All posts by ddlang

May 2021: Rampant, Ravaging Rusts

May 2021 Column IconI really love this time of the year as plants emerge once again after their long winter naps.  I also love the fact that I now get to start looking once again for some of my favorite plant diseases.  At the top of the list at this time of the year are the rust diseases.  Rusts encompass a large group of fungal diseases, where the fungi produce brightly-colored (yellow to orange to bown) spores.  Each rust fungus has a very specific host range.  The following are a few of the rusts (one on a broad-leafed tree, one on a conifer and one on an herbaceous plant) that I have recently seen either through the clinic or in my own yard.

Crown Rust Buckthorn
Crown Rust on Buckthorn

Crown rust:  Crown rust is classic rust of grass species such as turfgrass and oats.  If you’ve ever walked through your lawn and gotten orange shoes, you’ve encountered this disease.  The fungus that causes crown rust is Puccinia coronata, which has several variants adapted to infect specific grass hostsThe disease and pathogen names come from the look of the resting spores of the fungus.  These spores have spikes that give them the appearance of a crown.  At this time of the year, I don’t see crown rust on grass or oats (that comes later in the growing season), but I see it on a second host (called the alternate host) of the fungus, buckthorn.  Buckthorn is actually required by the crown rust fungus to complete its life cycle.  Puccinia coronata causes yellow-orange, powdery patches on the buckthorn leaves and green stems, and I actually use crown rust as an ID feature for buckthorn.  If I see seedlings that I think are buckthorn, but I’m not quite sure, I look for the characteristic orange patches of crown rust to confirm.  And if you need another reason get rid of buckthorn, in addition to this plant being incredibly invasive, here it is.  If you remove buckthorn, you will prevent the crown rust fungus from completing its life cycle and reduce the severity of the disease on turf and oats.

Weirs Cushion Rust
Weirs Cushion Rust on Spruce

Weir’s cushion rustThis is rust disease of spruce that I see infrequently, but I just received a sample of it this past week in the clinic.  I was over the moon!  (Yes, I know I’m weird and lead a very sheltered life.)  The fungus that causes this disease is Ceropsora weirii (formerly Chrysomyxa weirii), a single-host rust fungus that only requires spruce to complete its life cycle.  Infection leads to yellow banding on one-year-old needles.  Within these bands in the spring (typically April or May), fruiting bodies (i.e., reproductive structures) of Ceropsora weirii form yielding orangish spores that blow to newly emerging needles where the fungus infects.  The fruiting bodies are easily visible with a hand lens or even with the naked eye.  Eventually the infected3 needles brown and drop off the tree.  Management of Weir’s cushion rust can be a challenge and typically involves use of fungicides to protect newly emerging needles.

Mayapple_Rust
Mayapple Rust

Mayapple rust:  I’d like to give a shout-out to Brenda Dahlfors, Master Gardener Program Coordinator with University of Illinois Extension for sending me photos of this cool rust.  The fungus involved here is another species of Puccinia, Puccinia podophylli.  This is another single-host rust, where the fungus that only infects mayapples.  The disease is most visible in the spring when bright orange, powdery patches develop on the undersides of leaves.  On the upper leaf surfaces above these patches, you will see yellow spots/discolored areas.  The orange spores produced by the pathogen reinfect mayapple plants, causing additional disease.  The bright orange patches tend to fade to a duller brown as they age and convert to producing brown overwintering spores.  These overwintering spores germinate in the spring to produce yet another type of spore that causes the initial infections in the spring.  Careful removal of infected leaves and plant debris (burn, bury or hot compost this material) combined with fungicide sprays where appropriate is the typical management strategy for this disease.

These are just a few of the cool rust diseases that you may encounter as you are out and about.  Watch for these and other rusts, and enjoy them when you find them.  There are the most visually colorful and attractive diseases that I see.  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).

