Yellow leaves on Ulmus 'Morton Glossy'

Asked July 30, 2017, 7:09 PM EDT

Hello, I have a 12' Triumph Elm that was planted about 2 years in its present location in a new home development in NW Rochester. Over the past few days, I've been noticing some of the leaves turning yellow. The yellow leaves are mostly on the interior of the tree, while the majority of the leaves look green and healthy. There is new, healthy leaf growth that is still forming. The tree is in my front lawn which is well irrigated. About 3 weeks ago, I noticed Japanese Beetles on the tree and about 10% of the leaves showed beetle damage which I treated with "Sevin" (Carbaryl) applied in hose sprayer. A week later, I applied some diluted Neem oil with a pump sprayer after seeing the beetles return. For the past week, I have not seen any Japanese Beetles. I'm wondering if the yellow leaves might be an indication of stress caused by the application of insecticide, or perhaps the beetles themselves. I'm hoping it is not a sign of "Elm Yellows" (Elm Phloem Necrosis) or Dutch Elm Disease. Triumph is supposedly a DED resistant cultivar, but I don't know how much it occurs notwithstanding. I am hoping this is just some type of superficial thing, but I'd appreciate any educated input you might be able to provide. Many thanks!

Olmsted County Minnesota tree health elm trees horticulture

1 Response

Thank you for the question. The triumph elm is a hybrid Asian elm resistant to Dutch elm disease but not immune. It is also susceptible to Japanese beetles as you discovered and I do see clear signs of feeding on the leaves but I don't think the yellowing is due to the beetle damage which really looks quite minimal.
I can't diagnose the problem from the photos but there is always the possibility of an adverse reaction between the two products sevin and neem oil. Perhaps you haven't seen new beetles because we are getting to the end of their adult cycle.
There is the possibility of Dutch elm but I don't see wilting or dying branches. Other considerations are elm yellows or botryodiplidia canker. Please see our publications on DED, Japanese beetle control, and self diagnostic program "What's wrong with my plant" to research these listed options.
This tree is barely established. Consider having a certified arborist come out to diagnose your tree. Many a young tree suffers in the immediate years after planting due to poor planting practices which weaken it and leave it susceptible to disease, insects, and environmental factors.