, snap beans) and use of Verticillium wilt-resistant varieties of susceptible vegetables (e.g., tomatoes) are common means of managing this disease. 

Veriticillium wilt is not only a vegetable disease, but it can also be a serious problem on woody and herbaceous ornamentals.  So far in 2024, I have diagnosed this disease on Japanese maple (a very common host), catalpa (another common host), gas plant, and buttonbush.  My buttonbush detection this year is only the second time in my 26+ year career that I have seen Verticillium wilt on this host.  And, I have never seen the disease on gas plant before. 

Powdery Mildews

As with Verticillium wilt, I have only seen a single case of vegetable powdery mildew this year, and that was on cucumber.  I have also seen limited powdery mildew on other non-vegetable plants this year, with detections only on pear, serviceberry, and delphinium.  Part of the reason I’ve likely not seen a lot of powdery mildew samples in the clinic is that many people are familiar with these diseases.  They readily recognize the powdery white growth associated with powdery mildews and don’t need my help with an ID.  In addition however, we’ve had a very wet growing season in 2024.  Powdery mildew fungi don’t perform well when there is a lot of rain and leaves are wet.  These fungi prefer dry leaves and high humidity.  Limited rain and muggy conditions (which favor powdery mildews) are typical in Wisconsin in July and August, but not so much in 2024.  We’ve had regular rains this year, so powdery mildew infections have been suppressed. 

Interestingly, in one of the powdery mildew samples that I received, I found Ampelomyces, a fungus that parasitizes powdery mildew fungi.  Ampelomyces provides natural biological control of these diseases.  Interestingly, this fungus has been commercialized and is the active ingredient in certain fungicides that are used for powdery mildew control. 

What vegetable diseases are you seeing in your garden?  

If you find something interesting and need help in identifying the problem, please contact me at (608) 262-2863 or pddc@wisc.edu for advice.  As always, for more information on plant diseases and their management, be sure to check out the UW-Madison PDDC website.  To keep up to date on clinic activities and resources, follow the PDDC on Facebook or Twitter (@UWPDDC), or subscribe to the clinic’s listserv, UWPDDCLearn (by emailing or phoning the clinic to subscribe). 

June 2024: Fruitful Plant Diseases

Fruit IconThe 2024 field season is in full swing, and samples have been coming into the clinic at a breakneck pace.  As I think about the samples that have been submitted thus far, I’m struck by how may fruit samples I’ve looked at.  Here’s a summary of the fruit diseases I’ve been seeing. 

Apple scab

Wow!  In my (almost) 26 years in the clinic, I’ve never seen a year as good for apple scab as 2024.  We’ve had perfect weather for an apple scab epidemic.  We had substantial rains around the time that trees were first leafing out, and this is the optimal time for initial infections to occur via spores released from apple and crabapple leaf litter.  These early rains also prevented people from being able to make protective fungicide applications to their apples and crabapples (if they were so inclined).  We continued to have rains throughout the spring, and that provided the leaf wetness needed to allow additional infections to occur via spores that were produced from the initial infections.  I have received so many calls and received so many samples from clients complaining that their apple and crabapple leaves are turning blotchy and brown, and then falling from trees.  This is virtually all due to apple scab.  Expect to see more leaf loss as we head into the summer. 

Cedar-apple rust

On apple and crabapple trees that haven’t defoliated due to apple scab (i.e., that are resistant to that disease), I have been seeing a lot of yellow/orange spotting.  This includes one of the crabapples in my front yard.  This spotting is caused by one of the Gymnosporangium rusts, most likely cedar-apple rustCedar-apple rust is a fungal disease, where the pathogen spends part of its life on junipers (where it produces a brown, brain-like galls that sprout bright orange, gelatinous growths) and part of its life cycle on apples and crabapples where it leads to yellow/orange leaf spots.  I received several photos of the gelatinous juniper phase of this disease in mid-spring.  We had a lot of rain around that time, so I’m not surprised to now see a lot of leaf spotting.  Watch your apples and crabapples for this disease, and if you happen to see a variant where the spotting is red/fuchsia rather than yellow/orange, give me a shout and send me some photos.  You could be dealing with a new Gymnosporangium rust (red star rust) that recently has been found in Wisconsin.  I’m attempting to track this disease, so if you’re in a county where red star rust has not been formally confirmed, I’ll ask you to send in a leaf sample for testing. 

