All posts by ddlang

April: April Showers Bring…Plant Diseases (Yay!)

It appears that spring is slowly arriving, and with the spring typically comes regular, often frequent rain showers.  The upside to this moisture is that it helps thaw the ground and stimulate plants to grow.  The downside however can be that this moisture provides a favorable environment for plant diseases to develop.

Damping-Off

Lower stem collapse of Zinnia seedlings due to damping-off.
Lower stem collapse of Zinnia seedlings due to damping-off.

If you like to plant early when soils are colder and moisture is high, you may run into problems with damping-off.  Damping-off pathogens (e.g., Pythium, Rhizoctonia, Fusarium) are found, at least at some level, in many soils and when combined with wet conditions and young, tender seedlings, death and destruction can be the result.  Watch for plants that never emerge (the seed rot or pre-emergence phases of damping-off) or those that do and then fall over onto the soil surface with collapsed lower stems (the post-emergence phase of the disease).  You can often avoid damping-off by planting later when soils are warmer and there is slightly drier weather.  The warmer soil stimulates plants to grow rapidly out of early stages of growth when they are most susceptible to infection.  Using a good seed fungicide treatment (often commercial seeds are pretreated prior to packaging) can also help prevent the disease.  Just be sure to handle any fungicide-treated seed according to the directions on the package to minimize any direct exposure to the fungicide.

Root Rots

Brown discoloration of roots typical of root rots.
Brown discoloration of roots typical of root rots.

Root rots are caused by many of the same organisms that cause damping-off including Phytophthora, Pythium, Rhizoctonia and Fusarium.  Root rots differ from damping-off however in that affect older herbaceous and woody plants.  The pathogens destroy root tissue, thus reducing water uptake, and that can eventually translate into dieback, general plant decline and, in extreme cases, death.  Root rot organisms tend to perform better in wet soils, and Pythium and Phytophthora actually reproduce more efficiently under cooler, wetter conditions.  So, making sure soils are well drained can be critical for root rot prevention.  Adding organic matter to heavier, clay soils to improve drainage prior to establishing a landscape can have a big impact long term on reducing root rot problems.  Also, making sure to mulch properly can help moderate soil moisture to a level that makes root rots less likely.  I typically recommend using approximately one to two inches of a high quality mulch (e.g., shredded oak bark mulch or red cedar mulch) on heavier, clay soils and roughly three inches of mulch (perhaps up to four inches) on lighter, sandier soils.  The mulch should be applied out to at least the dripline of trees and shrubs (i.e., the edge of where the branches extend) and kept away (approximately four to six inches) from tree trunks and crowns of shrubs.

Leaf Spots and Blights

Symptoms of tar spot on silver maple leaves.
Symptoms of tar spot on silver maple leaves.

Spring rains can also have a huge effect on the severity of many types of leaf spots and blights like anthracnose, tar spot and apple scab.  If extended rainy periods arrive when leaves are first emerging, then numerous infections can occur early and that can translate into severe disease and possibly even defoliation later in the summer.  Luckily trees seem to tolerate at least some defoliation, and long term effects due to leaf diseases are often minimal.  However, defoliation year after year can stress plants to the point where they become susceptible to more serious diseases (e.g., Armillaria root disease) and insect pests (e.g., two-lined chestnut borer).  While we have no control over Mother Nature and the rain she brings in the spring, using other disease management strategies can help lessen the effects of wet spring weather.  Careful cleanup and destruction (by burning, burning or hot composting) of plant debris in the fall can significantly reduce leaf pathogen carryover.  Proper pruning of trees to promote better air penetration, allowing for more rapid drying of foliage can also help reduce problems with leaf diseases.  For certain diseases like apple scab, growing a resistant apple or crabapple variety may be your best option.  And finally, in certain situations, use of preventative fungicide treatments may be warranted to keep leaf diseases in check.

So, as you dream of those warm spring rain, dream of them in moderation.  As with most things in life, balance is the key.  Hope for enough rain to get your plants to grow, but not enough to lead to disease problems.  As always, if you have questions about plant diseases and their management, feel free to contact me at (608) 262-2863 or pddc@wisc.edu.

