Q. I have a Chinese pistache tree which is nice and green but the leaves began to curl. I spoke to someone at the nursery where I bought it, I did what they said but I am not seeing any change yet. Can you help me save my tree that cost me so very much money when I had them plant it last year?
A. Chinese pistache is a tree that does very nicely in our desert climate with very few problems. One thing that it hates is a soil that stays wet.
Curling leaves on pistachio can be an indicator of a water or insect problem. Once the leaves are curled however, these leaves will not straighten out again. However new leaves that come out should be normal if you have corrected the problem.
Curled leaves can indicate water stress; not enough water in the soil or watered applied to often. If watered too often, curled leaves can be an indicator of root rot or trunk rot at the soil level which is called collar rot which results if the soil is kept constantly wet or it is buried too deep.
Whatever you do, be sure not to water this tree daily! You will kill it if you do. You are far better off giving it more water than it needs, but applying less often.
The amount of water to apply depends on its size. How often you applied the water depends on the time of year. In midsummer you should not be watering more often than three times a week. For desert adapted trees like this one you should be able to get by on one, or at the most, two watering's in one week.
I wish I could tell you how many minutes of water to apply but water does not work in minutes, it works in gallons. If your tree is watered by drip irrigation, you should have four drip emitters around the tree.
Once the tree is above 10 feet, you should be adding more emitters around the tree. The emitters should be no closer than about 18 inches from the trunk.
If the problem is from insects feeding on the leaves and causing them to curl, a systemic insecticide intended to be applied to the soil above the roots should kill the insects. The leaves that are curled will stay curled. You will not see normal leaves until you see new growth.