All posts by ddlang

February 2020: Yacking It Up About Plant Diseases

Yacking It UpLast month in my summary of my activities for 2019, I mentioned that I had given 111 talks/presentations/workshops during the course of the year.  This month I’d like to elaborate a bit on the types of outreach presentations that I provide.

Audiences

Quite frankly, I’m willing to talk about plant diseases on any crop/plant other than turf (there are other Extension specialists who handle this crop).  I truly think that plant diseases are INCREDIBLY COOL.  I give talks to both commercial (i.e., agricultural/horticultural grower and consultant) and consumer (i.e., general public) audiences.

Most typically though, I provide education for the general public, often concentrating on teaching about diseases of herbaceous ornamentals, woody ornamentals and vegetables.  I often partner with county Extension staff, Master Gardener Volunteer groups, technical college instructors, professional organizations, public libraries and garden clubs to reach as wide a range of home gardeners (and horticulture professionals) as possible.

Types of Talks

To learn more about the specifics on the types of talks that I do, check out a couple of sections of the Plant Diseases Diagnostics Clinic (PDDC) website:

2020 Events Calendar

On my events calendar, I try to list every talk/presentation/workshop that I give during the year.  The calendar changes constantly as I book new presentations.

The calendar entries includes the titles of my talks, as well as the dates, times and towns where I will be.  If you ever see a presentation in a town near you and are interested in additional details on the program, feel free to contact me and I can provide those details.

Watch the entries as the date approaches.  I typically create handouts for my talks and link to the handouts on my calendar.  You are welcome to view these handouts online or download them to see what I’m talking about and hopefully learn a thing or two, even if you can’t attend the presentation.

Master Gardener Resources

The presentations/programs described on this page are a series of talks and hands-on opportunities that I have put together specifically to address the continuing education needs of Master Gardener Volunteers.  That said, virtually all of these presentations could be of interest to a general public audience.

Many of the talks fall into the “Diseases of” category, where I discuss diseases of broad plant groups such as vegetables, herbaceous ornamentals, evergreens and deciduous trees and shrubs.  Other of these talks cover more specific plants such as hostas and orchids.

Also included on this page are talks that are more conceptual in nature including my The Science (and Art) of Plant Disease Diagnosis and Growing Healthy Plants:  Basics in Plant Disease Management talks.

Some of the talks are just fun topics that I like to get geeky about, such as my Plant Diseases in History presentation.  The newest addition in this latter category is Confessions of a Black Thumb:  Plants That I Have Killed (or at Least Seriously Maimed), a cautionary tale of my personal gardening disasters (and there have been many).

If you are interested in getting down and dirty about plant diseases, I offer my Signs and Symptoms Workshop.  In this hands-on activity, participants have the opportunity to see and work with actual diseased plant specimens.

Finally, I offer tours of the PDDC (located on the UW-Madison campus), and typically combine this tour with tours of the Insect Diagnostic Lab, the Wisconsin Insect Research Collection and/or the Allen Centennial Garden.

Intrigued? 

If you have a group that might be interested in learning more about plant diseases, don’t be bashful about contacting me to explore the possibility.  You can contact me at pddc@wisc.edu.  Book early as my calendar often fills up quickly.  And for addition information on the PDDC, its activities and resources, check out other sections of the PDDC website, or follow the clinic on Twitter or Facebook (@UWPDDC).

Keep warm!  And don’t worry because spring gardening season (with all those uber-cool plant diseases) is coming soon!!

January 2020: 2019 in Review

Jan 2020 Column Icon

Wow!  It’s 2020 already and I can’t say that I’ve recovered yet from the avalanche that was 2019.

 

Sample Processing

Clinic staff processed 1506 samples, up roughly 17.5% from 2018.  Samples came from 64 of Wisconsin’s 72 counties, as well as FL, IA, IL, IN, MA, ME, MI, MN, and NY.  Sample numbers were up sharply (despite the PDDC having increased fees in 2019) most likely in part due to having had two seasons back to back that were incredibly wet and thus favorable for disease development.

Quick Stats:

  • 1506 samples processed
  • 1500+ email and phone consults
  • 111 talks/presentations in 22 WI counties
  • 224,000 people interacted with at outreach events
  • 3,435 Garden Facts fact sheets distributed at Garden Expo alone

Molecular Diagnostics

I also believe that the PDDC’s expanding molecular (i.e., DNA-based) diagnostic offerings have helped drive higher clinic sample numbers.  Many of the molecular tests that the PDDC offers are particularly popular and useful for commercial vegetable producers.  Once again, kudos to Sue Lueloff, the PDDC’s Assistant Diagnostician, for stepping up and handling all of the molecular samples.  Sue tested numerous samples for bacterial soft rot pathogens, the oak wilt pathogen and phytoplasmas.  In addition to processing routine samples (included in the total mentioned above), Sue also worked on a survey with the Wisconsin Department of Natural Resources (WI DNR), testing ~100 tree samples from around the state for phytoplasmas.  Testing from this survey will be completed in early 2020.

Sample Highlights

As always, while Sue handled the molecular side of things at the PDDC, I handled the more classical side of the diagnostic process that involved culturing (i.e., growing pathogens from plant tissue) and microscopy.  My highlight, sample-wise, for the year was confirming my first case of boxwood blight.  This disease had been first reported in nurseries in Wisconsin by the Wisconsin Department of Agriculture, Trade and Consumer Protection (WI DATCP) in 2018, but the sample I received at the PDDC was the first instance of the disease popping up in a landscape setting (i.e., in a home garden).  I also spent a fair amount of time dealing with samples suspected of having sudden oak death/Ramorum blight.  This disease has caused wide-spread death of oak trees (as well as other trees, shrubs and herbaceous plants) in California and Oregon.  The first Wisconsin case was confirmed by WI DATCP in 2019.  Thus far, none of the putative sudden oak death samples submitted to the PDDC has tested positive for the disease.

