Culture Methods and Pest and Disease Control for Potted Azaleas (Rhododendron) on Family Balconies
Azalea is one of China's top ten famous flowers, admired for both its blooms and foliage, suitable for both ground planting and pot culture, and extremely versatile. Many people grow it on family balconies, so do you know what the culture methods are for potted azaleas on family balconies? How do you control common pests and diseases? What should you do if the leaves dry up?
I. Culture Methods for Potted Azaleas on Family Balconies
1. Growing medium
When growing azaleas at home, the soil must be mentioned. The reason azaleas often show yellow leaves in the second year and die in the third year is mostly due to alkalinization of the growing medium. Azalea is a typical acid-loving flower, and a soil pH of 5.5-6.5 is most suitable. Therefore, when choosing a growing medium for potted azaleas, be sure to choose an acidic soil with good permeability and rich in humus.
Soil in the south tends to be acidic, so you can dig red mountain soil from the hills for planting. Soil and water in northern regions tend to be hard, so it is recommended to mix leaf mold with pine needles yourself, or you can buy azalea-specific soil.
2. Fertilizing
Azaleas do not like heavy fertilizer, and especially dislike raw or concentrated fertilizer, so stop pouring leftover tea water, milk and the like into azalea pots. During fermentation this can easily cause massive yellowing and leaf drop in azaleas.
Adding an appropriate amount of slow-release fertilizer to the potting soil is a good choice for growing azaleas. For regular topdressing, decomposed soybean cake water can be used.
It should be noted that azaleas should frequently be given acidic fertilizer to regulate soil acidity and alkalinity. Applying ferrous sulfate fertilizer once a week can effectively alleviate the problem of soil alkalinization. This is especially true in northern regions.
3. Watering
When it comes to watering, no matter what flower it is, there is one principle: water thoroughly only after the soil has dried out. But azaleas always seem to need relatively more water, and different azalea varieties have different water requirements. If there is not enough water, the leaf edges easily turn yellow and curl, and leaves drop. Therefore, during care, observe carefully and adjust watering times promptly.
4. Light
Azalea is a shade-tolerant flower that likes light but fears strong light. In late spring, summer and early autumn, attention should be paid to shading, or the plant should be placed on a north-facing balcony at home for care.
5. Air humidity
Azaleas need relatively more water, but when watering there must not be waterlogging, otherwise the roots will rot, so increasing air humidity becomes very necessary. Southern regions are relatively humid and this can basically be ignored, but northern regions have a dry climate, so attention should be paid to frequently misting the plant and the area around it to increase air humidity.
II. How to Control Common Azalea Pests and Diseases
Azalea brown spot disease
1. Symptoms: Azalea brown spot disease is also called leaf spot disease. At first, small pale yellow round spots appear on the leaves, gradually expanding into irregular shapes, and the lesions turn light reddish brown with a dark brown center. Diseased leaves drop prematurely, and in severe cases plant growth is stunted. When examining diseased leaves, small black granules can be found on the lesions; these are the pathogen's pycnidia. Azaleas grown in greenhouses develop severe disease, and the condition is worse when humidity is high.
2. Pathogen: Septoria azaleae Vogl. belongs to the Deuteromycotina. The pathogen overwinters as mycelium and pycnidia in host plant tissues or on fallen leaves, and the following year large numbers of conidia are produced on diseased leaves and spread to cause damage.
3. Control methods: In winter and spring, promptly sweep up and burn fallen leaves. After the plant leafs out, spray Bordeaux mixture (1:1:100) once every half month, for 2-3 consecutive sprays, to prevent disease. In the early stage of disease, spray 50% thiophanate-methyl wettable powder at 1000 times dilution 1-2 times to inhibit disease development.
Azalea lace bug
1. Symptoms: Both adults and nymphs gather on the underside of leaves to pierce and suck sap. The underside of damaged leaves shows a black sticky substance that looks like splatter stains. This feature makes it easy to distinguish from other sap-sucking pests. The entire underside of damaged leaves becomes rusty yellow, while the upper surface forms many pale spots. When damage is severe, the spots merge into patches, so that the whole leaf loses its green color and looks pale from a distance, leaves drop early, and flower buds no longer form.
