End of the Season, "My Spruce is Dying" -Cytospora Canker

The U of I Plant Clinic has been receiving calls and samples from clients because their spruce is dying.  We received one sample that consisted of just spruce branches.  There were no signs of disease on these branches.  Unfortunately, there were no needles included with the sample, but the client did include a CD with several pictures.  I called him to get further information on what may be going on with his trees.  On the phone, he said that some of his spruces were dying and he was afraid that whatever was killing them might spread to his other trees.  He continued to tell me he had a row of spruces on his property that were 15 to 20 years old.  One of the spruces had already died.  Travis Cleveland, U of I Extension, PSEP (also an urban tree expert) and I both examined his pictures, which were included with his sample.  I suspected Cytospora canker and Travis suspected an injury at the base of the tree.  I told the client to please check for "oozing cankers" or white sap on the trunks or the branches of his spruce trees, because this is a sign of a fungal disease called, Cytospora canker.  In addition, I wanted him to check for any possible injury at the base of his trees. 

Here are the pictures he later sent to me via email:

Note the twine/plastic girdling the base of the tree.

As it turns out, Travis and I both were correct.  A few trees that had been described by the client as "runts" or smaller trees had twine/plastic left on the base of the tree when planted.  As these trees grew, the twine/plastic girdled the base of the spruce, causing tree death.  Other trees did not have an injury at the base, but must have been stressed, because they were clearly infected with Cytospora canker.  You can see in these pictures where the white sap is running out cankered areas on the trunk.  These oozing cankers are sometimes confused with bird droppings.  Some things that may have stressed these trees: heat, drought, clay soils, ????  If branches are infected with Cytospora canker, they may die, and you can trim/destroy them.  However, if the trunk of the tree becomes infected with Cytospora canker...... that can be bad news!  Cankers on the trunk/stem of a spruce can cause tree death.

The Cytospora fungus invades weakened or stressed wood. We can't always determine the cause of stress from the lab, but any site or environmental conditions that are not good for the species could be the actual cause of the problem. Spruces do not do well in hot, dry, poorly drained soil with high clay content. Sometimes problems do not develop on spruce until roots outgrow the area, grow into poor soil, or until weather stress aggravates the situation. Fungicides are not effective. You need to help tree vitality by pruning out dead wood now, watering in periods of drought lasting two weeks, and fertilizing in the fall or early spring with a balanced tree fertilizer. If you can determine the cause of stress, of course, correct that as well. A fact sheet on Cytospora Canker of spruce can be found at the following link:
Cytospora Canker

The Difference Between Bacterial and Fungal Plant Pathogens

(This week's blog brought to you by: Diane Plewa (U of I Plant Clinic Student Worker)

The most common pathogens we see at the U of I Plant Clinic are fungi. However, there are plenty of bacteria that can cause problems for plants, and one of the first things we do is try to determine if we’re looking at a fungal or bacterial disease.

There are two ways for us to determine what kind of plant pathogen (fungi or bacteria) we’re dealing with: looking at the disease symptoms displayed by the plant and using the microscope to check for fungal spores or bacterial oozing. When we look at the plant’s symptoms, there are a few that tend to indicate a bacterial infection. Yellow haloing around lesions on leaves is one sign of bacterial disease (though there are several fungi that can cause similar symptoms). Bacterial lesions tend to be limited by veins in the leaves. We also suspect bacteria when we find sticky exudate or stringy ooze in diseased tissue.

 Bacterial lesions on pumpkin and pepper. Photo credit: U of I Plant Clinic.

Fungal lesions usually aren’t surrounded by yellow halos. They may manifest as round, oval, or irregular necrotic areas. Some lesions will have a characteristic “bulls eye” appearance. Under a dissecting microscope or strong hand-lens, fungal fruiting bodies (which contain spores) may be observed.

Clockwise from upper right: Fungal lesions on peony; Fungal lesions on hosta; Magnified fungal fruiting structures on spruce. Photo credit: D. Plewa

Identification of the actual pathogen is done by the appearance of the spore and its fruiting body for fungi.  Using a compound microscope, we can observe the actual fungal spores.

A microscopic view of a few common fungal spores. Photo credit: D. Plewa

While an individual bacterium is too small for us to see, we can see masses of bacteria known as “bacterial ooze” or “bacterial streaming.”  Many bacteria, as well as viruses, can be identified using an ELISA immunostrip assay.  You are unable to see a virus particle under a compound microscope.

Bacterial streaming observed under the microscope. Photo credit: D. Plewa

An ELISA immunostrip assay indicating the presence of the bacteria Xanthomonas campestris. Photo credit: D. Plewa

Lightning Only Strikes a Tree Once?

This week's blog brought to you by: Mike Kwiatek (U of I Plant Clinic Student Worker)

Any tree can be hit by lightning, but oaks, elm, maple, poplar, ash, spruce, fir, pine and tulip trees are known to be prone to lightning strikes. As they are trees that grow large and tower over the forest canopy damage is not uncommon from the forces of nature. Water and sap in a tree provide a conduit for the lightning as it travels toward the ground. As the lightning travels through the tree, water and sap boil, gases inside the tree expand, and often the wood and bark of the tree can split or commonly explode. When the bark is wet, damage is usually less severe as lightning will travel more along the outside. 

