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Monday - September 10, 2007

From: Elephant Butte, NM
Region: Southwest
Topic: Non-Natives, Trees
Title: Care of desert willows
Answered by: Barbara Medford

QUESTION:

We have three desert willows. Two are doing well, but the third, which was planted at the same time as the others, is about 1/3 the size of the other two, the foliage is thin, and the leaves have dry, rusty brown spots. They finally dry up and fall off. We have been told we are overwatering, but we don't water it any more than the others. We also have a globe willow that has a few leaves that appear to be doing the same thing.

ANSWER:

What a neat opportunity to compare two trees, one native and the other non-native, whose names sound alike and whose appearances are in some ways similar. We at the Lady Bird Johnson Wildflower Center are always looking for demonstrations of the strengths and weaknesses of native and non-native plants in our landscape. We are committed to the promotion and protection of native plants for their value in preserving resources and avoiding destruction of native habitats by escaping non-natives.

Chilopsis linearis (desert willow), not actually a willow but a member of the Trumpet-Creeper Family, is native to your home area in New Mexico, and adapted to use as erosion control. Its natural habitat is creeksides, ditches, etc. It is an excellent desert plant, and it's always startling to come across those incredible white-to-pink-to-purple flowers that look, to us, like orchids, in a plant that is so drought resistant and can grow in otherwise pretty unpromising environments. Since you have three plants, two of which are doing fine and one of which is not, we have to ask questions about location and sun exposure. You did not mention any insect problem and, since it IS a native, it's not as likely that would be a problem. If the three trees are all planted together, then we would say there is a possibility that some root damage might have occurred before the tree was even planted. If it has not been too long since it was planted, it could be suffering from transplant shock but, again, why would just the one tree be singled out? A suspect could be poor drainage around the roots. Since the desert willow is so adapted to hold soil and prevent it washing away, perhaps on a slope, drainage around the roots is probably important. If the soil around the problem tree allows water to stand for a period of time after irrigation or rain, the roots may simply be drowning. Without actually physically moving the tree, treating this might simply consist of improving the drainage in some way or, if you're watering, water that tree more frequently but for shorter times, to permit the soil to drain.

Salix matsudana (globe willow), shares only a part of the name with the desert willow. It is a true willow, but not a native of North America. Rather, it originated in northeast China and Korea. Willows ordinarily thrive alongside waterways or in moist soils. The willow is a very fast-growing and, therefore, somewhat short-lived tree. And, being a non-native, it is susceptible to a number of insect and disease problems. The worst of these is a frothy flux, likely caused by a yeast or other secondary organism that invades mostly young trees through wounds, causing fermentation of plant tissue. About the only suggested treatment we could find was to hose off the flux or slime, and improve drainage for the tree. It also can be subject to aphid damage. Aphids can also be discouraged by spraying water over the foliage and washing them off, but they will come back. Again, examining your cultural practices around this tree might help: improve drainage, keep soil moist but not standing in water, and watch for pest outbreaks.