Garden Detective

Garden Detective: Chinese pistache tree may need more water

We have two Chinese pistache trees in our backyard. One of them is on an incline; the other is not. Also we get a lot of wind since our property is on a hill. It looks like one of the trees has grape-like leaves that have fallen to the ground. The other tree does not have the grape-like leaves. They both get plenty of sun from the early morning on.

I just fertilize both of them. Am I too late? Watering is done by a drip method for at least 12 minutes – three times a week. Should I increase this, or water by hand once a week?

Pat Clisham, Sacramento

According to UC master gardener Veronica Simpson, established Chinese pistache trees are susceptible to verticillium wilt. This causes foliage to turn brown, yellow or faded green, sometimes affecting only portions or branches of the tree.

Infection can occur in the spring but may not be noticed until warm weather stresses the plant. Mature trees may take years to die or may recover if conditions improve for plant growth.

What stumped the master gardeners is the description of “grapelike leaves.” Are you certain that it is a Chinese pistache? Known for its excellent fall color, this deciduous tree has distinctive pinnate (or featherlike) compound leaves with 10 to 12 small pointed leaflets. While these trees lose their leaves in winter, none of those leaves can be described as grapelike. Perhaps a vine of some sort is growing in the tree?

To improve the trees’ condition, provide the trees with proper irrigation, infrequent deep watering and modest amounts of slow-release fertilizer. Deep watering ensures that the water reaches a depth of at least 18 inches. You can determine what the penetration is by inserting a sharp probe or by digging down with a shovel.

Additional information is needed to determine frequency of irrigation – the trees’ ages, type of irrigation system and what kind of nozzle or emitters, soil conditions and thickness of mulch. That is why digging down and checking soil moisture is the best method.

For example, many drip systems provide only 1 or 2 gallons per hour (gph); 12 minutes on a 1 gph system is less than a quart of water. That’s not enough for a full-grown tree.

On the other hand, soggy soil increases the risk of verticillium wilt.

If the tree needs to be removed and you plan to replace it, plant wilt-resistant species such as birch, Chanticleer pear, Capital pear or hawthorn. You can also check the Sacramento Tree Foundation website for lists of trees and their various attributes at www.sactree.org.

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