Trees struck by lightning can survive many years after a lightning strike, but this is based on the extent of the damage and the treatment of the tree afterward. Most trees that die from lightning strikes years later die as a result of infection or infestation by insects. When pruning can be done to remedy damage, it is suggested. Lightning strikes can be extremely stressful to trees so it is advised that trees be watered in times of drought and fertilized in fall. Do not paint the wound, this can do more damage than good.

To prevent lightning damage a lightning protection system may be installed. Protection systems consist of a series of copper cables attached to the tree’s highest branches and grounded a safe distance from the tree. If lightning strikes the tree, the current flows down the cables to ground. If interested in a lightning protection system, consult with an arborist although the damage may already be done.

During the summer at times of drought leaf abscission may also occur in response to heat stress but we do not suspect that this is the main issue. This issue should also, however, be resolved by watering in times of drought. Fertilize the tree in early fall.

Which trees are less likely to be hit by lightning? -beech, birch, and horsechestnut

For additional information, see http://joa.isa-arbor.com/request.asp?JournalID=1&ArticleID=1862&Type=2

How We Identify Corn Leaf Diseases (Goss's wilt, Gray Leaf Spot, Common Rust and Physoderma brown spot) at the U of I Plant Clinic

In the last week, we had a high number of corn leaf samples submitted to the U of I Plant Clinic.  Most of are interested in knowing if their corn is infected with Goss's wilt, a bacterial disease showing up in many fields this growing season in Illinois.  For more information on Goss's wilt, you can go to the following links:
Goss's wilt spreads across Illinois
Goss's wilt of Corn

After a corn leaf sample is "checked-in" to the Plant Clinic by our awesome secretary, Deb, they are evaluated for disease.  One of the first steps is to "check for ooze".  If leaves are showing symptomology of a bacterial leaf disease, a cross-section is cut from the leaf tissue and examined under a microscope for bacterial streaming as seen in the picture below:

Bacterial ooze or streaming that can be seen under a microscope.

If we see come bacterial streaming, we have immediately been testing the area showing symptoms, with an ELISA ImmunoStrip quick strip test for the bacteria, Clavibacter, which is the Genus of the bacterial pathogen that causes the disease, Goss's wilt (Clavibacter michiganensis).  If the sample does not test positive for Clavibacter, we assume that it is Stewart's wilt.

Corn leaf sample that has been found to show microscopic, bacterial streaming.

Corn leaf tissue is ground up, put in the special bag with buffer solution, and a test strip is placed upright in the bag.

Two red lines means that the corn sample was positive for Goss's wilt.

Other corn leaf diseases that we have been finding are as follows:  

Lesion of Common leaf rust (Puccinia sorghi) of corn.

Common leaf rust (Puccinia sorghi) pustule as seen under a compound scope.  Picture taken by Mike Meyer.

Spores from Common leaf rust (Puccinia sorghi) as seen under a microscope.  Picture taken by Mike Meyer.

Gray leaf spot (Cercospora zeae-maydis) lesion.

Gray leaf spot (Cercospora zeae-maydis)  fruiting structures as seen under a compound scope.

Gray leaf spot (Cercospora zeae-maydis) fruiting structure with spores as seen under a microscope.

Cercospora zeae-maydis spores as seen under a microscope.

Physoderma (Physoderma maydis) brown spot (Sorry no other spore pictures available at this time)

Therefore, bacterial disease diagnosis is based on whether or not bacterial oozing is present as well as an ELISA ImmunoStrip quick strip test for Clavibacter reads as positive or negative.

Fungal disease diagnosis are based on morphology of fungal fruiting structures and spores that are observed under a compound scope and microscope.

Where are the Cicadas Now? An Update on the Great Southern Brood

By: Jean Burridge, 
Certified Illinois Arborist, and U of I Plant Clinic Volunteer

This has been an emergence year for periodical cicada in much of the southern part of the state. (See Phil Nixon's article in Home, Yard, and Garden Pest Newsletter, Issue 2). After thirteen years of subterranean existence, adults surfaced in late spring. Males sang, females listened; eggs were laid. Female cicadas possess a saw-like ovipositor, which they use to cut slits in twigs and small branches. They then insert their eggs into the wounds. The eggs will hatch in late summer, and the nymphs will drop to the ground and disappear into the earth. By August, an aggregation of insects so large and impressive that it has its own name (like Ann Arbor) will exist only inside the twigs of trees. Magicicada, indeed.

This feat of compression is not without cost. If you live in an area that is home to the brood, you may be seeing damage to trees, shrubs, or even perennials. Large trees look bedraggled – a bad hair year about sums it up. Trees that have been badly hit will have a fringe of dangling twigs. Weakened branches may snap immediately, or hang on until wind or ice loading finishes them off. 

