| AFFECTING LEAVES: |
|
CONDITION |
CAUSE |
 |
Leaves
skeletonized, primarily on leaf underside |
Elm leaf beetle
(larvae) (Xanthogaleruca luteola)
|
|
Holes
chewed through leaves |
Elm leaf beetle (Xanthogaleruca
luteola)
|
|
Leaves
irregularly chewed |
Spiny elm caterpillar
(Nymphalis antiopa); Fruittree
leafroller (Archips argyrospila), Forest
tent caterpillar (Malacosoma disstria), or
Fall
webworm (Hyphantria cunea)
|
|
Masses
of dark, spiny caterpillars on leaves |
Spiny Elm Caterpillar - Morning Cloak Butterfly
(Nymphalis antiopa) - No significant damage.
|
|
New
leaves small, twisted |
Eriophyid mites (Eriophyidae)
or Phenoxy herbicide injury. See Abiotic Injury
|
|
Leaves
curled, thickened |
Woolly aphids (Eriosoma
spp.)
|
|
Leaves
with white flecks |
Leafhoppers (Erythroneura
spp.)
|
|
Pale
green or yellow leaves |
Iron chlorosis
|
|
Sucking
insects on leaves, often with associated honeydew |
European elm scale (Gossyparia
spurai) or Elm leaf aphid
(Myzocallis ulmifolii)
|
|
Yellowing,
wilting foliage |
Scale “flagging" - European elm scale, Dutch elm disease (Ophiostoma
ulmi), or Verticillium
wilt (Verticillium spp.)
|
|
| AFFECTING TWIGS AND SMALLER BRANCHES: |
|
CONDITION |
CAUSE |
|
Scales |
European fruit
lecanium (Parthenolecanium corni) or European elm scale (Gossyparia
spuria)
|
|
| AFFECTING LARGER BRANCHES OR TRUNK: |
|
CONDITION |
CAUSE |
|
Borers |
Elm borer (Saperda
tridentata Oliver) or Flatheaded appletree
borer (Chrysobothris femorata)
|
|
Areas
of dead bark With discoloration and small pimple-like fruiting bodies
(pycnidia) |
Cytospora canker (Valsa
spp., Leucostoma spp.)
|
|
Open
wounds, internal decay, or swollen areas on stem |
Stem decay fungi (Collybia
velutipes, Phellinus igniarius and various genera)
|
|
Fungal
fruiting bodies (mushrooms, conks) present |
Stem decay fungi (Collybia
velutipes, Phellinus igniarius and various genera)
|
|
Clear to
white oozing or frothy malodorous liquid exiting from wounds |
Bacterial wetwood /
slime flux
|