Rainbow

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March: The Irish – Good Luck in Life, Bad Luck in Plants

As March arrives, being in part Irish by ancestry, my thoughts tend towards St. Patrick’s Day and as a plant pathologist, I imagine what havoc plant disease might cause for the holiday.

Shamrocks

Shamrocks
Shamrocks

A major symbol of St. Patrick’s Day is the shamrock.  While several plants can be called shamrocks, the most common plant to be so-named is white clover (Tifolium repens).  This plant was once a common component of lawns (in combination with grasses such as Kentucky bluegrass) and served the important function of enriching soil with nitrogen.  Interestingly, it’s not the clover plant itself that is instrumental in this nitrogen enrichment process.  Actually, the credit goes to the bacterium Rhizobium which colonizes the roots of clover (along with the roots of other plants in the pea family) and causes formation of nodules (swellings) on the roots.  Inside the pinkish, elongate nodules, Rhizobium takes nitrogen gas (which is very common in the air) and converts it to a form of nitrogen that is more easily used not only by the bacterium, but by the clover plant it colonizes.  In exchange for this ready supply of nitrogen, the clover plants provide Rhizobium with sugars (produced through photosynthesis) that it needs to grow and reproduce.

Root-knot nematodes cause swollen, distorted roots that can interfere with movement of water and nutrients within a plant.
Root-knot nematodes cause swollen, distorted roots that can interfere with movement of water and nutrients within a plant.

This interesting symbiosis between clover and Rhizobium, can be disrupted by the plant pathogenic nematode Meloidogyne, more commonly known as the root-knot nematode.  Nematodes are small (typically microscopic) worm-like organisms.  Many nematodes are beneficial, but root-knot nematode infects the roots of a variety of plants (including clover) causing damage.  Root-knot nematode females tunnel into roots and set up feeding sites.  In the process of feeding, they secrete saliva that stimulates root cells to grow larger than normal, grow faster than normal, and divide like crazy.  This uncontrolled growth leads to a tumor-like swelling on the infected root (called a gall or knot).  Formation of the galls can interfere with root function (i.e., movement of water and nutrients to leaves and stems above ground) and can also interfere with proper nodulation by Rhizobium.  Thus plants with root-knot nematode often look stunted and discolored due to nutrient deficiencies caused by the presence of the pathogen.  You’re not going to find a lot of four-leafed clover leaves on plants with root-knot.

Cabbage

Cabbage
Cabbage

The food that comes to my mind as a symbol of St. Patrick’s Day is corned beef and cabbage.  While I can’t say too much plant pathological about beef, cabbage is another matter.  The primary disease that I can think of that would prevent you from enjoying your cooked cabbage is black rot.  I have seen an amazing increase in the incidence of this bacterial disease over the past five years or so.  The disease not only affects cabbage, but virtually all types of brassicas, the group of plants that includes cabbage, broccoli, cauliflower, kale, rutabaga and turnip, as well as weed plants such as shepherd’s purse and wild mustard.  Often the causal bacterium (Xanthomonas campestris pv. campestris) comes into a garden on contaminated (but asymptomatic) seed or transplants.

Black rot causes V-shaped yellow and brown/ dead areas in affected leaves. (Photo courtesy of Amanda Gevens)
Black rot causes V-shaped yellow and brown/ dead areas in affected leaves. (Photo courtesy of Amanda Gevens)

Eventually wedge-shaped yellow, then dead areas develop on leaves or other plant parts leading to deterioration of the plant.  Black rot can be followed by soft rot (another bacterial disease), leading to even more extensive damage.  It’s not a happy day when cabbage with black rot and soft rot arrives in my clinic.  The stench is overpowering!  Good debris clean up, decontamination of gardening tools, proper weed control, proper vegetable rotation, and hot-water seed treatments can all help in managing this disease.

Potato

And no discussion of the Irish would be complete without a mention of late blight, the cause of the Irish potato famine.  This devastating disease wiped out the Irish potato crop for several years in the 1840’s and 1850’s.  For a variety political and social reasons, potato was the primary food of the Irish during this period.  Loss of the crop due to late blight led to the starvation of over 1 million Irish and the emigration of over 1 million more Irish, many of them to the US.  I am sitting, writing this article in Madison, WI due to this disease.

