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ELYTRODERMA
NEEDLE CAST
(Elytroderma deformans)
Host:
Ponderosa pine, rarely lodgepole pine
Quick ID:
- Narrow,
long black spots on 2-year-old needles
- Reddened,
dead 1-year-old needles ("flags")
- Current
season needles green
- Witches'
brooms
- Inner bark
of older twigs has dead patches
 Field
Identification
Tree:
In the spring, needles infected the previous fall die and turn red-brown.
This color fades through the summer. At the tip of the twig, the
current year's needles remain green. If the tree is infected year
after year, witches' brooms, or abnormal proliferations of many
small twigs which appear as a mass of twigs and foliage, may form.
These are more compact and rounded than the witches' brooms from
dwarf mistletoe infections, and have upward-turning branches and
many dead needles. Twigs that have been infected for more than three
years have small patches of dead tissue under the inner bark.
Fungus:
Dull black, elongated fruiting bodies appear as spots on dead needle
surfaces in the late summer.
May be confused
with: Dwarf mistletoe, Dothistroma needle blight, Lophodermella
needle cast.
Disease
cycle: Elytroderma needle blight is the most important foliage
disease of ponderosa pine in Washington. Windborne spores are disseminated
from the hysterothecia in late summer and autumn, infecting the
current year's foliage. The fungus grows from the needle into the
twig without initially killing either one. The following spring,
the needles die and new hysterothecia form on the dead needles.
Infections
in the woody twigs can remain for many years, reinfecting needles
that produce spores that infect other trees. The spread of the disease
in the twigs causes the characteristic brooming and deformation.
Predisposing
agents: Cool temperatures and high humidity in the late summer
and fall promotes infection by the windborne spores. Certain sites
that typically have these conditions such as around lakes, in stream
bottoms, in canyons, near meadows and in other cool moist areas
have more problems with the disease, especially as the air recirculates
in the stand. Elytroderma is itself a predisposing factor for Armillaria
root disease and bark beetle attack as it weakens the tree.
Impact:
Infection becomes damaging around 3,500 feet of elevation in Washington,
though it occurs at lower elevations. The damage from this disease
occurs mainly as growth loss and predisposition to disease and bark
beetles, although infections year after year can kill the tree.
No information is known about the disease's impact in terms of cubic
feet lost each year, but trees with 30% to 60% of the crowns infected
lose 52% to 65% of normal diameter growth, and trees with more than
60% of the crown infected lose 93% to 99% of normal diameter growth.
Management:
In immature stands, good spacing should be maintained but large
openings in the stand should not be created. Severely infected trees
should be removed when thinning (do not leave trees with flags within
6 feet of the leader). Infected branches should be pruned if it
is economically feasible to remove sources of inoculum. In mature
stands, it is important to avoid hasty action as infection can occur
without catastrophic loss. Watch the stand carefully for signs of
more serious damage (bark beetles, Armillaria, etc.). When harvesting
damaged or diseased trees, carefully inspect the residual stand
taking care to remove all infected trees.
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