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

Walnut toxicity

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

Drought stress

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

Bacterial canker

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

Verticillium wilt

Many gardeners are familiar with this disease in the context of the death and destruction it brings to woody trees and shrubs.  However, Verticillium, the cause of Verticillium wilt, is an equal opportunity destroyer and can kill a wide range of herbaceous plants as well, including popular vegetables such as solanacoues crops (e.g., tomato, potato, eggplant, pepper) and vine crops (e.g., cucumber, squash, pumpkin).  This fungus is routinely found in the soil and can build up over time if susceptible vegetable crops are grown over and over again in an area where the fungus is located.  Verticillium infects through the roots and colonizes and plugs a tomato’s (or other plant’s) water-conducting tissue, leading to wilting.  Discoloration of a tomato plant’s vascular tissue is a typical symptom of this disease, but stem cracks and cankers are not.  Rotation can be useful as a control strategy for Verticillium wilt, although it is less effective than for bacterial canker because of the wider host range for Verticillium (including many weeds).  For tomatoes, use of resistant varieties can also be useful.  To identify resistant varieties, look for a “V” after the variety name on a tomato seed packet or in the variety description in your favorite seed catalog.

Fusarium wilt

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

Need help or more information?

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

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

It‘s the time of year where I am once again getting questions about apple and crabapple trees with dead branches.  Often, in these situations, clients assume that their trees are suffering from fire blight.  This bacterial disease has received a lot of press over the years and can be a serious problem.  However, fire blight is definitely not the only reason that branches on apples and crabapples die.

There are myriad of fungal diseases that can lead to branch dieback.  In particular, fungal canker diseases can be an issue.  I often find fungi like Cytospora, Phomopsis and Sphaeropsis in dead apple or crabapple branches.  These fungi, like the fire blight bacterium, locally infect and girdle branches (thus leading to branch death), often in a somewhat random pattern in a tree.  Sphaeropsis is particularly common.  This fungus not only infects branches but can also infect fruits (causing black rot) and leaves (causing frogeye leaf spot).  More systemic fungal diseases like root and crown rot, Armillaria root disease and black root rot (dead man’s fingers) can also lead to branch dieback.  The pathogens involved in these diseases infect and disrupt root and trunk function, preventing proper water movement from roots to branches.  This lack of water leads to branch death, often over a fairly substantial portion of the tree canopy.

Environmental stresses can also lead to branch death in apples and crabapples.  Drought can lead to branch dieback symptoms similar to those caused by the systemic diseases I described above.  Cold injury can also be a contributing factor.  Growing a non-hardy apple or crabapple variety often leads to dieback issues.  Even on hardy varieties, branch dieback can occur if cold snaps occur in the spring right as or just after trees leaf out.  Lack of snow cover (which insulates soil) coupled with extremely cold winter temperatures can lead to physical injury to roots, which in turn limits water uptake, leading to branch dieback.

So, with all of these potential causes of branch dieback on apples and crabapples, how can you tell if your tree is suffering from fire blight?  The answer is, “It’s not easy!”  People often claim that fire blight leads to a branch with a shepherd’s crook (a downward bend at the branch tip).  However, after years of seeing dead and dying apple and crabapple branches, I just don’t consider this a reliable symptom for diagnosing fire blight.  To me, a shepherd’s crook just indicates that the branch didn’t get enough water and wilted.  That could be due to any of the causes I outlined above.  And conversely, I have seen cases of fire blight where branches don’t have a shepherd’s crook.  What I tend to look for as I’m attempting to diagnose fire blight is oozy material (a combination of sap and bacterial cells) that seeps from affected branch.  I also look for some indication that the infection may have started where flowers were attached.  I look for this latter indicator because trees are often inoculated with the fire blight bacterium by bees that carry the bacterium and drop it off in the flowers as they pollinate.  Even when I see these symptoms, I will only diagnose fire blight if I have evidence that the fire blight bacterium is present.  There are dipstick serological tests (these use the same technology as home pregnancy kits) that I use to confirm the presence of the fire blight bacterium.  If I don’t find evidence of the bacterium, I look for other possible causes of the branch dieback.

So, why do I really need to know if branch dieback is really due to fire blight?  It all comes down to management.  If fire blight is the cause, I recommend very aggressive pruning (roughly 12 inches below where there are obvious symptoms).  The fire blight bacterium can move rapidly down a branch under the bark, so you want to make sure to prune down far enough to remove all of the bacterium.  Fungal pathogens tend to move less rapidly, so you can get by with pruning roughly six inches below where there are obvious symptoms.  If the problem is a root disease of some kind, pruning will not resolve the problem.  Fungicide treatments to the roots may be needed in some instances, or there may be ways of reducing tree stress that slow down the progression of these types of diseases.

It all comes down to the fact that if you don’t know what the underlying problem is with your tree, it is unlikely that you will be able to fix the problem.  So, get a proper diagnosis and then tailor your management strategy to the specific problem(s) you are facing.  Without a proper diagnosis, you can spend a lot of time, effort and money, and not improve the health of your trees one bit.

Need help?

For help with proper diagnosis of plant problems, contact the PDDC at pddc@wisc.edu or (608) 262-2863.  To find out more about the clinic and its activities, check out the PDDC website.  To keep up-to-date about new PDDC education materials and programs, follow the clinic on Twitter or Facebook (@UWPDDC) or contact the clinic at pddc@wisc.edu and ask to be added to the PDDC’s listserv (UWPDDCLearn).

I 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

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 hosts.  The 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.

Weir’s Cushion Rust

This 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

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.

Need additional information?

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).