Guignardia Leaf Blotch

Guignardia Leaf Blotch of Aesculus is a fungal disease that is commonly observed on buckeyes and horsechestnuts in Ohio at this time of the year. However, don’t leap to the conclusion that all leaf blotches are symptomatic of this disease.

Everything is in the details, including the genetics of plant crosses and plant disease susceptibility. Here is a tale of two Aesculus and their different genetics and susceptibility to Guignardia leaf blotch disease.

Summertime: And Diagnosis is never easy.  Even with something as dear to my pathological brain as apple scab and cedar-apple (or hawthorn) rust on crabapple. I was on a walkabout at a northeast Ohio commercial landscape two weeks ago and came upon side-by-side crabapples – and the different symptoms of these two diseases on crabapple.

 

On one crabapple, apple scab infections caused some affected leaves to turn yellow before dropping; on the other crabapple the leaves turned orangish-red (the cover photo). As for rust, the lesions on the upper leaf surfaces of one crabapple...

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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