Plant Diseases to Watch For in 2021

Septoria Leaf Spot Septoria Leaf Spot and Early Blight
Host:  Tomato
Pathogens:   Septoria lycopersici and Alternaria solani
Signs/Symptoms:  Spotting and eventual total collapse of leaves working from the bottom of the plant up
For more information see:       UW Plant Disease Facts D0100/46
Late Blight Late Blight
Hosts:  Tomato, potato
Pathogen:   Phytophthora infestans
Signs/Symptoms:  Water-soaked spots on leaves, leathery areas on tomato fruits, rapid plant death
For more information see:       UW Plant Disease Facts D0068
Septoria Leaf Spot of Lilac Septoria Leaf Spot of Lilac
Host:  Lilac
Pathogen:   Septoria sp.
Signs/Symptoms:  Dead spots on leaves, potentially leading to complete leaf browning
Rhizosphaera Needle Cast Rhizosphaera Needle Cast
Hosts:  Colorado blue spruce, other spruces
Pathogen:   Rhizosphaera kalkhoffii
Signs/Symptoms:  Browning/purpling of interior needles of lower branches, followed by needle drop
For more information see:       UW Plant Disease Facts D0093
Gymnosporangium Rusts
Hosts:  Juniper, apple, crabapple, hawthorn, quince
Pathogen:   Gymnosporangium spp.
Signs/Symptoms:  Brown blobs with orange gelatinous masses (juniper); yellow/orange leaf spots (other hosts)
For more information see:       UW Plant Disease Facts D0058
Elderberry Rust
Hosts:  Elderberry
Pathogen:   Puccinia sambuci
Signs/Symptoms:  Light yellow, powdery growths on branches
For more information see:       UW Plant Disease Facts D0049
Scab Scab (Apple and Pear)
Hosts:   Apple, crabapple, pear, mountain-ash
Pathogens:   Venturia inaequalis, Venturia pirina
Signs/Symptoms:  Feathery-edged spots on leaves and fruits often leading to leaf loss and tree defoliation
For more information see:       UW Plant Disease Facts D0004
Bur Oak Blight
Host:   Bur oak
Pathogen:   Tubakia iowensis
Signs/Symptoms:  Wedge-shaped dead areas on leaves leading to dead leaves that stay attached to trees
Powdery Mildew
Hosts:   Herbaceous and woody ornamentals, fruits, vegetables, turf
Pathogens:   Miscellaneous powdery mildew fungi
Signs/Symptoms:  Powdery white growth on leaves
For more information see:       UW Plant Disease Facts D0084/86/87
Diplodia Shoot Blight and Canker
Hosts:  Austrian pine, other pines
Pathogen:   Diplodia spp.
Signs/Symptoms:  Dieback of branch tips with dead needles showing uneven lengths
For more information see:       UW Plant Disease Facts D0042
Boxwood Blight
Host:  Boxwood
Pathogen:   Calonectria pseudonaviculata
Signs/Symptoms:  Circular, brown leaf spots followed by leaf drop and shrub death
For more information see:       UW Plant Disease Facts D0023

For more information on plant diseases to watch for:  See https://pddc.wisc.edu/ or contact your county Extension agent.

May 2021: Smart Shopping: Dodging Disease When Purchasing Plants

Potted Plant IconMay is a prime time to visit your local greenhouse, nursery or garden center to buy annuals, perennials and vegetables for your home garden.  Unfortunately, these plants can be carriers of plant disease-causing organisms.  Here are some pointers on what to look for when buying plants.

  • Select plants that are vigorously growing, but aren’t overly leggy. Stunted plants often have diseases (e.g., root rots or viral diseases).  Leggy plants may be healthy, but often have growth that is wimpy and easily injured.  Injured tissue can provide entry points for plant pathogens.
  • Avoid plants with brown leaf spots. Dead spots on leaves can indicate fungal or bacterial infections.  The pathogens involved continue to reproduce in these areas and can spread on the plant, and potentially to other plants.
  • Avoid plants with odd leaf coloring. Some plants have variegated foliage.  That’s normal.  However, if you see plants with unexpected blotchy light and dark-colored leaves, yellow lines or yellow ring patterns, avoid these.  They may be infected with a virus.
  • Avoid plants with fuzzy growth on the leaves. Such growth typically indicates a fungal or water mold infection.  For example, white growth on upper and lower leaf surfaces can indicate a powdery mildew problem; white, gray or purplish growth on the undersides of leaves is typical of a downy mildew
  • Choose plants with healthy, white roots. Examine plant roots whenever possible.  If roots are brown or otherwise discolored, root rots or some sort of physical root injury (e.g., heat injury) may be an issue.
Avoid plants with blotchy leaf color, an indication of a viral infection.
Avoid plants with blotchy leaf color, an indication of a viral infection.