Late Blight on Potato Tubers, photo courtesy of Prof. Amanda Gevens
Late Blight on Potato Tubers. (Photo courtesy of Amanda Gevens)

Even today, late blight can have a huge negative impact on both commercial and home garden potato (and tomato) production.  Without proper treatment the disease can wipe out entire potato and tomato patches/fields in a matter of a few days.  It is critical therefore to identify any occurrences of the disease in Wisconsin as early in the growing season as possible and also identify which variant(s) (and there are many) of the pathogen is(are) causing problems.  For that reason, my clinic provides free diagnoses for late blight for anyone growing potatoes and tomatoes in Wisconsin.  All you need to do to get the free diagnosis is send in a potato or tomato sample and invoke the words “late blight” and the diagnosis is free.  Even if you don’t think your potato or tomato problem is late blight, send in a sample, mention “late blight” and I’ll provide a diagnosis and management recommendations for free.  You can send samples to:

Plant Disease Diagnostics Clinic
Department of Plant Pathology
University of Wisconsin-Madison
1630 Linden Drive
Madison, WI  53706-1598

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

With that, go forth, wear green, drink green beer, think about the contributions that the Irish have made to US culture and of course, don’t forget about the all-important plant diseases.  Happy St. Patrick’s Day!!

Shamrock and Claddagh Banner

 

February: The Facts Ma’am, Just the (UW Garden) Facts

The winter months are the prime period at the PDDC when staff are able to concentrate on outreach activities that do not involve diagnosing diseases on plant specimens.  One of the major outreach efforts of the PDDC has been and continues to be the University of Wisconsin (UW) Garden Facts fact sheet series.

The UW Garden Facts were originally conceived and developed by the University of Wisconsin-Extension Horticulture Team.  These one-page fact sheets were designed to be user friendly for home gardeners.  They are short, concise and easy to read, with an emphasis on answers to questions that homeowners often ask about horticultural issues.  Due to their popularity, the UW Garden Facts series was eventually expanded to include UW Farm Facts (covering more agriculture-oriented topics) and UW Pest Alerts (covering new and emerging disease/pest issues in both the agricultural and horticultural arenas).

The UW Garden Facts/Farm Facts/Pest Alerts series currently has over 250 titles, all of which are available in several formats for download free-of-charge from the “Fact Sheets” section of the UW-Madison/Extension Plant Disease Diagnostics Clinic website.  A web friendly version of the fact sheets (for reading online) is also available on the website.  If you are a horticulture or agriculture professional and would like to distribute the fact sheets as part of your business (which is encouraged), there is space to customize each fact sheet with personal or business information (e.g., a company logo).

A two CD compilation of University of Wisconsin Facts is also available.  The compilation contains the full set of the fact sheets and costs $30 for the general public and $20 for Master Gardener volunteers, plus shipping and handling (approximately $3.00 per CD).  To order a compilation, contact:

Brian Hudelson
Plant Disease Diagnostics Clinic
Department of Plant Pathology
University of Wisconsin-Madison
1630 Linden Drive
Madison, WI  53706-1598
Telephone:  (608) 262-2863
Email:  pddc@wisc.edu

Complimentary copies of UW Garden Facts/Farm Facts/Pest Alerts are also available in the display outside the PDDC (Rm. 183 Russell Labs at the address listed above), and complementary horticulture-related disease titles will also be available February 9-11, 2018 at the PDDC booth (booth 833-834) at Garden Expo 2018.  To keep up to date on new and revised fact sheets, be sure to follow the UW-PDDC on Facebook and Twitter @UWPDDC, or contact the PDDC at the phone number or email address listed above.

Happy reading!!

San José Scale

San José scale (Diaspidiotus perniciosus) is a fruit tree pest that can be found in most fruit growing regions of the United States.  Native to China, this insect was introduced into the United States in the late 1800s.  In well-managed orchards, populations of San José scale are generally too low to cause economic damage.  In poorly managed orchards however, populations can become high enough in one to two growing seasons to cause tree and fruit injury.  Once established, San José scale can be difficult and expensive to control.  San José scale is of historical interest because, in the early 1900’s, it was the first insect observed to develop resistance to an insecticide.

