Tuliptrees will sometimes develop a black spotting or speckling between the veins of the leaves.
These spots vary from pinpoint- to pinhead-sized. The rest of the leaf tissue eventually turns
yellow and then brown, with early defoliation the final stage. In cases we have seen, the spotting
does not occur on all leaves, and only the spotted leaves drop from the tree. We usually receive
several samples with this problem each year at the Plant Clinic.
What is the cause of this spotting? Like any curious diagnostician, I have tried the usual methods
to find a pathogen. This includes incubating the tissue for fungal pathogens, observing leaf cross-
sections with a compound microscope to look for bacterial exudate, and culturing spots on various
laboratory media. The symptomatic tissue has never yielded a pathogen.
The book Diseases of Trees and Shrubs (by Sinclair, Lyon, and Johnson) briefly describes this
condition and includes a photograph as well. The authors attribute the spotting to environmental
stress, especially in the hot, dry weather of late summer. We agree with that diagnosis, even
though we have seen it already this summer in very wet areas. Apparently the same injury can
occur when roots are injured from too much water (lack of soil oxygen). The common factor
appears to be root stress. We have not seen a tree die from this condition; instead, the early leaf
drop appears to serve as a type of self-pruning.