The Texas Mountain Laurel (Sophora secundiflora) is a highly valued evergreen known for its striking purple, grape-scented flowers and exceptional drought tolerance. Native to Texas and arid regions, this slow-growing plant offers glossy, dark green foliage and is a favorite for homeowners seeking a low-maintenance, ornamental tree. However, it can experience specific issues related to pests and environmental conditions.
Managing the Most Common Pest: Texas Mountain Laurel Webworms
The most frequent pest is the Genista Webworm (Uresiphita reversalis), often called the Texas Mountain Laurel Webworm. The caterpillar stage is yellowish-green with black and white spots, appearing during new growth in spring and fall. These larvae feed on tender leaves and shoots, creating a loose, silky webbing over branch tips.
While a mature tree can tolerate defoliation, heavy infestations slow growth and remove next season’s flower buds, which form on the current year’s growth. Small infestations can be managed by handpicking, pruning affected terminals, or using a strong jet of water.
For widespread issues, apply a targeted biological control. Products containing Bacillus thuringiensis var. kurstaki (Btk) are highly effective because this stomach poison only affects caterpillars and is safe for beneficial insects. Apply Btk when caterpillars are small and actively feeding, ensuring it covers the new foliage.
Addressing Environmental Stress and Poor Growth
Issues not caused by pests often stem from improper cultural practices, specifically soil and water management. The Texas Mountain Laurel evolved in rocky, well-drained, alkaline soils and is intolerant of conditions that retain too much moisture.
Root Rot and Drainage
Root rot occurs when the tree is planted in heavy, poorly draining soil that stays waterlogged. This condition deprives the roots of oxygen, leading to fungal infection and root death. To prevent this, never plant the tree deeper than its nursery container, ensuring the root flare is visible above the soil line. For existing trees, reduce watering frequency and ensure water does not collect around the base; incorporating compost can help improve soil texture and drainage.
Chlorosis (Yellowing Leaves)
Yellowing leaves with dark green veins, known as interveinal chlorosis, signals iron deficiency. Although iron may be present in the soil, the high alkalinity typical of native Texas soils renders the iron insoluble, making it unavailable for the plant to absorb. This problem is often exacerbated by poor drainage or compacted soil, which damages feeder roots. Treatment involves applying chelated iron supplements directly to the soil or as a foliar spray to provide the nutrient in an accessible form.
Lack of Flowering
When a mature Texas Mountain Laurel fails to produce blooms, the cause is generally environmental or a result of pruning errors. Since these trees form flower buds on the previous year’s growth, pruning in the fall, winter, or early spring will remove the developing buds. To ensure blooms, only prune immediately after the current year’s flowering cycle is complete, typically in late spring or early summer. The plant also requires full sunlight (at least six to eight hours per day) to maximize flower production, and excessive nitrogen fertilizer encourages leafy growth at the expense of flowers.
Toxicity and Safety Precautions
The toxicity of the plant’s seeds is an important safety consideration. The bright red seeds, found inside hard, woody pods, contain the highly toxic quinolizidine alkaloid cytisine. Ingestion by children or pets can cause severe illness. While the flowers and leaves are less dangerous, the seeds pose the greatest threat. Homeowners should monitor their trees for developing pods, especially in areas accessible to children or pets. To mitigate the risk, mature pods should be removed and safely discarded before they open and the seeds drop. If accidental ingestion is suspected, immediate medical attention is necessary.