San José scale damage on apple fruit (left). San José scale black cap stage (center), female (upper right) and male (lower right). [Photos courtesy of Greg Krawczyk (Penn State University), E. Beers (Washington State University) and S. Schoof (North Carolina State University).]
San José scale damage on apple fruit (left). San José scale black cap stage (center), female (upper right) and male (lower right). [Photos courtesy of Greg Krawczyk (Penn State University), E. Beers (Washington State University) and S. Schoof (North Carolina State University).]
Appearance:  San José scale females are yellow, wingless and legless, have a soft, globular shape and are approximately 1/12 inch long.  Male scales are 1/25 inch long, are yellowish-tan with a dark band across the back and have wings and long antennae.  Immature San José scales (called nymphs) go through three stages (crawler, white cap, and black cap).  Crawlers are roughly the diameter of the tip of a pin, are yellow, and have six legs and antennae.  Crawlers develop into the white cap stage as they become immobile and secrete hard, white, waxy coverings.  The black cap stage follows as the waxy coverings turn gray-black.

Host Range:  San José scale feeds on a variety of fruit hosts including apple, pear, plum, cherry, peach, apricot and berries (e.g., raspberry, blackberry), as well as on nut-bearing trees (e.g., walnut) and many ornamental trees and shrubs (e.g., elm, maple, mountain-ash, serviceberry, juniper, white cedar, yew).

Symptoms and Effects:  San José scale sucks sap from branches, leaves and fruit causing overall decline in plant vigor, growth, and yield.  If left uncontrolled, San José scale can ultimately kill plants.  On fruits, San José scale feeding causes slight depressions with red to purple haloes.  If San José scale populations are low, fruit damage is usually concentrated on the bottom of the fruit.  When infestations occur early in the season, fruit may become small, deformed, and poorly colored.  Damage by San José scale (even cosmetic spotting) decreases fruit quality and in commercial settings makes the fruit more difficult to sell.

Life Cycle:  San José scale can complete its life cycle in approximately 37 days.  There are typically two generations of the insect each year, and generations overlap so that all stages of the insect occur at the same time during the summer.  San José scale overwinters in the black cap stage.  Development of the insect resumes in spring when temperatures exceed 51°F.  Around petal fall, mature females and short-lived males emerge.  Males can fly from tree to tree, but females move very little.  After mating, females produce approximately 400 live crawlers over a period of six-weeks.  The first generation of crawlers appears between early and mid-June, with white and black cap stages developing over approximately the next month.  A second generation of adults appears between July and early September.  If warmer temperatures continue into the fall, a third generation of San José scale can occur between late October and early November.

Monitoring:  The first indication of a San José scale problem may be when infested fruit is found at harvest or (in commercial settings) at packing.  However, sometimes the insect can be found earlier on branches.  If a San José scale infestation is detected, careful examination of trees/orchards during dormancy can help determine the level of infestation and the extent of spread.  Watch for trees that retain leaves during winter (a good indication of a San José scale infestation) and check both branches and trunks for the insect.  Mark (e.g., with flagging tape) infested areas on trees to identify where sprays should be applied the following growing season.

In the spring and summer, use pheromone traps to detect the presence of males.  Begin using traps at the pink stage of apple flower bud development, in areas where infestations have been detected.  Place traps on the northern or eastern side of trees at a height of six to seven feet.  Check traps at least weekly.  Traps are effective for four to six weeks.

Monitor for crawlers by wrapping two-sided sticky electrical tape (coated with a thin layer of petroleum jelly) around infested tree limbs at both ends of the infested area.  Start checking tape for crawlers approximately four to six weeks after bloom.

A San José scale pheromone trap. (Photo courtesy of S. Schoof, North Carolina State Univeristy)
A San José scale pheromone trap. (Photo courtesy of S. Schoof, North Carolina State Univeristy)

Control:  The best strategy for managing San José scale is to prevent serious infestations.  The best cultural control is to prune out infested branches.  This reduces scale numbers and opens up the tree canopy so that if spray treatments are used, there is better penetration.  Several parasites and predators attack San José scale; however, use of these alone does not provide enough control to prevent damage.

