The mimosa tree is a landscape ornamental increasingly being infected by the fungal disease Fusarium wilt. Infected mimosa trees have been found in the USDA growing zones 6 through 9 in the Southeast and Southwest areas of the United States. Spread through soil contamination, the disease is vascular in nature and eventually leads to death of the tree.
Mimosa wilt, also called fusarium wilt, is a lethal disease caused by the asexual fungus Fusarium oxysporum. Once the disease infects the Mimosa plant, the pathogen is carried through the water-conducting vessels. The fungal spores establish in the soil and can live on non-host plants, such as grass, to continue infecting susceptible plants.
The Mimosa wilt fungus penetrates and is absorbed through the roots of the plant and spreads up through the stem and branches. The vascular nature of the pathogen will block the water-conducting cells and plant nutrients–resulting in the tree wilting and eventually dying. The pathogen originates in the soil, enters the tree through the small roots, moves to the large roots and crown and spreads up the trunk of the tree.
A Mimosa tree infected with this fungus will present symptoms of wilted leaves that will dry and shrivel. The leaves will fall from the tree and the branch will die. Once the leaves have fallen, the bark will show signs of an orange fungus growth (and sometimes a dark ooze). It is possible for one side of the tree to be infected, since the disease is vascular and can infect one vascular section of the tree at a time. The roots of an infected plant will have dark rings and discoloration when cut open.
There is no treatment option available for a Mimosa tree fusarium wilt infection–aside from removing and destroying the tree. You can slow the progression of symptoms by feeding the tree with a 10-10-10 fertilizer to increase the health of the tree. Also, frequent watering decreases the pathogen saturation rate in the tree.
Prevent a wilt infection by not moving soil that is known to be infected with the fungus. Choose trees and shrubs that show a resistance to the fungus. The hybrid cultivars Charlotte and Tyron are resistant to wilt–as are redbud, New Mexico locust and honey locust. Use a bleach solution to disinfect all pruning and cutting tools after use on trees that have the disease.