Fire blight

I talked about this disease in my May web article (Wisconsin’s Wild Weather Woes), so check out that article for details.  As I predicted, I’ve been seeing an uptick in the number of cases of fire blight in 2024.  My most interesting fire blight cases have been on quince, a fruit crop that I rarely see. 

Taphrina diseases

I have seen three of these diseases so far this season, caused by three different species of the fungus Taphrina.  Two of the diseases have been on stone fruits.  Peach leaf curl (caused by Taphrina deformans) leads to distorted (sort of bubbly-looking) and typically colorful (creamy white, light green, or pink) areas on peach and nectarine leaves.  Plum pockets (caused by Taphrina pruni) affects plum fruits causing them to become enlarged and hollow.  Early in the development of this disease, the fruits are spongy, but they eventually dry and become brittle.  Finally, I’ve seen oak leaf blister (caused by Taphrina caerulescens), where the fungus leads to irregular, puckered areas on leaves.  Management of severe cases of peach leaf curl and plum pockets (you can just ignore oak leaf blister) often involves making an application of a copper-containing fungicide to branches (where the fungus overwinters) after leaf drop in the fall or before leaf emergence in the spring. 

Bacterial canker

You can think of this disease as being the “fire blight” of stone fruits (i.e., cherry, plum, peach, apricot).  The bacteria involved in this disease can infect through flowers causing them to wither and die.  This phase of the disease is often referred to as blossom blast.  On branches and trunks, the pathogens often gain entry via wounds (e.g., cold injured tissues, pruning wounds), and you will typically see blobs of sap oozing from the infected areas.  These blobs can range from large and obvious to small, subtle, and nondescript.  Aggressive and timely pruning of infected branches is critical for management of this disease.  Pruning will prevent movement of bacteria into the main trunk, which will ultimately lead to tree death. 

Root/crown rots

I can see these diseases on virtually any fruit crop, but my most recent case was on raspberries.  The client complained that his raspberries were stunted and had purplish foliage, two symptoms that I often associate with root/crown rots on raspberry.  I tested root/crown tissue from his plants for Phytophthora and sure enough, the plant tested positive.  Phytophthora (a type of fungus-like water mold) is the most common organism that I see causing root/crown rot issues on raspberries.  It produces thick-walled resting spores that can survive for years in the soil and becomes particularly active and problematic when soils are wet.  Unfortunately, there are few management options for home raspberry growers because of how aggressive this pathogen is and how long it can survive in a garden.  My typical recommendation is to establish a new raspberry patch in a new location with new plants. 

Hopefully, your fruit crops are healthy and growing well, but if not please contact me at (608) 262-2863 or pddc@wisc.edu for advice.  For more information on plant diseases in general and their management, be sure to check out the UW-Madison PDDC website (https://pddc.wisc.edu/).  To keep up to date on clinic activities and resources, follow the PDDC on Facebook or Twitter (@UWPDDC), or subscribe to the clinic’s listserv, UWPDDCLearn (by emailing or phoning the clinic to subscribe). 

May 2024: Wisconsin’s Wild Weather Woes

Storm IconWhile 2023 was excessively hot and dry, Wisconsin’s spring 2024 weather has been particularly wet.  That wet weather has come in the form of regular rounds of severe weather.  The third week in May saw a particularly violent set of storms move through the state with heavy rains, high winds (including tornadoes), and hail.  With these severe storms, there came extensive physical damage to many trees across the state.  Some trees lost large branches, and others completely succumbed to the winds and toppling over.  These were the immediate effects of the storms, but other delayed effects are yet to come.  Here are three diseases that I suspect we will see an increase in over the summer in the aftermath of May’s severe weather.

Oak wilt

Oak wilt is a lethal fungal disease that affects oaks of all kinds.  The disease most rapidly develops in oaks in the black oak group (those oaks with pointed-lobed leaves).  White oak group oaks (those with rounded-lobed leaves) are also killed by the disease, although typically more slowly than red oaks.  The fungus that causes oak wilt (Bretziella fagacearum) colonizes the xylem (i.e., the watering-conducting tissue) of infected trees, leading to blockages that prevent movement of water to branches.  Branches wilt, and trees eventually die from the disease.  Introduction of the oak wilt fungus often first occurs via sap beetles, which are attracted to wounded oak trees.  Wind damage to oaks during our recent storms, high sap beetle activity, and the prevalence of the oak wilt fungus in oak trees across the state will likely lead to spread of the fungus and an increase of oak wilt this year.  Watch for flagging (i.e., dying) branches on oaks, and if you see this symptom, consider submitting a sample to the PDDC for oak wilt testing. 

