Key Points for Integrated Disease Control Techniques for Azaleas in Summer
Besides the "large-flowered azalea," there are other varieties of azalea, such as the Japanese azalea and the Belgian azalea. The former belongs to the East Asian azalea group, while the latter belongs to the Western azalea group, and both are suitable for pot cultivation; however, if daily cultivation is improper and care is neglected, the following diseases are likely to occur:
1. Black spot disease - If the location where azaleas (including large-flowered azaleas and various Western azaleas) are placed is stuffy and unventilated, and is also kept in shade for a long time, then when humid weather occurs, or when daily watering is excessive, this disease is easily triggered; it is caused by a fungus and spreads through the air.
If the air in the surrounding environment where they are cultivated is polluted, it is also easy for spots to form on the leaves. The fungal spores will fall into the potting soil and first grow hyphae on old and weak leaves, spreading quickly and causing the leaves to fall off from the bottom upward.
2. Brown spot disease - During the plum rain season, with high temperatures and high humidity, small brown spots easily form on the leaves, causing the leaves to turn yellow, dry out, wrinkle, and then drop. The usual control method is the same as for dealing with black spot disease: increase stronger scattered light and move the plants to a well-ventilated and drier place. For chemical treatment, use "Thiophanate" at 800 times dilution, or "Zhibao" at 1,000 times dilution.
3. Chlorosis - It is caused by iron deficiency and insufficient trace elements, or by the planting soil being too alkaline; you can bury a few rusty iron nails in the soil, or sprinkle a little ferrous sulfate into the pot, 1 gram each time.
4. Stem rot - Damp and cloudy weather allows fungi to invade the cortex, cutting off the transport channels for water and nutrients, and the leaves dry up. In daily care, appropriately increase potassium fertilizer, increase light, and move the plants to a well-ventilated place.
Causes and Control of Azalea Diseases in Spring and Summer
Besides “large-flowered azalea,” there are other varieties of azalea, such as the Japanese azalea and the Belgian azalea. The former belongs to the East Asian azalea group, while the latter belongs to the Western azalea group, and both are suitable for pot cultivation; however, if daily cultivation is improper and care is neglected, the following diseases are likely to occur:
(1)Black spot diseaseIf the location where azaleas (including large-flowered azaleas and various Western azaleas) are placed is stuffy and unventilated, and is also kept in shade for a long time, then when humid weather occurs, or when daily watering is excessive, this disease is easily triggered; it is caused by a fungus and spreads through the air. If the air in the surrounding environment where they are cultivated is polluted, it is also easy for spots to form on the leaves. The fungal spores will fall into the potting soil and first grow hyphae on old and weak leaves, spreading quickly and causing the leaves to fall off from the bottom upward.
(2)Brown spot diseaseDuring the plum rain season, with high temperatures and high humidity, small brown spots easily form on the leaves, causing the leaves to turn yellow, dry out, wrinkle, and then drop. The usual control method is the same as for dealing with black spot disease: increase stronger scattered light and move the plants to a well-ventilated and drier place. For chemical treatment, use “Thiophanate” at 800 times dilution, or “Zhibao” at 1,000 times dilution.
(3)Chlorosis
Causes
1. Light: The direct cause of leaf yellowing is a lack of chlorophyll, and the formation of chlorophyll requires light; only sufficient sunlight can make the leaves show normal green. Insufficient light causes the leaves to turn yellow, and at the same time the branches become thin and weak.
2. Nutrient elements: The formation of chlorophyll requires elements such as iron, copper, magnesium, and nitrogen. When these nutrient elements are deficient, chlorosis occurs. However, copper and magnesium deficiency generally does not occur in soil; the common deficiencies are iron and nitrogen.
3. pH: Because the soil or water is on the alkaline side, the plant may also develop chlorosis. When alkalinity increases, that is, when the pH value rises, it severely affects the root system's absorption of nitrogen and iron, leading to iron and nitrogen deficiency and thus chlorosis, manifested as leaves gradually yellowing and dropping from the bottom upward.
4. Soil: Poor water permeability of the soil can also cause chlorosis.
5. Fertilizer damage: The azalea root system is as fine as silk and has very strict requirements for fertilizer concentration. Fertilizer water must be dilute; if it is too concentrated, the plant will show stunted growth, thin leaves, pale yellow leaf color, sudden or gradual leaf drop, and even death.
1. For iron deficiency chlorosis, supplement the iron element in the soil. Ferrous sulfate can be sprinkled around the potting soil, applying 1 to 2 grams each time depending on the pot size, and then water to dissolve it into the soil. It can also be dissolved in water for irrigation at a concentration of 1%, once a week, for several consecutive times, until recovery.
