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How to Identify and Manage Dutch Elm Disease Page 10 of 16 retained for use as firewood or sawlogs if it is de-barked or covered from April 15th to October 15th with 4 to 6 mil plastic. The edges of the cover must be buried or sealed to the ground. If it is impossible to destroy all elm wood before the beetles emerge, the wood can be sprayed with a registered insecticide until disposal is possible. If insecticides are used, consider potential exposure to chemical residues when burning or handling the treated wood. Many communities have regulations on the removal of diseased elms and storage of elm firewood; make sure your activities comply with local regulations. Insecticides to kill insect vectors. In areas where the native elm bark beetle is the principal vector, sanitation may be augmented by applying a registered insecticide to the lower stem of healthy elms in late summer to early fall (Le., at the first sign of autumn leaf color change) to kill adult beetles as they prepare overwintering sites. In areas where the smaller European elm bark beetle are common, spring feeding in twig crotches can be prevented by spraying the crowns of elm trees with a registered insecticide. However, this may not be a preferred treatment method because of the difficulty in getting thorough coverage of all susceptible twig tissue, the risk of insecticide drift and exposure, and high expense. Insecticide registrations and recommendations are frequently updated, and may vary considerably between states. Cooperative Extension Services at land grant colleges and certified arborists are able to provide current insecticide recommendations. Disruption of root grafts. Large trees within 25 to 50 feet of each other are likely to have root grafts. Breaking root grafts between infected trees and adjacent healthy trees is an important means to prevent movement of the fungus into the healthy trees. Root grafts should also be disrupted between the healthy tree adjacent to a diseased tree and the next healthy tree. It may even be desirable to sever grafts between very valuable trees before DED is observed in the vicinity, as a proactive measure. Root graft disruption should be completed before the infected trees are removed. Otherwise the transpirational pull from healthy trees will rapidly draw in the contents of diseased tree's root system when the vascular tension on the roots of the diseased tree is released by severing the stem. Root graft disruption can be accomplished by use of a vibratory plow or any trenching machine equipped with the longest blade available (preferably five-feet long, but at least three-feet long). Biocidal soil fumigants may also be used to kill root grafts if no other alternatives are available. However, these chemicals are generally restricted use pesticides and may only be applied by professional pesticide applicators. In addition, biocidal chemicals may not be effective if soil temperatures are below 50 OF. Injecting elms with fungicide. Certain fungicides, when properly injected, are effective in protecting elm trees from infection via beetle transmission. This treatment is expensive and must be repeated every one to three seasons, thus it is appropriate only for high value or historically important trees. The treatment itself also may pose risks to the health of the tree. In order to be effective, the fungicide must be present at adequate concentration at all potential points of infection. Thus the dosage and means of application are critical to success. The injection of chemical into root flares in large volumes of water (macroinjection) provides http://www.na.fsJed.us/spfo/pubslhowtoslht_ded/ht_ded.htm 8/25/2004