With just a little care, you can buy healthy, pathogen-free plants that will provide months, if not years, of gardening enjoyment.

For more information on plant diseases and their management, check out the fact sheet section of the UW-Madison PDDC website (https://pddc.wisc.edu/fact-sheet-listing-all/).

Ten Common Plant Diseases/Disorders You Can Diagnose by Eye

Powdery Mildew Powdery Mildew
Hosts:   Herbaceous and woody ornamentals, fruits, vegetables, turf
Pathogens:   Miscellaneous powdery mildew fungi
Signs/Symptoms:  Powdery white growth on leaves
For more information see:       UW Plant Disease Facts D0084/86/87
Tar Spot - Ten Common Plant Diseases Tar Spot
Hosts:  Maples
Pathogen:   Rhytisma spp.
Signs/Symptoms:  Tarry areas (either solid spots or clusters of small spots) on leaves
For more information see:       UW Plant Disease Facts D0110
Peach Leaf Curl Peach Leaf Curl
Hosts:  Peach
Pathogen:   Taphrina deformans
Signs/Symptoms:  Light-green, yellow or purplish-red puckered areas on leaves
For more information see:       UW Plant Disease Facts D0076
Sooty Mold Sooty Mold
Hosts:  Any plant
Pathogen:   Miscellaneous sooty mold fungi
Signs/Symptoms:  Powdery black growth on leaves or needles
For more information see:       UW Bulletin A2637
Chlorosis Chlorosis
Hosts:  Oak, red maple
Cause:   Iron or manganese deficiency, often induced by high soil pH
Signs/Symptoms:  Yellow leaves with dark green veins
For more information see:       UW Plant Disease Facts D0030
Gymnosporangium Rusts Gymnosporangium Rusts
Hosts:  Juniper, apple, crabapple, hawthorn, quince
Pathogen:   Gymnosporangium spp.
Signs/Symptoms:  Brown blobs with orange gelatinous masses (juniper); yellow/orange leaf spots (other hosts)
For more information see:       UW Plant Disease Facts D0058
Black Knot Black Knot
Hosts:  Prunus spp. (plum and cherry)
Pathogen:   Apiosporina morbosa
Signs/Symptoms:  Black poop-like growths on branches
For more information see:       UW Plant Disease Facts D0018
Elderberry Rust Elderberry Rust
Hosts:  Elderberry
Pathogen:   Puccinia sambuci
Signs/Symptoms:  Light yellow, powdery growths on branches
For more information see:       UW Plant Disease Facts D0049
Golden Canker Golden Canker
Hosts:  Pagoda dogwood
Pathogen:   Cryptodiaporthe corni
Signs/Symptoms:  Gold-colored branches with orange spots
For more information see:       UW Plant Disease Facts D0055
Dog Vomit Slime Mold Dog Vomit Slime Mold
Hosts:  Any plant and on mulch
Cause:   Fuligo septica
Signs/Symptoms:  Scrambled egg-like masses on mulch or at the base of plants
For more information see:       UW Plant Disease Facts D0102

For more information on common plant diseases:  See https://pddc.wisc.edu/ or contact your county Extension agent.

April 2021: Tomato in the Basement, Canary in the Coalmine

Canary IconI have the coolest job on the planet.  Everyday, I get to help people with their plant disease problems.  This may entail helping someone learn how to grow healthy, nutritious vegetables to feed their family or assisting a grieving family select the just the right tree to plant to serve as a lasting memorial for a recently lost loved one.  On occasion, I get to help Wisconsin farmers avoid severe economic losses due to plant diseases or help prevent the introduction of federally regulated plant pathogens that potentially can have negative impacts nationwide  This month, I’d like to share with you a diagnostic case where a proper diagnosis had the potential to save someone’s life.

I recently received photos from a home gardener who was growing tomato transplants indoors.  She was concerned that her plants were not doing well and losing leaves.  Her photos showed plants with leaves that were cupping downward and showed twisted petioles and other growth distortions.  I was immediately suspicious that the plants had been exposed to ethylene.  Ethylene is a gas that is a plant growth hormone that can be very beneficial for proper plant development; in particular, ethylene is important in fruit ripening.  But in other situations, when plants are exposed at the wrong time or at too high of a concentration, ethylene can have negative effects, in fact exactly the sort of symptoms I was seeing in my client’s photos:  distorted plant growth and premature leaf loss.

