Earlier this 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. 

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. 

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. 

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!

In 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). 

The 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 rust.  Cedar-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). 

While 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). 

Our 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!

I’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!

The 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!