Russian olive (Elaeagnus angustifolia) is a small and sturdy deciduous tree. Drought and pest resistant, it can be found flourishing in many soil types. It is more often planted for its ornamental, silver-grey foliage and vase-shaped growth habit. Only a few diseases can take a Russian olive down. Diagnose the problem before trying to treat a dying tree.
Check the soil conditions surrounding a dying olive tree. If branches are wilting on one or more areas of the tree, it may be a fungus called verticulum wilt. The fungus is transmitted through the soil and roots, and occurs in wet, cool conditions.
Amend the soil to improve drainage around a dying olive. They can resist periods of great drought, but can't tolerate standing water. If clay is present in the soil, amend it with equal parts peat and sand to a depth of at least 90 cm (3 feet).
Prune away affected branches, cutting them up and disposing of them in garden waste bags to reduce further infection. Angle the blades of the shears at 45 degrees, cutting down and away to leave an angled, 1.2 cm (1/2 inch) stub that will drain moisture instead of collecting it and causing rot.
Fertilise the tree. There is no effective fungicide for verticulum wilt. The best you can do is fertilise the olive tree with a balanced 10-10-10 fertiliser after amending the soil to help it recover. Follow instructions on the package for correct proportions for the size and age of the tree.
Watch for signs of phomopsis canker on a dying olive tree. The wilting of branches caused by phomopsis canker looks similar to verticulum wilt. The difference is that reddish-brown cankers appear on branches and trunk bark, restricting water movement and eventually girdling the tree.
Prune away diseased branches and wilted foliage in winter or early spring, before the fungus begins to produce spores. Destroy the infected wood and leaves by burning or disposing of it in garden waste bags.
Cut back surrounding vegetation around the dying tree to give it better air circulation and light penetration in the canopy. This will eliminate moist, dark conditions that help phomopsis canker thrive.
Keep the olive tree well-watered and fertilised to help it fight back. Both verticulum wilt and phomopsis can be fatal to olive trees. Take these measures at the first sign of wilt for the best chance of survival.
Plant disease-resistant varieties of olive trees to avoid phomopsis canker, such as Autumn Olive (E. umbellata).