Tomatoes Damaged by Ethylene
Tomatoes suffering from ethylene exposure. Photo courtesy of Kristine Meixensperger.

After an exchange of several emails, the puzzle pieces started to fall into place.  My client had been growing her tomatoes in the basement (not uncommon for many gardeners) next to the boiler that provided heat for her home.  As the weather warmed up, she moved the plants to her garage where she parks her car and where she has a full kitchen.  She had been cooking in this kitchen recently to provide a bit of additional warmth for her plants.  Both her boiler and stove burn propane.

At this point, alarm bells were going off.  If propane burners malfunction and don’t burn propane completely, one of the breakdown products of this incomplete combustion is ethylene.  You can also find ethylene in exhaust fumes from motor vehicles, in the smoke produced by wood-burning stoves and as a contaminant in natural gas.  I suggested to my client that she should have her boiler and stove checked immediately for problems.  One or both of these (and possibly also fumes from her car) were likely the source of ethylene that was causing problems for her tomatoes.  She emailed back to tell me that what I had told her made perfect sense as her tomatoes nearer the boiler had more severe symptoms than those farther away.  Another sentence from this email became the inspiration for the title of this article:  “So the tomatoes plants in the basement acted like a canary in a coalmine.”

I told her that she was spot on with her analogy, and at that point, I gave potentially even more serious news.  In addition to producing ethylene, malfunctioning propane burners (and other types of heating systems) also can produce carbon monoxide, a potentially deadly gas.  According to the CDC, approximately 50,000 people visit hospitals with carbon monoxide poisoning each year and at least 430 of these people die from this poisoning.  Luckily, my client had a carbon monoxide detector near the boiler and it hadn’t gone off.  But, the unit was old, and my client indicated that our conversation had made her realize that she needed to replace that unit.

What if she hadn’t had a carbon monoxide detector?  Then, those distorted tomatoes would have been her first hint that a potentially deadly carbon monoxide situation was developing.  Similarly, if she had had distorted tomatoes growing near a natural gas-fueled furnace, that could have indicated a natural gas leak, another potentially lethal situation.

Ah, the power of a lowly vegetable and a bit of knowledge about how they grow!

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).

April 2021: Water, Water, Everywhere, but Never, Ever on the Leaves

Thundercloud with RainApril conjures up visions of spring rain showers, eventually leading to May flowers.  While Mother Nature waters plants using an overhead sprinkling system (i.e., rain), from plant disease standpoint, this type of watering is less than optimal.

What’s the problem with watering from above?  Overhead watering wets leaves creating what plant pathologists call a “leaf wetness period,” a time when a thin layer of water coats the leaf.  This layer of water is exactly what most plant diseases-causing fungi require for their spores to germinate and infect.  The longer the leaf wetness period, the more likely leaf diseases will be a problem.

Wet Leaves - Photo by Diana Alfuth

What do I do to prevent watering issues?  You can’t prevent rain, but during dry periods when you need to water, don’t simulate rain by using a sprinkler.  Instead, use a soaker or drip hose that directs water into the soil rather than onto leaves.  Water at low pressure so that any sprays from these hoses are minimized.  When it does rain, promote rapid drying of leaves by spacing plants as far apart as possible in new plantings, and thinning existing beds to increase spacing.  Wider plant spacing increases air flow, promotes more rapid drying of leaves (when leaves do get wet), and shortens leaf wetness periods, making it more difficult for plant pathogens to get a foothold.  Don’t overwater either.  Excessive soil moisture eventually increases humidity around plants, which slows leaf drying and lengthens leaf wetness periods.

By taking just a little extra care in how you water, you can have a big impact on the health of the plants in your garden.

For more information on leaf diseases, check out the fact sheet section of the UW-Madison PDDC website (https://pddc.wisc.edu/fact-sheet-listing-all/).

Photo courtesy of Diana Alfuth.

March 2021: Gardening Ideas for the 2021 Growing Season

Plant Light BAs the temperatures begin to warm and the snow melts, gardeners are chomping at the bit to be outdoors working away.  Thoughts tend towards “What should I plant this year?” and “When should I plant and seed?”  Those are great questions, but there are other aspects of gardening that I think are important to consider.  This month, I’d like to share what I think about at this time of year as I try to prepare for a successful growing season.

