Douglas Fir: Laminated root rot

Biology

Laminated root rot is a fungal disease of conifers throughout the Pacific Northwest. Douglas-fir, grand fir, and mountain hemlock are highly susceptible and are usually killed by the disease; many other conifer species are moderately susceptible, especially when growing near highly susceptible species. Native pines and cedars (including western red cedar) are considered tolerant; they may develop a butt rot but are almost never killed by the disease. Hardwoods such as maple and alder are immune. Laminated root rot attacks the root system of susceptible trees of any age, causing roots to decay and resulting in poor water and nutrient uptake and decreased growth. Affected Douglas-fir trees often develop rounded crowns due to stunting and short needles on the leader and branches. Symptoms in the crown appear as yellowing and thinning of the canopy, production of a distress crop of cones (Douglas-fir), and decline and death of the tree. These symptoms often do not appear until root damage is advanced. In the early stages of disease, freshly cut stumps (within about 3 feet of the soil surface) will show reddish-brown semicircular stains that fade when exposed to the air. On living trees, grayish-white to tawny or purplish mycelia of the fungus may be found sheathing the outside of infected roots. The wood of infected trees shows a characteristic layered decay in the roots and butt of the tree. Annual rings separate easily, with pits in the wood on both sides of the sheets or laminae. Reddish-brown, whiskery fungal strands (hyphae) may be present between the layers. The disease spreads by root contact and will persist in infected stumps and large roots remaining in the soil. Trees infected with laminated root rot are also predisposed to attack by bark beetles. Tree death results either from nutrient and water deficiency or from affected trees blowing down or breaking in the wind. Damaged trees may be wind-thrown due to loss of anchoring roots before above-ground symptoms are obvious, especially west of the Cascades, making this disease both difficult to diagnose and potentially hazardous.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• Do not plant conifers of high or intermediate susceptibility in areas where laminated root rot is known to be present. Douglas-fir, white fir, grand fir, and mountain hemlock are highly susceptible; western hemlock, western larch, Pacific silver fir, subalpine fir, noble fir, California red fir and spruces are considered intermediately susceptible.
• Remove all susceptible hosts in infected areas. Clearing a 50-foot buffer zone outside the last known infected tree is recommended to prevent spread by root contact with infected materials in the soil.
• Replant cleared areas with resistant or immune species only.
• Infected trees are considered hazardous and extremely prone to wind damage.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• None recommended