Category Archives: Monthly Column

April 2023: The Best Things in Life Are Free!

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

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

Late Blight

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

Boxwood Blight

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

Japanese Apple Rust

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

Questions?

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

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

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

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

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

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

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

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

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

March 2023: Reading is Fun(gi)damental

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

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

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

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

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

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

Happy reading!!

February 2023: Recovering from Garden Expo 2023

PDDC Booth IconI have just finished catching up from the 2023 PBS Garden and Landscape Expo (Friday, February 10 through Sunday, February 12). My booth displays are back in storage, and I’ve documented all of the various education materials that I provided for visitors. This was my first in-person Garden Expo post-COVID. I have to say the weather for the actual event was perfect (sunny and warm), after a challenging set-up day of snowy weather and hazardous driving. Attendance at this year’s Garden Expo was 13,584, with visitors not only from Wisconsin, but from all around the Midwest.

This year, I coordinated and staffed the UW-Madison Plant Disease Diagnostics Clinic (PDDC) booth. Garden Expo organizers Amanda Balistreri and Heather Robbins were very generous in allowing me to have a double booth for my display at no charge. This spacious area provides lots of room for Garden Expo visitors to move about, look at disease specimens and photos, browse free fact sheets (116 titles this year), talk to booth denizens (myself included), and watch segments that I did over the years with Shelley Ryan on WPT’s Wisconsin Gardener. I really like visitors to know that Garden Expo exists because of Shelley and her show.

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). Many thanks go to Lisa Johnson of Extension Dane County, Diana Alfuth of Extension Pierce and St. Croix Counties, and longtime horticulture friend, Lis Friemoth (aka The Garden Hoe) for helping staff the booth. A special shout out goes to Tim Lorenz of the UW Russell Labs Hub for helping transport and unload my booth materials on Thursday and Lis Friemoth for helping pack up and load my van at the end of the show on Sunday.

During the three days, I gave three talks (New and Emerging Plant Diseases, Vegetable Diseases and Growing Healthy Plants: Basics in Plant Disease Management) and helped answer questions with Lisa Johnson Larry Meiller’s in-person Garden Talk session on Saturday morning. I also had a steady stream of visitors to the PDDC booth all three days and pretty much talked with and answered questions for folks the entire time. In fact, this is the busiest I have been at my booth for many, many years. I distributed 4,319 fact sheets, 720 brochures/informational handouts of various kinds and 248 handouts for my talks. The top ten fact sheets selected by booth visitors were (in alphabetical order):

Blossom End Rot
Home Vegetable Garden Fungicides
Lawn Disease Quick Reference
Plant Problems to Watch for in 2023
Powdery Mildew (Deciduous Woody Ornamentals)
Powdery Mildew (Herbaceous Ornamentals)
Powdery Mildew (Vegetables)
Septoria Leaf Spot
Ten Common Plant Diseases/Disorders You Can Identify by Eye
Vegetable Disease Quick Reference

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 and thus provided advertising for UW-Madison.

All-in-all, I had a great, productive weekend, and I think provided a valuable service to the general public. By the time the weekend was over, I physically felt like I had been hit by a truck, but mentally and emotionally, I felt rejuvenated due to all of the positive feedback that I received. I heard numerous positive comments about, and thanks for the work that I do (and more generally about the outreach work that UW as an organization does). PBS Garden & Landscape Expo is by far the most important in-person event that I do every year and, quite frankly, my absolute favorite work activity. I encourage any of you who have not attended Garden Expo to consider doing so in 2024. If you do attend, be sure to stop by the PDDC booth and say hello.  I will be there!

Questions?

If you have questions about PDDC outreach activities and diagnostic services, 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 their management, as well sample submission.  You can follow the PDDC on Twitter and Facebook (@UWPDDC) or email pddc@wisc.edu to subscribe to the PDDC listserv, UWPDDCLearn, to receive updates on clinic services and educational materials.

January 2023: Plant Disease Diagnostics Clinic Services for 2023

Turquoise Microscope Icon2023 has arrived, and I’m already thinking ahead to the deluge of samples that are likely to arrive at the UW Plant Disease Diagnostics Clinic (PDDC) this summer.  PDDC personnel continue their efforts to balance providing high quality services to the public with keeping clinic staff and clients healthy and safe.  The following are current guidelines for submitting samples and tapping into the PDDC’s outreach programs and resources.  Our world is ever evolving, and there will likely be changes in how the PDDC functions as 2023 unfolds.  Be sure to check this document routinely for updates.

