What to Do When the Leaves of White Magnolia Turn Yellow and Wither
As the city flower of Shanghai, the white magnolia is deeply loved by horticulture enthusiasts for its pure white and elegant appearance. However, yellowing and withering of leaves often occur during maintenance, directly affecting the ornamental value and healthy growth of the plant. This article will systematically analyze the five main causes of yellowing leaves in white magnolias, from pest and disease control to daily maintenance.
Analysis of the Five Main Causes of Yellowing Leaves in White Magnolias
1. Infestation by Red Spider Mites
If a red spiderweb-like substance appears on the back of the leaves, it is highly likely to be an invasion by red spider mites. These piercing-sucking insects, only 0.5 millimeters long, absorb the sap from the leaves through their mouthparts, causing chlorophyll loss and forming yellow spots. It is recommended to use a combination of Abamectin and螺螨酯 (Spinosad) pesticides, focusing on spraying the back of the leaves, and applying treatment every 7 days.
2. Fungal Infection Causing Chlorosis
Caused by Fusarium, a systemic disease, initially showing irregular yellow spots between the veins, and later the entire leaf turns brown and crispy. Diseased leaves should be promptly removed, and the root zone should be treated with a solution of Mancozeb at 800 times dilution, combined with Pyraclostrobin foliar spray for double protection.
3. Soil Alkalinity Imbalance
White magnolias thrive in a slightly acidic environment with a pH of 5.5-6.5. When the soil pH is greater than 7.2, iron fixation occurs. Applying a 0.2% ferrous sulfate solution to the roots monthly, combined with using decomposed pine needle soil, can effectively adjust the soil pH.
4. Improper Watering Management
Fleshy roots are susceptible to both waterlogging and drought. Maintain soil moisture at 60% (clumps when held, crumbles when dropped) in spring and autumn, water twice a day in summer, and control water in winter to keep the soil slightly dry. It is recommended to use a ceramic pot with a volcanic stone layer to enhance drainage.
5. Deficiency of Nutrient Elements
Lack of magnesium causes yellowing between the veins of old leaves, while lack of nitrogen results in yellowing of new leaves. Applying a special orchid fertilizer (N-P-K=20-20-20) once a month during the growing season, combined with foliar application of chelated trace element fertilizers, can comprehensively supplement nutrition.
Key Points for Daily Maintenance of White Magnolias
In addition to targeted treatment, it is necessary to ensure 4 hours of scattered light daily and maintain an ambient temperature of 8℃ or above in winter. Replace the pot and prune the roots early each spring, removing 1/3 of the old roots to promote the development of new roots. Regularly wipe the leaf surface with a damp cloth to increase photosynthetic efficiency and facilitate the observation of pests and diseases.
Through scientific diagnosis and maintenance, the leaves of white magnolias can gradually recover their green color within 2-3 weeks. It is recommended to establish a maintenance log, recording watering and fertilizing times, to form a systematic plant health management plan, ensuring that this "jade tree" remains vibrant.