Disease Consulting by Email and Phone

In addition to coordinating efforts with live samples in the PDDC, I continued to provide digital disease diagnostics via email, through the UW-Madison Division of Extension PlantDOC online diagnostic website, and through the Association of Specialty Cut Flower Growers Facebook page.  I also spent a lot of time on the phone answering plant disease-related questions.  All told, I likely had 1500+ exchanges in the process of handling online plant disease inquiries and phone calls.

Outreach

PDDC outreach activities, once again, hit an all-time high in 2019.  I did 111 talks/presentations/workshops in 22 Wisconsin counties (many of these in-person).  My biggest outreach event was again Wisconsin Public Television’s Garden Expo.  I spent three days at the event, gave three talks (two on diseases of trees and shrubs, one on plant disease management) and helped answer questions with Lisa Johnson of Extension Dane County at Larry Meiller’s Garden Talk session.  As always, I had a steady stream of visitors to the PDDC booth, talking with and answering questions for folks the entire time.  I distributed 3,435 University of Wisconsin Garden Facts fact sheets, brochures/informational materials and other written materials.  Across all outreach programs in 2019, I interacted with almost 224,000 people.  As always, a big thanks goes out to Larry Meiller for having me on his radio show with its awesome listenership.

Team Effort

What happens at the PDDC is not a solo effort.  I have LOTS of help.  I have already mentioned Sue Lueloff (molecular diagnostician extraordinaire) above.  Also part of my team are Ann Joy (who does data entry that is instrumental in keeping federal funds through the National Plant Diagnostics Network flowing into the clinic), Dixie Lang (who makes the PDDC website look beautiful and keeps the PDDC billing database running and up to snuff), Laurie Ballentine of the Russell Labs support staff (who prints and folds and otherwise produces all of the written handouts I use for my outreach efforts), and finally Alex Mikus (an undergraduate here at the UW-Madison) and Gisele Guzman (a participant in the TOPS program at East High School), my hard-working student hourlies who helped process the bulk of PDDC samples and kept me on my toes.

Onward Ho!

Now, 2020 has arrived and it’s time to gear back up!  “It’s showtime, folks!”  (Brownie points if you can identify the film that quote comes from.)


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.

Typhula Blight

Typhula blight causes circular patches of bleached turf that often merge to form larger, irregularly-shaped bleached areas.
Typhula blight causes circular patches of bleached turf that often merge to form larger, irregularly-shaped bleached areas.

What is Typhula blight?  Typhula blight, also known as gray or speckled snow mold, is a fungal disease affecting all cool season turf grasses (e.g., Kentucky bluegrass, creeping bentgrass, tall fescue, fine fescue, perennial ryegrass) grown in areas with prolonged snow cover.  These grasses are widely used in residential lawns and golf courses in Wisconsin and elsewhere in the Midwest.

What does Typhula blight look like?  Typhula blight initially appears as roughly circular patches of bleached or straw-colored turf that can be up to two to three feet in diameter.  When the disease is severe, patches can merge to form larger, irregularly-shaped bleached areas.  Affected turf is often matted and can have a water-soaked appearance.  At the edges of patches, masses of grayish-white fungal threads (called a mycelium) may form.  In addition, tiny (1/64 to 3/16 inch diameter) reddish-brown or black fungal survival structures (called sclerotia) may be present.  Typhula blight looks very similar to Microdochium patch/pink snow mold (see University of Wisconsin Garden Facts XHT1145, Microdochium Patch), but the Microdochium patch fungus does not produce sclerotia.   

Where does Typhula blight come from?  Typhula blight is caused by two closely related fungi Typhula incarnata and Typhula ishikariensis.  In general, T. incarnata is more common in the southern half of Wisconsin while T. ishikariensis is more common in the northern half of the state.  To distinguish between the two Typhula species, look for sclerotia.  Sclerotia of T. incarnata are reddish-brown and 1/16 to 3/16 inches in diameter.  Sclerotia of T. ishikariensis are black and 1/64 to 1/16 inches in diameter, resembling flakes of pepper.  Typhula blight develops when there is a prolonged period (more than 60 days) when snow covers unfrozen ground and soil temperatures are just above freezing (30 to 40˚F).  Typhula blight typically does not develop if the ground freezes before the first snowfall in the fall/winter, or if snow melts during the middle of winter exposing the ground to colder temperatures.  Damage from Typhula blight is usually not noticed until snow melts in spring.  Applying high nitrogen fertilizers in the fall can increase the risk of Typhula blight developing over the winter.

Sclerotia (survival structures) of Typhula incarnata are small and red or rust-colored.
Sclerotia (survival structures) of Typhula incarnata are small and red or rust-colored.

How do I save a turf with Typhula blight?  Turf with Typhula blight may or may not recover depending on the fungus involved.  Both T. incarnata and T. ishikariensis can infect and kill turf leaves, but only T. ishikariensis kills the plant crown.  Turf infected with T. incarnata typically recovers quickly once normal turf growth resumes in the spring.  Turf infected by T. ishikariensis often suffers from crown injury and death making it less likely to recover and more likely to require replanting in spring.  Lightly raking infected turf and reseeding in spring can help speed turf recovery.

How do I avoid problems with Typhula blight in the future?  Consider planting less-susceptible turfgrass species (e.g., fine fescues) to limit the impact of Typhula blight.  Also, avoid using fast-release fertilizers in late fall that can predispose turf to Typhula infections.  Finally, continue to mow turf until it goes dormant as this will help prevent excessive turf top growth that is more easily infected by Typhula.

