Have you noticed tuliptrees with scattered yellow leaves and black spots between veins? These leaves may even have green veins like chlorosis, but leaves are scattered in the trees. You certainly will notice them when they fall from trees soon.|
The spotting described is not caused by a pathogen. A few affected trees have been assayed for pathogens and none found. This condition is attributed to environmental stress and appears after hot, dry weather in midsummer. I have had a few calls about this condition and would expect more from drought-stricken areas as leaves fall. This appears to be a condition that occurs only in hot, dry weather. We have records of this problem occurring in August of most years. There is a row of tulip trees on campus that shows scattered yellow leaves whenever we have a drought period. This year, the condition has been occurring since about mid-July. Affected leaves will drop early.
What can you do to help the trees? Water them as described in article no. 3 of this newsletter. You can see a picture of affected leaves on page 477 of Diseases of Trees and Shrubs by Sinclair, Lyon, and Johnson.