All posts by ddlang

Vegetable Varieties for Containers

Growing plants in containers (referred to as container gardening) is an easy way to grow and maintain vegetables.  Vegetables grown in containers can easily fit on a window sill, balcony, deck, door step or any other place where space is limited but where environmental conditions are suitable for vegetable production.

The list below contains recommendations on varieties of popular vegetables that are well-suited for growing in containers.

Click the vegetable names to expand the panel and view the variety info. The panel expands downward.

To close the expanded panel, click the vegetable name below it.
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[accordion-item autoclose=”true” clicktoclose=”true” title=”Bean” class=”Bean”]

  • ‘Derby’
  • ‘Eureka’
  • ‘Mascotte’
  • ‘Porch Pick’
  • ‘Tendercrop’
  • ‘Topcrop’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Beet” class=”Beet”]

  • ‘Burpee’s Golden’
  • ‘Chioggia’
  • Detroit Dark Red Medium Top’
  • ‘Ruby Queen’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Carrot” class=”Carrot”]

  • ‘Danver’s Half Long’
  • ‘Little Finger’
  • ‘Nantes Half Long’
  • ‘Paris Market’
  • ‘Yaya’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Cucumber” class=”Cucumber”]

  • ‘Bush Champion’
  • ‘Bush Pickle’
  • ‘Iznik’
  • ‘Parisian Gherkin’
  • ‘Patio Snacker’
  • ‘Salad Bush’
  • ‘Saladmore Bush’
  • ‘Space Master’
  • ‘Sugar Crunch’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Eggplant” class=”Eggplant”]

  • ‘Dusky’
  • ‘Early Midnight’
  • ‘Gretel’
  • ‘Hansel’
  • ‘Ivory’
  • ‘Ophelia’
  • ‘Patio Baby’
  • ‘Pinstripe’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Okra” class=”Okra”]

  • ‘Carmine Splendor’
  • ‘Clemson Spineless’
  • ‘Jambalaya’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Pea” class=”Pea”]

  • ‘Caselode’
  • ‘Peas-in-a-Pot’
  • ‘Sugar Ann’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Pepper” class=”Pepper”]

  • ‘Cajun Belle’
  • ‘Cayennetta’
  • ‘Cherry Stuffer’
  • ‘Cute Stuff Red’
  • ‘Gypsy’
  • ‘Just Sweet’
  • ‘Lady Belle’
  • ‘Mariachi’
  • ‘New Ace’
  • ‘Orange Blaze’
  • ‘Red Chili’
  • ‘Sweet Golden Baby Belle’
  • ‘Tangerine Dream’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Radish” class=”Radish”]

  • ‘Champion’
  • ‘Comet’
  • ‘D’Avignon’
  • ‘Early Scarlet Globe’
  • ‘French Breakfast’
  • ‘Red Satin’
  • ‘Rido Red’
  • ‘Sparkler’
  • ‘White Icicle’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Squash” class=”Squash”]

  • ‘Astia’
  • ‘Golden Scallopini Bush’
  • ‘Golden Zebra’
  • ‘Multipik’
  • ‘Supersett’
  • ‘Sweet Zuke’
  • ‘Zebra Zuke’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Swiss Chard” class=”SwissChard”]

  • ‘Bright Lights’
  • ‘Fordhook Giant’
  • ‘Lucullus’
  • ‘Peppermint’

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[accordion-item autoclose=”true” clicktoclose=”true” title=”Tomato” class=”Tomato”]

  • ‘Amish Paste’
  • ‘Atlas’
  • ‘Baby Boomer’
  • ‘Bush Big Boy’
  • ‘Bush Champion’
  • ‘Bush Early Girl’
  • ‘BushSteak’
  • ‘Celebrity’
  • ‘Champion Bush’
  • ‘Cherries Jubilee’
  • ‘Cherry Cascade’
  • ‘Cherry Falls’
  • ‘Cherry Punch’
  • ‘Cocktail Red Racer’
  • ‘Container Superbush’
  • ‘Early Resilience’
  • ‘Fantastico’
  • ‘Husky Red’
  • ‘Jet Star’
  • ‘Lizzano’
  • ‘Maglia Rosa’
  • ‘Orange Pixie’
  • ‘Patio’
  • ‘Patio Choice Red’
  • ‘Patio Choice Yellow’
  • ‘Patio Paste’
  • ‘Patio Princess’
  • ‘Peardrops’
  • ‘Pony Express’
  • ‘Power Pops
  • ‘Primo Red’
  • ‘San Marzano’
  • ‘Sunrise Sauce’
  • ‘Super Bush’
  • ‘Sweet ‘n’ Neat’
  • ‘Sweetheart of the Patio’
  • ‘Tasmanian Chocolate’
  • ‘Terenzo’
  • ‘Tidy Treats’
  • ‘Tumbler’
  • ‘Tumbling Tom Red’
  • ‘Tumbling Tom Yellow’
  • ‘Veranda Red’

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In addition to the vegetables listed above, most varieties of herbs and salad greens are perfectly suitable for containers.

