The chances of a valuable elm being kept free of the disease are improved if all nearby dead and dying elm trees are removed and buried or burned as soon as possible. Eliminate, if possible, all potential elm bark beetle breeding material within 1,000 feet of the trees to be protected. This material will include elm branches that are infected, weak, dead, or recently cut. This will also mean destroying or debarking stumps and elm logs which are being kept for firewood. Sanitation reduces the fungus population as well as that of the bark beetles which vector the disease.
Good sanitation is most important within and immediately adjacent to trees that are to be protected.
Without sanitation, the other measures suggested here are of little use. The Dutch elm disease fungus can spread from a diseased tree to an adjacent healthy tree via these root grafts. Potential root grafts can be severed by digging a narrow trench 18 to 24 inches deep midway between the infected and healthy trees. Injecting Vapam into the soil will accomplish the same thing. Seal by tamping.