Diplodia shoot blight and canker

Back in 2017, an EF3 tornado cut an 83-mile path through four northern Wisconsin counties (Polk, Barron, Rusk, and Price).  The following year, I started receiving red pine samples from areas near where the tornado had traveled.  The trees, which had survived the storm, started to exhibit extreme needle browning and eventual tree death.  When I examined needles and branches from these trees, I noted extensive numbers of fruiting bodies (i.e., reproductive structures) of Diplodia, the fungus that causes Diplodia shoot blight and canker.  Although these trees had survived the 2017 storms, they apparently were damaged by the high winds, and these wounds provided entry points for Diplodia.  The fungus subsequently colonized and killed the trees.  Given wind damage from our recent storms, I am concerned that we will see a repeat of this scenario in 2024.  So, watch your red, Austrian, mugo and jack pines for needle browning and branch dieback.  If you see these symptoms, Diplodia may be the cause. 

Fire blight

The bacterium (Erwinia amylovora) that causes this disease is most commonly introduced into susceptible trees (e.g., apples, crabapples and pears) via honeybees.  These insects pick up the bacterium when they feed on a combination of sap and bacterial cells that oozes from infected tree branches.  Honeybees drop off the bacterium in the flowers of healthy trees as they pollinate.  Alternatively, Erwinia amylovora can gain entry into trees via wounds created during stormy weather.  In particular, I have seen an increase in fire blight after hail.  During our recent stormy weather, certain areas of the state experienced quite large hail that did significant damage.  These wounds could provide easy access for the fire blight bacterium.  If you see rapid dieback of apple, crabapple, or pear branches over the next few weeks, be sure to contact me about testing for the disease. Early detection, followed by pruning to remove infected branches is critical to get this disease under control.  

Need Help?

Hopefully, you will not see any of the diseases that I have described above.  However, if you see evidence of these or any other plant disease problems, feel free to contact me at (608) 262-2863 or pddc@wisc.edu for advice.  For more information on plant diseases and their management, be sure to check out the UW-Madison PDDC website (https://pddc.wisc.edu/).  To keep up to date on clinic activities and resources, follow the PDDC on Facebook or Twitter (@UWPDDC), or subscribe to the clinic’s listserv, UWPDDCLearn (by emailing or phoning the clinic to subscribe). 

April 2024: Dodging Plant Disease Bullets at the Greenhouse

Dodging IconOur early warm weather has me chomping at the bit to visit local greenhouses to spend money on my favorite annuals and perennials.  Greenhouse growers do their best to produce plants that are healthy and vigorous, but even with the best of care, plants can sometimes end up with unintended disease issues.  As consumers, we need to be diligent and watch for potential issues to make sure we don’t bring diseases home to our ornamental and vegetable gardens.  Here are a few tips on what to look for when buying plants to avoid problems. 

Select plants that are vigorously growing, but aren’t overly leggy. 

Stunting in plants can be caused by several types of diseases including root rots and a variety of plant viruses (more on virus diseases in a bit).  To get a better sense if plants have a root rot problem, carefully pop plants out of pots and look for root discoloration.  Healthy roots should be white, but if you see roots that are brown or black, there’s a good possibility that root rot pathogens are present.  That said, root discoloration can also be caused certain non-disease issues such as heat or salt injury, and plants with these sorts of injuries should be avoided as well.

Leggy plants may be healthy, but often this leggy growth is wimpy and easily injured, particularly as plants are moved and transplanted.  Whenever you injure plants, the wounds you create can provide entry points for a variety of plant pathogens, particularly bacterial pathogens. 

Avoid plants with leaf browning. 

Browning around the edges of leaves typically indicates that plants have been stressed for water.  This marginal browning could mean that the plants weren’t watered enough during production but can also be another symptom of root rots

Brown leaf spots can arise due to a variety of disease-causing organisms.  If leaf spots are roughly circular, then the most likely cause is some sort of fungal pathogen (and there are a myriad of fungi that can cause leaf spots and blights).  If you see spots with concentric rings (i.e., looking like a target), then you could be dealing with certain viral pathogens like Impatiens necrotic spot virus (INSV) or Tomato spotted wilt virus (TSWV)These viruses are common in greenhouse settings and are easily moved around by thrips (a type of insect). 

