Control Methods for Iron Deficiency Chlorosis in Azaleas

Azalea iron deficiency chlorosis, also known as yellow leaf disease or chlorosis, is a common disease of potted azaleas in various regions.

Symptoms

This disease mostly occurs on young leaves of new shoots. In the early stage, the mesophyll between the veins loses its green color and luster, then gradually turns yellow-white, but the veins remain green, making the green on the leaves appear in a net-like pattern. Subsequently, the degree of yellowing gradually intensifies, and except for the larger veins, the entire leaf turns yellow or yellow-white. In severe cases, the leaf tips and leaf margins wither and scorch inward.

Causes

Azalea iron deficiency chlorosis is a physiological disease, mainly caused by a lack of iron in the soil or the inability of iron to be absorbed and utilized, thereby affecting the synthesis of chlorophyll and turning the leaves yellow-green.

Under normal circumstances, the following situations may occur: In calcareous alkaline soil, the available soluble ferrous iron is converted into insoluble ferric salts and precipitated, so that the roots cannot absorb it; frequent watering of potted flowers causes excessive leaching and loss of soluble iron in the soil; in areas with heavy clay soil, poor drainage, or a high water table, the development of the plant root system is affected, the normal physiological activities of the roots cannot proceed, and the ability of the roots to absorb iron is reduced.

Control Methods

Azaleas prefer acidic soil and fear alkaline soil, so avoid planting them in alkaline soil or soil containing a large amount of calcium; when planting in open garden beds, do not place them near cement, brick walls, or places where lime has been used. Potted azaleas should use acidic soil, and if the soil is somewhat alkaline, acidic soil can be added or replaced; when planting azaleas in nursery fields, compost, green manure, or other organic fertilizers can be applied. The organic acids produced by these fertilizers can dissolve insoluble iron in the soil, making it easier for the plants to absorb.

Alternatively, ferrous sulfate can be mixed into the fertilizer for application. The preparation is: ferrous sulfate 2.5-3 gong, oil cake 5-7.5 gong, manure 10-15 kg, water 200-250 jin. After mixing, wait until it decomposes and turns black before use. This method has good results.

In slightly alkaline soil, a 0.1-0.2% potassium dihydrogen phosphate solution can be watered on. The pH value of this solution is 4.7, which can turn alkaline soil into acidic soil, thereby treating the yellowing of young leaves. At the same time, potassium dihydrogen phosphate also contains phosphorus and potassium elements, which are beneficial for flowering and increasing flower quantity.

Frequently applying ferrous sulfate solution can cause excessive sulfur and available iron in the soil, poisoning the plant. To avoid this, 0.14 g of disodium edetate and 0.1 g of ferrous sulfate (chemically pure) can be mixed and dissolved in 500 mL of tap water for foliar spraying. Both the front and back of the leaves should be sprayed, once every 3 days, for several consecutive times, which can achieve good results.