Because turf often recovers naturally from Typhula blight, fungicide treatments are typically NOT warranted for home lawns.  However, fungicide treatments may be needed to prevent severe damage when a lawn has a history of the disease and when predictions for the upcoming winter suggest that snow cover will persist on unfrozen ground for longer then three months.  Many effective fungicides are available for snow mold control in home lawns and include the active ingredients azoxystrobin, propiconazole, pyraclostrobin, and tebuconazole.  For the most up-to-date fungicide recommendations for Typhula blight, please visit the Turf Pest Management Mobile website (https://turfpests.wisc.edu/).  Fungicide applications should be made in October or November to prevent disease in the spring.  If you decide to use fungicides for control, read and follow all label instructions to ensure that you use the product that you select in the safest and most effective manner possible.

For more information on Typhula blight:  Contact the Turfgrass Diagnostic Lab (https://tdl.wisc.edu/) or your county Extension agent.

Sudden Oak Death – Pest Alert

What is sudden oak death?  Sudden oak death (also called Ramorum leaf blight or Ramorum dieback) is an oftentimes lethal disease that has caused widespread death of tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), California black oak (Quercus kelloggii), and Shreve oak (Quercus parvula var. shrevei) in California.

Rapid wilting and die back of branch tips can be a symptom of ramorum dieback.
Rapid wilting and die back of branch tips can be a symptom of ramorum dieback.

The disease can affect or has been reported in association with a wide range of woody and herbaceous plants including, but not limited to bigleaf maple (Acer macrophyllum), Bodnant viburnum (Viburnum X bodnantense), ‘Brouwer’s Beauty’ pieris (Pieris floribunda X japonica), California bay laurel (Umbellularia californica), California buckeye (Aesculus californica), California coffeeberry (Rhamnus californica), California honeysuckle (Lonicera hispidula), canyon live oak (Quercus chrysolepis), coast redwood (Sequoia sempervirens), doublefile viburnum (Viburnum plicatum var. tomentosum), douglas-fir (Pseudotsuga menziesii var. menziesii), evergreen huckleberry (Vaccinium ovatum), Formosa firethorn (Pyracantha koidsumii), ‘Forest Flame’ pieris (Pieris formosa X japonica), Himalaya pieris (Pieris formosa), Japanese camellia (Camellia japonica), Japanese pieris (Pieris japonica), laurustinus (Viburnum tinus), madrone (Arbutus menziesii), manzanita (Arctostaphylos manzanita), rhododendron (Rhododendron spp.), Sasanqua camellia (Camellia sasanqua), toyon (Heteromeles arbutifolia), western starflower (Trientalis latifolia), and witch hazel (Hamamelis virginiana), Burkwood viburnum (Viburnum X burkwoodii), California hazelnut (Corylus cornuta), Camellia X williamsii, cascara (Rhamnus purshiana), Chinese pieris (Pieris formosa var. forrestii), common lilac (Syringa vulgaris), David viburnum (Viburnum davidii), drooping leucothoe (Leucothoe fontanesiana), European beech (Fagus sylvatica), European cranberrybush viburnum (Viburnum opulus), European turkey oak (Quercus cerris), European yew (Taxus baccata), fragrant viburnum (Viburnum farreri), grand fir (Abies grandis), Holm oak (Quercus ilex), horse-chestnut (Aesculus hippocastanum), lingonberry (Vaccinium vitis-ideae), mountain laurel (Kalmia latifolia), Northern red oak (Quercus rubra), Pieris formosa var. forrestii X Pieris japonica, poison oak (Toxicodendron diversiloba), Prague viburnum (Viburnum X pragense), reticulate camellia (Camellia reticulata), salmonberry (Rubus spectabilis), Southern red oak (Quercus falcata), strawberry tree (Arbutus unedo), sweet chestnut (Castanea sativa), Viburnum X carlcephalum X Viburnum utile, Victorian box (Pittosporum undulatum), wayfaringtree viburnum (Viburnum lantana), and wood rose (Rosa gymnocarpa).

Sudden oak death was first reported in the US in California and has subsequently been found in other US states, including in Wisconsin in 2019.  Sudden oak death has also been reported in Europe.

What does sudden oak death look like?  Symptoms of sudden oak death vary depending upon the plant species infected.  On some hosts, infections occur primarily on leaves leading to light brown leaf spots and blotches.  These leaf symptoms may be indistinguishable from other, more common, leaf spots and blights, or may mimic sunburn or leaf scorch symptoms.  Twigs and branches that become infected often wilt, forming a “shepherd’s-crook”, and subsequently die back.  Infection of tree trunks leads to cankers (i.e., sore-like areas) that produce large amounts of an amber to black colored ooze.  This ooze can dry to form a stained area on the bark.  Removing the bark over the affected area will reveal discolored wood beneath that sometimes (but not always) has a black border.  Cankers can eventually expand to girdle trunks, thus resulting in the death of the tree or shrub.  Trunk infections appear not to extend into the root system of the plant.  Once sudden oak death cankers develop, other pathogens may invade the infected areas, accelerating tree or shrub death and complicating the diagnosis of the disease.

Where does sudden oak death come from?  Sudden oak death is caused by the fungus-like water mold Phytophthora ramorum, which was first recognized as a pathogen in 1995.  Phytophthora ramorum can be spread over long distances through movement of infected plants or infested plant parts.  The organism can also be moved with contaminated soil (e.g., on vehicle tires, tools, or shoes), or in contaminated water.  Once established on plants in a given location, the fungus produces reproductive structures (called sporangia) that can be moved from plant to plant by rain splash, or wind.  Phytophthora ramorum was introducing into Wisconsin in 2019 on nursery stock grown in the state of Washington.

Ramorum leaf blight symptoms can mimic those of other leaf spots and blights.
Ramorum leaf blight symptoms can mimic those of other leaf spots and blights.