The most effective spray control for San José scale is the use of 2% horticultural oil with or without an insecticide just before or right after bud break, but before flowers open.  During this period San José scale resumes its development after being dormant during the winter and the sprays will smother the insects.  After applying horticultural oil, continue to monitor for adults and crawlers (as described above) and if you still find active San José scale, consider using chemical insecticides for additional control.  Insecticides containing insect growth regulators (e.g., pyriproxyfen or buprofezin), neonicotinoids, organophosphates, or spirotetramat can be effective.  Start applications when you find the first adults in pheromone traps or the first crawlers on sticky tapes (usually around early to mid-June).  Apply another spray approximately 10 days later if you continue to find active crawlers.  When using two applications, be sure to use two products with active ingredients in different Insecticide Resistance Action Committee (IRAC) chemical classes (i.e., with different modes of action) to delay development of insecticide resistance.  See http://www.irac-online.org/modes-of-action/ for guidance.  Note that late-fall and postharvest applications are NOT effective for San José scale control.  Also, remember that whenever you use insecticides, you should consider the effects of products on non-target and beneficial insects.  Check the current year “Midwest Fruit Pest Management Guide” (available at https://learningstore.uwex.edu/) for additional insecticide recommendations.

For more information on San José scale:  Contact your county Extension agent.

January: 2017 in Review

The PDDC was a busy place in 2017.

Clinic staff processed 1445 samples, with samples coming from every county in Wisconsin other than Lincoln, Menominee and Price Counties.  The PDDC also received samples from FL, IA, IL, ME, MI, MN, MO, NY, PA, SD, TX and WA.  I personally also provided digital disease diagnostics via email and through the UW-Extension PlantDOC online diagnostic website.  I also continued with my interaction with members of the Association of Specialty Cut Flower Growers via their Facebook page, providing plant disease expertise for the group.  And of course, the phone rang off the hook for much of the year as I talked with folks about their plant disease problems.

In addition to my clinic duties, I also spent a fair amount of time providing plant disease outreach around the state.  In 2017, I did 91 talks/presentations/workshops visiting 19 Wisconsin counties in the process.  My biggest outreach event (in terms of time and effort) was, as always, Wisconsin Public Television’s Garden Expo.  During my three days at the event, I gave two talks on diseases of herbaceous ornamentals and helped answer questions with Lisa Johnson of Dane County UW-Extension to a standing-room-only crowd of almost 300 at Larry Meiller’s Garden Talk session.  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.  I distributed 3,024 University of Wisconsin Garden Facts fact sheets, 850 brochures/informational handouts of various kinds and 99 handouts for my talks.  Across all of my talks/presentations/workshops in 2017, I interacted with just over 300,000 people.  A big thanks goes out to Larry Meiller for having me on his radio show which has a HUGE listenership.

On a personal note, I had wonderful opportunity to visit New Zealand and eastern Australia for three weeks in late November and early December (their late spring).  I had to smile as I walked off the plane in Auckland, NZ to be greeted by a warning poster about brown marmorated stink bug, which has yet to arrive in the country.  On my first full day in NZ, I took a beautiful ferry ride from Auckland to Waiheke Island to hike, only to find a warning sign about the recently described Phytophthora agathidicida which is causing dieback in native kauri trees.  There was even a station at the entry point of the hiking area with disinfectant to use on my shoes!  And as I traveled around the country, I noted some very stunning invasive plants.  Common or Scotch broom was blooming everywhere in the mountains around Queenstown, and lupines covered acres and acres of the valleys as I drove from Queenstown to Christchurch.  Both were in full, spectacular bloom.  And on a helicopter trip to Milford Sound, I noticed huge areas on the mountainsides where all of the trees were brown and dead.  These turned out to be nonnative pines that were being killed in an attempt to reestablish native flora.  What a trip!!

Acres of of invasive lupines line New Zealand roadways.
Acres of of invasive lupines line New Zealand roadways.
Scottish Broom adds a vibrant, if invasive, touch of color to New Zealand mountains.
Scottish Broom adds a vibrant, if invasive, touch of color to New Zealand mountains.

