Disease Digest

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 taylor.8 Thu, 08/04/2016 - 10:47
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 chatfield.1 Sat, 07/30/2016 - 16:34
  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 chatfield.1 Wed, 07/27/2016 - 23:38

  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 boggs.47 Thu, 07/07/2016 - 14:08

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
Guignardia Leaf Blotch Red Alert boggs.47 Thu, 07/07/2016 - 14:04

Guignardia leaf blotch of Aescelus produced by the fungus, Guignardia aesculi, is becoming evident on buckeyes and horsechestnuts in many areas of Ohio.  The fungal spores require moisture to spread to new growth in the spring and to germinate to initiate foliar infections.  Infections and resulting symptoms then progress rapidly during warm summer months.

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Joe Boggs

I Love Rust: Sometimes

Rust diseases of plants may of course be devastating, from black stem rust of wheat which contributed to famine after World War I to cedar apple rusts which must be controlled by orchardists and (sometimes) landscapers today. Yet, it must be admitted, they are fascinating. They can be autoecious (occurring on only one host plant) such as may-apple rust commonly seen in spring woodlands, but often they must complete their life cycles on wildly different hosts, such as wheat & barberry, juniper & apple.

 

About a month ago I came upon a rust disease I had not...

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Jim Chatfield

Coneflower Calamities: Round 3

Stunted and deformed coneflower plants are symptoms of Aster Yellows.  Of the three coneflower problems I'm presenting in this series, Aster Yellows is the most serious and its control requires the most extreme measures.  This is a serious, chronic disease that occurs throughout North America and may affect over 300 species of plants in 38 families including a number of vegetables such as carrots and potatoes.  However, as its common name implies, the disease most occurs on members of the aster family (Asteraceae (= Compositae); coneflowers appear to be particularly susceptible.

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Joe Boggs
Marsonnina Leaf Spot Diagnostics chatfield.1 Sun, 06/26/2016 - 19:10

Marsonnina leaf spot of aspen is something I used to see out West when I lived and worked in Colorado, and maybe once or twice in Ohio, but the example I saw yesterday in Vermont was more about diagnostics. As you can see from this image the Marsonnina fungus causes considerable leaf blotch damage on aspen leaves. Note the pattern however.  The fungus overwinters on twigs and buds and then infects leaves during cool, wet conditions at first leaf emergence. Typically, and as seen here, damage is less or non-existent on subsequent leaf emergence. This pattern is common with many (...

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Jim Chatfield