Methods for controlling yellowing of chrysanthemum leaves

The yellowing of chrysanthemum leaves may be caused by multiple factors such as environment, care, or diseases. Below are specific prevention and treatment methods along with corresponding cause analysis:

---

1. Excessive light exposure causes yellowing.
- Reason: Strong sunlight in summer causes leaf scorch, resulting in withering and yellowing.
- Prevention and Treatment Methods:
- Move the chrysanthemum to a semi-shaded environment, avoiding direct sunlight at noon.
- Use shade nets or curtains for shading.

---

2. Improper watering causes yellow leaves
1. Overwatering
- Symptoms: Soil waterlogging causes root rot, tender leaves turn dark yellow and lack luster, and new shoots wilt.
- Prevention and Control Methods:
- Loosen the soil immediately and enhance ventilation to accelerate moisture evaporation.
- If the situation is serious, new soil needs to be replaced and rotten roots should be pruned.

2. Long-term water shortage
- Symptoms: The lower leaves gradually dry and turn yellow before falling off.
- Prevention and Control Methods:
- Follow the principle of "seeing dry and wet", and water thoroughly in the summer mornings or evenings.
- Avoid watering during high temperatures at noon.

---

3. Excessive or insufficient fertilization
1. Over-fertilization
- Symptoms: Root burn due to excessive fertilization, overall yellowing of the leaves.
- Prevention and Control Methods:
- Stop fertilizing and increase watering to dilute the fertilizer.
- Soil replacement treatment in severe cases.

2. Lack of Fertilizer
- Symptoms: Leaves are thin and yellow, and the plant grows slowly.
- Prevention and control methods:
- Apply diluted fermented soybean cake liquid or potassium dihydrogen phosphate every 10 days.
- Pay attention to "thin, fat, and diligent application"; it can be appropriately concentrated during the budding stage.

---

4. Soil Issues
1. Alkaline soil
- Symptoms: The entire plant or lower leaves turn yellow, and the soil becomes compacted.
- Prevention and control methods:
- Water used for washing rice that has been fermented or rainwater to adjust pH levels.
- Replace with loose, breathable acidic soil (pH value recommended ≤7.5).

2. Soil compaction or nutrient deficiency
- Symptoms: Poor root development due to not changing the soil for a long time.
- Prevention and control methods:
- Change the soil every 1-2 years, trim the old roots and disinfect.
- Add organic fertilizer to improve soil fertility.

---

5. Disease Infection
1. Leaf blight
- Symptoms: Brown spots appear on the leaves, gradually wilting and falling off.
- Prevention and control methods:
- Remove and destroy diseased leaves to prevent spread.
- Spray a 500-fold solution of mancozeb or zinc mancozeb every 15 days.

2. Wilt Disease
- Symptoms: the whole plant or half of it wilts, and the roots turn black and rot.
- Prevention and treatment methods:
- Avoid continuous cropping; disinfect the soil with copper acetate or chlorothalonil before planting.
- Control the watering frequency to prevent a high temperature and high humidity environment.

---

6. The Impact of Pests
- Common pests: aphids, red spiders, etc.
- Prevention and Treatment Methods:
- Regularly check the plants, and use biological pesticides (such as dichlorvos and cypermethrin) to spray and kill pests in a timely manner.
- Manually remove pests and improve the environment with ventilation.

---

Comprehensive Management Recommendations
| Type of Issue | Typical Symptoms | Prevention and Control Measures | Reference Source |
|--------------------|----------------------------|----------------------------------|--------------|
| Overwatering | Tender leaves turn dark yellow, roots rot | Loosen soil for drainage, replace with new soil | |
| Alkaline soil | Whole plant leaves yellowing | Use rice water to adjust pH, replace with acidic soil | |
| Leaf Blight | Brown spots on leaves, wilting and falling off | Spray with Mancozeb, prune diseased leaves | |
| Excessive fertilization | Leaves overall yellowing | Stop fertilizing and dilute with water, change soil treatment | |
| Excessive Light | Leaf Burn and Withering | Shade Treatment, Move to Semi-Shaded Environment | |

By making targeted adjustments to care measures, the yellowing of chrysanthemum leaves can be effectively improved, and the healthy growth of the plants can be restored.