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to burning and burying since chipped wood cannot support beetle development. Elm should not be used as firewood unless ~ has been debarked. AI1 attempts at eim utiliZation must take into account the primary concern of wood disposal. the timely elimination of beetles and beetle breeding material. Prim8TY .q barrier :.. /!~' I.> ~ <\ :~J~~~h~ 7 ~ i'J~ 1'\ :~ !'i L' .J ,- Figure 8. Tvpical root graft barrier installation. Primary bal'"rier Secondary barrier J1\ 30 ft. 30 ft. Elms on one side Figure 9. Root graft barriers on one side and on all sides. Prevention of Root Graft Spread (Isolation) Elms on all s.ides The fungus causing Dutch elm disease commonly spreads from infected to nearby heal1hy trees through naturally grafted root systems. This spread can be prevented by isolation of the diseased tree (I.e., by disrupting the root grafts) either by mechanically trenching around infected trees, using a soil trencher or vibratory plow, or by using a chemical, SMDC (Vapam). A secondary barrier is suggested between the trees closest to the diseased tree and the second ciosest trees, since some apparently healthy trees may already be infected at the time of treatment (flQure 8). Root graft barriers shouid completely encircle the diseased tree when elms are present on al1 sides. If elms are only on one side, the barrier should extend to a point at lease 30 feet from the diseased tree and from the healthy tree (figure 9). A trench 36-40 inches deep between diseased and healthy trees immediately disrupts root grafts between these adjacent trees. The easiest way to trench is with a vibratory plow or a mechanical trenChing machine, buttheir use may be lim~ed in rocky soils or where underground utilities are present. Afterthe trench is dug, refill it, and immediately remove the diseased elm trees. 7