We have confirmed our first case of Dutch elm dis-ease (DED) at the Plant Clinic this year. It was also reported this past week at The Morton Arboretum in Lisle. If you have elms, be aware of the symptoms of this disease so you can catch it early. Some think this disease occurs only on “Dutch elm,” but that is not where the name originated. Dutch plant pathologists did the original studies on the disease and gave the disease its name. American elms are very susceptible to the DED pathogen. Although Chinese elm and Siberian elm are known to be more resistant, infection of these species can occur as well. Work is still under way to develop resistant elms. So far, breeding programs have produced the more resistant Sapporo Autumn Gold, American Liberty, and Urban elms.
Dutch elm disease is caused by a fungal pathogen, Ophiostoma ulmi (Ceratocystis ulmi). The fungus works much as the other vascular pathogens, causing plugging of the vascular tissues and resultant wilting and death of foliage.
Watch for yellowing of the leaves in the elm, followed by wilting and browning. A single branch usually shows symptoms first (called flagging) with rather rapid spread to adjacent branches and the entire tree. Look for vascular discoloration to help with diagnosis. As with oak wilt (issue 5), DED causes a streaking of the sapwood. Peel the bark of a symptomatic branch to reveal the brown streaks in the otherwise tan outer sapwood. We generally select branches of about thumb thickness with wilted leaves. Verticillium wilt and Dothiorella wilt can also cause this streaking in elm. Positive identification would require laboratory culturing of the fungus. Cut several 6- to 8-inch long sections from wilting, but living, branches that show definite streaking in the sapwood. Send us sections you have not peeled. The fresh wood sections should be thumb thickness and can be sent in plastic or foil for testing. Chilling the wood is necessary for oak wilt suspects but should not be necessary with Dutch elm suspect samples. Expect about 7 days of lab time for the fungus to grow to where it can be positively identified. There is a $12.50 fee for this service. Remember that payment must accompany the sample or it will not be processed.
No chemicals are available to homeowners for control of DED. Some products available to commercial applicators are used as preventive or therapeutic treatments when the disease is caught early. Consult the 2001 Commercial Landscape and Turfgrass Pest Management Handbook for details. For more information on DED, including control procedures, consult Report on Plant Disease (RPD) no. 647. A similar disease caused by a phytoplasma is discussed in RPD no. 660, “Elm Yellows or Phloem Necrosis and Its Control.” These reports are available in your local Extension office or on the Vista Website, http://www.ag.uiuc.edu/~vista/horticul.htm.