Common Diseases and Pests of Rhododendron
The editor answers questions for everyone about the experience of growing rhododendron at home, common diseases and pests of rhododendron, let's take a look together!
There are some common diseases and pests of rhododendron that lovers of growing flowers can prevent and treat according to specific situations.
I. Red Spider Mite
1. Symptoms: Mainly吸食the sap of the plant and cause grayish-white spots on the leaves. Severe cases can lead to yellowing and falling off of the leaves. Poor growth of new shoots and weakened plant vigor.
2. Incidence Pattern: It is particularly severe during June to August when it is hot and dry, but the damage is lighter during heavy rain and rainy weather.
3. Control Methods: In winter, remove withered branches and fallen leaves to eliminate overwintering adults. In March, when damage starts to occur, use a 10% Emperor Star Emulsion diluted 1000 times, 7051 insecticide (Miechongling) diluted 3000 times, or Pyridazine (速螨酮) diluted 1000 times to spray and kill.
II. Iron Deficiency Chlorosis
Iron deficiency chlorosis of rhododendron is also known as yellow leaf disease or chlorosis, which is a common disease in potted rhododendron everywhere.
Symptoms: This disease often occurs on the tender new leaves. Initially, the mesophyll between the veins turns greenish, loses its luster, and gradually turns yellowish-white, but the veins remain green, giving the leaves a net-like green pattern. Subsequently, the degree of yellowing gradually worsens, with the entire leaf turning yellowish or yellowish-white, and in severe cases, the edges and margins of the leaves turn brown and crispy inward.
Causes of Disease: Iron deficiency chlorosis of rhododendron is a physiological disease, mainly caused by a lack of iron in the soil or iron not being absorbed and utilized, thus affecting the synthesis of chlorophyll and turning the leaves yellow-green. Under normal circumstances, the following situations can occur: in calcareous alkaline soil, the soluble ferrous iron that can be used is converted into insoluble ferric salts and precipitates, preventing the roots from absorbing it; frequent watering of potted flowers causes excessive leaching and loss of soluble iron in the soil; in areas with heavy soil, poor drainage, or high groundwater levels, the development of the plant roots is affected, and normal physiological activities of the roots cannot take place, reducing the ability of the roots to absorb iron.
Control Methods: Rhododendron prefers acidic soil and dislikes alkaline soil, so avoid planting it in alkaline or calcareous-rich soil. When planting in open ground, do not plant near concrete, brick walls, or places where lime has been used. For potted rhododendron, use acidic soil, and if the soil is slightly alkaline, replace it with acidic soil. For rhododendron planted in nurseries, apply compost, green manure, or other organic fertilizers, which produce organic acids that can dissolve insoluble iron in the soil, making it easier for the plant to absorb. Alternatively, mix ferrous sulfate with fertilizer, with the following formula: 2.5-3 kg of ferrous sulfate, 5-7.5 kg of oil cake, 10-15 kg of manure, and 200-250 liters of water. Mix well and let it rot into black before use. This method is effective. In alkaline soil, pour a 0.1-0.2% solution of potassium dihydrogen phosphate, which has a pH of 4.7 and can convert alkaline soil to acidic soil, thereby treating the yellowing of young leaves. Potassium dihydrogen phosphate also contains phosphorus and potassium elements, which are beneficial for flowering and increasing flower yield. Regularly applying ferrous sulfate solution can lead to excessive sulfur and available iron in the soil, causing plant poisoning. Use 0.14 grams of EDTA disodium and 0.1 grams of pure ferrous sulfate, mixed into 500 milliliters of tap water, and spray on the leaves. Spray both sides of the leaves every 3 days, several times for good results.
III. Grey Mold Disease
Symptoms: Grey mold disease occurs on the leaves and flowers of rhododendron. Frost damage is often a trigger for leaf disease. In spring, rhododendron flowers grown indoors and outdoors often become infected with grey mold disease. Initially, necrotic spots appear on the petals, which quickly expand and connect to form large lesions. Under high humidity, a large amount of grayish conidia layer is produced on the affected area, hence the name grey mold disease.
Causal Agent: Grey Mold [Botrytis cinerea Pers.ex Fr.] belongs to the Deuteromycetes. The fruiting bodies of the pathogen grow from mycelium or sclerotia. The conidiophores are tufted, gray, and later turn brown, with ovoid conidia. Its sexual generation is Botryotinia ****eliana (de Bary) Whetze, which belongs to the Ascomycetes.
The above is the full content of common diseases and pests of rhododendron, hoping it is helpful to green plant enthusiasts!