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Mr. Smarty Plants - Sticky leaves on non-native weeping willow

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Sunday - August 03, 2008

From: Lockeford, CA
Region: California
Topic: Non-Natives
Title: Sticky leaves on non-native weeping willow
Answered by: Barbara Medford

QUESTION:

Our weeping willow trees look healthy but have sticky leaves that attach to everything. They sparkle/shine from this very sticky mess. They are watered regularly, are they getting too much water? We live in the Zone 9 area, an hour from Sacramento, CA.

ANSWER:

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.

Now, to address your specific problem: We found this information from Wikipedia, but never found any scientific references to back up the remark about excessive sap. "The willows all have abundant watery sap, bark which is heavily charged with salicylic acid, soft, usually pliant, tough wood, slender branches and large, fibrous, often stoloniferous roots. The roots are remarkable for their toughness, size, and tenacity of life, and roots readily grow from aerial parts of the plant." Whether your tree is exuding an unusual amount of sap, and why, we don't know. Just on speculations, we would note that willows are supposed to be hardy only to Zone 8 and you are in Zone 9. Could this be a product of heat stress? We doubt that you can water a willow too much, as it is considered a tree for pond and river edges, and that might also help to alleviate the heat, if that is indeed the problem.

We are more inclined to believe you have giant willow aphids, Pterochlorus viminalis. Aphids of all sorts are well know for exuding honeydew, which will drip on your lawn, your car and innocent passers-by. Giant willow aphids drink the juice of willows. They get this from leaves, stems and flowers. Aphids can do great damage to their host plants when colonies are large. While the Lady Bird Johnson Wildflower Center recommends neither for nor against pesticides, this Iowa State University Department of Entomology website on Bark Aphids has some good information on possible treatments. And you might also contact your University of California Extension Office for San Joaquin County. They could have more specific information, particularly if there is an outbreak in this sort of problem in your area.

 

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