Garden clean-up.  I often talk about the importance of fall clean-up for plant disease management.  Plant pathogens often overwinter in debris from infected plants left over from the previous growing season.  Removing this material from a garden helps eliminate a source of pathogens that can reinfect plants during the current growing season.  While fall is a great time to do this removal, there are a variety of reasons why gardeners might choose not to do clean-up in the fall.  Some people just don’t have the time.  Some like to use leaf litter to insulate flower beds.  Others like to maintain plants that have died back for winter visual interest in their gardens or as overwintering sites for beneficial insects.  If you’re one of the people who likes keep plant debris around for the winter, spring is the time to take care of this material.  Try to remove the debris before plants begin to produce new growth, and burn (where allowed), bury or hot compost it.

Watering concerns.  This can be a tough time of year for many evergreens (particularly yews and boxwoods), as they tend to be prone to winter burn.  Sometimes winter burn develops during the winter months, but spring is a prime time for symptoms to develop as plants start to photosynthesize and thus lose more water through stomates on needles and leaves.  So, as the ground begins to thaw and new needles and leaves begin to emerge, make sure evergreens are receiving sufficient water.  Established plants (those planted three years or more) require approximately one inch of water per week from rain or from supplemental watering with a drip or soaker hose placed at their driplines (i.e., the edges of where the branches extend).  Newly transplanted plants (those planted within the past three years) require roughly two inches of water per week.

Decontaminating pots.  If you grow plants in pots or other containers, and particularly if you have issues with root rots or other diseases caused by soil-borne pathogens, you should seriously consider decontaminating your containers before reusing them this year.  Empty any soil from the containers and discard the soil (especially if the plants previously grown in the containers have had disease issues), wash the containers thoroughly to remove any remaining soil, then soak the containers for 30 minutes in a 10% bleach solution (one part of a disinfecting bleach and nine parts water).  Rinse the containers thoroughly to remove any bleach residues and you’re ready to plant.  Note that this techniques works best for clay or ceramic pots, but may not be reliable for plastic pots.  Sometimes the best way to decontaminate plastic pots is to throw them away.

Mapping vegetable gardens.  For long-term success with vegetable gardening, crop rotation is a must.  Growing the same (or related) vegetables in the same spot in your vegetable garden year after year is a great way to build up disease-causing organisms in the soil.  These pathogens can cause problems for years, if not decades, to come.  So, if you haven’t been mapping out where you plant your vegetables each year, make this the year when you start doing that.  Buy some graph paper, draw your vegetable garden space to scale and preplan where you will plant your various vegetables this year.  Keep this plan as a reference so that next year when you create your 2022 map, you can properly rotate your vegetables to new areas in your garden.  If possible, don’t grow the same (or related) vegetables in the same area for a period of at least three to four years.

Keeping a garden journal.  Also, make this the year that you start documenting what goes on in your garden.  Record information on when plants emerge or begin to leaf out, and when they flower.  Keep track of the weather including temperatures, rain (and snow), significant storm events (hail, high winds, driving rains) and note when you see particular insects and diseases in your garden.  This sort of information can be very useful (particularly after you have several years’ data) in predicting insect pest and disease activity and thinking ahead about how to fend off these sorts of problems.

I hope these pointers help you have a successful 2021 gardening season.  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).

Elderberry Rust

What is elderberry rust?  Elderberry rust is a visually striking fungal disease that affects stems, leaves and flowers of plants in the genus Sambucus (i.e., elderberries).  The disease also affects sedges (Carex spp.).  On elderberries grown as ornamentals, as well as on sedges, the disease is primarily a cosmetic problem.  However, if elderberries are grown for fruit, the disease can disrupt flower and fruit formation, thus reducing fruit yield.

An elderberry rust gall on elderberry (left) and leaf spots caused by elderberry rust on sedge (right). Photos courtesy of Jenell Bindl (left) and Michele Warmund, University of Missouri (right)
An elderberry rust gall on elderberry (left) and leaf spots caused by elderberry rust on sedge (right). Photos courtesy of Jenell Bindl (left) and Michele Warmund, University of Missouri (right)

What does elderberry rust look like?  Elderberry rust is most noticeable on elderberries where it causes growth distortions and swellings (i.e., galls) on leaves and stems.  Galls are often very large, bright yellow and powdery from spores produced by the causal fungus.  In extreme cases, galls can resemble banana slugs that have attached themselves to branches.  Infected flowers become thick, swollen and green-tinged rather than white.  Affected plant parts are covered with a network of small (approximately 1/16 inch in diameter) ring-like spots.  These spots are reproductive structures of the rust fungus and produce the powdery spores that coat the galls.

