The silk tree, also called mimosa or silky acacia, is a relatively short-lived tree even under the best conditions, with a typical lifespan of 10 to 20 years. However, they still make lovely landscaping trees thanks to long, ferny leaves and bright flowers. To help your silk tree live as long as possible, it is important to keep an eye out for disease symptoms. By being aware of potential threats to the tree's health, you can act quickly if need be to restore your mimosa before it fails.
Mimosa (Silk Tree) Vascular Wilt
Mimosa vascular wilt is nearly always deadly, but it is important to spot it quickly since otherwise it can spread to all mimosas in the vicinity. At first, leaves yellow and curl, finally falling off the tree completely. In later stages, the bark of the tree may crack and ooze a frothy, foamy liquid. Since wilt enters through the roots, removing affected limbs will not be sufficient to control the infection. However, using sterile pruning to remove wilted foliage and limbs--and disposal of this plant material using a sealed bag or by burning--can limit the spread of infection and, in some cases, when combined with the administration of a low-nitrogen, high-potassium fertilizer, may save the tree.
Mimosa webworms have been infesting American silk trees since 1949, according to Penn State's Woody Ornamental Pest Management. You can detect an infection by the white, cobwebby substance on the tree and by isolated patches of brown, dead leaves. Minor infestations can be removed by hand or by pruning affected branches, but you must be sure to completely dispose of the plant material to prevent reinfection. Insecticides are a good preventative measure, but will usually not entirely eliminate an existing infection.
Silk Tree Canker
Cankers are bacterial or fungal infections that form as a result of a wound to the tree. Cankers start out as small, slightly depressed and discolored areas on the bark of the tree. They are very hard to see in this stage. However, left untreated, they will swell until they are a large, woody bulge. These bulges can elongate and spread, eventually girdling and killing branches via defoliation and malnutrition. Cankers should be removed using sterile pruning techniques during cool weather when reinfection is less likely. If a branch has many cankers on it, then remove it entirely from the tree about 4 inches below the last canker.