The most beautiful, profusely flowering rhododendrons will be etched in the memory of everyone who has ever seen them for a long time. But often all the leaves of your favorite rhododendrons turn yellow. Responsible gardeners should be clear about the causes and how to correct this problem. Only in this case will the plants actively develop and be able to please their owners for many years without any problems.
Causes of yellowing
Many factors influence plant health.Therefore, the reasons for yellowing of the foliage of rhododendrons are different.
Failure to comply with watering rules
Rhododendron is a moisture-loving plant. Therefore, with irregular and insufficient watering, especially in the hot season, the leaves become lethargic, quickly turn yellow and partially fall off. It is necessary not to overwater the rhododendron, otherwise the root may simply rot. When water stagnates, yellowing of the foliage is also observed.
Lighting
Rhododendrons, especially those growing in the southern regions, suffer from intense solar radiation in the summer. The leaves are the first to signal a problem - they turn yellow and dry out. They are shaded using shade nets, dense agrofibre or sheets of colored polycarbonate. Rhododendrons grow best in partial shade.
Wrong soil
Rhododendron belongs to the extensive Ericaceae family and requires acidic soil to grow. Only then will the plant be able to absorb nutrients from the soil. Typically, the soil for Heathers consists of acidic high-moor peat and rotted pine litter. To maintain the required level of acidity, the soil is regularly acidified. Citric acid, colloidal sulfur, and electrolyte are used.
Damage to the root system
The rhododendron root system is fibrous and is located in the top layer of soil. It is sensitive to damage and does not have strong growth. During agricultural activities (loosening, weeding) it is easily damaged. This will cause the foliage to turn yellow. Overheating the soil during the hot summer months will also cause the foliage to change color.
The solution is shading plants or planting large trees in the diffuse shade. A good option would be to plant under conifers. Mulching the soil will help save the root system from overheating and excessive evaporation of moisture.Suitable acidic (high-moor) peat, moss, softwood sawdust and pine needles.
Pests
Pests cause many problems to cultivated plants; unfortunately, rhododendrons are no exception. And often, pest damage is one of the reasons for yellowing of leaves.
Rhododendron bug
When affected by this pest, the leaves lose their usual color and become light, pale, and later acquire a yellowish tint. With severe damage, the leaves curl and then fall off. Sticky traces of insect excrement are visible on the underside of the leaf. Insecticides BI-58 and Karbofos are used for control. Moreover, several treatments should be carried out.
Mealybug
This pest actively reproduces in warm and dry conditions; high humidity prevents its reproduction. Mealybugs resemble small balls of cotton wool. They attach to the surface of leaves and settle in their internodes.
It is important before chemically treating the plant to try to mechanically clean all affected parts of the scale insects. Use cotton swabs and soapy water. And only then should it be sprayed with a systemic insecticide; Aktara and Konfidor are suitable.
Aphid
When attacked by such a common pest as aphids, rhododendron leaves gradually lighten and acquire a yellowish tint. Aphids usually settle on the underside of the leaf. Control measures - spraying insecticides – Actellik, Nurel D, Konfidor.
Black thrips
When infested with thrips, the upper surface of the leaves becomes covered with grayish holes, and the bottom with black holes. The affected areas become gray, then turn yellow and fall off en masse. Control measures - spraying with an insecticide solution
Khrushchev
The root system can also be damaged by such a dangerous pest as the larva of the May beetle (Khrushchev). This leads to yellowing and falling leaves. If the damage is severe, even the shoots dry out.
Diseases
Rhododendrons are often affected by various diseases, and this is often the cause of yellowing and falling leaves.
Septoria
It is the most dangerous fungal disease of rhododendrons. With septoria, small red spots appear on the leaves, which quickly increase in size and become lighter. Then the foliage turns yellow, dries out and falls off. Without timely help, rhododendron may be left completely without foliage. The fight against it is the removal of the diseased part of the bush, as well as treatment with fungicides, for example, Ridomil Gold is often used.
Chlorosis
In many plants, including rhododendrons, the cause of yellowing of foliage is non-infectious chlorosis. This is especially evident in the spring, at the beginning of the season. Chlorosis occurs when there is a deficiency of nitrogen and iron in the soil. With chlorosis, the foliage becomes light, yellowish in color or covered with spots of a characteristic shade.
Fusarium
Dangerous fungal disease of the root system. When affected by rot, the leaves first turn yellow and dry out, then the shoots dry out.
Requires quick treatment using fungicides, otherwise the plant will quickly die.
What is this process
Yellowing of leaves in rhododendrons (azaleas) can occur both due to natural biological reasons and as a result of improper agricultural practices. It is especially dangerous if the change in leaf color is accompanied by the appearance of various spots. This will most likely be the beginning of a disease or pest attack.
If they turn yellow in the fall
Changing color in autumn is a completely natural process.Depending on the variety, rhododendron foliage turns yellowish, brown or red. In this case, the gardener should not worry, but needs to carry out sanitary cleaning by removing all dried leaves and twigs.
If the stem has yellowed
If the stem of a rhododendron begins to turn yellow, then, in most cases, you need to pay attention to the plant’s nutritional pattern. It is advisable to use special fertilizers for Heathers; In addition to fertilizing, they also acidify the soil.
Prevention
For prevention, it is necessary to carry out systematic spraying, as well as spilling drugs against diseases and pests. It is necessary to monitor the frequency of watering, while at the same time avoiding overflow.
And, of course, maintaining the right soil acidity, as well as shading during the hot summer months, will help keep the foliage healthy and green.
