Lirula needle blight
Photo by P.Hennon USDA FS
Lirula needle blight is caused by the fungus Lirula macrospora.
This disease can occur in Colorado blue spruce, Picea pungens, and white spruce, Picea glauca. White spruce, including Black Hills spruce, is the more susceptible species.
- In late summer second year needles become discolored, yellow to brown.
- In the following year (third year needles) a raised black line forms along the midrib of infected needles, mostly on the lower surfaces.
- In some cases horizontal black bands form across infected needles.
- Needles on lower branches are commonly infected first.
- Infected needles turn grayish brown after spores are released but remain attached to tree for several years.
Photo by P.Hennon USDA FS, Bugwood.org
It takes several years for Lirula macrospora to complete its lifecycle. The fungus overwinters in infected needles on the tree. During late spring through midsummer infected needles release spores that spread in splashing and dripping rain to new needles. First year needles appear to be the most susceptible. On second year needles, a raised black line, which is a spore producing structure created by the fungus, forms on the midrib on the underside of the needle. Spores are released from these structures on third year needles.
- Avoid planting spruce where Lirula needle blight already occurs.
- Inspect new seedlings and trees for signs of infection prior to purchase.
- Apply Chlorothalonil or Bordeaux mixture when new needles are half the length of mature needles and a second time, one month later. Since the disease cycle is 3 years long, fungicide application must occur for 3 consecutive years to be effective.
- Remove the most heavily infected trees in the landscape to protect neighboring spruce trees.