For more information on vegetable varieties for containers and container gardening in general:  See Extension Bulletin A3382, Container Gardening, or contact your county Extension agent.

Cranberry Flea Beetle

The cranberry flea beetle (CFB) or redheaded flea beetle, Systena frontalis, is native to the United States ranging in the east from Maine to Florida and in the west from Texas to Montana.  CFB has historically been an important pest in nurseries, greenhouses and agricultural crops.  In the last decade, the insect has become an emerging, sporadic pest on cranberries.  CFB has likely always been present in cranberry marshes in Wisconsin but probably was not a problem in the past because of widespread use of broad-spectrum insecticides for control of other cranberry insect pests.  The relatively recent appearance of problems with CFB may be a consequence of growers using more selective insecticides for pest control.

A cranberry flea beetle adult (left) and larva (right). Note the fleshy projection at the rear end of the larva (white arrow). Photos courtesy of Shannon Schade (left) and Tim Dittl, UW-Madison (right).
A cranberry flea beetle adult (left) and larva (right). Note the fleshy projection at the rear end of the larva (white arrow). Photos courtesy of Shannon Schade (left) and Tim Dittl, UW-Madison (right).

Appearance:  Adult CFBs are shiny, black beetles with a reddish head.  They are approximately 1/10 to 1/4 inch long with antennae nearly half as long as their bodies.  They also have enlarged hind legs, which they use for jumping when disturbed.  Adult females are slightly larger than males.  Larvae are 1/5 to 1/4 inch long with a fleshy projection at the tip of their rear ends.

Host Range:  CFB has a very broad host range that includes many woody and herbaceous plants.  In cranberry production areas, the insect prefers to feed on weeds such as marsh St. John’s-wort, Joe-pye weed, smartweed, jewelweed, and hardhack spirea.  If these weedy species are not present or are kept mowed, CFB will move to cranberry beds and feed on cranberry foliage and fruits.  CFB is also an occasional pest of other commercial crops, including alfalfa, beans, beets, blueberries, cruciferous vegetables, eggplant, grapes, horseradish, potato and sweet potatoes.

Symptoms and Effects:  CFB larvae feed on cranberry roots and underground runners.  When CFB infestations are severe, larval feeding can lead to girdled roots and vine death.  Adult CFBs feed on foliage and on the surface of cranberry fruit.  Severe adult infestations can lead to skeletonization of leaves (i.e., loss of the tissue between veins) and death of upright vines.  Heavy feeding by adults can also impact bud development, leading to yield reductions the year following an infestation.  Because adults prefer areas of lush growth, adult CFB populations and damage are usually patchy.

Life Cycle:  In Wisconsin, female CFBs deposit single eggs into the soil in late summer through early fall, and the eggs serve as the overwintering stage of the insect.  In the spring, the eggs hatch, and CFB larvae feed on roots from June through August.  Larvae eventually pupate (this stage of the insect’s life cycle has not been formally described) and adults begin to emerge in July and are present through September.  In Wisconsin, CFB has one generation per year.

Scouting Suggestions:  Monitoring for CFB focuses on adult beetles, because finding larvae in the soil is difficult.  To evaluate CFB numbers, use a sweep net to capture adults.  Be sure to sample thoroughly across different areas within a cranberry bed to account for the patchy distribution of CFB adults.  There is no established action threshold for CFB in cranberry.  However, University of Maine Extension recommends taking action if you find more than 15 CFB per 25 sweeps in a cranberry bed.

Leaf damage with skeletonization (left) and root damage (right) due to cranberry flea beetle feeding. Photos courtesy of Tim Dittl, UW-Madison.
Leaf damage with skeletonization (left) and root damage (right) due to cranberry flea beetle feeding. Photos courtesy of Tim Dittl, UW-Madison.

Control:  Current management of CFB targets the adult stage.  If scouting indicates significant numbers of adult CFBs, consider using insecticide sprays for control.  Products that are effective against CFB adults include neonicotinoids (e.g., clothianidin, thiamethoxam, acetamiprid, dinotefuran), diamides (e.g., chlorantraniliprole, cyantraniliprole), spinosyns (e.g., spinetoram), organophosphates (e.g., chlorpyrifos, phosmet, diazinon) and carbamates (e.g., carbaryl).  When using insecticides, be sure to alternate use of at least two active ingredients in different IRAC chemical classes to help delay the development of insecticide resistance.  Also be sure to consider any adverse effects that the insecticides you use may have on non-target and beneficial insects.  Check University of Wisconsin Bulletin A3276 (Cranberry Pest Management in Wisconsin), available at https://learningstore.extension.wisc.edu/, for additional insecticide recommendations.

