Figure 1. Lirula needle cast Photo: Chad Behrendt

Lirula needle cast is caused by the fungus Lirula macrospora. This disease can be found on white and Colorado blue spruce. Lirula needle cast is one of a number of needle cast diseases that can affect spruce. The primary difference between Lirula and other needle cast diseases is that with Lirula, second year and older infected needles tend to remain attached to the branch.

All spruce needles can be divided into age classes. If you look closely, each year of needle growth is identified by the terminal bud scale scars along the branch. Current year needles, which are on the terminal ends of the branches, usually are brighter green than other needles located on the tree. After an initial Lirula infection occurs, these current year needles remain green and no symptoms of the disease can be seen on them. Second year needles, or those whose initial growth occurred the previous year, turn purple to brown during the current year. Infected third year needles, or those needles whose initial growth occurred over two seasons ago, produce black bands or lines down the length of the needle in the early spring (fig. 2). These lines or bands are the fruiting bodies of the fungus and are usually found on the underside of the needle. Mature fruiting bodies of the fungus release spores that are wind blown to other susceptible trees to initiate further infections.

Figure 2.

To prevent infection, ensure that spruce trees are planted on favorable sites for proper growth and development. Blue spruce are not native to Minnesota, so finding a preferable site is an important consideration. Avoid overcrowding when planting. Cultural practices such as watering during dry periods, mulching, and fertilizing may increase vigor of stressed trees. No fungicides are currently registered for this disease.

References
Ash, C.L. et. al. 1995. Disease Management Recommendations for Trees and Shrubs. Minnesota Extension Service, University of Minnesota, St. Paul MN.

Harting, R. 1874. Important Diseases of Forest Trees (Contributions to mycology and phytopathology for botanists and foresters). Berlin J. Springer, 127 pp. (English translation in Phytopathological Classics 12, 1978.).

Hightshoe, Gary L. 1988. Native Trees, Shrubs, and Vines for Urban and Rural America. New York: Van Nostrand Reinhold.

Sinclair, W.A. 1987. Diseases of Trees and Shrubs. New York: Cornell University Press.

Walla, J.A. 1984. Needle Blight in Spruce in North Dakota Caused by Lirula macrospora. {Note} Plant Disease 68:1.

P430L
Revised 1/2000
Chad Behrendt, Crystal Floyd