Fungus (black spot) on Tabebulia Leaves
Question from Ellen:
Every year our pink Tabebulia leafs out nicely then immediately starts losing its leaves to this black spot business. First the leaves’ tips turn brown, then the leaves get covered in black spots. The leaves dry up and fall off and turn black. The whole while it’s sprouting healthy new growth. It’s been planted for about 3-4 years, before that it was in a pot for many years. I assume it’s a fungus problem – and last year even applied the systemic 3-in-1 Bayer granules to the soil. But the problem just comes back again. Is this tree doomed?
Additional info: We have another, older tabebulia tree nearby with no problem at all. This younger (problem) tree is planted in a bed near the east side of the house. The bed also contains a snowball viburnum which has no issues. BUT, it is across the path from a set of murraya paniculata with a chronic powdery mildew problem that also will NOT go away despite many different treatments. It has spread to all five of my murraya plants which I have always loved – so if you have any additional advice about that I’d love to hear it. They were planted about 4-5 years ago. Everything else in our yard is pretty much normal. We are in La Habra Heights – zone 23 I think. I have googled these problems and not found any solutions. And I can’t find anyone that even has heard of black spot on tabebulias – so maybe I have mis-diagnosed the problem. Can you help???
Answer from Pat:
Lack of drainage is a frequent problem with Tabebuia and judging by the fact that this tree and also your Murraya paniculata suffers from powdery mildew close by makes me wonder if there are a group of conditions contributing to both disease problems on the east side of your home? Could it be that poor drainage, crowded conditions and a damp atmosphere in that area combined with too much shade is causing these problems? And is the water system perhaps of a type that sprays onto leaves so they stay wet? This situation can contribute to powdery mildew and other disease problems and should be corrected. Murraya is not usually prone to mildew, except in Japan, and is adapted to part shade but not to solid gloom or wet conditions.
Unfortunately, Tabebuia can get leaf spot problems unless growing in full sun and also with good drainage. If too much shade on the east side of your home, possibly poor drainage and lack of air circulation are creating problems with plants we have to think how to out-wit each one. I suggest you completely clean out that area of the garden, remove all fallen leaves, cut off any dead branches and leaves, remove the mulch and replace with fresh mulch. Then try spraying with Serenade and see if that works. If not, you could have this tree professionally sprayed with a chemical fungicide but in my opinion it would be better to remove the tree and plant something better adapted to that area of your garden. It has been my philosophy for many years to yank out the trouble makers and grow things that are naturally healthy and do well in a specific area. If you love Murraya maybe you can find a better spot for it? But first try cleaning up, testing drainage and spraying with Serenade. As far as correction of drainage is concerned a raised bed would help but it’s too late for that. Instead, if the soil is compacted clay, apply gypsum once a year according to package directions and water it in.