Many thanks to Susan Lueloff (the PDDC Assistant Diagnostician and molecular diagnostician extraordinaire), John Lake (my hard working student hourly and lab cleaner supreme), Ann Joy (she of the nimble data entry fingers) and Dixie Lang (webmistress and database guru) for helping me keep my sanity and making 2017 such a fun year.  Now onward to 2018!  Let’s see what the new year has to offer.

For addition information on the PDDC and its activities, check out the PDDC website, follow the clinic on Twitter or Facebook (@UWPDDC) or contact the clinic at pddc@plantpath.wisc.edu.

February 2018

Interested in scheduling Brian Hudelson for presentation, workshop or other outreach activity?
Check out the calendar below to find out if Brian might have the date open.
Contact Brian directly [bdh@plantpath.wisc.edu or (608) 262-2863] to verify his availability.

February Heart Icon

February 7, 2018

Plant Disease Update
(10:00 AM – 10:45 AM, West Allis, WI)

February 9, 2018

Garden Expo – UW Plant Disease Diagnostics Clinic Booth
(Booth 833-834)
(Noon – 8:00 PM, Madison, WI)

Diseases of Vegetables
(2:45 PM – 3:45 PM, Madison, WI)

February 10, 2018

Garden Expo – UW Plant Disease Diagnostics Clinic Booth
(Booth 833-834)
(9:00 AM – 6:00 PM, Madison, WI)

Garden Talk with WPR’s Larry Meiller
(9:30 AM – 10:30 AM, Madison, WI)

Diseases of Vegetables
(4:45 PM – 5:45 PM, Madison, WI)

February 11, 2018

Garden Expo – UW Plant Disease Diagnostics Clinic Booth
(Booth 833-834)
(10:00 AM – 4:00 PM, Madison, WI)

February 27, 2018

Plant Disease Diagnostics Clinic:  2017 Highlights
(1:00 PM – 1:20 PM, Fitchburg, WI)

February 28, 2018

Commonly Misdiagnosed Diseases (and What They Really Are)
(8:30 AM – 10:00 AM, Bristol, WI)

Commonly Misdiagnosed Diseases (and What They Really Are)
(1:00 PM – 2:30 PM, Waukesha, WI)

December: ‘Tis the Season. . .

It’s holiday time and while most folks have visions of sugar-plums dancing in their heads, my mind takes a detour to the dark side as I think of how plant pathogens can influence the holidays.  Interestingly, the examples that first come to my mind are positive influences on the holiday season.

Poinsettias anyone? 

If you are lover of brightly-colored poinsettias and enjoy them sitting on tables in your home, you have a plant pathogen to thank for the look of most modern poinsettia varieties.  In their native, tropical habitat, poinsettias have an upright tree-like form, and grow up to 10 ft. in height.  Modern, ornamental varieties of poinsettias are infected with phytoplasmas, bacteria-like organisms that colonize the phloem (i.e, the food-conducting “piping”) inside the plant.  The presence of phytoplasmas leads to a stunted, compact growth form with lots of extra branching.  And guess what you get with all of that branching?  You got it:  lots and lots of flowers.

Hitting the slopes

If you are a skier and hate the thought of dry, snowless winter, don’t despair.  There is a plant pathogen that can come to your rescue.  When Mother Nature doesn’t cooperate and you’re speeding down the slopes on artificial snow, take a minute at the end of your run to talk to the owner of your favorite ski slope about how the artificial snow is made.  Chances are he/she is using a product called Snomax®.  The active ingredient in Snomax® is a protein derived from Pseudmonas syringae pv. syringae, a bacterial pathogen involved diseases such as bacterial blight of lilac, bacterial canker of stone fruits and bacterial brown spot of snap beans (a personal favorite given that this disease was the subject of my PhD thesis).  So while Pseudmonas syringae pv. syringae can wreak havoc in the summer, it can atone for its sins in the winter by helping provide a snowy wonderland for skiers to enjoy.

Pathogenic kiss? 