DO NOT use soil insecticide applications in an attempt to target CFB larvae.  Such treatments are not effective.

Alternative management strategies for CFB have not been adequately researched.  Because CFBs prefer to feed on weed species, researchers speculate that use of trap crops may eventually become a useful management strategy.  In the area of biocontrol, current research at the University of Wisconsin-Madison indicates that native Wisconsin entomopathogenic nematodes significantly suppressed CFB larvae populations in soil.  At this time however, these nematodes are not available commercially.  In addition, work is needed to identify natural enemies of CFB that might be used to help manage the pest.

For more information on cranberry flea beetle:  Contact your county Extension agent.

Fungus Gnats on Houseplants

Fungus gnats (Family Sciaridae) are insects commonly associated with overwatered houseplants.  They can become a nuisance when they are present in large numbers and fly around inside a home.  In most situations, fungus gnats are a cosmetic problem.  However, on occasion, fungus gnat larvae can cause plant damage.

A fungus gnat adult. Note the Y-shaped wing veins (arrow). Photo courtesy of B. Schoenmakers (Waarneming.nl)

Appearance:  Adult fungus gnats are delicate, dark brown or black flies that are approximately 1/8 inch long.  They have dark, translucent wings that fold on their backs when they are at rest.  Adult fungus gnats can be distinguished from other small flies by the vein patterns of their wings.  When viewed with a magnifying glass, fungus gnat wings have a distinct rounded Y-shaped set of veins near the wing tips.  Fungus gnat larvae (maggots) resemble pale worms and have a black head.  They are ¼ inch in length when mature.  Fungus gnats are often mistakenly identified as fruit flies (see University of Wisconsin Garden Facts XHT1102, Fruit Flies in the Home), but these are two distinct insects.

Symptoms and EffectsFungus gnats are usually noticed indoors when adults fly around light sources (e.g., windows, lamps), or when they fly around or walk across and rest on the soil of potted plants.  Adult fungus gnats do not feed on or damage plants but are a cosmetic nuisance.  Fungus gnat larvae typically feed on decaying organic matter and fungi in the soil.  However, if larval numbers are high, they may damage roots by feeding on root hairs or tunneling into the roots themselves.  This sort of damage is rare in home settings.

Life CycleFungus gnats can go through multiple generations per year.  Indoors, fungus gnats tend to have overlapping generations where eggs, larva, pupae and adults are all present at the same time.  Fungus gnat females lay up to 200 eggs (in clusters) in cracks and crevices on the surface of the moist soil of potted plants.  The eggs typically hatch within three to six days.  Larvae go through four stages (called instars) over the course of one to two weeks before they pupate near the surface of the soil.  Approximately four to five days after pupae form, adult fungus gnats emerge.  Adults are short-lived, surviving approximately one week.  Under optimal conditions, fungus gnats can develop from egg to adult in three to four weeks.

Scouting SuggestionsMonitor for fungus gnat adults using yellow sticky traps placed near a plant’s leaves.  You can buy these traps at your local hardware or garden store.  Sticky traps are inexpensive and often include small stakes making them easy to use with potted plants.  Sticky traps not only help capture adult fungus gnats (and other insect pests as well), but they can help you keep track of the number of fungus gnats (and other insects) over time.  Vinegar traps and other methods commonly used to monitor for fruit flies do not work for monitoring for fungus gnats.

To monitor for fungus gnat larvae, place potato slices on the soil surface of potted plants.  If there are fungus gnat larvae in the soil, they will come to the surface to feed on the potato tissue.  Check the slices for maggots after three to four days.

Control:

Use yellow sticky cards to trap fungus gnat adults.

Non-ChemicalAs noted above, using sticky traps can help control fungal gnats.  However, altering environmental conditions of houseplants is the single most important step in managing this insect.  Keep the soil surface dry to eliminate favorable egg-laying sites for the insect.  You can do this by allowing the top inch of the soil to dry out before you water.  Alternatively, you can water from the bottom to provide moisture for the roots while keeping the soil surface dry.  In addition, you can cover the soil with a ½ to one inch layer of coarse sand or fine gravel, which will help keep the surface drier and make the soil less attractive for egg-laying.

Fungus gnats are often more of a problem in the fall when houseplants that have been outdoors for the summer, and have become infested, are brought back indoors.  It may take three to four weeks of modified watering and use of sand/gravel to get fungus gnats in check.

BiologicalProducts containing Bacillus thuringiensis subsp. israelensis (Bti) are available to homeowners (e.g., Gnatrol, Mosquito Bits, etc.) and can be used to control fungus gnat larvae in soil.  These treatments do not affect eggs, pupae or adult fungus gnats.  Apply these products with adequate water to help the Bti filter through the soil to reach the larvae.  Use several applications spaced five to seven days apart to control newly hatched larvae until the infestation is under control.

