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Sunday - August 03, 2008

From: Springdale, AR
Region: Southeast
Topic: Non-Natives, Diseases and Disorders, Trees
Title: Yellowing leaves on weeping willow
Answered by: Barbara Medford


We have a 4 year old Weeping Willow, 12+/- ft. tall and this week the leaves are starting to become yellow. This willow is full and robust in appearance, best it's ever looked. We have 2 other Weeping Willows, not as large, but attractive trees, 100ft. north and 100 ft. east. They show no sign of yellow. Could you please advise me? Is this common and should it effect the remaining willows?


If it's not No. 1, "What's wrong with my weeping willow?" is right up there close to the top of most frequently asked questions to Mr. Smarty Plants. On today's slate, alone, there are three questions. If you search on "weeping willow" in the Ask Mr. Smarty Plants section, you get ten possibilities. The problem is, the question is the wrong question asked at the wrong time. We wish that gardeners would ask "Should I plant a weeping willow?" BEFORE they purchase and plant it. 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. 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. See this University of Florida Extension website on Weeping Willows for more information. Also, in case you think we're exaggerating, see this Q&A from North Dakota State University Extension on weeping willows.

The Genus Salix is considered to have intermediate tolerance for flooding around its roots, especially in the growing season. The water on the trunk and roots over an extended period of time can lead to yellowing of the leaves (chlorosis), defoliation, and reduced leaf size. Young trees may be more intolerant of flooding than more mature trees. Chlorosis is also caused by inaccessibility of trace elements in the soil, especially iron, to the roots. This is sometimes caused by poor drainage, meaning too much water is around the roots, or impacted soil from foot traffic or construction. If the two trees that continue to do well are in a more neutral or acidic soil, they are probably able to access the trace elements in their soil. If the tree you are concerned about either has poor drainage or too much water over its roots or is in a more alkaline soil, the lack of trace elements could explain the yellowing leaves. We picked up this information from the University of Florida website referenced above: Rust causes yellow spots on the lower surfaces of leaves and, if severe, defoliation. Rake up and destroy leaves from diseased trees. The North Dakota State website had several references to poplar borers as being a possible cause of yellow leaves.

Most to be hoped for would be that the problem is being caused by poor drainage, etc. preventing the access of iron in the soil. Getting some compost or other organic material into the soil, and even putting some iron tablets into the soil would be the easiest fix. The other possibilities are not something we can diagnose from a distance. If there are borers, you should be seeing some small holes, possibly with a red stain draining from them. If survival of your willows is important enough to you, even after we've given you all the downsides, we suggest you have a trained arborist look at the tree. If some pesticide is called for, the arborist should be licensed to do so in Arkansas. Since Springdale is in two counties, you could also contact the University of Arkansas Extension office at Washington County, or Benton County.


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