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Sunday - June 15, 2008

From: Charleston, WV
Region: Mid-Atlantic
Topic: Diseases and Disorders
Title: Decline in willow tree in West Virginia
Answered by: Barbara Medford

QUESTION:

I planted a willow tree about three years ago and it was progressing just beautifully with full leaves this spring in a nice green color. We staked it back about three weeks so it would grow straighter. This week I have noticed all of the new baby leaves are yellow in color. I cannot find anything wrong with the tree (such as bugs, holes, splits) I am so worried it is dying, is there anything I can do to help it, or can it be normal for young leaves to be yellow? I love this tree and have always wanted one since I was a child. I would love to be able to help it.

ANSWER:

First, we need to define some terms. There are 55 species of the Genus Salix, all willows, in our Native Plant Database. We are going to assume (hope) that yours is a native species, and not Salix x babylonica or weeping willow, which is a hybridized non-native, a somewhat weak, short-lived tree that is very susceptible to disease and insect damage. We found three willows that are native to West Virginia and chose Salix nigra (black willow) as our subject. It is considered a very good example of the genus, which provides erosion protection and shade, as well as sheltering wildlife. As nearly as we can determine from this USDA Plant Profile of the location of Salix nigra (black willow) in West Virginia, Kanawha County is easily in the range where the tree grows naturally.

Yellowing leaves are usually the result of chlorosis, or lack of chlorophyll, in the leaf. It does you no good to know what causes it, if you don't know how to prevent it. We will present you with some possibilities and maybe you can determine for yourself the cause and cure. Sorry, we haven't kept up with weather in West Virginia this year, but has it been flooding or at least raining a great deal in the area where your willow lives? 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. How about the urban air pollution in which your tree grows? Ozone and sulfure dioxide in the air can enter the tree and inhibit leaf function, again producing chlorosis, which means it is probably not a very good "street tree." 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.

Sadly, you can do very little about air pollution or flooding, if that proves to be the case. If the tree is in what you consider to be a poor location, it may still be small enough to consider moving it. But not in the Summer! Our favorite time for transplanting is late Fall or very early Spring, when the tree is semi-dormant. Read this article from about.com on How To Transplant for the practical how-to and techniques that are recommended. You can spend the time from now until transplanting season determining if the tree location really is the problem and, if so, where else on your property it would be in a better situation.


Salix nigra

Salix bebbiana

 


Salix discolor
 

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