Plant Disease Diagnostics

The PDDC continues to offer digital diagnoses, and I really encourage you to submit digital photos of your plant disease problem before submitting a physical sample.  Use the PDDC online form for photo submissions.  In some situations, I will be able to provide a diagnosis and management recommendations based on your photos.  There is a $20 fee for this service.  If I cannot make a diagnosis from your photos, I will not charge the fee, but I will use the photos to provide you suggestions on what sort of physical sample to submit as a follow-up.  Note that if I charge a digital fee and you end up submitting a follow-up physical sample, the digital fee will be credited towards any lab fees for the physical sample.

You can submit physical diagnostic samples either by mail or in person.  If you opt to drop off a sample in person, PDDC staff will not likely be available for in-person consultations.  While I am committed to providing personalized service to my clients whenever possible, the PDDC is short-staffed at this time, and PDDC staff members need to concentrate their efforts on sample processing in order to keep up with incoming samples and provide timely diagnoses.

The PDDC provides an area for physical sample drop off in the hall outside the clinic.  Check for the large, black, wood shelving unit in the alcove just down the hall from the clinic door.  You can drop your sample(s) there.  Be sure to fill out a submission form to include with each sample.  You can find forms in the wall pocket to the left of the clinic door.  The form is also available online if you would like to print and fill it out ahead of time to speed up the submission process.  Please print neatly on the form and make sure to include your complete mailing address (with zip code), your phone number and your email address.  If you are a commercial client, please include the name of the business that you work for.  At this time, I am emailing virtually all reports and invoices.  If you do not have email however, just let me know, and I definitely can and will send out a hard copy of your report and invoice.

Presentations

I will be providing more in-person plant disease presentations in 2023.  However, due to the cost of traveling (both in terms of time and monetary expense), I will continue to encourage clients to consider virtual presentations (e.g., via Zoom) whenever possible and practical.  If you are interested in having me provide a presentation for a group that you are affiliated with, click here to check out a list of topics that I routinely speak on.  Email me at pddc@wisc.edu or call me at (608) 262-2863 to discuss what talk might be best suited for your audience and to schedule a date and time.

In addition in 2023, I will be sponsoring monthly Zoom presentations on a range of plant disease topics.  Click here to check out these presentations and sign up if you are interested.

Online Resources

Via the PDDC website, I will continue to provide weekly updates of my PDDC diagnoses (the Wisconsin Disease Almanac), as well as web articles (hopefully monthly, but frequency will depend on clinic sample volume).  Also check out the PDDC website for the UW Plant Disease Facts (formerly the plant disease-related titles of the University of Wisconsin Garden Facts).

I will be recording the monthly PDDC plant disease talks (mentioned above) and will eventually be working these into online playlists (with full transcripts to fulfill UW-Madison accessibility requirements) that I will make available on my nascent YouTube channel (@UWPDDC).  My Fundamentals of Plant Diseases presentation is currently available as a playlist on my YouTube channel.

Outreach teasers

I am currently working on several new outreach projects.

Limerick Book

First is my book, Limerickettsia:  A Plant Pathologist’s Book of Verse.  This is a book of 52 plant disease-related limericks with supplemental prose discussions of the diseases and original artwork.  I am in the final throes of completing this and getting it printed.  April 3, 2023 update:  Now complete!!  Click here for details.

Plant Disease Medallions

I am also working on the UW Plant Disease Facts Medallions project.  For each of the 130 fact sheets in the UW Plant Disease Facts series, I have created electronic medallions and quizzes.  Eventually, you will be able to read one of the fact sheets and take the corresponding quiz.  If you get a score of 100%, you will be emailed the corresponding medallion.  Collect them all!  Hopefully, this project will be launched to the public this winter or early spring.  April 3, 2023 update:  Now complete!!  Click here for details.

Building Block Plant Diseases

Finally, I am developing building block kits (akin to LEGO kits) of common plant diseases (with supplemental educational materials).  I have designed models for blossom end rot, powdery mildew, downy mildew of grape, apple scab, silver leaf, Armillaria root disease, and (most recently) common smut of corn.  I am now working on getting the blocks for the kits 3-D printed so that I will have prototypes available for view by this spring.  October 27, 2023 update:  The blossom end rot building block kit is set to debut in early December at the Monona Public Library courtesy of the UW-Madison Department of Plant Pathology’s graduate student outreach group, What’s Eating My Plants (WEMP).

