Valentine’s Day is coming soon, and people are always looking for gifts to buy for their sweethearts.  Even if you don’t have a significant other, Valentine’s Day can be a time to buy something fun for yourself!  But, what to buy?  Tired of the typical and somewhat cliché chocolates and red roses?  If so, consider a novel plant disease-related gift that will hopefully put a smile on your or your loved one’s face. 

Floral bouquets

I just dissed rose bouquets, but there are options for making plant-disease inspired floral arrangements for Valentine’s Day. 

First, I suggest that you include fantail willow.  Every time I see this plant, I wonder if it is infected with a phytoplasma of some kind.  Phytoplasmas are bacteria-like organisms (often moved from plant to plant by leafhoppers) that colonize a plant’s phloem (i.e., food-conducting tissue).  Symptoms associated with phytoplasma infections can include flattening and curlicuing of branches, both of which are characteristics of fantail willow.  Someday, I’m going to buy some branches of this plant and test them for phytoplasmas in my clinic. 

Next, I would include tulips with striped, puckered, and/or fringed petals.  Nowadays, these floral characteristics are likely due to the genetics of specific tulip varieties.   However, these features pay homage to the Rembrandt and parrot tulips of the past that were infected with Tulip mosaic virus (an aphid-transmitted plant virus).  Virus-infected tulips contributed to “tulip mania” in The Netherlands in the 1600s.  People went gaga over tulip bulbs that produced these unusual flowers, paid way too much for single bulbs (e.g., the equivalent of the purchase price of a house or a seafaring vessel), and subsequently lost their shirts when the market for these bulbs crashed. 

Finally, I’d throw in a few snapdragons.  There’s nothing specifically plant pathological about snapdragons, but if you ever grow them in your garden and let them go to seed, you’ll notice that the mature seed pods look like tiny human skulls!  So, as Dr. Death, I find this plant very “on brand”. 

Nobel rot wines

Need a bottle of wine to go with your plant disease bouquet?  If so, consider noble rot wines.  These wines are produced from grapes that have been infected by Botrytis cinerea.  If growing conditions are wet for an extended period, then this fungus can devastate a grape crop, rotting the fruits on the vine.  However, if there is only a short wet period (which promotes infection), followed by drier conditions, then the fungus causes a dehydration of the grapes without destructive decay.  This raisining of the grapes causes a concentration of sugars, and wines produced from noble rot grapes tend to be sweeter wines.  The presence of Botrytis cinerea also adds to the flavor profile of the wine, giving noble rot wines subtle hints of honey, beeswax and/or ginger.  Common noble rot wines include (but are not limited to) Tokaji (from Hungary/Slovania), Sauternes (from France) and Beerenauslese (from Germany/Austria).

Oud perfumes and colognes

Perfumes are a traditional Valentine’s Day gift, and oud perfumes are the plant disease versions that you can enjoy.  Oud (also spelled oudh) refers to a dark, fragrant resin that is produced in the heartwood of agarwood trees (Aquilaria spp.) in response to infection by the fungus Phialophora parasitica.  Only a small percentage of agarwood trees (maybe 2%) become infected.  The combination of sap and fungus has a scent that evokes leather, saffron and smoke.  Unfortunately, oud has historically has been so valued (for a variety of purposes in addition to perfume production) that agarwood trees have been overharvested to the point where many species are endangered.  There is now a move afoot to more sustainably produce oud by cultivating agarwood trees and artificially inoculating them.  So, if you decide that an oud perfume is your gift of choice, I suggest making sure the oud therein is from a sustainable source.

Artisan wood bowls

If you know of someone who really loves cherry wood (a reddish wood appropriate for Valentine’s Day), then consider finding a local woodworker who makes bowls from burls that form on the trunks of cherry trees.  These masses of wood (galls) are often the result of a fungal infection by Apiosporina morbosa, the black knot pathogen.  When infections occur on smaller branches, I affectionately refer to this disease as poop-on-a-stick, and the galls are not of much use.  However, larger black knot trunk galls are highly prized for their amazing grain patterns and can be used to make distinctive one-of-a-kind bowls that unfortunately, while beautiful, can be a bit pricey. 

Other types of bowls (or wooden art objects) that are made from diseased trees are those exhibiting spalting.  These wooden objects are produced from trees that are typically suffering from white rot, a kind of fungal wood rot.  As the fungus colonizes the wood and begins to degrade it, dark lines can form at the interface between healthy and diseased wood.  If caught at the right time (before substantial degradation has occurred), the diseased wood can be shaped into stunning artisan pieces with the decorative line patterns intact. 

Wood accessories and furniture

Do you or your significant other like to hike?  If so, then consider a diamond willow walking stick.  Diamond willow is not a type of willow tree, but the result of certain species of willows being infected by canker-causing fungi (in particular the fungus Valsa).  Infection leads the formation of diamond-shaped sunken areas (cankers) on affected branches.  These sunken areas have a Valentine’s day vibe as they exhibit a distinctive light and dark (often reddish) contrast between healthy and diseased tissue.  The diamond shapes and color combination make the infected branches highly prized for making not only walking sticks but also furniture.  Fancy a diamond willow love seat anyone? 

Some good reading

Finally, I’ll finish my list by shamelessly promoting my recently published book, “Limerickettsia:  A Plant Pathologist’s Book of Verse”.  Poetry is the language of love, is it not?  So, why not gift yourself or your loved one a book of 52 disease-themed limericks (including a Valentine’s Day appropriate one about Tobacco rattle virus on bleeding heart), with additional prose information, photographs, and original artwork. 

Questions?

If you have questions about any of the disease gifts discussed above, or have additional ideas for plant pathology-related gifts, feel free to contact the PDDC by email at pddc@wisc.edu or by phone at (608) 262-2863.  Also, feel free to check out the PDDC website (https://pddc.wisc.edu) for additional details on plant diseases and sample submission.  You can follow the PDDC on Facebook, Twitter (X), and Bluesky (@UWPDDC) or email me to subscribe to the PDDC listserv, UWPDDCLearn, to receive updates on clinic services and educational materials. 

Happy Valentine’s Day, and good luck in love and life!

Note

Links in this article lead to sites that are for illustrative purposes only and are not an endorsement of any particular vendor or item for sale.

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).