Mimosa (Albizia julibrissin), also called silktree, is a fast-growing deciduous tree from west-central Asia that has attractive feathery foliage and puffy pink flowers. Few diseases are a problem on this tree except for mimosa wilt, also known as fusarium wilt, caused by a soil-borne fungus (Fusarium oxysporum f. perniciosum). This disease infiltrates the water-conducting tissues and blocks the flow of sugars, water and nutrients, quickly killing the tree.
A soil-living fungus, fusarium wilt is caused by Fusarium oxysporum f. perniciosum. When it affects mimosa trees, it is commonly called mimosa wilt. Cracks in tree roots, caused by physical damage to roots can be infiltrated by the spores of this fungus. Poorly draining soils or unusually wet and warm weather can increase the spread or threat of fusarium wilt on mimosa trees of any size or age.
In the United States, fusarium wilt affects mimosa trees primarily from New York southward to the Gulf Coast and westward to southern California.
Symptoms of Fusarium Wilt
The first noticeable symptom of an infected mimosa is yellowing and wilting leaves in early summer. At first it afflicts one or two smaller branches but spreads to larger limb connections. Cracks begin to appear in the bark of afflicted branches. In severe cases, a froth or sticky sap is exuded from the cracks while the balance of the tree yellows and wilts its foliage. Cuttings of branches reveal brown streaks in the sapwood.
After a mimosa tree is killed, suckering sprouts of foliage stems may grow from the still living roots. However, as the fungus matures, pinkish orange spore clusters may be seen on the trunk. The spores are then spread via the wind, insects, shoe bottoms or rainwater to adjacent soils and plants.
There is no cure for mimosa trees inflicted by fusarium wilt. In areas where this soil fungus is known to exist, replacing mimosa with other tree species that are resistant to fusarium is undertaken. Three cultivated varieties of mimosa are reputed as being resistant to the fungus, including 'Tryon', 'Charlotte' and 'Union'. Elizabeth Bush of the Virginia Cooperative Extension warns that these varieties' resistance is diminished if root knot nematodes are also present in the soil.
Although not diseases, mimosa trees may become afflicted by insect pests during different seasons or weather conditions. Cottony cushion scale, mimosa webworm and spidermites are known to cause dieback of foliage or new growth twigs.