ChemicalUnless a fungus gnat infestation is severe, chemical controls are not warranted.  If adult numbers are excessive however, insecticides containing pyrethrins or synthetic pyrethroids can provide temporary control.  If you decide to use insecticides, select a product that is labeled for indoor use on houseplants, and read and follow all product label instructions.  Apply insecticides to plants and to the surface of potting soil where adults typically rest.  DO NOT spray the air with these products as such treatments are ineffective.  Even in those situations where insecticide use may be warranted, keep in mind that chemical treatments should not be your sole management approach.  Insecticides should always be used in combination with other non-chemical practices (see above).

For more information on fungus gnats:  Contact your county Extension agent.

Tomato Pruning

Tomatoes are a popular vegetable that many people grow in their home gardens.  Pruning tomatoes can create stronger and healthier plants that will grow larger numbers of higher quality tomato fruits later into the growing season.

Remove suckers from indeterminate tomato plants EXCEPT for the sucker below the lowest flower/fruit cluster.
Remove suckers from indeterminate tomato plants EXCEPT for the sucker below the lowest flower/fruit cluster.

Which tomatoes should I prune?  There are two broad categories of tomatoes:  determinate and indetermi­nate.  Determinate tomatoes grow to a certain size, then stop growing.  Indeterminate tomatoes continue to grow throughout the growing season.  Seed catalogues, seed packets or plant identifi­cation stakes will indicate which type of tomato you have.  Prune indeterminate tomatoes only.

Why should I prune my tomatoes?  Pruning indeterminate tomatoes improves fruit production by removing extra growth that diverts energy away from developing fruits.  Removing extra growth redirects energy back to the fruits and reduces fruit shading, both of which will help fruits mature more quickly.  Pruning also allows for more airflow within a plant, which reduces humidity and speeds the drying of any remaining leaves.  This drier environment is less favorable for fungal and bacterial disease development.  Removing the bottommost leaves of a tomato plant serves a similar purpose.

When should I prune my tomatoes?  Start pruning in late June or early July when the first tomato flowers are open and easy to identify.  Continue with a second and third pruning (as needed) every 10 to 14 days following the first pruning.  Stop pruning one to two weeks before your expected first harvest to allow time for tomato plants to produce canopies that will protect fruits from sunscald (pale, injured areas caused by exposure to direct sun).

How should I prune tomato plants?  Use the illustrations on this fact sheet as a guide.  Identify the main stem of the plant, and locate any suckers.  Suckers are branches that form in the leaf axils (the junctions between the true leaves and the main stem).  Next, identify the lowest flower/fruit cluster on the plant (i.e., the flower/fruit cluster closest to the ground).  Remove every sucker from the plant EXCEPT for the first one below the lowest flower/fruit cluster.  That sucker is the strongest one on the plant and should be left to grow and bear fruit as a second stem.

Remove suckers as indicated with your fingers, scissors or pruning tools.
Remove suckers as indicated with your fingers, scissors or pruning tools.

Suckers may be small, especially early in the season, but remove them as soon as possible.  Suckers left to grow will produce their own leaves, flowers, fruits, and even additional suckers, which will divert energy from tomato fruits produced on the primary and secondary stems.  Also, during the growing season, watch for and remove any root suckers that form at the bases of plants.

Remove suckers by pinching them close to the stem using your thumb and index finger (if the suckers are small), or using scissors or hand pruners.  Decontaminate your fingers by routinely washing your hands with soap and water or by using an alcohol-based hand sanitizer.  Decontaminate scissors/pruners (both prior to pruning and between each plant) by treating them for at least 30 seconds with rubbing alcohol.  Decontamination will help prevent the spread of disease-causing fungi, bacteria and viruses.

For more information on tomato pruning:  Contact your county Extension agent.

February 2021: Deep Freeze Search and Destroy

Magnifying glass and hatchetIn this month’s Plant Disease Pointers, I discussed the advantages of pruning trees and shrubs in the winter to increase structural soundness and overall aesthetics.  Winter is also a great time to inspect trees and shrubs for certain diseases and, where needed, prune out these problems.  Diseases that can be corrected, at least in part, by winter pruning include canker and gall diseases.

Canker diseases:  There are a wide range of fungal and bacterial pathogens that infect branches and eventually lead to branch dieback.  With some of these diseases (e.g., Diplodia shoot blight and canker, white pine blister rust), the pathogens initially infect through needles.  With others (e.g., fire blight), the pathogens enter through flowers.  Once in the plant, these pathogens work their way relatively rapidly down branches and can cause significant damage.  Catching these diseases early and pruning out affected branches can reduce the overall damage that they cause.  If not managed properly and removed, these pathogens can eventually reach and girdle the main trunk, thus killing the tree.