2. Morphological characteristics: Adults are about 3.5 mm long, flat in shape, and dark brown. Antennae are filiform, with 4 segments. The center of the pronotum is longitudinally raised and extends backward into a leaf-like process, and both sides of the pronotum protrude outward into feather-like structures. The forewings are slightly rectangular. The forewings, both sides of the pronotum, and the leaf-like processes on the dorsum all have very uniform reticulate markings. At rest, the forewings fold together, and when viewed from above the entire body resembles an "X" shape made of multiple wings. Eggs are long oval, curved at one end, about 0.6 mm long, light green and semi-transparent when first laid, later turning light yellow. Larvae are milky white when newly hatched, gradually turning dark brown, about 1.9 mm long. By the 3rd instar the wing pads are obvious and the appearance resembles the adult, with obvious conical spines on both sides of the prothorax, mesothorax and abdominal segments 3-8.
3. Life history and habits: The number of generations per year is 4-5 in the Yangtze River basin and 3-4 in North China. In all regions, adults overwinter in dead branches, fallen leaves, weeds, bark cracks, and gaps in soil and stones. In early to mid-April, overwintering adults begin activity and gather on the underside of leaves to feed and lay eggs. Eggs are laid within leaf tissue and covered with a yellow-brown gelatinous substance, with the egg stage lasting about half a month. Most newly hatched nymphs gather on both sides of the main vein to cause damage. Nymphs molt 5 times and become adults after about half a month. First-generation adults appear in early June, and subsequent generations occur respectively in mid-July, early August, and late August to early September. Because the adult stage is long and the egg-laying period is long, generations overlap and all stages often exist at the same time. Damage is heaviest in July-August, pest density is highest in September, and from late October they gradually overwinter. Adults like to be active at noon. The number of eggs laid by each female adult varies with the host, ranging from dozens to over a hundred, laid in batches, often several to dozens adjacent to one another, with a small black dot slightly depressed in the center on the outside of each egg-laying site.
4. Control methods: In winter, thoroughly clear fallen leaves and weeds around potted flowers and bonsai gardens. For plants with thicker and rougher stems, apply white wash. The period from the emergence and activity of overwintering adults to the beginning of hatching of first-generation nymphs is the most favorable time for chemical control. Spray 50% fenitrothion at 1000 times dilution, or 40% omethoate at 1000-1500 times dilution, or 10-20% pyrethroid insecticides at 1000-2000 times dilution, once every 10-15 days, for 2-3 consecutive sprays.
Azalea root rot
1. Symptoms: Water-soaked brown spots and soft rot appear on the roots, followed by rotting and peeling of the bark. The xylem turns dark brown, and the bark gradually turns gray-white and spreads step by step, "then expands until the entire cortex of the trunk dies, cutting off the transport of nutrients and water, causing the tender leaves at the top to gradually dry up, and the branches and leaves to wilt, lose water and dry up from top to bottom, until the whole plant dies.
2. Occurrence pattern: Root rot is a soil-borne disease caused by Fusarium fungi, mostly occurring at the root collar of azaleas, because these parts are often moist and lack sunlight, and Deuteromycotina Fusarium fungi are highly active there. Once they invade the cortex, rot soon follows.
3. Control methods: Deuteromycotina Fusarium fungi survive on plant residues in the soil and can remain infectious for several years when they encounter a suitable host. Alkaline soil, high humidity and relatively high temperatures all favor the development and spread of the disease, so after diagnosis, dead plants and potting soil should be dealt with promptly.
For nearby plants, the whole plant can be soaked or drenched with 0.1% potassium permanganate, then rinsed with clean water before repotting, and the potting soil can first be drenched with 70% thiophanate-methyl at 1000 times dilution.
Attention should be paid to improving site ventilation, increasing light in the morning and evening, and applying more potassium fertilizer to improve disease resistance.
Around May each year, apply thiophanate-methyl at 200 times dilution to the main trunk, once every 7 to 10 days, for three consecutive applications, to prevent infection.
Azalea red spider mite
1. Symptoms: It mainly sucks plant sap and causes gray-white spots on leaves. In severe cases it causes leaves to turn yellow and drop. New shoot growth is poor and tree vigor weakens.
2. Occurrence pattern: Damage is especially severe during high temperature and drought from June to August, but lighter during heavy rain and rainy weather.
3. Control methods: In winter, remove dead branches and fallen leaves to eliminate overwintering adults. When damage begins in March, spray 10% Tianhuangxing emulsifiable concentrate at 1000 times dilution, 7051 insecticide (Miechongling) at 3000 times dilution, or pyridazinone (speed acaricide) at 1000 times dilution.