On sedges, elderberry rust causes brownish leaf spots, often with yellow halos.  The spots eventually erupt releasing powdery, rusty-orange spores.

Where does elderberry rust come from?  Elderberry rust is caused by the fungus Puccinia sambuci, also known as Puccinia bolleyana.  The fungus overwinters in sedge debris, and spores produced in this debris blow to elderberry plants in the spring, leading to infection and gall formation.  Spores produced in elderberry galls blow back to sedges, where infection of newly produced leaves (and other plant parts) occurs.  These infections lead to spotting and to the formation of a third type of spore that reinfects sedges causing additional spotting.  Late in the season a fourth type of spore is produced that serves as the overwintering phase of the fungus.  Infection of both elderberries and sedges is favored by wet weather.

How do I save plants with elderberry rust?  Elderberry rust is not a lethal disease on either elderberry or sedge.  When galls form on elderberry, simply prune these out.  This will make elderberry plants more aesthetically pleasing and limit spread of the fungus to sedges.  When pruning, cut branches four to six inches below each gall.  Between cuts, decontaminate pruning tools by treating them for at least 30 seconds with 70% alcohol (e.g., rubbing alcohol straight out of the bottle), a spray disinfectant containing 60-70% active ingredient, or a 10% bleach solution (i.e., one part of a disinfecting bleach and nine parts water).  If you decide to use bleach, be sure to rinse your tools thoroughly after you are done pruning and then oil them to prevent rusting, which can be caused by bleach use.  Dispose of galls by burning (where allowed by local ordinance) or burying them.

How do I avoid problems with elderberry rust in the future?  In landscape settings, the best way to avoid problems with elderberry rust is to remove any sedges that are growing near elderberry plants.  The farther the distance between elderberries and sedges, the less likely that elderberry rust will be an issue.  Also, increase airflow around elderberry plants by thinning them and removing surrounding plants.  Increased airflow will dry plants more rapidly and make the environment less favorable for infection.  DO NOT use a sprinkler to water plants, as that wets leaves and provides a better environment for infections to occur.  Instead, use a soaker or drip hose to apply supplemental water to the soil at the drip lines of the plants (i.e., the edges of where the branches extend).  While fungicides are available for rust control in commercial elderberry production, these products are not recommended for use in home garden settings.

For more information on elderberry rust:  Contact your county Extension agent.

March 2021: Dampening Damping-Off: Tips on Seed Starting to Avoid Disease

Germinating Seed IconAfter a long, cold winter, it’s time to start growing plants from seeds for the upcoming growing season.  Damping-off is a common disease that can prevent seed-starting success.  Here are tips that can help prevent damping-off from being a problem.

Damping Off
Damping Off

Buy high quality seed from a reputable source.  High quality seeds are less likely to carry damping-off organisms.

Use pasteurized soil.  Pasteurized soil has been steam treated to kill pathogens.

Use clean pots/containers.  Store new pots or flats in sealed plastic bags to prevent possible pathogen contamination prior to use.  When reusing pots, soak them in 10% bleach (1 part of a disinfecting bleach, 9 parts water) for 30 minutes, then rinse well to remove bleach residues.

Plant seeds at the proper depth.  This will promote quick germination and rapid growth of seedlings out of the early stages of growth when they are most susceptible to damping-off.

Start seeds at higher temperatures.  This will again help plants grow out of their susceptible phase quickly.  Consider using a seed-starting heat pad (available at your local garden center), particularly if you start seeds in a colder part of your home (e.g., a basement).

Don’t overwater!  Damping-off organisms are more active in wet soils.  Water enough to keep seedlings alive, but keep plants a bit on the dry side to slow development of damping-off pathogens.

Seed starting can be a fun way to start the gardening season.  With just a little extra effort, you can prevent damping-off from dampening your gardening efforts.

For more information on damping-off and its management, check out University of Wisconsin Garden Facts XHT1124 (Damping-Off), available at https://pddc.wisc.edu/fact-sheet-listing-all/ or https://hort.extension.wisc.edu/articles/damping/.