The loss of apical dominance in an injured branch results in bushy unbalanced growth, as a host of lateral buds vie to replace the lost leader. The damage – broken branches, oviposition scars and aberrant growth – will be visible for years. 

It is too late to protect trees at this time. Native trees have co-evolved with cicadas – large trees usually grow out of their injuries and are not permanently harmed. Anything you can do to relieve stress would be helpful; water during dry spells and fertilize in the fall. 

Small trees or shrubs can succumb to this death of a thousand cuts; they may need to be replaced. If an emergence is anticipated, it is best to delay planting new trees until ovipositon has ceased.

Biologists suspect that periodical cicadas may have evolved to emerge on a thirteen or seventeen year cycle, in part because these are prime numbers. (Such protracted phenomena are very difficult for biochronologists to isolate – see Zivkovik. Mathematicians have modeled cicada broods – see Lehmann-Ziebarth et al.) Cicadas on this schedule can evade their predators, whose reproductive cycle cannot track them effectively. Animals who grew fat on cicadas have offspring who partake of no such abundance. When the brood reappears, there are no extra mouths to greet it. There is one animal, however – Homo sapiens - that is fully capable of exploiting a thirteen year interval. The Great Southern Brood will rise from the earth in 2024; be prepared….

Lehmann-Ziebarth, Nicholas , et al. “Evolution of Periodicity in Periodical Cicadas”. Ecology 86 (12) 2005. pp 3200-3211. http://www.math.wisc.edu/~milewski/Paul_Milewski,_Professor_of_Mathematics/Publications_files/cicadas.pdf  Web. 7/14/2011.

Nixon, Phil. “Periodical Cicada”. Home, Yard and Garden Pest Report Issue 2, May 2 2011. http://hyg.ipm.illinois.edu/article.php?id=263 Web. 7/14/2011

Zivkovik, Bora. “Centuries to Solve the Secrets of Cicadas”. http:www.scientificamerican.com/blog/post.cfm?id=too-hard-for-science-bora-zivkovil-2011-05-16. Web. 7/14/2011

The Corpse Flower is Blooming at the U of I Conservatory!

Excitement has been in the air at the U of I Plant Biology Conservatory as they anxiously await the bloom of the Titan arum or Corpse Flower.  It is 10 years old and is blooming for the very, first time right now!  It also is expected to be stinky, when the bloom opens!  The U of I Plant Biology Conservatory has recently extended it's hours for the public to see this flower. 

If you are unable to visit, you can see it on the live webcam !

Everyone at the U of I Plant Clinic was very excited about the bloom of this stinky flower.  In fact, we made sure the U of I Plant Clinic was "in on the action", by sending one of our students to visit the flower at the U of I Conservatory and wave to us from the webcam (Oh, yeah........ and put up a sign with a message from the U of I Plant Clinic)!

The "UI Plant Clinic "hearts" Titan"

The Titan and other plants can be seen at the U of I Plant Biology Greenhouse

Pictures of the Titan arum can be seen on the U of I Conservatory's Facebook Page

For more information, check out this fact sheet at U of I Plant Biology Greenhouse Plant Highlights


Press Releases:

Rare 'corpse flower' about to bloom at U of I Greenhouse

Rare Flower Expected to Bloom at UI

Seeds of Collaboration: Illinois Titan Arum Traces Roots to UW

A Few Tomato Diseases Seen at the U of I Plant Clinic this Week and How to Manage Them.

We confirmed 2 tomato samples from Cook County Illinois with TMV (Tobacco Mosaic Virus).  More information about this disease can be found at:  TMV - UMN.edu

How to manage TMV:
Rouge out the affected plants and sterilize pruning equipment. The virus is soil-borne, so crop rotation should be used to reduce the levels of inoculum. Avoid planting tomatoes, potatoes, peppers, and other solanaceous crops in the affected area for several years. Control solanaceous weeds, including jimpson weed as well as nightshade. Resistant varieties of tomato are available.

Septoria leaf blight is one of the most common diseases of tomato.  I have also two samples of tomatoes infected with this disease this week.  A University of Illinois publication about this and other tomato leaf diseases can be found at Tomato leaf diseases - UIUC.edu.  

How to manage Septoria leaf blight:
Due to the wet weather earlier this season, Septoria leaf spot has been particularly severe. To control Septoria leaf spot in the current growing season, remove infected plant parts and consider spraying weekly with an approved fungicide (or just accept losses). Be sure to avoid overhead irrigation which spreads disease, and stake plants to improve air circulation within the canopy. At the end of this season destroy all plant material. Rotate to a non-host crop next year. Products containing chlorothalonil (Bravo or Terranil, or others), copper, mancozeb (Dithane or pencozeb), or maneb are registered for use on tomato. Be sure to abide by the label you choose, especially the days between spraying and harvest.  Additionally, saving seed from season to season may increase disease because seed infection is possible with Septoria lycopersici.