Little gem (Magnolia grandiflora 'Little Gem') is a variety of the southern magnolia. It is a compact, shrub-like tree that will reach a height of 30 to 35 feet. A versatile little tree, little gem can be used as privacy hedging, in containers and as a specimen in the residential landscape. In spring and summer little gem offers fragrant, white flowers which can create a bit of a mess when they fall from the tree. Overall, little gem is a low-maintenance plant that isn't particular about soil, can be grown in sun or shade and is moderately drought-tolerant. Although not bothered by pests, little gem is susceptible to several diseases.
Nectria canker, a fungal disease, is transmitted to the little gem magnolia via injuries on the trunk or branches. Symptoms of this disease include rounded lesions that look like targets, and dead or decaying bark. If not treated, the canker will eventually spread and kill the tree. Prevent Nectria canker by keeping the tree healthy through proper watering and fertilization. Treatment for the disease involves pruning the diseased branch several inches below the canker. If the canker is on the trunk, cut into it and remove any diseased wood. Burn any infected wood that you remove from the tree.
Verticillium wilt is a soil-borne fungal disease that attacks the roots and spreads throughout the tree via the xylem, clogging the system as it as it spreads. Symptoms of verticullium wilt include wilted and curling leaves that may turn yellow and dead branches. This disease, for which there is no cure, may result in the death of the tree.
Remove and destroy any diseased branches, and remove all fallen leaves and other debris from around the base of the tree. To prevent verticullium wilt, water and fertilize the little gem tree consistently and regularly to keep it healthy. Fertilizer low in nitrogen and high in potassium seems to strengthen the tree against the disease. Always sterilize pruning materials prior to use on the little gem magnolia.
Algal Leaf Spot
This disease, caused by parasitic algae, is most common in the southeastern part of the United States, where it is hot and humid. Symptoms include raised patches on the leaves that can be either gray, brown or yellow. Leaves will curl and fall from the tree.
The first step in dealing with an infected little gem magnolia is to rake up and destroy all fallen leaves. Prune any trees that are in close proximity to allow better air flow around the little gem. Cooperative extension agents with the University of Arkansas suggest using a fungicide spray, such as copper hydroxide, and covering the entire tree with the spray. Read and follow label directions when using fungicides.