Tobacco Mosaic

Tobacco mosaic causing a blotchy light and dark coloring (mosaic) of tobacco leaves.
Tobacco mosaic causing a blotchy light and dark coloring (mosaic) of tobacco leaves.

What is tobacco mosaic?  Tobacco mosaic is a common viral disease of worldwide distribution that affects over 200 species of herbaceous and, to a lesser extent, woody plants.  Common hosts include tobacco, solanaceous vegetables (e.g., pepper, tomato) and vining vegetables (e.g., cucumber, melon, squash), as well as a wide range of ornamentals (e.g., begonia, coleus, geranium, impatiens, million bells, petunia).  The disease has its biggest impact on vegetables, where it can reduce yield and affect quality to the point that commercial crops cannot be marketed.

What does tobacco mosaic look like?  Symptoms of tobacco mosaic vary in type and severity depending on the plant infected, plant age, the variant of the virus involved, and environmental conditions.  On leaves, typical symptoms include blotchy light and dark areas (called mosaic); cupping, curling, elongation (strapping), roughening, wrinkling and other growth distortions; and smaller than normal size.  Fruits may have a blotchy color, ripen unevenly, be malformed or have an off flavor.  Entire infected plants are often stunted.  Other viral diseases like cucumber mosaic (see UW Plant Disease Facts D0036, Cucumber Mosaic) can cause symptoms similar to tobacco mosaic.  Often, multiple viral diseases can simultaneously affect a single plant.  Certain herbicide exposures (see UW Plant Disease Facts D0060, Herbicide Damage), nutrient deficiencies or toxicities, high temperature and even insect feeding can also cause similar symptoms.  Proper diagnosis of tobacco mosaic requires lab testing.

Where does tobacco mosaic come from?  Tobacco mosaic is caused by Tobacco mosaic virus (TMV), the first virus ever identified.  Numerous variants (strains) of the virus have subsequently been described.  TMV survives in infected plants (including viable seeds), as well as in debris from these plants.  Plant-based products (most notoriously tobacco products) can harbor the virus.  TMV is very stable and can survive for long periods of time; there are reports of TMV surviving and remaining infectious after 50 years in storage at 40°F.  Because of its stability, TMV can survive on and be picked up from hands, clothing, gardening tools, work surfaces and any other object (e.g., door knobs) that gardeners may handle.

TMV is highly transmissible and is commonly spread by handling infected plants, then healthy plants.  Spread via gardening tools is also very common.  No specific insects spread TMV (the way that aphids spread Cucumber mosaic virus).  However, bees and chewing insects (e.g., grasshoppers) can transmit TMV through casual contact or their feeding as they move from plant to plant.

Leaf growth distortions caused by tobacco mosaic.
Leaf growth distortions caused by tobacco mosaic.

How do I save a plant with tobacco mosaic?  There is no cure for tobacco mosaic.  Once infected, plants remain infected for life, and typically the virus spreads throughout the plant from the point of infection.  Infected plants and any associated debris should be burned (where allowed by local ordinance) or double-bagged and disposed of in a landfill.  DO NOT compost plants with this disease.  Thoroughly decontaminate any items that have come into contact with infected plants or their debris by treating them for a minimum of one minute with:

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

These ingredients can be ordered on the internet.  If you decide to use SLS (SDS), be sure to wear gloves, safety goggles and a dust mask, and mix the solution in a well-ventilated area as SLS (SDS) is a known skin and eye irritant.  Once treated, rinse items with sufficient water to remove any residues.  Also, thoroughly wash your hands with soap and water, and launder any clothing that you wore while disposing of infected plants and debris.

How do I avoid problems with tobacco mosaic virus in the future?  Inspect plants prior to purchase for any symptoms of tobacco mosaic, and DO NOT buy symptomatic plants.  Purchase seed from a reputable supplier that routinely inspects their seed-producing plants for symptoms of viral (and other) diseases.  If you use tobacco products, DO NOT use them around plants.  Also, wash your hands thoroughly with soap and water prior to handling plants, and consider wearing freshly laundered clothing when gardening.  Finally, decontaminate (as described above) any items that might harbor TMV to help prevent spread.  Even if you do not use tobacco products, routine handwashing and decontamination of gardening tools and other items can help prevent tobacco mosaic from being a problem.

For more information on tobacco mosaic:  Contact your county Extension agent.