How do I save a plant with sudden oak death?  If you believe you have seen a plant that has sudden oak death, please IMMEDIATELY submit a sample to the Plant Disease Diagnostics Clinic (PDDC), care of the address in the box at the bottom of this page.  Double bag suspect plant tissue in sealable plastic bags and place the bagged specimen in a box or envelope for shipping.  Include contact information (complete address, phone number, email address) in a separate sealable plastic bag with the sample.  Tape over all of the edges of boxes and envelopes used for shipping to keep everything sealed inside.  Write on the box or envelope that the box or envelope contains a suspect SOD sample.  If you have questions about collecting or submitting a sample, contact PDDC staff at (608) 262-2863 or at pddc@wisc.edu.

Because Phytophthora ramorum is a regulated, quarantined pathogen, DO NOT remove the affected plant (or parts thereof) or take the plant from the site where it is located, other than to collect a specimen for submission for a diagnosis.  Be sure to decontaminate any tools or other items that come into contact with the plant (including those used to collect a diagnostic sample) by dipping them for at least 30 seconds in 10% bleach.  If a plant tests positive for Phytophthora ramorum, it will be removed and destroyed to help prevent further spread of the pathogen.

How do I avoid problems with sudden oak death in the future?  Carefully inspect any new nursery stock upon delivery (or prior to purchase, if possible) for symptoms of sudden oak death.  Keep new stock isolated from older stock as long as possible, to minimize possible movement of the pathogen should the disease develop after plants have arrived.  If you see any suspect symptoms, alert the PDDC so that arrangements can be made for proper testing for Phytophthora ramorum.

For more information or help in diagnosing sudden oak death:  Contact Brian Hudelson, UW-Madison Plant Disease Diagnostic Clinic, Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Drive, Madison, WI  53706-1598, phone: (608) 262-2863, email: pddc@wisc.edu, see the USDA APHIS sudden oak death website https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/pests-and-diseases/phytophthora-ramorum/sod, or contact your County Extension agent.

July: Cool Fungal Friends for a Hot and Muggy July

MushroomOver the past two weeks, I have received a number of photos of incredibly cool microorganisms that have popped up in people’s gardens or around their homes.  These organisms have all turned out to be non-pathogens (i.e., they don’t cause plant diseases), but they are some of the more extraordinary organisms that I encounter in my job.

Bird’s Nest FungiIf you’ve recently spread new mulch, you may eventually notice small (maybe ¼ to ½ inch in diameter) cup-like structures forming in groups on the mulch surface.  Closer examination of the cups will reveal egg-shaped structures inside.  Looking at these tiny structures as a whole, you’d swear that some sort of miniature bird has built a series of nests in your flowerbed.  But these mini-“nests” are actually reproductive structures of one of the bird’s nest fungi.  The “eggs” are packets of fungal spores attached to the interior of the cup by a cord-like structure.  When a raindrop hits the nest, the momentum of the falling water catapults an “egg” into the air.  The attached “cord” stretches and eventually breaks.  The broken end is sticky and eventually adheres to some object (e.g., a branch or leaf) as the “egg” flies through the air.  The attached “egg” swings around on the cord (think of a bola) and eventually gloms onto something as well.  As the walls of the catapulted “egg” degrades, the spores inside are released.  Being elevated, the spores are more likely to be picked up in air currents.  What an amazing adaptation that increases the likelihood that the spores are spread over a large distance!

Bird's Nest Fungi on Mulch in a Flowerbed
Bird’s Nest Fungi on Mulch in a Flowerbed

StinkhornsSometimes when people dig in their gardens they encounter large (an inch or larger in diameter), soft, egg-like structures in the soil.  Folks often think these are actual bird or reptile eggs.  However, if you cut the “eggs” through the center along the long axis, you discover inside a mushroom-like structure with a stalk and an oftentimes honeycomb-like cap.  These mushrooms enlarge (eventually causing the “eggs” to “hatch”) and poke up above the soil surface.  These emerging mushrooms often resemble a certain, uh-hem, part of the male anatomy.  I have had a number of amusing conversations over the years as clients have attempted to describe stinkhorns without naming the offending body part.  The name stinkhorn comes from the fact that as they produce spores, these fungi tend to smell pretty rank.  The foul small (akin to rotten meat) attracts certain insects (e.g., flies) that pick up the spores and move them long distances.  Again, this is another amazing dispersal mechanism.

Stinkhorn "Eggs"
Stinkhorn “Eggs”
Inside the Stinkhorn "Eggs"
Inside the Stinkhorn “Eggs”

Slime MoldsSlime molds are not true fungi, but members of a unique group of organisms called the myxomycetes.  These organisms spend part of the lives in an amoeba-like stage (so in a sense are animal like), but when they reproduce, form spores the way true fungi do.

The most common slime mold I encounter is one I affectionately call dog vomit slime mold, but is more commonly called scrambled egg slime mold.  This slime mold really looks like someone’s dog upchucked in your flowerbed.  Watch for this slime mold (usually in the genus Fuligo) after you’ve spread a new layer of mulch on your flowerbeds.

Dog Vomit Slime Mold on Mulch in a Flowerbed

Another slime mold you may encounter is Physarum which is often found on turfgrass.  I remember seeing this slime mold in a lawn walking home from work one day.  I thought that someone had been out on their lawn spray painting some furniture and left gray paint residue on their grass.  On closer inspection however, the gray turned out to be thousands of small, spherical fruiting bodies (i.e., reproductive structures) of the slime mold.  I have also seen this slime mold crawl over and fruit on other plants such as ginseng and tomato.

Physarum Slime Mold on a Tomato Leaf
Physarum Slime Mold on a Tomato Leaf

Perhaps the most dramatic slime mold I see is the chocolate tube slime mold (Stemonitis), which often fruits on the walls of houses.  It can form HUGE masses of what appear to be clusters of miniature cattails.  One of my friends saw this slime mold and claimed it was straight out of Stranger Things (the horror television series I’ve been binge-watching of late).  There’s no accounting for taste!  Sigh.  Slime molds will ever remain cool in my book.