If you notice angular leaf spots (i.e., spots bordered by veins, giving the spot a straight-edged look), check to see if there is a yellow halo bordering the dead tissue.  If so, you’re likely dealing with a bacterial disease of some kind.  If the angular spots don’t have a halo, then you could be seeing symptoms cause by foliar nematodes

Whether spotting is caused by a fungus, a bacterium, a virus, or a nematode, don’t bring these symptomatic plants home.  All of these pathogens can potential spread to other plants in your garden. 

Avoid plants with odd leaf coloring.

Some plants naturally have variegated foliage and this is a highly prized horticultural feature.  However, if you notice plants with unexpected blotchy light and dark-colored leaves, yellow lines or yellow ring patterns, avoid these.  These sorts of symptoms are often caused by plant viruses such as Tobacco mosaic virus (TMV), Hosta virus X (HVX), Cucumber mosaic virus (CMV), and Tobacco rattle virus (TRV).  Once introduced into a garden, plant viruses can easily be spread to other plants by touch (TMV), gardening tools (virtually any plant virus), insects such as aphids (CMV), and naturally occurring soil-borne nematodes (TRV). 

Avoid plants with fuzzy growth on the leaves.

Fuzzy growth typically indicates a fungal or water mold infection of some kind. 

White fuzzy growth on upper and lower leaf surfaces can indicate a powdery mildew problem.  Powdery mildews are ubiquitous and readily develop in humid conditions that are common in greenhouse settings.  These diseases are often relatively cosmetic, but on certain plants (e.g., cucumbers, squash, pumpkin, bee balms, phlox), powdery mildews can cause substantial leaf browning and loss. 

White, gray, or purplish fuzzy growth on the undersides (and only the undersides) of leaves is characteristic of downy mildew diseases.  I routinely find downy mildew on basil wherever this plant is sold.  The first symptom of the disease that I notice is typically leaf yellowing.  When I see this symptom on basil, I then flip the leaves over to look for typical fuzzy gray/purple growth on the undersides.  Downy mildews tend to be more destructive than powdery mildews, so it’s best not to bring these diseases home on your newly purchased plants. 

Don’t panic. 

Most plants available at your local greenhouse and nursery will be healthy and disease free.  With just a little care, you can avoid those rare diseased plants that may pop up, and end up buying healthy, pathogen-free plants that will provide months, if not years, of gardening enjoyment. 

Need help?

For more information on plant diseases and their management, check out the UW-Madison PDDC website (https://pddc.wisc.edu/).  Alternatively, if you have disease questions, feel free to call (608) 262-2863 or email pddc@wisc.edu for advice and guidance.  To keep up to date on clinic activities and resources, follow the PDDC on Facebook or Twitter (@UWPDDC), or subscribe to the clinic’s listserv, UWPDDCLearn (by emailing or phoning the clinic to subscribe). 

Happy shopping everyone!

March 2024: Warming Wisconsin Weather

Rising Temperature IconI’ve been pretty amazed by the recent temperatures in Wisconsin.  Here in Madison, we hit 70°F in late February.  There have been some colder days this winter, but in general temperatures have been warmer than I remember, particularly compared to what I recall from when I moved to Madison in the mid-1970s.  The warm winter of 2023-2024 followed an extraordinarily warm and dry summer in 2023.  In the context our warmer weather trends, I’ve been trying to think of how plant diseases might be impacted.  Three diseases come to mind that likely could be more problematic in the coming years if warmer conditions continue. 

Southern blight  

This disease is by far the most destructive fungal disease that I see in home landscapes.  The fungus that causes Southern blight (Athelia rolfsii) has a wide host range, and virtually any herbaceous plant in the path of this fungus is likely to be killed.  The fungus can also kill small trees under the right conditions.  The first time I encountered Southern blight was about 20 years ago when it popped up in a flowerbed at the Allen Centennial Garden.  By the time I visited the garden to make a diagnosis, the fungus had killed off every plant in about a 40 square foot area.  As I examined the dead plants, I noted characteristic sclerotia (i.e., resting structures) of the fungus (they look like Osmocote® pellets) all over the bases of the dead plants and in a layer across the mulch in the bed. 

Early in my diagnostic career (i.e., the late 1990s), I occasionally saw Southern blight in Wisconsin.  However, because the pathogen is adapted to tropical and sub-tropical climates, it did not survive the harsh Wisconsin winters at that time.  Extended periods where high temperatures were in the negative digits were common, and these temperatures killed the fungus.  Nowadays, with our relatively mild winters, A. rolfsii seems to be better able to overwinter in the state.  That’s a huge problem because the fungus is easily moved around (via those pesky sclerotia), and if it is not killed by cold weather, then there is increased risk of spread and subsequent wholesale plant destruction. 

