Russian olive are in the olive family and are the only olive tree that grows in this state naturally. Russian olive trees can look very nice if they are well maintained but when given no attention can be one of the worst looking trees you can possible buy. They do not have many diseases that are fatal. Most of the diseases like the leaf rust on the right hand side of the page are cosmetic. In rare cases you will be able to find a disease that is so far along that it causes the damage associated with the picture second front he top right of the page.
Personally, I think planting these trees is a case for disaster. This might be one of the only times I come out and say don't buy this tree that does not get diseased. These trees have a mind of their own and can grow in any which way. The nicest Russian olive I have every seen is pictured to the left side of this page. They get so much dieback in them and usually never look good. They also have very nice thorns that can be 2" long or more. They are pretty dangerous and not a tree to have little kids around. All in all I would never suggest buying a Russian olive. Here are things to look for in your Russian olive: