Elms eliminated? Pests have taken their toll on American elms but there are more replacement options now than in past for this mainstay Wyoming tree
By Scott Schell across the U.S. and parts of lms have been important to Canada, and efforts to develop Emany Wyoming communi- Dutch elm disease-resistant ties for decades. cultivars are underway. In fact, the American elm Topsoil Protector (Ulmus americana) is native Many Wyomingites are to the low-elevation areas of familiar with the Siberian elm northeastern Wyoming; howev- (Ulmus pumila). It is actually a er, few of these trees now exist fairly recent introduction to the due to long-established forest state. In the past, trees from threats like Dutch elm disease areas of the world with harsh spread by the European elm climates similar to ours were bark beetle (Scolytus multistria- introduced into the American tus) and the native elm bark West for conservation pur- beetle (Hylurgopinus rufipes). poses. Often, these non-native A small population of trees came without the insects American elm trees still persist and diseases that attacked
spring 2013 11 Whitney Cranshaw, Colorado S tate University, Bugwood.org
much Siberian elm mortality in the western U.S. and is now the most fre- quently reported cause in Wyoming. Newcastle lost more than 300 Siberian elm city trees to this insect in 2004. It is a very effective vector of Dutch elm disease, and it will also in- fest willow, Russian olive, stone fruit trees, and carangana trees. A New Pest Banded elm bark beetle The newest elm tree pest to ar- rive in the U.S. is the elm seed bug (Arocatus melanocephalus). It was their native ranges, and they flour- The Culprits found in Idaho in July 2012. Not con- ished here. Seeing the competition between sidered a major threat to tree health, Windbreaks of Siberian elms and the different insects has been inter- it is a nuisance pest with the habit of Russian olives (Elaeagnus angusti- esting from an entomologist’s point entering homes to over-winter similar folia) helped save the topsoil in our of view. The long-established exotic to boxelder bugs – only stinkier due grain belt from wind erosion and pests of elm trees are the elm leaf to powerful scent exuded from a provided welcome shade on many beetle (Xanthogaleruca luteola) and gland when alarmed. prairie homesteads. Their abilities to the European elm bark beetle. The Siberian elm has served its survive, spread, and crowd out other The elm leaf beetle is less and purpose in Wyoming. If we look at plants helped make the Siberian elm less of a problem, and the European a positive side of the eventual elimi- and Russian olive tree species suc- elm flea beetle (Orchestes alni), first nation of this tree species from our cessful. However, the same proper- found in the U.S. in 1982, is now urban and rural landscapes, it is that ties that made the Siberian elm and much more common. we can use the shade and shelter of Russian olive trees good competitors A new pest, the banded elm bark Siberian elms still living to protect have caused many to consider them beetle (Scolytus schevyrewi), was and nurture young trees of more de- weeds. first reported in the U.S. in Colorado sirable species. Nature, however, is never in stasis, in 2003. Elm wood pallets and crates If your Siberian elm is dead or dying and Siberian elm has recently lost from Asia may be the source of the and needs to be removed, the choice some of its competitive advantage as pest. This insect has spread rapidly of suitable replacement tree species is more insect pests native to its place of and was found in 21 other states by much greater than before. origin have found their way to the U.S. 2007. This bark beetle has caused
Bur oak American linden Hackberry
12 BARNYARDS & BACKYARDS These can include: • American elm varieties – Princeton, Prairie Expedition, Valley Forge • Hybrid elm varieties – Accolade, Triumph, New Horizon, Discovery • American linden – Sentry, Legend, How to protect your Redmond, Boulevard • Honeylocust – Skyline, Shademaster, Imperial, Northern trees from pests Acclaim Pest insects will attack stressed plants first. To keep any tree • Bur oak unstressed in most arid parts of Wyoming requires adequate wa- • Horsechestnut ter year-around. • Ohio buckeye Try to prevent root damage caused by compaction and con- • Kentucky coffeetree struction activities. Accidental herbicide exposure when lawns • Hackberry are treated for weeds can also seriously harm a tree. Reading and following the label of those products, if used near your trees, For more information is important. • http://www.botanic.org/discover/ Protection from bark beetles requires applying labeled insec- high-plains-arboretum/ ticides, commonly containing carbaryl- or permethrin-active ingre- • http://lands.state.wy.us/index. dients, to the bark before the insects become active early in the php/forestry/community-forestry/ growing season. The treated bark surface prevents bark beetles trees-for-wyoming from chewing into the living plant tissue, which, in turn, prevents the fungal disease they carry from getting into the tree. • http://www.wyomingextension. Systemic insecticides with active ingredients such as imida- org/agpubs/pubs/B1090.pdf cloprid and dinotefuran can protect the elms from aphids, scale • http://treehealth.agsci.colostate. insects, and foliage feeders such as elm leaf beetle, elm flea edu/research/nationalelmtrial/ weevil, and elm leafminer, that can severely weaken the trees. NationalElmTrial.htm However, the systemic insecticides have not been shown to prevent bark beetles from introducing Dutch elm disease into the trees. • http://bit.ly/elmbeetles • Elm leaf beetle bulletin http://bit.ly/elmleafbeetle European elm flea beetle
Siberia, Europe, Wyoming – makes no difference to Scott Schell, University of Wyoming Extension assistant entomologist. Their insect pests are on his to-do list. He can be reached at (307) 766-2508 or at [email protected].
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Whitney Cranshaw, Colorado State University, Bugwood.org