2. For soil and water that are on the alkaline side, first acidify the water (the pH value can be measured with pH test paper). The simplest method is to use vinegar to neutralize the alkalinity of the water so that the pH value is between 5 and 6. For soil improvement, the method is the same as using ferrous sulfate to control iron deficiency chlorosis.
3. For chlorosis not caused by a simple deficiency of a certain element, but by improper management leading to a disorder of the physiological functions of the azalea, that is, comprehensive chlorosis. At this time, first, fertilization should be stopped immediately, and ferrous sulfate should not be applied too much either, otherwise it is like adding frost to snow. After new roots grow out and the leaf color turns green, a stable period is still needed, and fertilization can only be carried out after the new branches have become woody; otherwise the old disease may recur. Second, do not waterlog. Improve soil permeability, control the amount of water used, and keep the potting soil moderately dry and wet, that is, “dry but not cracked, moist but not wet,” to promote the production of new roots. Third, do not expose to the sun. Because the root system of diseased plants is weak and the leaves are fragile and easily wilt, special attention should be paid to shading during the strong-light and high-temperature seasons of summer and autumn, but it should not be excessively dark; especially in winter and spring and late autumn, light should be appropriately increased to facilitate photosynthesis. Fourth, avoid the plant flowering. Diseased plants bloom poorly, and the flower buds should be removed in time to avoid consuming nutrients.
(4)Stem rotBecause of damp and cloudy conditions, fungi invade the cortex, cutting off the transport channels for water and nutrients, and the leaves dry up. In daily care, appropriately increase potassium fertilizer, increase light, and move the plants to a well-ventilated place.
Integrated Pest and Disease Control in Specialized Azalea Gardens
Because azaleas have many flower colors and varieties, abundant flowers and lush leaves, and a long flowering period, in recent years they have been planted in large patches in plazas and roadside landscape belts, playing an obvious beautifying role. However, they are also easily attacked by dozens of pests and diseases and lose their ornamental value. Over the years, many units have spent a great deal of manpower and material resources on control, but often fail to achieve good results. The reason is mainly that they have not truly put prevention first. Through three years of investigation and research, we have explored some integrated control methods. 1. Selection of planting siteAzaleas are shade-loving plants, and direct sunlight is unfavorable to their growth, so specialized azalea gardens should preferably be chosen in places shaded by tree shadows, or when doing greening design, this point should be taken into consideration and trees should be intentionally arranged in the specialized garden.
2. Soil
Azaleas prefer acidic soil with good drainage, but because specialized gardens and landscapes all need to use cement for roads and paving, the soil in azalea planting sites becomes compacted and severely alkaline, so the soil at the planting site must be replaced and a certain amount of peat soil added.
3. Planting of azaleas
Azaleas are most suitable for planting in early spring or late autumn. If planted in other seasons, a shade shed must be set up. When planting, the root system and soil must be made even and firm, but not too compacted, and the soil surface near the root crown should be shaped in an arc, which can both protect the shallow root system of the plant from severe cold and freezing damage and facilitate drainage.
4. Daily management of azaleas
4.1 Watering
The azalea's requirement for soil dryness and moisture is moist but not wet. Generally, in spring and autumn, open-ground planted azaleas can be given a thorough watering every 2—3 days, and in hot summer, at least once a day. In daily watering, never use alkaline water, and also note that the water temperature should not be too cold, especially in hot summer, because watering thoroughly with too-cold water causes the soil temperature to drop suddenly, affecting root water absorption and disturbing the plant's physiological balance.
4.2 Misting
Azaleas like an environment with high air humidity, but some specialized azalea gardens are built in plazas or on both sides of roads, where air flows quickly and is relatively dry, so it is necessary to frequently spray water on azalea leaves or mist the surrounding air, keeping the air around the azalea garden moist, which is beneficial to the growth of azaleas.
4.3 Fertilization
At the end of winter and beginning of spring each year, it is best to apply some organic fertilizer to the azalea garden as a base fertilizer. After azaleas bloom in April—May, because the plants consume a large amount of nutrients during the flowering period, as leaf buds sprout and new shoots extend, a topdressing can be applied about every 15 days. After the beginning of the dog days, most branch tips have stopped growing; this is the high-temperature season, physiological activity weakens, and topdressing can be stopped. After autumn, the climate gradually becomes cooler, and there are often continuous autumn rains; the temperature and humidity are suitable for azalea growth, and at this time the last topdressing can be applied. After winter begins, fertilization is generally not suitable.
4.4 Pruning
Pruning and branch training are important measures in daily maintenance and management work. They can regulate growth and development, thereby making growth vigorous. Daily pruning requires cutting off a small number of diseased branches and slender old branches, and removing some overly dense branches according to the crown shape to increase ventilation and light penetration, which is beneficial to plant growth. Specialized azalea gardens must be inspected frequently, and dead branches and diseased branches should be removed in time when found, to reduce the spread of pests and diseases among azaleas.