Several reports have been received of dead of dying mimosa trees (ialbizia julibrissin Durazz), also called silktrees. These are fast-growing small trees, much admired or theie delicate, feathery leaves as well as for light-pink to rosy-red flowers that are produced almost all summer long. There are thousands of them in this area, and they are subject to a fungus disease called Fusarium wilt (Fusarium oxysporum f. perniciosum ).
Leaves on infected trees first appear yellowish, then wilt, turn brown and shrivel. Entire branches then die. For positive diagnosis, look for partial or complete brown rings that can be seen in the sapwood when an infected branch is cut through.
Infected trees usually die within a year (often within a month) from the time symptoms are first observed. There is no recovery and infected trees should be removed and destroyed, according to specialists.
Because of the highly destructive and epidemic nature of the disease, USDA conducted a program to select and propagate wilt-resistant trees. Two resistant cultivars, Charlotte and Tryon, were released to the nursery trade.
These disease-resistant cultivars appeared to be the answer to the disease problem until a new race of the fungus was reported that could attack the previously resistant trees. This new fungus race is now present in areas where the tree is grown, as evidenced by the recent wilt and death of several of the resistant Charlotte cultivars that have been under observation for the past several years.
Despite the disease, many trees in the area have escaped infection, because trees 20 to 30 years old can often be seen.
The Coastal Plain Agricultural Experiment Station, in Tifton, Georgia, and USDA Science and Education Administration recently announced the development and introduction of another disease-resistant variety, Albizia julibrissin 'Union,' a selection from seed obtained by Forest Service personnel in 1951 through self-pollination of a resistant tree. It was transplanted in 1953 to Union, South Carolina, an area naturally and heavily infested with the mimosa wilt organism. In 1955 the tree was planted Tifton, Georgia, and the area was artificially infested yearly from 1955 to 1960 with the wilt fungus from several areas.
No evidence of the wilt has been seen on plants grown at Tifton or at the National Arboretum since 1970, or at Mobile, Alabama, or Wachapreague since 1972.
The original tree of Union has a crown, spread of approximately 14 meters (about 45 feet) and a height of 8 meters ( about 26 feet) at 27 years of age. Individual flower clusters are approximately 14 centimeters (about 51/2 inches) wide and 4.5 centimeters (almost two inches) deep. Flower color is light red, which extends from the tip of the cluster of approximately a quarter of its depth. The remainder is yellow and white The tree has proven cold-hardy at the Arbit retum since 1970, weathering the severe winters of 1976-77 and 1977-78.
Plants of Union will be available to the nursery industry October 15 from G Stream Nursery, Watchapreague, and a limited number from Science and Education Administration, Agricultural Research Coastal Plain Experimental Station, Tift Georgia 31794.