Other canker diseases tend to be more localized in their effect.  For some, like Nectria canker, the pathogens often enter through wounds (e.g., pruning wounds, wounds from storm damage).  For others, like Thyronectria canker of honeylocust or Cytospora canker of spruce, direct infection of branches appears to be the norm.  With these diseases, the pathogens progress somewhat slowly, causing localized sunken areas (a “classic” canker symptom) around the point of infection.  Eventually these diseases will progress to the point where the entire circumference of the branch is affected, which leads to branch death.  Movement of these pathogens into the main trunk tends to be a slower process, although if left unchecked, these organisms can eventually cause significant damage as well.

Gall diseases:  The classic diseases in this category include black knot of Prunus species (particularly plum and cherry) and the Gymnosporium rusts like cedar-apple rust and cedar-hawthorn rust.  These diseases typically do not cause branch dieback but can reduce the aesthetic appeal of infected trees and shrubs.  In the case of black knot, you will see fairly large black masses (what I call “poop-on-a-stick”) on infected branches.  These are particularly visible in the winter when there is no foliage to hide them.

Galls associated with Gymnosporium rusts are much smaller and more subtle.  They look like tiny brown brains that form on the branches of junipers, particularly Eastern red cedar.  In the winter, if you don’t look carefully, you might miss these.  In the spring however, the galls reach the pinnacle of their visual glory when they sprout gelatinous, orange arms/masses that produce spores.  These spores infect certain trees and shrubs in the rose family (e.g., apple, crabapple, hawthorn, quince, pear and serviceberry) leading to brightly-colored leaf spots (in the case of cedar-apple rust and cedar-hawthorn rust) or spiny fruits and branch galls (in the case of cedar-quince rust).  Spores produced in these diseased leaves, fruits and branches eventually infect junipers completing the life cycle of the pathogen.

Once either canker or gall diseases become established, pruning is the method of choice for management, and wintertime is a great time to do this pruning.  Symptoms are often more visible during the winter months, and pruning in colder, drier winter weather tends to reduce the risk of infections through pruning cuts.  For diseases caused by fungal pathogens, I suggest pruning four to six inches below where you see obvious symptoms.  For diseases caused by bacteria, I suggest pruning more aggressively, roughly 12 inches below where symptoms are visible.  When pruning in the winter, it may seem that decontaminating tools is not necessarily.  However, I recommend decontamination no matter when you prune.  Treat pruning tools between cuts for at least 30 seconds with 70% alcohol (e.g., rubbing alcohol straight out of the bottle), a commercial disinfectant that contains roughly 70% active ingredient or 10% bleach.  If you decide to use bleach, be sure to thoroughly rinse your tools after you are done pruning and oil them to prevent rusting that can be caused by bleach use.  You can dispose of branches by burning (where allowed) or burying them.

So, as temperatures start to hover in the upper 20s or lower 30s this winter, think about pruning your trees.  Remove diseased branches, and at the same time, prune out healthy branches to improve the structural integrity and aesthetic appeal of your trees.  All of this said, please DO NOT prune when it is excessively cold:

  • Pruning diseased branches in winter:  GOOD!
  • Frost bite and freezing to death:  BAD!!

For additional information on the PDDC and its activities, check out the PDDC website.  To learn 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).

February 2021: Bypassing Plant Pathogens: Promoting Tree and Shrub Health Through Proper Pruning

Pruning in the winter can reduce the risk of disease-causing organisms infecting trees and shrubs through pruning cuts.
Pruning in the winter can reduce the risk of disease-causing organisms infecting trees and shrubs through pruning cuts.

Although it doesn’t seem like the optimal time to be gardening, February is actually a great time to be out pruning your trees and shrubs to make them more structurally sound and aesthetically pleasing.

Why prune now?  Whenever you prune, you create wounds that potentially can serve as entry points for disease-causing fungi and bacteria.  If you prune in the spring and summer (when it’s warmer and often wetter), these organisms are very active and more likely land on fresh pruning cuts and infect.  When the weather is colder and drier (as it tends to be in February in Wisconsin), disease-causing organisms are much less active and the chances of them infecting though pruning cuts is much reduced.

How do I go about pruning?  Check out University of Wisconsin Garden Facts XHT1013 (Pruning Evergreens), XHT1014 (Pruning Deciduous Trees) and XHT1015 (Pruning Deciduous Shrubs) for pointers on how to prune.  Prune only when it’s dry, and decontaminate pruning tools between cuts (or at a minimum between each tree or shrub) by treating them with 70% alcohol (e.g., rubbing alcohol right out of the bottle, spray disinfectants containing ~70% alcohol) or (in a pinch) 10% bleach.  Decontaminating tools kills off disease-causing organisms that you might pick up as you prune.  Once done pruning, if you’ve used bleach, be sure to thoroughly rinse your tools, and oil them to prevent them from rusting.

By pruning regularly and taking a few simple precautions as you do, you will end up with trees that are beautiful, structurally sound and healthy.

