Q. We have a twenty year old olive tree in our front yard diagnosed with Verticillium wilt disease. The north third of the tree appears to be healthy. If we remove this tree, what distance from the old hole is needed for the new tree? We would a replacement tree to provide shade. We are looking at oak, pine, ash, spruce or fir.   Olive leaf drop and branch dieback may be a sign of verticillium wilt in olive. A. That’s unfortunate. Hopefully the diagnosis was correct and it is not something else that caused it. The information you received about the disease sounds correct. This disease is present in the soil and enters the tree via the roots.             Olive has very few pest problems and an excellent tree for the desert. Verticillium wilt disease is rare in olive here but does occur. Symptoms include the death and dieback of individual limbs for no apparent reason.             Trees resistant to Verticillium wilt disease and good choices for you in our desert include live oak such as Heritage or holly oak, ornamental pear, European pear, honeylocust, apple, crabapple and any of the conifers such as pines.             Eucalyptus is also resistant but a lot people do not like eucalyptus since it can be “messy”. I would not recommend spruce or firs since they do not grow well in our climate.             If you want warmth from the winter sun then conifers (pine) or any evergreen tree (such as our southern oaks) is not a good choice for you. I would stay with ornamental pear or honeylocust for seasonal shade, disease resistance and good looks.             If you stay with Verticillium resistant trees, planting in the same general area should not present a problem.