Chocolate Tube Slime Mold on a House Soffit
Chocolate Tube Slime Mold on a House Soffit

For addition information on the PDDC and its activities and the cool disease samples I get to see, check out the PDDC website, follow the clinic on Twitter or Facebook (@UWPDDC) or contact the clinic at pddc@wisc.edu.

June: June is Bustin’ Out All Over (With Plant Health Problems)

SunWith the arrival of June, the plant disease floodgates have burst and the PDDC has been deluged with plant specimens with a wide range of plant health issues.

Probably the most striking samples showing up at the clinic right now are those that are showing symptoms of winter/cold injury.  I continue see samples from trees and shrubs where the entire plant has died over the winter with no signs of life this spring.  In particular, I have seen (and have also heard about) burning bushes that did not survive the winter.  While my clients have been distraught over this death and destruction, I have been trying to offer a silver lining (shocking, I know for Dr. Death!).  I point out that burning bush is classified as invasive plant in Wisconsin and that the death of these plants provides an opportunity to replace the shrubs with something more exciting and environmentally friendly.

When entire trees and shrubs have not died over the winter, in many cases parts of them have.  In particular, I have seen boxwoods, arborvitaes and other evergreens where branch tips have died and bleached over the winter.  This is a fairly classic symptom of winter burn/winter injury that I see every year.  This symptom might be a consequence of direct cold injury to tissue (a distinct possibility due to the extreme cold temperatures that we experienced in late January) or due to loss of moisture (from lack of sufficient water in the fall and/or exposure to dehydrating winds over the winter).  Slightly more subtle winter injury comes in the form of deciduous trees that leaf out, typically producing small leaves that then collapse and dry up.  I have been seeing this a lot on fruit trees (e.g., apples, pears, plums, cherries).  In these situations, there was likely sufficient internally stored water in the trees to initiate bud break and start leaf expansion, but also enough cold injury to the vascular (i.e., water-conducting) tissue to limit subsequent water movement into the leaves to further expand them and keep them alive.  I expect to see this collapse of leaves continue throughout the summer.  Many folks see this dieback on apples and pears and assume the problem is fire blight, but I have yet to diagnose this disease so far this year (and I’ve been trying very hard to find it).  Management for this type of dieback is simple pruning.  I suggest pruning four to six inches below obviously dead areas on branches.  The best time to prune for most trees and shrubs tends to be in the winter, but if you need to prune during the summer, be sure to prune only when it is dry.  Even though I don’t believe the dieback that I have described above is disease related, just to be safe, I still recommend that you disinfest pruning tools between cuts by dipping them in 10% bleach or (even better) 70% alcohol (e.g., rubbing alcohol).  Spray disinfectants can be used as a source of alcohol as well.  I do not recommend using pruning paints except if you are forced to prune an oak tree during the growing season (to prevent transmission of the oak wilt fungus via sap beetles).  You can dispose of branches by taking them to your municipal yard waste recycling center (if you have one available), burning them (where allowed by local ordinance) or burying them.

Another variation on leafing out that I have seen this year that I am attributing to cold injury is where trees leaf out completely, but have smaller than normal leaf size.  In these situation, I am suspicious that there is minor damage to the vascular tissue the trees, but not sufficient to totally prevent water from reaching branch tips.  I have a redbud tree in front of my home showing this symptomology.  The tree typically has large, lush foliage that provides a privacy screen for my front door.  This year the leaves are quite small and I can easily see through the thin canopy.  This tree also had much reduced flowering this year compared to previous years.  I have also seen smaller leaves on a lot of maples (particularly silver maples) this year, but these trees have shown excessive seed production compared to other years.  I call this overflowering/seeding phenomenon the “Oh my gosh, I’m going to die, I’d better reproduce” syndrome.  Over-flowering/seeding is typical for stressed trees.  However, because this year’s flower buds were formed last summer, the underlying stress that led to over-flowering/seeding was not our winter weather, but other stresses that occurred during the growing season of 2018.  For trees with smaller leaves, I suggest making sure they are adequately watered.  I typically recommend that trees and shrubs receive approximately one inch of water per week.  If Mother Nature doesn’t cooperate, then I suggest setting up a soaker or drip hose at the drip line of the tree (i.e., the edge of where the branches extend) and applying whatever additional water is needed.  Affected trees should continue to receive water until they start to turn their normal fall color in the autumn.

And if all of the environmental stress-related issues aren’t enough, I’ve been getting inquiries about (and finally receiving samples of) what appears to be anthracnose on maples.  I expect to eventually see this disease on other trees as well.  Typical symptoms of the disease are brown to black, necrotic (i.e., dead), blotchy areas on leaves.  Our wet spring weather has been very favorable for this disease to develop.  Luckily, anthracnose tends to be a very cosmetic disease and typically causes little long-term damage to trees.  Cultivating the ability to ignore anthracnose symptoms and doing good fall clean-up of the leaves and removing them from your property typically are the best ways to handle this disease.

Phew, what a June!  Now, onward to July.  I have a feeling the deluge is going to continue!

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.

P.S.:  Brownie points for those of you who recognize the origin of the title of this month’s article.

May: Heinous Hitchhikers – Purchased Plants as Pathogen Providers

As we get into May, many gardeners begin thinking about buying perennials to replace plants that have died over the winter, or annuals to fill decorative pots and hanging baskets.  Being the optimist that I am (NOT), whenever I’m visiting my local nursery or garden center, I’m always evaluating plants as potential sources of plant pathogens.  For me, having diseased plants can be good (demo plants for classes and workshops, anyone?).  For sane, rationale gardeners however, avoiding potentially diseased plants is a must.  Here on some pointers on what you can do to try to minimize the likelihood that you will bring home unwanted guests as you garden.

