The Russian Olive is one of the hardiest Trees that grow here. Not planted as much as it should be, it is still uncommon.The Tree is planted throughout the dry American west and does very well in drought conditions. The Tree can get huge in maturity and I have seen a couple of monsters on the university campus in Pocatello, Idaho. The main reason for its hardiness in dry country is its tap root. This is one of only two Trees growing here that has a true deep penetrating tap root. The other is the Burr Oak. Known for its silvery blue leaves, it is a welcome addition to the varied greens of most of our Trees. While the tap root is an amazing adaptation to drought, it does present some transplanting problems.
Every Tree gets something; the Russian Olive's main pathogen here is Phomopsis, a fungal canker-forming disease. The first sign is dried up leaves and branches during the growing season; sometimes called flagging, they are hard to miss. These flags show that branches have been girdled by the canker and thus cut off from their water source. The main symptom is the discolored sunken cankers, which turn the bark a chestnut brown and are sometimes black. There are often gummy sap deposits near the edge of the cankers. As with all fungal and bacterial afflictions, the main defense is pruning. Locate the cankers and remove those branches, cutting down into healthy wood.
Drought resistant as it is, the Russian Olive still needs water, and the healthiest thriving Trees without this disease will be the ones that got some water during the worst of summer's desiccation.