Need information on the PDDC? 

As new PDDC resources become available, 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.

Have a great 2023 everyone!

December 2022: A Plant Pathologist’s Holiday Shopping List

Present Icon‘Tis the Season to buy holiday gifts.  I often have a difficult time coming up with ideas for what to buy for friends and family who seem to have everything.  Similarly, I’m a frustrating person to buy for; I just have too much stuff.  If you’re trying to come up with that perfect gift, and socks, a scarf or a necktie won’t do, consider a nifty plant disease-related gift that may put a smile on a loved one’s face.  I’m not talking about a greeting card or t-shirt with a plant disease design or pithy plant disease quote but actual diseased plant materials that you can gift to a friend.

Artisan wooden bowls

There are a couple of variations on this gift idea.  If you know of someone who really loves cherry wood (me, me!!), 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 refer to this disease affectionately 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.

The other types of bowls (or other wooden art objects) that are produced from diseased trees are those exhibiting spalting.  These wooden objects are produced from trees that are suffering from wood rot (typically white rot).  These rots are fungal in nature.  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 in to stunning artisan pieces with the decorative line patterns intact.

Walking sticks

Do you have a hiker friend who needs a gift?  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 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.

Poinsettias

For a less expensive disease-related gift (the wood gifts described above can be quite pricey), consider giving a friend or loved one a poinsettia.  “What’s diseased about a poinsettia?” you may ask.  Well, the poinsettias that you buy at your local greenhouse or floral shop are infected with phytoplasmas.  Phytoplasmas are bacteria-like organisms that colonizes a plant’s food-conducting tissue.  Poinsettias, in their native habitat, are tall (we’re talking 10 ft. or more) and lanky.  The presence of phytoplasmas stunts infected poinsettia plants and makes these plants produce extra branches, thus yielding the beautiful, compact, bushy poinsettias that we have come to love.

Huitlacoche

For the gourmand on your shopping list, a can of huitlacoche (alternatively called cuitlacoche) might be the perfect stocking stuffer.  Huitlacoche is the polite name for common smut of corn.  This is a fungal disease where infection occurs through corn silks as the plants flower.  The fungus causes corn kernels to enlarge into huge, pasty gray masses (galls again).  Eventually, the interior gall tissue converts into powdery spores.  But, if you catch the galls when they are still solid and fleshy, you can use them for cooking.  Huitlacoche is a common ingredient in traditional Mexican cuisine, and many high-end restaurants now offer it on their menus.  While fresh huitlacoche is always a better choice, canned huitlacoche is readily available in specialty food stores, as well as online.

Questions?

If you have questions about any of the disease gifts discussed above, or need additional ideas for plant pathology related gardening 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 their management, as well sample submission.  You can follow the PDDC on Twitter and Facebook (@UWPDDC) or email me to subscribe to the PDDC listserv, UWPDDCLearn, to receive updates on clinic services and educational materials.

Happy Holidays and good luck with your shopping!

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.

Update 12/9/22 

Here’s another plant disease gift idea I stumbled across (although there are some caveats with this one). . .

Oud perfumes and colognes 

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 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.

Update 12/14/22:  

And Santa’s plant pathology gift list grows longer (courtesy of Patty McManus, the former UW-Madison fruit pathologist) . . .

Noble rot wines 

Have a wine connoisseur who needs a holiday gift?  Then, consider noble rot wines.  These wines are produced from grapes that have been infected by Botrytis cinerea.  This fungus, if growing conditions are wet for extended periods of time, 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, 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 appears to add 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).

 

March 2022: Checking Out the New Gym (or Flexing Your Muscles on a New Wisconsin Disease)

Barbell IconI’ve been around long enough at the PDDC (25 years next summer) that most of the diseases that I see at the clinic are old friends.  Rhizosphaera needle cast, oak wilt, Verticillium wilt and many others are part of the cast of plant disease characters that I see in Wisconsin every year.  It’s relatively rare that I see brand new diseases.  In recent years, boxwood blight, Neopestalotiopsis leaf spot and fruit rot of strawberry and zonate leaf spot (a disease that had been on my bucket list for years) are new diseases that have crossed my doorstep.  In 2022, I’m watching for yet another new disease:  Japanese apple rust.