As you stand under the mistletoe canoodling with your sweetie this holiday season, consider exactly what it is that you are standing under.  Mistletoes (there are lots of different kinds) are parasitic seed plants that infect their hosts (usually some type of tree or shrub) and siphon off water, minerals and sugars (as well as other organic compounds) that they use to grow and reproduce.  The typical “holiday” mistletoe is leafy and green and can photosynthesize, so it is not totally reliant on its host for all of its nutritional needs.  Other mistletoes are devoid of chlorophyll (the green pigment involved in photosynthesis) and are totally reliant on their parasitized host for water and nutritients.  Whichever mistletoe you choose to hang from the rafters, remember the sacrifice of its parasitized host each time you enjoy a clandestine kiss from a loved one.

With that, enjoy the holiday season and I’ll see you with my next article in the new year.

To learn more about common diseases and disease management, explore the Plant Disease Diagnostics Clinic (PDDC) website (https://pddc.wisc.edu/) and in particular, check out the University of Wisconsin Garden Facts fact sheets that can be found there.  Also, follow the PDDC on Facebook and Twitter @UWPDDC to receive updates on emerging diseases and their management.

November: A Plant Pathology Thanksgiving

As we head into November, I’m thinking ahead to the bounty of food that will be served on Thanksgiving Day.  Of course, being a plant pathologist, it’s also fun for me to think about what might go wrong (from a plant disease perspective) to prevent some of my favorite dishes from making it to the table.

Turkey

Turkey on PlatterGiven that turkey is an animal, rather than a plant-based food, one would think nothing could go wrong.  Ah, but then we have to consider the stuffing.  Stuffing is made, in part, from cereal grains (e.g., wheat) and one disease that could cause issues is Fusarium head blight (aka scab).  The Fusarium head blight fungus infects wheat grain heads causing shrunken kernels and thus reduced yields.  More importantly, the fungus can produce toxins that adversely affect human health.  Because of the health risks, grain crops are carefully monitored for Fusarium head blight (and other) toxins and may be destroyed if toxin levels are too high.

Potatoes

PotatoI have never met a potato product that I didn’t like, but mashed potatoes are my favorite.  I think this is because at Thanksgiving, my family’s tradition is to serve them not with gravy, but with homemade egg noodles cooked in turkey/chicken broth.  Everyone thinks this tradition is weird at best, but once folks have experienced “noodle gravy” they become converts.  From a plant pathology standpoint, the most famous disease that might limit my access to potatoes is late blight, the disease that caused the Irish potato famine of the 1840’s and 1850’s.  This disease can (and often does) decimate potato and tomato crops.  In potatoes, the pathogen not only totally wipes out foliage, but can infect tubers.  Once in storage, the tubers degrade not only due to the late blight pathogen, but also due to other pathogens that invade through the late blight-compromised tissues.  Eventually, late blight-affected tubers can end up a mushy mess (and not in a good, mashed potato sense).

Carrots

Baby CarrotsI have a great recipe for cranberry/butter/brown sugar glazed carrots I like to serve at Thanksgiving (the recipe is at the bottom of this page).  But if I store carrots too long in my refrigerator, they can turn to a slimy mess and be totally unusable for this delicious recipe.  The disease that causes this degradation is bacterial soft rot.  This disease is also one that causes potato tuber rot in combination with late blight.  Bacterial soft is an awe-inspiring disease.  The pathogen produces an enzyme that degrades pectin, the substance that “glues” plant cells together.  The enzyme, for all practical purposes, liquefies carrot roots (and a lot of other vegetables as well), making the carrots (and other vegetables) suitable for the garbage disposal and not the dining room table.

Cranberries

CranberriesWhat Thanksgiving dinner would be complete without a cranberry dish of some kind?  Cranberry relish, cranberry salad and cranberry bread are all delicious additions to a Thanksgiving meal.  But cranberries can have their disease problems as well.  Wisconsin is the largest cranberry producing state in the US, so I see a fair share of cranberry samples come into my clinic.  The most common problems I see are a variety of fungal fruit rots.  I was very lucky for many year to have Lindsay Wells (a graduate student in Patricia McManus’ fruit pathology lab here at the UW-Madison) work in my clinic and she is really the person who taught me about cranberry diseases, particularly fruit rots.  Although Lindsay has moved on to greener pastures, I still reap the benefits of her tenure here in my clinic every time I diagnose a cranberry disease.

