American Elm:
- Deciduous tree, to over 75 ft (23 m), vase, arching branches (most common form), a spreading form is also seen. Leaves alternate, simple, 3-6 in, ovate-oblong, unequal at base, doubly serrate (toothed), glossy dark green above, 13-18 parallel veins from midvein to the teeth.
- Flowers perfect, in groups of 3-4, yellow to reddish. Fruit rounded, disc-like samara, about 12 mm long, greenish sometime with a reddish tinge, maturing in early summer.
- Sun, prefers rich, moist, soils but grows under a variety of conditions. Once extensively used as a street and lawn tree. Dutch elm disease has changed that. Apparently no longer common in eastern North America. However, there are several hunderded elms (U. american, U. × hollandica, and others) in Corvallis, most on the OSU campus. Hybrids elms resistant to Dutch elm disease are now recommended for planting.
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Siberian Elm:
- Broadleaf deciduous tree, 50-70 ft (15-21 m) tall, its width about 3/4 its height, open habit, brittle, pedulus branches. Leaves simple, alternate, 3-8 cm long, 0.8-3+ cm wide, elliptic to elliptic-lanceolate, nearly equal at the base, usually simply serrate, dark green and smooth above, glabrous below, petiole tinged dark red. Flowers appear before leaves, inconspicuous, green. Fruit about 1 cm, almost a round disk, a closed notch at the tip of the wing.
- Sun. Very adaptable, often grows under adverse conditions. Resistant to Dutch elm disease. Frequently used as a hedge in rural areas (or subject to topiary?), but generally considered a poor ornamental tree, mostly because of its weak branches, messy habit, and susceptibility to insect attack, especially leaf beetles. Extensively planted in the 1930s. Sometimes sold as Chinese Elm, a name that is more commonly used to identify Ulmus parvifolia, a superior ornamental tree.
Common problems with Elm trees:
Insects:
| Aphids | Leafminers | Asian Longhorned Beetle | Twospotted Spider Mite |
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Aphids feed by sucking up plant juices through a food channel in their beaks. At the same time, they inject saliva into the host. Light infestations are usually not harmful to plants, but higher infestations may result in leaf curl, wilting, stunting of shoot growth, and delay in production of flowers and fruit, as well as a general decline in plant vigor. Some aphids are also important vectors of plant diseases, transmitting pathogens in the feeding process. A sticky glaze of honeydew may collect on lower leaves, outdoor furniture, cars, and other objects below aphid feeding sites. Honeydew coated objects soon become covered by one or more brown fungi known as sooty molds. Crusts of sooty mold are unsightly on man-made objects, and they can interfere with photosynthesis in leaves.
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Leafminers are
usually the larvae of flies, moths, or beetles that feed
or “mine” between the upper and lower epidermal leaf
surfaces. The larvae tunnel through the leaf creating a
narrow, whitish colored serpentine (winding) mine or
blotch (blister) type mine. The tunnel is clear, except for the
trail of black fecal material left behind as larvae
feed. Female flies puncture or "stipple" leaves with
their ovipositors to lay eggs in the leaf tissue or to
feed on sap. Many ornamental plants are attacked by leafminers, but azalea, bougainvillaea, ixora, hollies,
chrysanthemum, lantana, oak, and boxwood are some of the
preferred hosts. MORE INFO |
The Asian longhorned beetle (ALB) is an exotic pest threatening a wide variety of hardwood trees in North America. Adults are large (0.75 - 1.50 inches long) with very long black and white banded antennae. The body is glossy black with irregular white spots. Adults can be seen from late spring to fall depending on the climate. ALB attacks and kills many hardwood trees, such as maple, elm, horsechestnut, ash, birch, poplar, willow and many more. ALB could significantly disrupt the forest ecosystem if it became established over a large area.
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The twospotted spider mite prefers the hot, dry weather
of the summer and fall months, but may occur anytime
during the year. Spider mites feed by penetrating the plant tissue with their mouthparts and are found primarily on the underside of the leaf. All spider mites spin fine strands of webbing on the host plant — hence their name. For detection of spider mites, a 10X to 15X magnifying glass is a necessity. MORE INFO |
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Diseases:
| Dutch Elm Disease | Wetwood (slime flux) | ||
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The observable symptoms and the progression of the disease differ among trees which are inoculated through beetle feeding and those which are infected through root grafts. Trees infected by beetles first show wilting, curling and yellowing of leaves on one or more branches in the upper portion of the tree. Large trees may survive and show progressively more symptoms for one or more years. Trees infected through root grafts wilt and die rapidly; this frequently occurs in the spring soon after the trees have leafed out and progresses from the base of the tree upward. Trees infected with Dutch elm disease usually develop brown streaks in the sapwood of wilting branches. Cross sections of infected branches will show brown streaks in the outer wood in spring; in summer they will show a single ring of brown dots in the wood. Trees infected through root grafts or lower trunk infection do not show these symptoms in the branches but will show streaking in wood of the trunk if a chip or wedge is removed. MORE INFO |
Bacterial wetwood, also called slime flux, is a major bole rot of trunk and branches of trees. Slime flux has been attributed to bacterial infection in the inner sapwood and outer heartwood area of the tree. A tree with slime flux is water-soaked and "weeps" from visible wounds and even from healthy looking bark. The "weeping" may be a good thing as it is having a slow, natural draining effect on a bacterium that needs a dark, damp environment. A tree with this bole rot is trying its best to compartmentalize the damage.
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| TREATMENT | TREATMENT | TREATMENT | TREATMENT |