January 2021: Taking a Close Look at 2020

Magnifying Glass2021 has arrived and I can’t say that I’m sad to see 2020 gone.  Last year was incredibly challenging for everyone due to COVID-19.  I am very grateful to still have job and to be able to do the work that I love.  Here’s how things shook out in 2020 at the PDDC.

Clinic staff processed a whopping 2381 samples, up 58% from 2019 and an all-time record for my tenure at the PDDC.  Samples came from 69 of Wisconsin’s 72 counties, as well as 21 additional states (AZ, CA, CO, FL, GA, ID, IL, IA, ME, MD, MI, MN, MO, NV, NM, NY, ND, OH, SD, TN and WA) and three foreign countries (Canada, New Zealand and the United Kingdom).  Much of the increase in sample numbers resulted from the clinic formalizing and substantially promoting digital diagnostics for the first time.  This was necessitated by COVID-19, which limited clinic staffing (specifically student hourly help) and curtailed the clinic’s capacity to process physical samples.  In addition, having several wet seasons in a row prior to 2020, as well as a wet early 2020 season, helped promote a wide range of plant diseases.  People, sequestered at home for much of the year, seemed to take notice of and were curious about the diseases in their gardens and landscapes and as a consequence asked for more help with identifying the problems they observed.  No matter what the cause of the increase in sample numbers, I was certainly kept busy (and out of mischief) for the year.

In 2020, as in previous years, the PDDC expanded its molecular (i.e., DNA-based) diagnostic offerings.  One disease of note that was detected this year using molecular diagnostics was Potato mop top virus (a first report for Wisconsin)This virus is transmitted by the organism (a type of slime mold) that causes powdery scab.  As always, whenever I discuss the PDDC’s molecular efforts, I have to give a shout out to Sue Lueloff, the PDDC’s Assistant Diagnostician.  Without Sue, molecular diagnostics at the PDDC would not exist.  As in 2019, Sue not only tested routine clinic samples but also worked with the Wisconsin Department of Natural Resources (WI DNR) to test tree samples from around the state for phytoplasmas.

In other 2020 diagnostic highlights, Ralstonia wilt reared its ugly head once again in the US with an initial detection in Michigan.  The last occurrence of this disease in the US was in 2004.  The pathogen that causes Ralstonia wilt (Ralstonia solanacearum race 3, biovar 2) was introduced on contaminated geranium cuttings brought into the US from Guatemala and is of concern because of its potential to spread and cause severe disease on potatoes.  In fact, this bacterium is so destructive that the US government has listed it as a select agent, with potential to be weaponized by terrorists and used against US agriculture.  In 2020, potentially contaminated geranium cuttings were shipped to 650+ greenhouses in 44 states, with 19 greenhouses in Wisconsin involved.  Luckily there were no positive detections the disease in Wisconsin greenhouses.  My involvement with testing for Ralstonia wilt came in the latter half of 2020 through collaborative work with Dr. Caitilyn Allen, the UW-Madison’s world expert on Ralstonia wilt.  She was contacted by the geranium producer in Guatemala (through USDA APHIS) who was involved in the 2020 outbreak, to test current stock (for 2021 geranium production) for Ralstonia solanacearum race 3, biovar 2 contamination.  Dr. Allen’s group had insufficient staffing/resources to process the 1500 samples requested and ended up partnering with the PDDC to use the clinic’s Maxwell automated nucleic acid extraction system.  Using this equipment allowed Dr. Allen’s group to quickly obtain DNA samples from the plants that were subsequently tested for the bacterium.  Fortunately, all of the materials tested negative.

Other PDDC outreach activities were somewhat curtailed due to COVID-19.  I did end up giving 70 talks/presentations/workshops in at least 16 Wisconsin counties.  Many of these presentations were provided via Zoom with participants coming from multiple counties and sometimes the entire state.  My biggest outreach event in 2020 was Wisconsin Public Television’s Garden and Landscape Expo.  I spent three days at the event, gave three talks and helped answer questions with Lisa Johnson at two Q&A sessions (one hosted by WPR’s Larry Meiller).  I had a steady stream of visitors to the PDDC booth (newly redesigned and rebranded given Extension’s merger with the UW-Madison) and talked with and answered questions for visitors the entire time.  I distributed 4,023 University of Wisconsin Garden Facts fact sheets, brochures and other informational materials at the event.  Across all outreach programs in 2019, I interacted with almost 223,737 people (interestingly just a slight decrease from 2019).  As always, a big thanks goes out to Larry Meiller for having me on his radio show with its awesome listenership.

And finally, I can’t emphasize enough that the accomplishments of the PDDC are not a solo effort.  I have amazing help, including Sue Lueloff (molecular diagnostician extraordinaire mentioned above) Ann Joy (data entry expert who keeps federal funds flowing from the National Plant Diagnostics Network), Dixie Lang (IT support wizard who makes the PDDC website look beautiful and keeps the PDDC database running and up to snuff), Laurie Ballentine of the Russell Labs Hub staff (who never says no and happily prints, folds and otherwise produces all of the written handouts I use for my outreach efforts), and Alex Mikus (an undergraduate here at the UW-Madison who was able to help process samples in the clinic prior to the onset of COVID-19).