Japanese apple rust is a type of Gymnosporangium rust caused by the fungus Gymnosporangium yamadae.  This fungus is native to Asia (specifically China, Korea and Japan) and was first detected in the United States in Delaware and Pennsylvania in 2008 (with a first formal published report in 2009).  In 2021, Sam Fieweger of the Wisconsin Department of Agriculture, Trade and Consumer Protection (WI DATCP) Plant Industry Bureau Lab confirmed the first detection of the disease in Wisconsin.  The disease was identified on a crabapple tree in a nursery in southeast Wisconsin.

Like other Gymnosporangium rusts, Japanese apple rust is an altnernating rust.  The causal fungus requires two different host plants to complete its life cycle.  It spends half of its life on a wide range of apples/crabapples (Malus spp.) and the other half on Chinese juniper (Juniperus chinensis, Japanese garden juniper (Juniperus chinensis var. procumbens) and Sargent juniper (Juniperus chinensis var. sargentii).

Japanese apple rust on juniper.  Photo courtesy of Nancy Gregory, University of Delaware.
Japanese apple rust on juniper.  Photo courtesy of Nancy Gregory, University of Delaware.

Typical symptoms of Japanese apple rust are not radically different than those of other Gymnosporangium rusts.  On juniper hosts, the disease leads to the formation of relatively small branch galls that ooze orange gelatinous arms/masses in the spring.  These galls/masses look (at least to the casual observer) not that different from those produced by cedar-apple rust (CAR) and (particularly) cedar-hawthorn rust (CHR), two common Wisconsin Gymnosporangium rusts.  On apple/crabapple hosts, symptoms of Japanese apple rust are again similar to those of CAR and CHR:  large, brightly-colored leaf spots.  In the cases of CAR and CHR, the spots are yellow to orange.  In the case of Japanese apple rust, the spots are fuchsia to red.  On the undersurface of the leaves where the spots are located, short spiny structures eventually form.  These are reproductive structures that produce spores that reinfect the juniper hosts.

Japanese apple rust on crabapple.  Photo courtesy of Nancy Gregory, University of Delaware.
Japanese apple rust on crabapple.  Photo courtesy of Nancy Gregory, University of Delaware.

The presence of Japanese apple rust in Wisconsin puts a wrench in the recommendations that I typically make for managing Gymnosporangium rusts.  Chinese junipers are not great hosts for CAR, CHR and cedar-quince rust (the other common Gymnosporangium rust in Wisconsin), so I have historically recommended these junipers for clients who are desperate to grow junipers and apples, crabapples and hawthorns near one another.  If (more likely when) Japanese apple rust becomes more prevalent, Chinese junipers will no longer be a good choice to grow alongside apples and crabapples.  In the future, management of Gymnosporangium rusts will likely have to rely on not growing junipers and apples, crabapples and hawthorns anywhere near each other.

Because Gymnosporangium yamadae is not native to the US, Japanese apple rust is of regulatory importance in Wisconsin (and also elsewhere in the US).  There is interest in determining how widespread the disease may be in the state.  For that reason, I will be providing free diagnostics (as long as I am financially able – the testing is a bit pricey) for suspect Japanese apple rust samples.  The easiest hosts to verify the disease on will likely be apples or crabapples.  So, please watch for those fuchsia to red spots.  If you see anything suspicious, please submit digital photos via my online digital diagnostics form.  Let me know in the “Message” field that you suspect Japanese apple rust, and there will be no fee.  If your photos look suspicious, I’ll request a follow-up physical sample for additional lab testing.

Have questions?

If you have questions about Japanese apple rust or submitting a Japanese rust sample (or need advice about plant diseases in general), feel free to contact the PDDC by phone at (608) 262-2863 or email at pddc@wisc.edu.  Also check out the PDDC website (https://pddc.wisc.edu) for additional details on plant diseases and sample submission.  Feel free to follow the PDDC on Twitter and Facebook (@UWPDDC) or email me to subscribe to the PDDC listserv, UWPDDCLearn, to receive updates on clinic services and educational materials.

Good luck with your new workout!

 

February 2022: Optimizing Your Diagnosis at the PDDC

Diseased Leaves Branches and Fruits IconHere at the Plant Disease Diagnostics Clinic (PDDC), we strive to provide the best possible diagnoses of plant disease problems.  PDDC staff use a range of techniques to do this including visual and microscopic examination of plant tissue, incubation of tissue in moist chambers to coax fungal pathogens to sporulate, culturing techniques to grow pathogens from tissue, serological tests to detect proteins specific to certain pathogens, and DNA/RNA (i.e., genetic material) detection techniques.  The PDDC’s ability to provide a high quality diagnoses using these techniques however, is dependent on receiving a high quality sample to work with.

