Chinese Pistache Trees with Verticillium Wilt Disease?

Q. We have two Chinese pistache trees in our backyard that appear to have verticillium wilt. Any suggestions?

A. How did you confirm this disease? Do you have isolated branches that are dying back? It is rather rare to have this disease in a home landscape. Not impossible, but rare.If you are correct than this could impact your entire landscape and future plant selection.

            I am sending you a link so that you can look at pictures of this tree when it has verticillium wilt. Readers can also see this link on my blog. 

http://ipm.ucanr.edu/PMG/r605100811.html

            There is not much that you can do if you in fact your trees do have verticillium wilt. It is fairly easy to diagnose if you know what to look for.

            All you can do now is make sure the trees are not getting too much water, not fertilized with too much nitrogen and prune out the infected limbs.

            This disease is in the soil so planting in this spot with susceptible woody trees is not a good idea. You can use ornamental grasses and pines in this spot since they don’t get this disease.

Mulberry Trees Are Very Tolerant of the Desert but Have Their Problems

Q. I would like to replace a huge Mulberry tree in my front yard, roots are very invasive but the shade is wonderful. We have west facing home. I would like to replace with a small bay laurel for cooking purposes and a shoestring acacia for shade. Are these trees invasive and would both be too much?

Mulberries planted in home landscapes are usually male trees and these trees produce pollen. Mulberry is very tolerant of many types of soil and high temperatures. It is a great shade tree for the desert because it can produce 100% shade. But it also has many problems for communities in the desert.

Mulberries are normally shallow rooted. They don't typically have a deep root system even under the best conditions.

Mulberries flower in the very early spring before the leaves emerge. Some mulberry trees are male and others are female. The male trees produce pollen which many peopl are allergic to and the female trees produce fruit which can become very messy.

A. Invasive has several different meanings. If you mean, are the roots in they? Yes, Mulberry has a very invasive root system. Mulberry is a great tree for the desert if you are just talking about how easily it handles extremes of all kinds and produces 100% shade if it gets enough water.

            But it does have a lot of problems; very high water use, the mail tree produces a lot of pollen that can be a human health hazard and the roots will get into any place where there is water and nutrients.

            But that goes for almost every tree that's out there including many of our desert trees like Acacia and Mesquite. If given the chance, Bay Laurel will have an invasive root system.

            You will want to keep all trees added distance from the house and other structures including walls that is half of its mature height. Never plant them on top of a septic system, near a swimming pool or near the sewer lines.

            I think planting Bay Laurel in a Western exposure could be a mistake. It will do much better on the north or east side of a home with some protection from the late afternoon sun. As a warning to you, I have seen freeze damage to Bay Laurel in the Las Vegas Valley.

            I would try to put it in a spot that has some protection from strong winter winds. The Acacia will handle a Western exposure very nicely. However, it will not give you the same shade as a Mulberry. I think you could classify the Acacia as filtered sunlight which will allow you to plant beneath it. Planting under a Mulberry tree has a lot more restrictions because of the dense shade.

Shrub Dropping Its Leaves Could Be Lack of Water

Q. A month ago we had a shrub that was seemingly healthy.  It began losing its leaves since then.  I do not know the name of this shrub but it is ten years old and planted on the north side of our home getting only the early morning sun. My question is, is there a possibility of the leaves coming back or is this shrub a goner?  

A. Couldn’t tell 100% from the picture you sent but I think it is Pittosporum. First glance at the picture looked like it went through some sort of rapid shock. That's why there is leaf drop and many of them are still green. Otherwise, the plant looks healthy except for this leaf drop.

            I think the soil got too dry for a short time and caused the leaf drop. Take a hose and soak the area at the base of the shrub twice during this next week. I think you will see it produce new leaves and start to come back within 7 to 10 days.

            Check to make sure the drip emitters are not plugged and the plant is getting water. But I think it was a short-term water problem during excessively hot weather.