Disease Digest

Diagnostics: Canker on Heptacodium

  Today I met with OSU horticultural great Kenny Cochran at his garden in Wooster and we enjoyed checking out everything from his sweet cherry tomatoes to the two-toned leaves of his silver linden tree. One plant which gave us concern was a seven-son flower tree (Heptacodium miconoides). More on the tree later in an upcoming Tree of the Week post, but some stem dieback amidst the just-coming-into-flower panicles is what got our attention. Shoots with brown leaves amidst perfectly healthy-looking shoots with green leaves. 

 

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Jim Chatfield

Pear Rust Revisited

  While walking in German Village in Columbus with ONLA’s Frits Risor last week we revisited the Callery pears with rust disease noted earlier this season (http://bygl.osu.edu/node/342). I wanted to see if the rust was isolated to the two trees heavily affected in June. As earlier, the two trees in question were speckled with bright orange lesions on the upper leaf surfaces, but I suspected that by now the rust fungus would have undergone sexual reproduction in the leaves with aecial spore pustules developing  on the lower leaf surfaces as would be seen with the cedar-apple rust fungus (...

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Jim Chatfield

Tar Spots of Maple

  Tar spots of maple, caused by species of the Rhytisma fungus, are prominent now, although mostly not as severe as in wetter summers. There are two different tar spot diseases of maple, one affecting silver and red maples, caused by Rhytisma acerinum, resulting in dense, tarry spots that truly reflect the “tar” spot name (first picture below).
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Jim Chatfield

The Reddened Rose of Texas

“Rose rosette is an epidemic, and North Texas is the epicenter,” said David Forehand of the Dallas Arboretum: “This is a game changer for roses, I’m sad to say.” This was in a July article in the Fort Worth Star-Telegram by Sara Bahari, reflecting the anguish felt by Texans regarding the demise of so many of their beloved rose gardens.
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Jim Chatfield

Elm Yellows: The Re-Emergence of an Old Killer

Jim Chatfield and I visited the USDA Forest Service, Northeastern Research Station, in Delaware, OH, on Monday where they are waging a battle to eliminate Elm Yellows (EY) from their American Elm Restoration Project research plots.  I last saw the disease in southwest Ohio in 2013. 

The problem is that American elms (Ulmus americana) that are resistant to Dutch Elm Disease (DED) have no known resistance to Elm Yellows (EY).  DED is caused by a fungal infection; EY is caused by a phytoplasma which is a type of bacterium.  DED fungi plug the xylem.  The EY phytoplasma...

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Joe Boggs
Jim Chatfield

One Month Early! Gray Leaf Spot on Perennial Ryegrass Alert

Gray Leaf Spot has been confirmed on perennial ryegrass in Ohio! On Friday July 29, 2016 two cases of the disease were confirmed in the Clinic. This is at least a month earlier than normally detected in Ohio. Both cases were in central Ohio and at sites that have had a history of the disease. This can be a very destructive disease to ryegrass, both annual and perennial. To date this is only a serious disease on ryegrasses in the Midwest.
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Nancy J. Taylor

Diagnostic Double-Take: Scorch or Scab

  Last Friday, outside our bank in Orrville, Ohio, I espied a crabapple tree with a carpet of brown leaves underneath the tree. On first glance, I imagined this to be due to leaf scorch and then leaf drop due to recent dry weather. After all, we are almost eight inches below normal over the past three months in many northeast Ohio areas. Made sense. I was simply following Question #4 of the 20 Questions of Plant Diagnostics: What Do You See That Looks Abnormal?
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Jim Chatfield

Cedar Quince Rust Rages

  Christmas In July: Some hawthorns these past two weeks are sporting little orange sherbet-colored aecial spore masses of the cedar quince rust fungus (Gymnosporangium clavipes), pushing out from the haws. I am receiving many calls about this and, Frits Rizor, the Executive Director of the Ohio Nursery and Landscape Association, even sent me a text and image the other day – we are all plant pathologists!

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Jim Chatfield

Dogwood Powdery Mildew: Signs and Symptoms

Like many powdery mildew diseases, high relative humidity but not high rainfall is a key to dogwood powdery mildew, caused by the fungus Erysiphe pulchra. There is a good bit of this disease this year in northeast Ohio, which is quite dry, and yesterday I took a look at some flowering dogwoods (Cornus florida) growing in pots in trials. There was a good bit of fungal mycelial growth and spores en masse evident on the foliage (what is called the “sign” of the pathogen), which is something everyone is familiar with for many powdery mildew diseases. Good examples are lilac...

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Jim Chatfield

Ash Leaf Spot

There is no doubt that treatments with systemic insecticides can protect ash trees from the ravages of emerald ash borer (Agrilus planipennis) (EAB).  However, insecticide treatments against EAB will not produce super ash trees.  Treated trees are still susceptible to a range of pest and disease problems that were observed on ash trees long before EAB arrived on the scene.  This includes fungal leaf spots.

 

Fungal leaf spots on ash may be caused by two different fungi:  Mycosphaerella effigurata and M. fraxinicola.  The diseases associated with...

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Joe Boggs