Oak wilt

Oak wilt has been present in Wisconsin for the entirety of my diagnostic career, and I have watched the Wisconsin Department of Natural Resources map its spread in the state over the years.  Historically in Wisconsin, sap beetles have moved the oak wilt fungus (Bretziella fagacearum) from location to location.  These insects are attracted to wounded trees and drop off B. fagacearum as they feed on sap in the wounds.  The fungus infects, leading to blockages of a tree’s water-conducting tissue, subsequent branch dieback, and eventual tree death.  Once an oak tree is infected, B. fagacearum can move to nearby oak trees through root grafts. 

I am concerned that our warming weather pattern could contribute to increased risk for oak wilt in a couple of ways.  Warmer summer temperatures are often associated with an increase the frequency and severity of summer storms.  More (and more violent) storms increase the risk of damaged oak trees, which increases the risk of sap beetles visiting these trees and dropping off the oak wilt fungus.  In addition, sap beetles are not the only insect that can move the oak wilt fungus around.  Certain oak bark beetles have been documented to move the fungus as well.  These bark beetles have traditionally had a more southern native range and have not been found extensively in Wisconsin.  However, PJ Liesch, the UW-Madison insect diagnostician, recently commented to me that Pseudopityophthorus minutissimus (one of the oak bark beetles involved in transmission of the oak wilt fungus) has been very abundant in Wisconsin over the last few years.  He’s seen lots of this insect in oak samples that have come into his lab.  How important oak bark beetles are in transmitting Bretziella fagacearum in Wisconsin at this time is not known.  However, they will likely become increasingly important as they become more established and abundant in the state. 

Thousand cankers disease

This fungal disease of black walnut trees has not be reported in Wisconsin to date; the closest state with confirmed reports is Indiana.  Efforts to prevent the introduction of the pathogen (Geosmithia morbida) into Wisconsin currently involve limiting importation of raw walnut wood into the state.  The hope is to prevent introduction of G. morbida, as well as the walnut twig beetle (Pityophthorus juglandis).  This insect moves the thousand cankers disease fungus from tree to tree.  P. juglandis is native to Arizona, California, and New Mexico, but in the last decade or so has been introduced into states east of the Mississippi River (e.g., Indiana, Ohio, Tennessee).  While movement of walnut wood currently poses the greatest threat for introduction of G. morbida and P. juglandis into Wisconsin, milder long-term weather patterns open up the possibility of eventual natural spread of P. juglandis (carrying G. morbida) into the state.  I think it’s only a matter of time before thousand cankers disease pops up in Wisconsin. 

As our long-term weather pattern changes, I’ll be on the lookout for new diseases and changes in established diseases in Wisconsin.  I suggest that you watch your own gardens and landscapes for new diseases that you have not encountered in the past.  You’ll likely see changes.  If you’d like help in identifying your new finds, feel free to contact the PDDC for help.  Check out the clinic website at https://pddc.wisc.edu for details on sample submission, or call (608) 262-2863 or email pddc@wisc.edu for advice and guidance.  To keep up to date on clinic activities and resouces, follow the PDDC on Facebook or Twitter (@UWPDDC), or subscribe to the clinic’s listserv, UWPDDCLearn (by emailing or phoning the clinic to subscribe). 

Happy spring and happy disease hunting, everyone!

February 2024: Garden Expo Afterglow

Afterglow IconThe 2024 PBS Wisconsin Garden and Landscape Expo (February 9 – 11) has come and gone.  While I spent last week physically recuperating from Garden Expo (standing on a concrete floor gets rougher each year), my mind and spirit came away from the event rejuvenated and invigorated.  The weather was perfect with four warm, snow-free days (including set up day) that attracted almost 15,000 people to the event. 

As I do each year, I coordinated and staffed the UW-Madison Plant Disease Diagnostics Clinic (PDDC) booth at Garden Expo.  Organizers Amanda Balistreri and Heather Robbins again generously provided me with a double booth for my display at no charge.   This year I had an endcap booth in a prime location near the entrance to the exhibit hall.  The configuration of the booth (i.e., with visibility from three sides) provided me even more space than normal to display and highlight the full range of services and educational materials that I provide.   The booth allowed visitors the opportunity to get up close and personal with plant disease specimens and photos; to peruse and walk away with free UW Plant Disease Facts fact sheets (116 titles again this year); and to check out my plant disease-themed limerick book, building block plant diseases, and UW Plant Disease Facts medallions.  I also provided fliers on the monthly PDDC Plant Disease Talks that I organize, as well as the Ask-the-Experts Q&A sessions I participate in with colleagues from the UW-Madison Division of Extension Horticulture Program.  Finally, I played a looped video of segments that I filmed over the years with Shelley Ryan on Wisconsin Public Television’s The Wisconsin Gardener.  It’s been 10 years since Shelley’s passing, and it’s comforting to know that the outreach event that she and her show inspired is still going strong. 

