Miracle Trees: Part II, Austree®

One of the most common questions asked of people considered to be tree experts is, "what kind of tree can I plant that will make a screen in a year or two, has no pest problems, and will live a long time?" In many cases, the questioner goes on to mention that he or she read about a tree called the Austree® that is purported to grow 20 feet during the first growing season. Because the company that has the marketing rights for this tree (Rocky Mountain Austree® Inc, Colorado Springs, CO; http://www.rmausa.com/) has an outstanding promotional program, many people have heard of the Austree® and wonder whether it could possibly live up to all of the claims. While the tree has not been planted in the Midwest long enough to have much of a track record, the emerging answer is, "yes and no."

According to the distributor, Austree® arose from a 30-year, selective breeding program conducted at the Department of Science and Industrial Research of New Zealand. Technically, the plant is a hybrid between two species of willow, Salix alba and Salix matsudana and is vegetatively propagated (by cuttings). Because of its rapid growth rate, the promotional material claims that the tree is widely used for privacy hedges, noise and dust barriers, conservation plantings, or even as a shade tree from Canada to Texas and Florida to Montana. The tree is reputed to be hardy and to have no serious pest problems. It is also claimed to be sterile and, therefore, unlikely to become invasive.

Based on observations of a few Austree® plantings in Missouri and on reading reports from several nearby states, the tree appears to have some potential for planting where rapid screen development is important. There is no question that, given the right growing conditions, the tree will grow very fast. A ten-year-old tree at the Horticulture and Agroforestry Research Center in New Franklin, MO is 20 feet wide and 40 feet tall. However, the plant is located in a low spot on the center where it is rarely exposed to drought. All reports that I have seen have stressed that in order to obtain the growth rates claimed by the distributor, irrigation (at least for the first several years) is necessary. Some characteristics that I have noticed that reduce screening effectiveness of young trees is that the leaves are fairly narrow, and growth is thin and twiggy. As trees increase in size, the density improves and they appear to maintain branches near the ground.

Perhaps the most important unknown factors that may limit the potential for widespread use of Austree® in Missouri are disease and insect problems. In his book Tree Maintenance, Pirone lists at least 11 bacterial or fungal organisms that can cause stem cankers or twig blights on willows in general. He also lists a wide range of leaf spot diseases and a frightening array of borers, caterpillars, galls, aphids, scales and weevils that commonly affect willows. Early reports from Iowa State and the University of Wisconsin indicate that fungal canker diseases, such as black canker (Glomeralla) have been found on Austree® samples sent in to the diagnostic labs. Canker and leaf spot diseases may reduce the life- span of the tree in our climate relative to that attained in less humid regions of the country. One disadvantage of vegetative propagation is that if the tree turns out to be susceptible to one of our local strains of a disease, all individuals will have the same problem.

So, while the growth rate of Austree® may qualify as miraculous, it is premature to recommend it for widespread planting in Missouri. If you wish to give it a try, you would be well advised to plant a few in your location to see how they perform before doing a large planting. If using Austree® as a shade tree, it might be prudent to plant a proven performer like an oak nearby in case pest problems shorten the life-span of the willow.

For more information, consult the following websites:

http://www.rmausa.com/
Rocky Mountain Austree® Inc. Home Page

http://www.linnextension.org/mg/public/austree.htm
Linn Co Iowa Master Gardener Page

http://www.ipm.iastate.edu/ipm/hortnews/1996/3-15-1996/ads.html
Article in "Horticulture Home Pest News," Richard Jauron, Dept. of Horticulture, Iowa State University.

http://plantsbymail.net/
E-mail testimonials and reactions from Plants By Mail Frequently Asked Questions.

Chris Starbuck, Woody Ornamental Horticulture, UMC (573) 882-9630