Reasons for the Blackening and Drying of Azalea Leaves
As one of the top ten famous traditional Chinese flowers, azaleas are deeply loved by horticulture enthusiasts for their colorful blooms. However, when azalea leaves show signs of blackening and drying, it often leaves caretakers at a loss. This article will systematically analyze four key causes and provide targeted solutions.
I. Environmental Factors Leading to Leaf Lesions
Humidity Control Imbalance
Azaleas are typical moisture-loving plants, requiring a constant air humidity of 60%-70%. During the winter heating period in the north, when humidity drops below 40%, the cuticle layer of the leaves may experience dehydration damage, initially showing as leaf margin necrosis, and later developing into complete blackening. It is recommended to use the "Three-Step Moisture Increase Method": morning misting (avoiding the flowers) + saucer water culture + combination use of a humidifier.
Abnormal Light Intensity
In spring and autumn, azaleas can tolerate 4-6 hours of soft light, but when the UV index exceeds 5 between 10:00-15:00 in summer, the leaves can suffer photo-oxidative damage. Observations show that leaves exposed to strong light develop brown spots first, followed by complete carbonization. It is recommended to adopt a double-layer shading scheme: an outer layer of 30% shading rate shade net + inner layer of gauze filtering.
II. Abnormal Growth System Inducing Lesions
Air Circulation Obstruction
Enclosed environments can lead to CO2 concentrations below 300ppm, while hindered transpiration causes cellular metabolism disorders. Experimental data shows that in a wind speed environment of 0.3m/s, the photosynthetic efficiency of azaleas increases by 27%. It is recommended to implement the "3+3 Ventilation Method": open windows at least 3 times a day, each lasting for 30 minutes, and be careful to avoid direct drafts.
Pathogen Infection Mechanism
(T-J) disease and leaf spot disease are the main pathogens, visible under a microscope as mycelium spreading within leaf mesophyll cells. Initial symptoms are needle-like black spots, which expand into irregular patches within 7-10 days. It is recommended to alternate between biological agents and chemical pesticides for control: Bacillus subtilis (1:800) and tebuconazole (1:1500) every 10 days.
By systematically adjusting humidity, light, and ventilation, combined with scientific disease control, azaleas can recover their lush green leaf color. It is recommended to conduct monthly leaf inspections and use a ferrous sulfate solution with a pH of 5.5-6.0 for root irrigation to fundamentally enhance the plant's resistance, allowing azaleas to regain their extraordinary beauty as the "Queen of Flowers in the West."