  • Buy plants from a reputable business. Most businesses want to sell a good product.  The livelihood of a nursery or greenhouse depends on the quality of the products that it sells.  If a business sells poor plant materials, this reputation will get around and the business will likely not last long.  One way to decide on where to shop is to check with friends or colleagues on where they have purchased high quality plants in the past.  Word of mouth is often the best recommendation for a business.  That said, keep in mind that sometimes even the best, most conscientious plant producers/sellers can have disease problems.  In the past, diseases like Ralstonia wilt and impatiens downy mildew have been serious, and economically devastating diseases, for producers/sellers and no one has been immune to these disease issues.
  • Buy locally, when possible. Locally produced plants are often better adapted to the local climate, which can translate into better survival long term for perennial plants.  For annuals, plants grown in southern regions are often more likely to be exposed to pathogens earlier during production, with more opportunities for infections to occur.  These pathogens can travel north with plants as they are shipped into Wisconsin for sale.  Introductions of the Southern blight fungus and late blight pathogen have occurred in this manner in the past.
  • Avoid plants showing disease symptoms. Look carefully for any abnormalities in plant size, growth, or color that might indicate disease issues.  Common disease symptoms can include necrotic (i.e., dead) areas on leaves that might indicate a fungal, bacterial, nematode, or even viral  Also watch for lightning bolt-like line patterns, ringspots, or just blotchy light and dark patches on leaf tissue.  These symptoms are typical of viral diseases such as tobacco rattle, cucumber mosaic and hosta virus X.  Be sure to pop plants out of their pots to inspect the roots.  Roots should be plentiful and white.  If the roots are few and far between, or even worse, brown, then root rots could be a problem.  If you see abnormalities of any kind, DO NOT buy the symptomatic plants.
  • Avoid plants showing signs of disease-causing organisms. Some types of pathogens, particularly fungi and water molds, can produce spores on plant surfaces that will be visible to the naked eye.  Typical diseases where pathogens might be visible include powdery mildews and downy mildews, including the infamous impatiens downy mildew and basil downy mildew.  If you see any indication of this sort of growth, again DO NOT buy the plants.
  • Avoid plants with insects. Insects can cause damage to plants on their own through their feeding activities, so it is important not to bring home these pests with your plant purchases.  Insect pests can spread to other plants in your garden and cause substantial damage on their own.  From a disease standpoint, insects are important because they are plant pathogen vectors, moving disease-causing organisms from plant to plant as they feed.  There are insects that are known to move fungal, and bacterial pathogens in the environment, but where insects tend to have their biggest impact is through movement of viral and phytoplasma  In particular, aphids and thrips are important in moving viruses such as Cucumber mosaic virus and Impatiens necrotic spot virus from plant to plant.

With a little bit of effort and by using good observational skills, you can minimize the risk of bringing diseased plants into your garden.  However, even if you follow the advice outlined above, purchasing plants is not totally risk-free.  Sometimes plants harbor disease-causing organisms with nary a symptom nor sign in sight.  These pathogens may rear their ugly heads and start to cause problems once you’ve begun growing the plants in your garden.  Even if you dodge the bullet and successfully avoid purchasing infected plants, know that Mother Nature has tricks up her sleeve to bring plant pathogens to you.  So expect at least a little bit of disease, no matter how careful you are.  In the end though, plant diseases tend to be the exception and not the rule, so remember that most of time when you look at your garden, what you will see will be healthy and happy plants.  KEEP ON GARDENING AND LOVE EVERY MINUTE OF IT!

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.

 

Bagging Apples for Insect and Disease Control

Producing high quality apples in home gardens can be challenging due to damage caused by insects (e.g., apple maggot, codling moth, plum curculio, stinkbugs) and fungal diseases (e.g., apple scab, cedar-apple rust, flyspeck, sooty blotch).  Many insects damage apples when they lay their eggs in developing fruit.  Insect larvae can cause

Bagging apples can reduce fruit damage due to insects and diseases. (Photo courtesy of Janet van Zoeren)
Bagging apples can reduce fruit damage due to insects and diseases. (Photo courtesy of Janet van Zoeren)

additional damage as they tunnel into the fruit.  Wind-borne fungal spores can land on fruit leading to infections that damage fruit, reduce fruit aesthetics or affect long-term storage.

Although insecticide and fungicide sprays can help control insect pests and diseases, regular spraying can be inconvenient and costly for homeowners.  A non-pesticide alternative for protecting fruit is to encase apples in bags that provide protective barriers against insects and fungal pathogens.

What do I need to bag my apples?  First, you will need some sort of bagging material.  This could be a household plastic or paper bag, or a commercially-produced bag designed specifically for apple bagging.  Perhaps the most convenient choice is a common plastic sandwich or quart-size zip-type bag.  Zip-type bags are effective, weather proof, economical, and readily available.  You will also need something (e.g., a twist tie, tape, string, staples) to secure the bags to your apples and a pair of scissors to cut a drainage hole in each bag.

When do I bag my apples?  Start bagging when fruits are approximately ½ to 3/4 inch in diameter.  Apples typically reach this size approximately two weeks after petal fall.  Thin each cluster of apples to a single fruit, keeping the largest, best-shaped fruit in the cluster.  Make sure that the apples you select have not already been damaged.  In particular, plum curculio can damage fruit and codling moth can lay eggs before fruit are large enough to bag.  You may want to consider using an insecticide spray between petal fall and bagging to prevent this early damage.