As always, I was at Garden Expo all three days (noon until 7 pm on Friday, 9 am until 6 pm on Saturday, and 10 am until 4 pm on Sunday).  A special shout out goes to Chad Teubert of the UW Russell Labs Hub for helping transport and unload my booth materials on Thursday at the Alliant Energy Center, and for helping unload things back at Russell Labs the Monday after Expo.  Also, thanks go to Lisa Johnson of Extension Dane County who helped staff my booth when I was off giving talks. 

During the course of Garden Expo, I gave three talks:  Vegetable Diseases, Growing Healthy Plants:  Basics in Plant Disease Management, and Ten Diseases of Native Plants (and Non-Natives, Too).  I also helped answer questions with Lisa Johnson at Larry Meiller’s in-person Garden Talk session on Saturday morning.  I had a constant stream of visitors through the PDDC booth all three days (Friday was unusually busy this year) and pretty much talked with and answered questions for folks the entire time.  I distributed 4,805 fact sheets, 924 brochures/informational handouts of various kinds, and 228 handouts for my talks.  For the first time, I had to reprint some fact sheets early Sunday morning, because I had run out of certain titles (e.g., Blossom End Rot) by the end of the day on Saturday.  All of these materials were not only educational in nature but were branded with the UW-Madison Division of Extension logo and/or the UW-Madison CALS logo, thus providing advertising for the UW-Madison. 

I had a exhilarating, productive weekend and provided a valuable service to the public.  I heard numerous positive comments about, and thanks for, the services that I provide.  This positive feedback is what keeps me motivated to do the work that I do.  The 2024 PBS Wisconsin Garden and Landscape Expo continues to be, by far, the most important in-person outreach event that I do every year and, quite frankly, my absolute favorite work activity. 

If you’d like to learn more about the PDDC and the services it provides, feel free to check out the clinic website at https://pddc.wisc.edu.  Also, feel free to follow the clinic on Facebook or Twitter (@UWPDDC), or subscribe to the clinic’s listserv (UWPDDCLearn) by emailing me at pddc@wisc.edu or (608) 262-2863. 

Here’s to looking forward to Garden Expo 2025!

January 2024: New Kits on the Block

Building Block IconMark your calendar!  January 28, 2024 is LEGO* Day.  I have been a big fan of LEGO in my personal life for a long time, and I was particularly excited when, several years ago, LEGO came out with their “Botanical Collection”.  I must admit that I went a bit crazy and overindulged in purchasing (and building) every plant-themed kit that became available. 

One day, as I putting together one of the LEGO botanical kits, I thought, “If you can have kits for building plants, why couldn’t you have kits for building diseased plants?”  Thus was born what I now refer to as “Building Block Plant Diseases”. 

The first step in creating the plant disease kits that I envisioned was to design models.  Luckily, an IT friend directed me to a computer program that allowed me to 3-D model plant diseases in building block form.  Using this program, I designed building block versions of several plant diseases including apple scab, Armillaria root disease, blossom end rot, cedar-apple rust, common smut of corn, grape downy mildew, powdery mildew, and silver leaf

After all of this computer-modeling, I next wanted to build a physical model of at least one of the diseases.  I focused on blossom end rot of tomato, as I was able to find and purchase pre-fabricated blocks that would allow me to build this model.  I also ended up designing and building a healthy tomato fruit to provide a comparison with the diseased fruit .  I have to say, it was pretty exciting to see one my “theoretical” building block plant diseases become a physical reality. 

My ultimate goal was to use my kits as educational tools, so I next worked on developing materials to supplement and enhance the building block models.  For my blossom end rot kit, I designed instruction manuals for both the diseased and healthy tomato fruits, as well as adult– and kid-friendly fact sheets to teach users about the disease/disorder.  To add educational value, I developed a blossom end rot word search game to include in the kit. 