Here are some pointers on how to provide an optimal sample so that PDDC staff can provide an accurate, timely diagnosis.

Submit a sample when you first see a problem

Diagnosing plant diseases as early as possible allows for greater flexibility in management of diseases once they are identified.  So, contact PDDC staff as soon as you see a problem.  That said, disease-causing organisms may not produce structures that we need to see to make a diagnosis (e.g., fruiting bodies, spores) early in disease development.  We may need to work with you and have you repeatedly sample and submit materials over time to accurately diagnosis your plant disease problem.

Consider submitting photos prior to a physical sample

Sometimes, we can provide a reasonably accurate diagnosis based on photos (tar spot anyone?).  If not, photos can provide useful information on the sort of physical sample that you can send to the PDDC for a more detailed analysis.  You can use the online form at https://pddc.wisc.edu/digital-diagnosis/ to submit photos.  If for some reason that form doesn’t work for you, feel free to send photos to the clinic email address (pddc@wisc.edu).  If we are able to provide a diagnosis from your photos, there will be a $20 digital diagnosis fee.  If we make a preliminary diagnosis from the photos but suggest a follow-up physical sample submission for additional testing, the $20 digital fee will be credited towards any lab fees for your follow-up sample.

When submitting a physical sample, make sure you provide the appropriate plant part

If you have any questions about what to submit, contact the PDDC for advice.  Submitting the wrong plant part can lead to an inaccurate or delayed diagnosis.

For herbaceous plants (e.g., herbaceous ornamentals, vegetables), sending in an entire plant may be the best course of action.  In some situations, symptoms that you see on the leaves of plants are an indication of a problem in the root system.  With trees and shrubs, submitting an entire plant is not practical.  For these plants, submitting subsets of leaves/needles, branches and/or roots will likely be more appropriate.

Whatever you end up sending, send A LOT.  Often, we need to perform multiple tests to diagnose a problem.  We don’t want to run short on tissue.  For leaves, send half a dozen to a dozen (or more) showing a range of symptoms.  For branches, send three or more symptomatic branches (with attached leaves or needles where appropriate).  For roots, send a large handful of the small, fibrous roots.

In particular, appropriate branch selection can be critical for accurately diagnosing vascular wilt diseases such as Dutch elm disease, oak wilt and Verticillium wilt.  For these diseases, select branches that have recently wilted/died back.  DO NOT submit branches that easily snap off.  These branches have been dead too long and cannot be accurately tested for vascular wilt pathogens.  If you suspect Verticillium wilt, select symptomatic branches from as low on the tree as possible as the pathogen that causes this disease infects through the roots.  Choose branches that are roughly one inch in diameter.  Larger diameter branches (particularly from oak trees) tend to have thick bark that is difficult to remove without contaminating underlying tissue where vascular wilt pathogens reside.  This contamination will interfere with growing pathogens from branch tissue and can also interfere with DNA-based tests for pathogen detection.  Sometimes, clients like to send in trunk sections for testing for vascular wilts.  These sorts of samples can work, but only if the trunk slices are no more that about one inch thick.  We need to be able to easily pop off the bark from these slices with minimal contamination of the wood underneath.

Submit your sample as quickly as possible to the PDDC

If possible, collect samples just before you mail them or drop them off in person.  If there is going to be a delay in submission, keep samples as cool as possible.  High temperatures can kill certain pathogens and can degrade herbaceous plant tissues, leading to what we not-so-affectionately refer to as “slime in a bag”.  Degraded samples make diagnostic testing more difficult, if not impossible.  Mail samples by overnight mail when possible.  If mailing via regular mail, please mail early in the week (Monday or Tuesday) so that samples do not sit around in a mail facility over a weekend.  Click here for details on how to package samples to make sure they arrive at the PDDC in good shape.

Help us, help you

Providing us with a high quality sample can go a long way in us providing you with a high quality diagnosis.  Let’s work together to make this happen.  If you have questions about submitting a sample (or about plant diseases in general), feel free to contact the PDDC by phone at (608) 262-2863 or email at pddc@wisc.edu.  Also check out the PDDC website (https://pddc.wisc.edu) for additional details on sample submission.  Feel free to follow the PDDC on Twitter and Facebook (@UWPDDC) or email me to subscribe to the PDDC listserv, UWPDDCLearn, to receive updates on clinic services and educational materials.