How do I bag my apples?  Place an apple in the bag of your choice with the top of the bag around the stem.  Carefully secure the bag with a twist tie, tape, string or staple without damaging the stem.  If using a zip-type bag, place the stem in the middle and close the seal to within one inch of the stem on each side.  Staple the bag on each side of the stem to ensure that the bag will remain secure all summer.

Use scissors to cut approximately one-half inch from one of the bottom corners of the bag. This will allow condensation that may form inside the bag to drain.

Leave plastic bags on all summer.  Paper bags may deteriorate and need replacement if there is excessive rain during the growing season.  In addition, paper bags should be removed a few weeks prior to harvest to allow proper fruit color to develop.

Bagging apples can help prevent damage due to insect pests such as codling moth (left) and diseases such as apple scab (right). (Photos courtesy of Christelle Guédot and the UW-Plant Disease Diagnostics Clinic).
Bagging apples can help prevent damage due to insect pests such as codling moth (left) and diseases such as apple scab (right). (Photos courtesy of Christelle Guédot and the UW-Plant Disease Diagnostics Clinic).

What should my apples look like after they have been bagged?  Because bags prevent insects and fungal spores from reaching fruit, most of your bagged apples should be in near perfect condition.  Fruit that you do not bag will likely be blemished from insects and disease.  Blemished fruits should be removed (whether they fall to the ground or remain attached to your tree) and destroyed by burning (where allowed), deep burying or hot composting.  Diseased leaves from your apple tree should be treated similarly once they fall from the tree in the autumn.  Properly disposing of blemished fruits and diseased leaves will help limit overwintering of insect pests and disease-causing organisms, thus reducing insect and disease problems the following growing season.

For more information on bagging apples for insect and disease control:  Contact your county Extension agent.

African Fig Fly – Pest Alert

The African fig fly (AFF), Zaprionus indianus, is an invasive vinegar fly closely related to flies in the genus Drosophila [which includes the common vinegar fly (also sometimes called the common fruit fly) and spotted-wing drosophila (SWD)].  AFF is native to Africa, Eurasia and the Middle East.  It was first detected in the United States in Florida in 2005, where it is now well established.  In 2012, AFF (a single adult) was first detected in Wisconsin.  In 2017, larger numbers of AFF were found in the state in traps used to monitor for SWD.

An African fig fly adult. (Photo courtesy of Benjamin Davidson)
An African fig fly adult. (Photo courtesy of Benjamin Davidson)

Outside of Wisconsin, AFF has had its biggest economic impact in commercial fig production, and has not been found to have a significant economic impact on other agricultural crops.  In Wisconsin, the potential economic impact of AFF on fruit and other crops is not yet known.  Because AFF reproduces readily and can rapidly expand its range, careful monitoring for this insect in the state is warranted.

Appearance:  The adult AFF is slightly larger than the common vinegar fly or SWD, and has a light-colored body and bright red eyes.  An adult AFF has four black-bordered, white stripes that run along each side of its head and thorax (but not its abdomen).  These stripes can easily be seen using a hand lens and are not found on any other vinegar flies in Wisconsin.  An AFF larva (maggot) is legless and has a single hook-like tooth at its mouth-end.  The maggot uses this tooth to feed on rotted berries and other soft fruit tissues.  AFF maggots are nearly indistinguishable from maggots of common vinegar flies and SWD.

Host Range:  AFF can feed on a large number of fruit crops grown in Wisconsin, including blackberries, blueberries, grapes, peaches, raspberries and strawberries, with grape being a preferred host.

Symptoms and Effects:  Given that AFF is a newcomer to Wisconsin and its temperate climate, predicting which fruits the insect will affect, and to what extent, is difficult.  What is known about AFF is that it cannot initiate damage to intact, ripe fruit; it can only feed on and lay eggs inside of overripe or already damaged fruit.  The insect contributes to additional breakdown and decay of these fruit.  In Wisconsin, AFF and SWD (which can damage intact, ripe fruit) will likely occur together at a given location, and will likely interact.  AFF may end up laying eggs in fruit damaged by SWD, possibly leading to an increase in AFF populations.  The effects of AFF on SWD populations are not clear at this time.  However, some research conducted in grapes suggests that where AFF and SWD occur together, they may compete, leading to increased numbers of AFF and lower numbers of SWD.

Life Cycle:  As an insect native to the tropics, AFF will likely not be able to survive even a mild winter in Wisconsin; in fact, AFF does not appear to overwinter even as far north as Virginia.  However, AFF can travel long distances on air currents, and could potentially travel from the southern US to Wisconsin in the spring and summer, leading to fruit infestations in the state in the summer and fall.  AFF has only been detected in Wisconsin in 2012 and 2017, suggesting that if the insect does cause problems in Wisconsin, these problems will not likely be a yearly occurrence.

Exactly how many generations of AFF might develop in Wisconsin in a given year is not known.  In the laboratory (at 75°F), AFF develops from egg to adult in 20 days and females lay, on average, 60 eggs.  Based on its short generation time and ability to produce numerous eggs, AFF populations could potentially build quickly within a given year, once the insect arrives in Wisconsin.

Monitoring:  Monitor for AFF using the same traps that you would use to monitor for SWD.  You can buy commercially available traps, or alternatively, you can make simple, inexpensive traps using a 32-ounce clear plastic container with a lid.  To allow adult flies to enter the trap, drill or melt ten 3/16 inch diameter holes around the top of the container.  Bait traps with one tablespoon active dry yeast and four tablespoons sugar in twelve ounces of water.  Alternatively, use a two-inch layer of apple cider vinegar in the bottom of the container.