Given that my building block kits are targeted toward a youth audience (not a demographic that I normally work with), I then needed to find partners who could get the my kits into the hands of kids.  I was fortunate in that two groups showed interest.  First was the “What’s Eating My Plants” or WEMP graduate student group in my department.  This group does extensive outreach to schools and other kid-friendly venues in the Madison area.  WEMP debuted my blossom end rot kits at a program the Monona Public Library in December 2023.  WEMP was also instrumental in translating all of my written materials, so that a Spanish version of the kit would be available.  The other folks that I have been partnering with extensively are UW-Madison Division of Extension 4H educators.  These educators will be incorporating the blossom end rot kit into a curriculum that they are developing to teach kids about the history and uses of tomatoes, as well as about tomato-related careers.  Eventually, blossom end rot building block kits will be availble in every county in Wisconsin. 

If the idea of “Building Block Plant Diseases” piques your interest, and you are interested in seeing my blossom end rot building block models, I will have the models on display at my booth at the PBS Wisconsin Garden and Landscaping Expo at the Alliant Energy Center in Madison, February 9-11, 2024.  Feel free to stop by booth #533/#604 to take a look. 

So, what’s next?  Well, the big challenge for bringing other plant disease building block kits to fruition is that prefabricated blocks are not available for the other models that I have designed.  A possible work around for this problem would be to 3-D print the blocks that I need.  I currently have a 3-D printer in my basement, and with help from the IT friend that I previously mentioned, I hope to engage in a frenzy of block printing activity this winter and have physical versions of at least some of the other plant diseases that I have modeled by the end of the year. 

“Building Block Plant Diseases” has been a really fun and exciting project to work on.  If you would like to keep up to date on developments on this project, be sure to follow the PDDC on Twitter (aka X)  or Facebook (both @UWPDDC), or subscribe to the PDDC listserv, UWPDDCLearn (just email me to join).  As always, you can also contact me by phone at (608) 262-2863 or email at pddc@wisc.edu

With that, go forth and build!!

 

*DISCLAIMER:  References to LEGO products in this article is not an endorsement of these products by the University of Wisconsin or a criticism of other similar products.  Mention of LEGO is solely for the purpose of illustrating the process that led to the development of “Building Block Plant Diseases”. 

 

December 2023: 2023 in Review

Review IconIt’s the last day of 2023 and time to look back and see what went on during the year at the Plant Disease Diagnostics Clinic (PDDC).  In my mind, I see 2023 as probably the most creative year of my entire career.  While I continued to perform my routine diagnostics tasks, I also initiated several new outreach projects that were (at least to me) incredibly exciting.  Here’s a rundown of the highs and lows in the clinic for the year. 

Plant disease diagnostics

Diagnosing a Plant Disease at the Microscope
Diagnosing a Plant Disease at the Microscope

2023 was, quite frankly, a horrible year in terms of sample submissions.  I completed 1005 samples (a combination of physical and digital samples) during 2023, the lowest number ever during my tenure as director of the PDDC.  I received samples from 60 of Wisconsin’s 72 counties, as well as from six additional states in the US.  Most of the samples were ornamentals (i.e., trees, shrubs, herbaceous plants), but there were a fair number of vegetable, fruit, and field and forage crop samples as well.  I’d like to give a big shout out to Dante Tauscheck, the new molecular diagnostician at the PDDC, who helped with the processing of many of these samples. 

In large part, the low sample number in 2023 was due to our extremely dry weather during the growing season.  Plant disease-causing organisms (particularly fungi) are more active in wetter weather, and we just didn’t have much rain throughout Wisconsin in 2023.  Diseases/disorders that did make a big splash in 2023 included fire blight, powdery mildew, and chlorosis.  The uptick of all of these was likely influenced by our dry weather.  Bees move the fire blight bacterium from tree to tree, and these insects tend to be more active in dry weather.  Powdery mildew fungi are known to prefer dry (i.e., no rain) but humid conditions, and that’s exactly the sort of weather we had this past summer.  And finally, lack of soil moisture likely inhibited uptake of iron and manganese by plants, thus exacerbating the chlorosis problems that we see every year throughout much of the state due to high soil pH.    

Presentations

PDDC Booth at Garden Expo 2023
PDDC Booth at Garden Expo 2023

I notched 64 outreach presentations/talks during the year.  Three of those talks occurred at WPT’s Garden and Landscape Expo.  2023 marked my return to that event for the first time since the COVID pandemic started in 2020.  At Garden Expo, in addition to providing talks, I sponsored the PDDC booth, where I answered questions pretty much non-stop and distributed over 4000 UW Plant Disease Facts.  I also teamed up with Larry Meiller of WPR’s Garden Talk and Lisa Johnson of Extension Dane County to do a Q & A session.  It was a great three days.  For additional details on my experiences at the 2023 Garden Expo, check out my February web article.  