Good luck and happy plant disease sleuthing!

January 2022: Plant Disease Diagnostics Clinic Services for 2022

Turquoise Microscope IconAs we start 2022, COVID-19 continues to inform how the UW Plant Disease Diagnostics Clinic (PDDC) provides services to the public.  Clinic personnel continue to try to balance providing high quality services to the public with keeping clinic staff and clients healthy and safe.  The following are current guidelines for submitting samples and tapping into the PDDC’s outreach programs and resources.  Given that the COVID-19 situation is ever evolving, there will likely be changes in these guidelines as the year progresses.  Be sure to check this document routinely for updates.

Plant Disease Diagnostics

In 2020, I started offering formal digital diagnoses, and that service will continue in 2022.  I really encourage you to submit digital photos of your plant disease problems before submitting physical samples.  Use the online form at https://pddc.wisc.edu/digital-diagnosis/.  If I can see enough of what’s going on in your photos, I will provide you a diagnosis with management recommendations and charge the $20 digital diagnosis fee.  If I cannot make a definitive diagnosis, I will not charge the fee, but I will use the photos to help me provide you with suggestions on what sort of physical sample to submit as a follow-up.  Note that if I charge the digital fee and you end up submitting a follow-up physical sample, the digital fee will be credited towards any lab fees for your physical sample.

You can submit physical samples for diagnosis either by mail or in person.  For increased safety, I suggest submitting by mail.  If you opt to drop off a sample in person, PDDC staff will not be available for an in-person consultation.  While I am committed to providing personalized service to my clients, continuing issues with COVID-19 suggest that limiting person-to-person contact is prudent.  Also note that wearing a mask is required in all UW-Madison buildings at this time.

The PDDC provides a sample drop off location in the hall outside the clinic.  Check for the large, black, wood shelving unit in the alcove just down the hall from the clinic door.  You can drop your sample(s) there.  Be sure to fill out a submission form to include with your sample.  You can find forms in the wall pocket to the left of the clinic door.  The form is also available online if you would like to fill it out ahead of time to speed up the submission process.  Please print neatly and make sure to include your complete mailing address, your phone number and your email address.  At this time, I am emailing virtually all reports and invoices.  If you do not have email however, I definitely can send out a hard copy of your report and invoice.

Presentations

I was hoping to start providing in-person PDDC presentations in 2022, but with COVID-19 cases increasing at this time, I have cancelled the few in-person talks that I already had scheduled in early 2022 and will be limiting presentations to virtual presentations (e.g., via Zoom) until further notice.  If you are interested in having me provide a presentation, click here to check out a list of topics that I routinely speak on.  Email me at pddc@wisc.edu or call me at (608) 262-2863 to discuss what talk might be best suited for your audience.

Online Resources

Via the PDDC website, I will continue to provide weekly updates of my PDDC diagnoses (the Wisconsin Disease Almanac), as well as web articles (hopefully monthly, but frequency will depend on clinic sample volume).  Also check out the revised and rebranded UW Plant Disease Facts (formerly the plant disease-related titles of the University of Wisconsin Garden Facts).  I am also working on converting some of my in-person talks [Fundamentals of Plant Diseases and The Science (and Art) of Plant Disease Diagnosis] into online training modules with voiceovers.  As these new resources become available, I will announce their availability via Twitter, Facebook (@UWPDDC), or via my clinic listserv, UWPDDCLearn (email me to subscribe to this).

Consultations

As always, if you have questions about plant diseases, feel free to contact me by phone at (608) 262-2863 or email at pddc@wisc.edu.

Stay safe everyone and all the best for 2022!

July 2021: Summer Doldrums – Wilted Tomatoes in the Garden

Tomato IconI have recently received a slew of questions about wilted tomatoes in home gardens.  Here are the top five reasons that tomatoes can wilt based on samples that I have received in my clinic over the years.