Add one to two drops of unscented dish soap to the trap to break the surface tension of the liquid so that flies are more likely to

A homemade vinegar fly trap made from a 32-ounce clear plastic container with a lid. (Photo courtesy of Emma Pelton)
A homemade vinegar fly trap made from a 32-ounce clear plastic container with a lid. (Photo courtesy of Emma Pelton)

drown.  Hang traps in a shaded plant canopy where fruit is present.  For strawberries, place traps on the ground.  Check traps and replace liquid bait weekly, using a hand lens to identify trapped insects.  Be careful not to pour bait on the ground near the traps as this will confuse flies and reduce the effectiveness of the traps.  DO NOT bother testing fruit directly to determine infestation rates for AFF, as AFF larvae will be indistinguishable from those of other vinegar flies (e.g., common vinegar fly and SWD).

Control:  Because AFF cannot cause damage to sound fruit, and because recorded populations of AFF in Wisconsin have been low, AFF control may not be needed unless/until severe outbreaks occur.  Control methods recommended for SWD will likely also help control AFF.  In particular, cultural practices such as removing all damaged or rotting fruit and then solarizing (heating) or freezing this material to kill fly larvae may slow buildup of AFF at a given location in a given growing season.  However, because AFF is able to move over long distances from areas in the south where it can easily overwinter, reintroduction of the insect will be possible even if you follow strict sanitation practices.

Exclusion netting, which has been used with some success to manage SWD, will likely also help manage AFF.  When using netting, use a mesh size that is 1/32 inch or smaller.  Start using netting after early fruit set (so as not to interfere with pollination), but before fruit begins to ripen.  Make sure the mesh completely covers fruit with no gaps between sheets of netting or at the soil surface.  Any opening can provide an entry point for AFF.

Chemical control for AFF is not currently recommended in Wisconsin.  Observed AFF populations have not been high enough to warrant such treatments.  If spraying for AFF does become necessary, choose insecticides (e.g., spinosyns, carbamates and organophosphates) that also provide control of SWD.  As always, rotate active ingredients that are in different IRAC chemical classes (i.e., have different modes of action) to delay development of insecticide resistance.  For details on IRAC chemical classes, see https://www.irac-online.org/modes-of-action/.  Also, be sure to consider the effects of the products that you select, on non-target insects, particularly beneficial insects such as bees.  Please check the most recent Midwest Fruit Pest Management Guide (see https://learningstore.uwex.edu) for full product recommendations.

If you suspect that you have found an AFF, please contact the University of Wisconsin-Madison Insect Diagnostic Lab at (608) 262-6510, idl@entomology.wisc.edu or http://labs.russell.wisc.edu/insectlab/contact-us/.

For more information on African fig fly, as well as other vinegar flies:  See University of Wisconsin Garden Facts XHT1102 (Fruit Flies in the Home), University of Wisconsin Garden Facts XHT1237 (Spotted Wing Drosophila), or contact your county Extension agent.

April: To Prune, or Not to Prune, That is the Question.

ShearsAs warmer weather has spread through much of Wisconsin, I have talked with more and more gardeners who are chomping at the bit to get into their yards and start the 2019 gardening season.  One of the activities these gardeners are contemplating is the pruning of their trees and shrubs.  They often ask me whether spring is a good time to prune from a plant disease perspective.

The answer is:  It depends.

Overall, I am a proponent of winter pruning.  Typically there is a slight warming at the end of January or at the beginning of February where it’s warm enough to prune and not freeze to death, but not warm enough that disease-causing organisms are likely to be active.  In my mind, pruning during this window reduces the risk of pathogens infecting through pruning wounds.  There can be exceptions to this rule of thumb however.  There is some research that indicates that pruning honey-locust trees in the summer (during hotter, drier periods) can reduce the risk of Nectria canker compared to pruning in the winter.

When pruning in the spring, the trees that I have the most concern about are oak trees.  In particular, I worry about transmission of the oak wilt fungus, Bretziella fagacearum.  This fungus can be moved from tree to tree by sap beetles that become active as temperatures warm.  These insects are attracted to wounds, including those caused by pruning.  Some municipalities restrict pruning of oaks after April 1 in anticipation that temperatures will shortly be warm enough that sap beetles will be active.  Use of a calendar date as a cut off for pruning oaks can be problematic however if spring arrives early.  For that reason, I really ONLY recommend winter pruning for oaks.  If for some reason, you really need to prune an oak at another time of the year, paint over any pruning wounds.  You can use a commercial pruning paint if you like, but left over latex paint (from painting a room in your home) will work just as well.  The paint provides a physical barrier that makes a wound less attractive to sap beetles.  Be sure to paint wounds on oak trees IMMEDIATELY.  There is research that indicates that sap beetles can visit wounds in as little as 10 minutes.

In general, when pruning tress other than oaks in the spring (or any time other than the winter), always be sure to prune when it’s dry and when there is dry weather predicted for several days post pruning.  Dry weather is less favorable for fungal spores (which might land on a pruning cut) to germinate and infect.  Also be sure to prune properly based on the type of tree or shrub.  Laura Jull of the UW-Madison Department of Horticulture has authored several excellent fact sheets on how to prune evergreens, deciduous trees and deciduous shrubs.  Check these out!!  When pruning out diseased branches, prune four to six inches below obviously diseased areas if you suspect a fungal disease and 12 inches below obviously diseased areas if you suspect a bacterial disease.  In the best of all possible worlds, you should decontaminate your pruning tools between every cut to limit possible movement of pathogens via your tools from branch to branch or from tree to tree.  You can use a 30 second dip in 70% alcohol (e.g., rubbing alcohol) or in a commercial disinfectant for this.  Alternatively, you can use a spray disinfectant, spraying your tools until they drip and then allowing them to air dry.  Except in situations where oaks are pruned during the growing season, I do not recommend using paint on pruning cuts.  Paints tend to slow down the formation of callus tissue, the tissue plants produce to naturally cover over wounds.

Finally, avoid what I tend to try to do when I prune, which is to prune off my fingers.  OUCH!!

For addition information on plant diseases, 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.