Pumpkin pie

Slice of pumpkin piePumpkin pie is another of my favorites and I can scarf an entire pie in one sitting.  So, any disease of pumpkins is on my hit list.  The most common disease I encounter on pumpkins is powdery mildew.  While powdery mildews tend to be cosmetic diseases on most hosts, on pumpkins, powdery mildew can be severe enough to cause leaf browning and death, particularly of leaves in the centers of plants.  This loss of leaves is not lethal, but leads to smaller fruit size (and thus smaller pies).  This is definitely not good for a pumpkinophile like me.

Now that I have depressed you all, go forth and plan your own tasty Thanksgiving Day meal and have a great holiday!  Or if you’d like to join in the “fun”, let me know your favorite Thanksgiving dish (bean casserole or scalloped corn anyone?) and I’ll find a plant disease to ruin it for you.  I love my job!!

To learn more about common diseases and disease management, explore the Plant Disease Diagnostics Clinic (PDDC) website (https://pddc.wisc.edu/) and in particular, check out the University of Wisconsin Garden Facts fact sheets that can be found there.  Also, follow the PDDC on Facebook and Twitter @UWPDDC to receive updates on emerging diseases and their management.


Glazed Carrots with Cranberry Sauce

  • 1 16 ounce bag of baby carrots
  • 1/4 cup butter
  • 1/4 cup canned cranberry sauce (or use the whole can)
  • 2 teaspoons brown sugar
  • 1/2 teaspoon salt

Cook carrots in boiling water until tender.

Combine other ingredients in saucepan and cook until ingredients melt together.

Drain water from carrots and place carrots in serving dish.

Cover carrots with sauce.

Variation: try adding a little orange juice to the glaze.

 

 

October: Fall House Cleaning for the Garden

Fall LeavesOne of the easiest and most effective ways to help manage plant diseases is good fall cleanup of your yard and garden.  Many common fungal and bacterial plant pathogens, particularly those that cause leaf diseases, survive Wisconsin winters in leaf litter from trees and shrubs, as well as on herbaceous plant parts that have died back for the winter.  Disease-causing organisms can also survive on common gardening items like pots, stakes and tools.  So, as the temperatures cool and plants begin to go dormant for the season, here are a couple of things to think about doing to put your gardens and landscape to bed for the winter and have a head start on your gardening for next year.

Rake up the leaves from your trees and shrubs, cut back herbaceous perennials, and remove dead vegetable plants and annual ornamentals

RakeThe safest way to dispose of these materials is typically to take them to a local yard waste center (if there is one available in your community) where they can be properly composted.  If not, other options for disposing of this material include burning (not particularly environmentally friendly, but an option if allowed by local ordinance), burying (make sure the material is completely covered by approximately two inches of soil) or hot composting.  Note that for some diseases (e.g., late blight, white mold, Southern blight), burying or home composting may not be good options.  Therefore, if you are uncertain how to dispose of debris from plants that have had specific diseases, feel free to contact the Plant Disease Diagnostics Clinic at (608) 262-2863 or pddc@wisc.edu for advice.

Decontaminate other items from your garden

BleachFor clay or ceramic pots, wash the pots well with soapy water (to remove any remaining soil), then soak them for 30 minutes in a 10% bleach solution.  Rinse your pots well to remove bleach residues, allow them to air dry, then store them in a clean location where they will not be recontaminated.  Decontamination of plastic pots (or other plastic items like stakes) is often more challenging.  Often bleaching will not be effective and your best option may be to throw out plastic items and buy new ones next year.  Decontaminate gardening tools by dipping them for a minimum of 30 seconds in 70% alcohol (e.g., rubbing alcohol) or spraying them until they drip with a spray disinfectant that contains approximately 70% alcohol.  As with decontaminated pots, store clean tools in a location where they will not be recontaminated.

To learn more about common diseases and disease management, explore the Plant Disease Diagnostics Clinic (PDDC) website (https://pddc.wisc.edu/) and in particular, check out the University of Wisconsin Garden Facts fact sheets that can be found there.  Also, follow the PDDC on Facebook and Twitter @UWPDDC to receive updates on emerging diseases and their management.