Another installment in our series of posts where Texas Tree Surgeons answers your tree questions. Are you having problems with your trees and want to know what’s wrong? Let us know! [POST HAS BEEN UPDATED TO REFLECT RESULTS OF LAB SUBMISSION] Dear Texas Tree Surgeons, My Chinese pistaches are looking terrible! The leaves are yellowing, the berries are black, and it looks like it’s dying. What’s going on? -A.B. For many years, the Chinese pistache (Pistacia chinensis) has been well-regarded as a landscape shade tree for urban environments in Texas. Although native to China, this species of pistache (related to the nut-bearing pistachio tree) can thrive in a variety of conditions. The Chinese pistache is a fast grower and is resistant to heat, drought, and alkaline soil, all common in North Texas. Like the native red oak, the Chinese pistache is a reliable source of fall color. The dark red berries that female Chinese pistaches produce are not only striking, but can attract birds and other wildlife. For many builders and landscapers, the Chinese pistache is a go-to choice. This year, however, we have been seeing unprecedented dieback and wilting of leaves and berries in Chinese pistaches. Entire trees are exhibiting leaf spotting and extensive browning. Similar to the browning present in Italian cypresses the past two years, it seems that the Chinese pistache dieback is caused by a fungus. And much like the Italian cypress issues, there may not be much that can be done at this point.
Water, Water EverywhereRecent wet weather, combined with poor drainage in clay soils, creates a “wet feet” situation in trees, where their roots are inundated with too much moisture. Trees that are not suited to wet soils are not able to regulate the high moisture level in their roots effectively. The roots then become susceptible to pests, especially fungi, which thrive in damp, poorly-drained soil. As the tree root tissue becomes waterlogged, the fungi are able to gain a foothold in the roots and begin infecting the tree internally. Eventually, the tree’s vascular system itself becomes the mechanism by which the fungal spores are spread throughout the branches, leaves, and fruit. The fungus disrupts cell function in the above-ground parts of the tree, just as it did in the roots.
What Can We Do About It?Unfortunately, there is often little that can be done to improve overall drainage in clay soil. Still, there are some things that tree owners can do to give their trees the best chance:
- Select native species that are well-adjusted to the North Texas climate
- When planting, do not plant too deep, and follow good mulching practices
- For established trees, do not overplant the area near the root collar and inside the drip line with turf grass or other groundcover
- Consider root collar excavation (Airspading) for trees that were planted too deep
- Vertical mulching and soil aeration can help break up heavy clay and compacted ground
- Stop watering and turn off sprinkler systems during periods of heavy rain