Walnut toxicity

One of the lessons that I have learned after doing plant disease diagnostics for over 20 years is that when a home gardener consults me about wilting tomatoes, the first question I should ask is, “Do you have a walnut tree near your vegetable garden?”  More times than not, the answer is “Yes” and the walnut tree is the cause of the problem.  Black walnuts produce toxins (exuded by roots and produced in leaves and fruits) that adversally affect a wide range of plants,  Tomatoes are particularly sensitive and are often die from the exposure.  Anytime that tomatoes are grown in the root zone of a walnut tree (which extends three to five times the height of the tree from the trunk), problems can arise.  Cutting down walnut trees will not solve the problem in the short term, because roots from the cut tree can continue to exude toxins for 15 to 20 years.  Often the best recourse when walnut trees are present in a landscape is to grow tomatoes in raised beds or in pots to keep tomato roots as far above walnut roots as possible.

Drought stress

In 2021, lack of rain has been a potential cause for wilting in tomatoes and virtually every other plant.  Most established plants require about one inch of water per week.  When rain is insufficient (as it has been in much of Wisconsin this year), it’s important to apply supplemental water to plants with a soaker or drip hose.  Proper watering can not only prevent wilting in tomatoes, but it can also help improve calcium uptake and reduce problems with blossom end rot.  Using an inch or two of a high quality mulch (my favorites are shredded oak bark mulch and red cedar mulch) around plants can help retain moisture and lessen wilting issues.  Mulching around tomatoes also helps reduce movement of spores (produced in bits of old tomato debris in the soil) of the fungi that cause Septoria leaf spot and early blight.

Bacterial canker

The bacterium that causes this disease (Clavibacter michiganensis subsp. michiganensis – THERE’S a mouthful) is seedborne, so gardeners typically introduce this pathogen into their gardens on contaminated tomato seeds or transplants.  Plants initially look healthy, but the bacterium eventualy colonizes, discolors and disrupts the water-conducting (vascular) tissue inside the plant, leading to wilting.  Infections can lead to long, somewhat subtle cracks in stems and ultimately less subtle open wounds (i.e., cankers) in stems near the soil line.  Another telltale symptom of the disease can be ghostly-white spots with a darker center (called bird’s-eye spots) on tomato fruits.  Removal and destruction of infected plants, and rotation away from susceptible vegetables (e.g., tomatoes and peppers) for several years in the affected area of a garden are typical management strategies.

Verticillium wilt

Many gardeners are familiar with this disease in the context of the death and destruction it brings to woody trees and shrubs.  However, Verticillium, the cause of Verticillium wilt, is an equal opportunity destroyer and can kill a wide range of herbaceous plants as well, including popular vegetables such as solanacoues crops (e.g., tomato, potato, eggplant, pepper) and vine crops (e.g., cucumber, squash, pumpkin).  This fungus is routinely found in the soil and can build up over time if susceptible vegetable crops are grown over and over again in an area where the fungus is located.  Verticillium infects through the roots and colonizes and plugs a tomato’s (or other plant’s) water-conducting tissue, leading to wilting.  Discoloration of a tomato plant’s vascular tissue is a typical symptom of this disease, but stem cracks and cankers are notRotation can be useful as a control strategy for Verticillium wilt, although it is less effective than for bacterial canker because of the wider host range for Verticillium (including many weeds).  For tomatoes, use of resistant varieties can also be useful.  To identify resistant varieties, look for a “V” after the variety name on a tomato seed packet or in the variety description in your favorite seed catalog.

Fusarium wilt

This disease is very similar to Verticillium wilt except for the fungus involved.  For Fusarium wilt, Fusarium oxysporum f. sp. lycopersici is the culprit.  Fusarium oxysporum is a large fungal species with many special forms (that’s what “f. sp.” stands for), each one adapted to infect a specific host plant or a very small range of host plants (e.g., vine crops).  Fusarium oxysporum f. sp. lycopersici is specific to tomatoes and will not infect other vegetable crops.  If you ever encounter this disease, rotation away from tomatoes in the affected area for several years should work well as a management strategy.  In addition, you can use resistant tomato varieties.  Look for one or more ‘F’s” after the variety name.

Need help or more information?

As you can imagine, figuring out the exact reason your tomatoes are wilting can be challenging, particularly if there is disease involved.  For help with proper diagnosis of tomato wilts (and other plant problems in general), contact the PDDC at pddc@wisc.edu or (608) 262-2863.

To find out more about the clinic and its activities, check out the PDDC website.  To keep up-to-date about new PDDC education materials and programs, follow the clinic on Twitter or Facebook (@UWPDDC) or contact the clinic at pddc@wisc.edu and ask to be added to the PDDC’s listserv (UWPDDCLearn).