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Sunday - August 23, 2009

From: Savage, MN
Region: Midwest
Topic: Diseases and Disorders
Title: Failure to thrive of trees in Savage MN
Answered by: Barbara Medford

QUESTION:

I have a 20+ year old weeping willow. The last few years it is the last tree to get its leaves and the first to lose them. The few leaves that are still on the tree are covered with brown/black spots. I also have a 20+ year old Marshall's Seedless Ash in a different area. It's lost most of the leaves from the center of the tree. Many of the leaves that remain have some yellow to brown spots in the center and/or are brown at the edges. Any suggestions? Thank you.

ANSWER:

Thank you for your question. While we would like to answer all questions we receive, Mr. Smarty Plants' expertise is limited to plant species native to North America, their habitats and cultivation. Limited resources require us to decline answering questions that delve into other areas. We hope you understand.

Non-native to the United States, Salix x sepulcralis is a hybrid of a Chinese species (Peking willow) and a European species (white willow), and is said to grow in Zones 5 to 8 in the United States. We are astounded that it has lived as long as it has, since you are in Zone 4a, with average annual minimum temperatures of -30 to -25 deg. F. It is weak-wooded, fast-growing and, therefore, short-lived. It has aggressive roots, can lift sidewalks and interfere with sewer lines, often growing on soil surface, making a problem with mowing. It is susceptible to a number of pests and diseases, and notorious for littering the ground beneath it. You might check out this University of Florida Extension website on Weeping Willows for more information as well as this Q&A from North Dakota State University Extension on weeping willows.The UBC Botanical Garden Forum is also a good source of information on non-native plants. 

Fraxinus pennsylvanica (green ash) has been given the trade name which is discussed in this USDA Forest Service 'Marshall's Seedless' Green Ash.  It is hardy in Zones 3 to 8a, and native in and around Scott County in Minnesota, so it belongs there. However, like the weeping willow, it is fast growing, has roots which can disrupt foundations and sidewalks, and is short-lived. In fact, the USDA article mentioned above "no longer recommends this tree due to weak branch crotches, insect problems and fruit set." Since we are not plant pathologists and couldn't hope to diagnose or recommend treatment at this distance, we suggest you contact the University of Minnesota Extension Office for Scott County. They may recommend you have it looked at by a trained and licensed arborist, if you feel the tree is worth saving. 

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