2020 is over – Phew!  Let’s see what 2021 has in store!

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@wisc.edu.

Tomato Spotted Wilt of Potato

What is tomato spotted wilt?  Tomato spotted wilt is a common viral disease of worldwide distribution that can affect over 1000 plant species.  Economically important hosts include a wide range of vegetables, fruits, field crops, and ornamentals.  Many weeds are also potential hosts.  Tomato spotted wilt is especially important in greenhouse production where it can cause significant economic losses in horticultural and floral crops.  In potato production, tomato spotted wilt is uncommon but of enough concern that routine monitoring for the disease in greenhouse and field settings is warranted.

Leaf spots with concentric rings (left) and stem streaking (right) typical of potato plants due to Tomato spotted wilt. Photos courtesy of G. J. Holmes (left) and Joshua Kunzman (right).
Leaf spots with concentric rings (left) and stem streaking (right) typical of potato plants due to Tomato spotted wilt. Photos courtesy of G. J. Holmes (left) and Joshua Kunzman (right).

What does tomato spotted wilt look like?  Symptoms of tomato spotted wilt vary widely depending on host species, host variety and when during development a plant is infected.  Typical symptoms on leaves include yellow, brown or black ringspots (i.e., ring-like areas of discolored tissue).  On some hosts, the ringspots can form a target-like pattern.  Distorted leaf growth can also be a typical symptom.

On potato leaves, tomato spotted wilt can lead to necrotic (i.e., dead) areas with or without yellow haloes.  These symptoms can resemble symptoms of early blight (see UW Plant Disease Facts D0046, Early Blight).  Black streaks on petioles or stems and branch tip dieback are also common symptoms on potato (as well as other hosts).  Potato tuber symptoms include surface rings or dark patches, and internal discolored patches, rings, spots or flecks.

Where does tomato spotted wilt come from?  Tomato spotted wilt is caused by Tomato spotted wilt virus (TSWV), which is closely related to Impatiens necrotic spot virus (INSV), the cause of impatiens necrotic spot (see UW Plant Disease Facts D0067, Impatiens Necrotic Spot).  TSWV is found in the sap of infected plants and is most commonly spread by thrips (see University of Wisconsin Garden Facts XHT1022, Managing Thrips in Greenhouses).  At least eight thrips species can be involved in TSWV transmission.  Thrips larvae acquire the virus as they feed on infected plants, then transmit the virus as they move to and feed on healthy plants.  Once thrips acquire the virus, they can transmit it for their entire lifespans.  The severity of tomato spotted wilt depends on the size and activity of thrips populations at a location, as well as on the number of infected plants (often weeds, but potentially infected potatoes as well) serving as reservoirs for the virus.  TSWV can also be transmitted mechanically (e.g., on tools used to trim branches or cut potato tubers), but this method of transmission is much less common than transmission by thrips.

How can I save plants with tomato spotted wilt?  There is no known cure for tomato spotted wilt.  Infected plants should be removed and destroyed to eliminate a reservoir for the virus that can subsequently contribute to spread to other plants.  Infected plants can be burned (where allowed by local ordinance), deep buried or hot composted.

Surface and internal tuber symptoms due to Tomato spotted wilt . Photos courtesy of Joshua Kunzman.
Surface and internal tuber symptoms due to Tomato spotted wilt . Photos courtesy of Joshua Kunzman.

How can I avoid problems with tomato spotted wilt in the future?  Prevent introducing TSWV and thrips into your greenhouse by carefully inspecting any new plants for potential problems.  Test suspect plants for TSWV using dipstick tests [available from Agdia, Inc. (www.agdia.com)] or by submitting a sample to the UW-Madison Plant Disease Diagnostics Clinic (pddc.wisc.edu).  Remove and dispose of any infected plants.

To prevent new infections via thrips, remove weeds in and outside of greenhouses to eliminate TSWV and thrips reservoirs.  Place 400-mesh screens on vents to limit thrips movement.  Also limit thrips movement on clothing by avoiding colors (e.g., pink, blue, yellow, white or green) that can attract thrips.  Monitor for thrips using blue and yellow sticky cards placed above plants throughout the greenhouse and near doors and vents.  Use chemical and/or biological control products to control thrips.  See University of Wisconsin Garden Facts XHT1022, Managing Thrips in Greenhouses, for details on what products to use and when to use them.  Multiple applications will likely be necessary because thrips eggs are not killed by insecticides.  If you find plants that you suspect are infected with TSWV, remove and dispose of these plants immediately.

