Have you noticed tulip trees with scattered yellow leaves and black spots between veins? The leaves may even have green veins like chlorosis, but they are scattered in the trees. You certainly will notice them when they fall from the tree in August.
The affected trees have been tested in a few cases, and I have tried to find a pathogen associated with the leaf spots. I cannot find a pathogen to blame. The condition, which shows up after hot, dry weather in midsummer, is attributed to “unknown causes.” I have had a few calls about this condition but would expect more from the drought-stricken areas. It appears to occur only in hot, dry weather. A row of tulip trees on campus shows scattered yellow leaves whenever we have a drought period and, true to form, this condition appeared two weeks ago at the height of our heat wave. Affected leaves will drop early. What can you do to help the trees? Water them! A picture of affected leaves appears on page 477 of Diseases of Trees and Shrubs by Sinclair, Lyon, and Johnson.