The Red Push Pistache (Pistacia x ‘Red Push’) is a highly valued ornamental tree, especially in arid and semi-arid landscapes, due to its deep red fall foliage and general resilience. Like any landscape tree, however, the Red Push Pistache is susceptible to various issues that can compromise its health and appearance. Successful long-term care requires accurately diagnosing whether a problem stems from environmental factors, insect infestation, or a serious disease threat.
Cultural Stressors: Water, Soil, and Nutrient Imbalances
The most frequent causes of decline in the Red Push Pistache relate to improper cultural practices, which are the easiest factors for a homeowner to control. A common mistake is overwatering, particularly when the tree is planted in heavy clay or poorly draining soil. Excessive moisture suffocates the roots, leading to symptoms like droopy, yellowing, or prematurely crisp leaves that can mimic drought stress. The correct approach is deep, infrequent watering that encourages a strong, deep root system.
Conversely, insufficient water, especially during the establishment phase, can lead to leaf scorch, where the edges of the leaves turn brown and dry out. Once established, the tree is drought-tolerant, but deep watering is still required during extended periods of high heat and dryness. When planting, it is important to ensure the root flare, where the trunk widens at the base, is visible just above the soil line to prevent girdling roots and trunk rot.
The Red Push Pistache often faces nutrient problems when planted in the alkaline soils common in many arid regions. High soil pH locks up micronutrients like iron, making them unavailable to the tree, which results in a condition called iron chlorosis. Chlorosis is easily identified by a distinct pattern where the leaves turn a bright yellow while the veins remain a dark green.
For a quick, temporary fix, a foliar spray of iron sulfate or chelated iron can be applied directly to the leaves, though this only greens up the existing foliage and does not solve the underlying soil problem. For a longer-term solution, iron chelates formulated for high-pH soils, such as those containing EDDHA, can be applied as a soil drench around the root zone in early spring. Amending the soil with elemental sulfur and ferrous sulfate can also help slowly lower the pH over time, making iron naturally available to the tree.
Insect Pests and Their Management
While the Red Push Pistache is generally considered pest-resistant, it is still vulnerable to certain insects, with the Pistache Psyllid being a notable concern. This tiny, sap-sucking insect primarily feeds on the leaves and is recognized by the distinct damage it causes. Feeding activity irritates the plant, causing the leaves to curl, blister, or form small, pouch-like galls where the nymphs develop.
Psyllids also excrete a sticky, sweet substance called honeydew, which coats the leaves and branches. This honeydew then promotes the growth of sooty mold, a black fungus that covers the leaves, inhibiting photosynthesis. For management, non-chemical options include applying dormant oil to the tree in late winter to smother overwintering eggs and nymphs before new growth begins.
If an active infestation occurs during the growing season, a systemic insecticide can be applied to the soil to be taken up by the roots, providing long-lasting control of the feeding nymphs. Proper watering and fertilization often prevent secondary infestations from becoming a major problem.
Pathogens and Serious Disease Threats
The most serious pathological threat to the Red Push Pistache is Verticillium Wilt, caused by the soil-borne fungus Verticillium dahliae. This pathogen enters the tree through the roots and invades the xylem tissue, the vascular system responsible for transporting water. The infection clogs the water-conducting tissues, leading to symptoms of branch dieback and sudden wilting, often affecting only one side or a single scaffold branch of the tree.
If a suspect branch is cut, the diagnostic sign is a dark, discolored ring within the sapwood, indicating the plugged xylem vessels. Unfortunately, there is no chemical cure for Verticillium Wilt once the tree is infected. Management focuses on preventing the spread and minimizing the impact on the tree’s health.
The best defense is prevention, which includes planting stock grafted onto resistant rootstocks, such as UCB 1, and avoiding planting in areas previously used for susceptible crops like cotton or tomatoes. If a branch shows symptoms, it should be immediately pruned out and destroyed, and the pruning tools sterilized to avoid transferring the fungus. Maintaining tree vigor through balanced nutrition and avoiding excessive nitrogen fertilizer helps the tree compartmentalize the infection.