In 2023, I also debuted my PDDC Plant Disease Talks series.  I provided talks once a month on a wide range of plant disease topics and had 1465 participants over the course of the year.  While targeted toward WI residents, I ended up having participants from across the US (New York to Oregon, Minnesota to Arizona).  The talks provided general education for the public, as well as continuing education units (CEUs) to help professional arborists and Master Gardeners maintain their certifications.  I have to give a shout out to Ted Geibel and Lisa Johnson for helping behind the (Zoom) scenes to help make these talks a success.  The talks were popular enough that I will be continuing the series in 2024

Across all 64 of my presentations, including three visits to Garden Talk with Larry Meiller/The Larry Meiller Show, I helped over 210,000 people learn about plant diseases over the course of 2023. 

Online written resources

Sample Plant Disease Medallions
Sample Plant Disease Medallions

Via the PDDC website, I provided weekly updates of my clinic diagnoses (the Wisconsin Disease Almanac).  In addition, I wrote 13 web articles during the course of the year.  My favorite was probably 25 Years. . . 25 Cool Diseases, commemorating my 25th anniversary (July 1) as director of the PDDC.  Also housed on the PDDC website were the 130 titles in the UW Plant Disease Facts series.  A new twist for the fact sheets in 2023 was the debut of the Fact Sheet Medallions project.  For each fact sheet, I wrote a quiz and created a decorative electronic medallion.  You can now read a fact sheet, take the corresponding quiz, and once you get 100% on the quiz, you earn the corresponding medallion (automatically delivered to you via email).  So far, participants have taken over 1700 quizzes and earned over 450 medallions.  I know of one person who has collected all 130.  Earning medallions is not only fun, but it also qualifies as CEUs for Master Gardeners.  I have to give a special thank you to Dixie Lang, IT wizard extraordinaire, who helps maintain my clinic website and also figured out how to create the online quizzes and automation of medallion delivery that made the medallion project possible. 

The book! 

Limerickettsia: A Plant Pathologist's Book of Verse
Limerickettsia: A Plant Pathologist’s Book of Verse

I was so excited to publish my first book in 2023.  Titled Limerickettsia:  A Plant Pathologist’s Book of Verse, it contains 52 plant disease-related limericks with supplemental prose discussions of the diseases, photos, and original artwork.  I debuted the book at Garden Expo and have been selling the book as a fundraiser for the clinic since then.  Larry Meiller was kind enough to feature my book on his radio show (thanks Jill Nadeau for doing the interview!), and that’s helped with sales.  The book will never be a New York Times Bestseller (I’ve sold just over 160 copies thus far), but that was never the point.  My goal was to create a fun, alternate way for people (particularly a younger demographic) to learn about plant diseases.  I think I’ve accomplished that goal. 

Other crazy outreach

Building Block Blossom End Rot
Building Block Blossom End Rot

Another of my projects that came to partial fruition in 2023 was the plant disease building block kits that I started working on during the COVID pandemic.  I completed the blossom end rot kit this year, which includes LEGO pieces to construct diseased and healthy tomato fruits, instructions manuals, adult- and kid-oriented fact sheets, and a word search game.  The graduate student outreach group (What’s Eating My Plants or WEMP) in my department at the UW-Madison debuted the kits at the Monona Public Library in December.  I am also working with Extension 4H educators to provide kits to each county in Wisconsin in 2024.  I’m working on other kits as well (e.g., powdery mildew, downy mildew of grape, apple scab, silver leaf, Armillaria root disease, and common smut of corn) and that involves using 3-D printing to generate the parts that I need.  Hopefully, physical mock ups of these kits will be available sometime in 2024

Want to know more about the PDDC? 

All in all, 2023 was a great year at the PDDC.  As we get into 2024, and I develop new PDDC resources, I will announce their availability via Twitter (@UWPDDC) and Facebook (@UWPDDC), or via my clinic listserv, UWPDDCLearn (email me to subscribe to this).  In addition, you can always contact me by phone at (608) 262-2863 or email at pddc@wisc.edu

Happy New Year!

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.

Seeds

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 pddc@wisc.edu or (608) 262-2863 with your suggestions.  Happy Thanksgiving everyone!