Japanese Larch Tree Diseases

Sudden Oak Death

• In 2010, the Japanese larch tree made headline news at the BBC when it was found to carry a deadly, funguslike organism known as Phytophthora ramorum. The disease became known as sudden oak death because of the rate at which it could infect and kill North American oak trees such as the tanoak, according to the “Forestry Journal.” The WSU Puyallup Resource and Extension Center lists the symptoms of the disease as “dark lesions without a callus ridge, brown staining under the bark and bleeding.” The Ireland Department of Agriculture reports that symptoms can also include dieback, abnormal shoot growth and discoloration of needles. After a larch tree contracts the disease, little can be done about it. Avoid planting rhododendrons nearby because they can carry P. ramorum.

Pine Wilt

• Pine wilt disease can affect the Japanese larch. The disease is caused by an organism known as the pinewood nematode (Bursphelenchus xylophilus ), a microscopic roundworm. According to Fred Warner of Diagnostic Services at Michigan State University, it is carried from tree to tree by the sawyer beetle, also known as the round-headed borer. As the sawyer feeds, the nematodes alight onto the tree. Once they are on the tree, the nematodes enter resin canals where they destroy resin cells, one of the tree’s best defenses. “The Journal of Nematology” reports symptoms in the Japanese larch can include wilting, leaf fall, discolored leaves and seedling death. As with sudden oak death disease, trees infected with pine wilt should be removed. However, there is some hope of prevention. Warner says, “Systematic injections of pines with abamectin ... has been demonstrated to reduce the incidence of pine wilt.” Contact a landscape specialist familiar with ornamental pines for information on how to acquire and use abamectin.

Larch Needle Disease

• Larch needle disease is a broad term for two different fungal diseases: larch needle cast (Meria laricis) and larch needle blight (Hypodermella laricis). Both diseases cause the needles to turn yellow and red-brown in the spring. They differ in that larch needle cast produces white spots on the lower surface of the needle, while larch needle blight produces black spots. Also, larch needle cast causes the tree to shed its needles after they have turned brown. The USDA Forest Service says neither of these diseases kills the tree, but they can stunt its growth. Fungicide treatments for larch needle cast are helpful but must be well timed.

Armillia Root Rot

• Armarillia root rot is caused by a soilborne fungus known as Armarillia mellea. The University of Illinois Extension lists the external symptoms as premature color change in leaves, leaf loss, stunted growth and dieback in twigs, branches and main stems. Mushrooms may also be present at the base of the tree near the infected roots. The university does not recommend fungicides for treatment but recommends keeping roots and trees from being damaged as a means of prevention.