To prevent mechanical transmission of TSWV, be sure to routinely decontaminate any items (e.g., pruners, knives, pots, work surfaces) that come into contact with plants by treating them for a minimum of one minute with a solution of one of the following:

  • 2.75 tablespoons Alconox® (a type of lab detergent) plus 2.5 tablespoons sodium dodecyl sulfate (SDS) [also known as sodium lauryl sulfate (SLS)] in one gallon of water, or
  • 14 dry ounces of trisodium phosphate in one gallon of water.

In field settings, tomato spotted wilt does not appear to be a significant problem on potato (although it can be a significant problem on other crops).  Use of resistant or tolerant potato varieties may reduce yield loses, but unfortunately there is little information on which potato varieties are resistant/tolerant to the disease.  Removing symptomatic plants can reduce potential reservoirs of TSWV, but may not be feasible.  More important in field settings may be to keep weeds under control.  Current research suggests that TSWV does not persist long-term in the field unless there are perennial weeds to serve as TSWV reservoirs.

For more information on tomato spotted wilt:  Contact your county Extension agent.

December 2020: Launching into 2021

RocketshipI think it’s safe to say that 2020 was a surreal year for everyone, including those of us here at the Plant Disease Diagnostics Clinic.  COVID-19 fundamentally changed how the PDDC conducted business (e.g., check out my March 2020 Monthly Column for details on how the clinic handled sample submissions in 2020).  As I look ahead to 2021 (where COVID-19 is still likely to loom large), I am trying to adapt how the PDDC functions so that I can continue to provide timely and informative services to my clients around the state.  Below are some thoughts on how the PDDC will function in 2021.

Sample submissions:  Submitting samples to the PDDC in 2021 will be similar to 2020.  Due to COVID-19 safety concerns, having student hourly help in the clinic likely won’t be possible, and that will limit the number of physical samples that clinic staff (myself and Sue Lueloff, the PDDC molecular diagnostician) will be able to handle.  To manage sample volume, I will be requesting that clients initially submit photos of their plants using the PDDC online submission form.  Whenever possible, I will provide a disease diagnosis based on these photos.  If an accurate diagnosis is not possible, I will then request a follow-up physical sample.  As in 2020, in-person submissons will not be allowed, but you will be able to mail samples to the clinic.  As always, a completed  PDDC sample submission form should accompany each sample.

New in 2021 will be a $20 fee for all digital submissions.  If a follow-up physical sample is needed, this digital fee will be credited to any fees charged for processing the physical sample.  For a complete listing of PDDC fees, check out the PDDC Clinic Fee Schedule.  Note that as a public service, the PDDC will continue to offer free testing for plant diseases of regulatory importance (e.g., Ralstonia wilt, sudden oak death, boxwood blight) and for plant diseases that pose significant risks to Wisconsin’s agricultural economy (e.g., late blight).

Educational Outreach:  COVID-19 curtailed PDDC in-person educational outreach in 2020.  In 2021, I will be taking greater advantage of distance education platforms like Zoom to provide education.  I am planning to partner with county Extension educators across Wisconsin to offer monthly plant disease presentations.  The goal is to to give these presentations a local flavor by offering the first opportunity to participate to residents of the host and surrounding counties.  Eventually however, participation will be open to residents statewide.  On January 13, 2021, I will be partnering with Darrin Kimbler of Extension Iron County for the first of these talks.  I’ll be presenting on Early Season Landscape Diseases.  Stay tuned for additional details on this presentation and others in the series.

In addition to these monthly presentations, I am willing to entertain requests to provide other talks throughout the state.  I really LOVE talking to the public about plant diseases, and I have been beefing up my repertoire of talks in anticipation of getting requests.  Check out the Talks for the General Public section of the PDDC website for details on some of my favorite talks.

Also, if there is interest, I am considering sponsoring statewide online plant disease Q&A sessions once a month from May through September.  These sessions will be informal discussions of whatever plant disease-related topics are of interest to whomever chooses to participate.  I’ll be providing additional details on these sessions as we get closer to the 2021 growing season.

Online content:  As always, watch for new and revised University of Wisconsin Garden Facts/Farm Fact/Pest Alerts on the PDDC website.  Winter/early spring is definitely a prime time for me to put on my editor’s hat and crank out fact sheets.  I currently have fact sheets on container gardening and pruning tomatoes waiting in the wings.  I will also continue to post web columns (like this one) each month.  In addition, I will be adding a new online feature called Plant Pathology Pointers, which will provide short, timely advise on plant diseases and their management.  Watch for these to start early in January 2021.

Finally, I am always looking for new ideas on how to better serve my clients around the state.  If you have thoughts that you’d like to share, please contact me at pddc@wisc.edu.  To keep up-to-date on PDDC services and educational resources, feel free to follow the clinic on Twitter or Facebook (@UWPDDC).  Or alternately, put in a request (by emailing pddc@wisc.edu) to subscribe to the clinic’s listserv, UWPDDCLearn.

Happy Holidays, everyone!  Please be safe, and stay healthy!