Azalea iron deficiency chlorosis
Azalea iron deficiency chlorosis, also called yellow leaf disease or chlorosis, is a common disease of potted azaleas in various regions.
1. Symptoms: This disease mostly occurs on new leaves at tender shoot tips. At first the mesophyll between the veins loses green color and luster, then gradually becomes yellow-white, but the veins remain green, making the green on the leaf appear net-veined. Subsequently the yellowing gradually worsens, and except for the larger veins, the whole leaf becomes yellow or yellow-white. In severe cases, it scorches inward along the leaf and leaf margin.
2. Causes: Azalea iron deficiency chlorosis is a physiological disease, mainly caused by soil iron deficiency or iron being unavailable for absorption and use, thus affecting chlorophyll synthesis and turning leaves yellow-green. Under general conditions, there are the following situations: in calcareous alkaline soil, usable soluble ferrous iron is converted into insoluble ferric salts and precipitates, so 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 excessively high groundwater levels, root development is affected, normal physiological activity of the roots cannot proceed, and the roots' ability to absorb iron is reduced.
3. Control methods: Azaleas like acid and fear alkalinity, so avoid planting them in alkaline soil or soil containing much calcium; for open-ground planting in courtyards, do not place them near cement, brick walls, or places where lime has been used. Potted azaleas should use acidic soil; if the soil is on the alkaline side, add or replace with acidic soil. For azaleas planted 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 plant to absorb. Alternatively, ferrous sulfate can be mixed into fertilizer and applied; the preparation is: ferrous sulfate 2.5-3 gong de, oil meal 5-7.5 gong de, manure 10-15 kg, water 200-250 jin, mixed and then used after it decomposes and turns black. This method has good results. In slightly alkaline soil, a 0.1-0.2% potassium dihydrogen phosphate solution can be applied; this solution has a pH of 4.7 and can turn alkaline soil into acidic soil, which can treat the yellowing of tender leaves. At the same time, potassium dihydrogen phosphate also contains phosphorus and potassium, which help flowering and increase flower quantity. Frequently applying ferrous sulfate solution can cause excessive sulfur and available iron in the soil and poison the plant. To avoid this, 0.14 g disodium edetate and 0.1 g ferrous sulfate (chemically pure) can be mixed and dissolved in 500 ml tap water for foliar spraying, spraying both the front and back of leaves, once every 3 days, for several consecutive times, which can achieve good results.
Azalea gray mold
1. Symptoms: Gray mold occurs on azalea leaves and flowers. Freeze damage is often the trigger for leaf disease. In spring, the flowers of azaleas grown indoors and outdoors are often infected with gray mold. In the early stage, necrotic spots appear on the petals, spread quickly, and connect with one another to form large lesions. Under high humidity, the diseased parts produce large amounts of gray conidial layers, which is why the disease is called gray mold.
2. Pathogen: Botrytis cinerea Pers. ex Fr. belongs to the Deuteromycotina. The pathogen's fruiting bodies arise from mycelium or sclerotia. Conidiophores are clustered, gray, later turning brown, and conidia are oval. Its sexual stage is Botryotinia ****eliana (de Bary) Whetzel, belonging to the Ascomycotina.
3. Control measures: ① Strengthen cultivation management, prevent freeze damage, and reduce disease occurrence. ② When growing azaleas indoors, pay attention to ventilation and do not keep them too moist. ③ In daily management, if diseased leaves or flowers are found, remove and burn them promptly. ④ When necessary, spray with chemicals such as 50% dicloran at 1000 times dilution or 50% carbendazim wettable powder at 1000 times dilution for control.
III. What to Do If Azalea Leaves Dry Up
1. Temperature and humidity problems
Azaleas are very demanding about temperature and humidity. They generally grow at temperatures of 15-30°C, and humidity is required to be above 60%. Any other environment is unsuitable for azalea survival, otherwise it can lead to problems such as dried leaves, leaf drop and death.
Solution: If azalea leaf drying is caused by temperature and humidity problems, we should regulate the temperature and humidity of the environment by adjusting light, watering and other means, so as to keep it in an environment suitable for azalea growth, and its leaves will return to normal.
2. Light problems
Azalea is a sun-loving plant and likes sunlight. If it is kept out of sunlight for a long time and always placed in a dim corner, its leaves will dry up and may even drop later. However, if the light is too strong, or if it is kept in light for a long time, azalea leaves can also develop the same problem, so what should be done if azalea leaves dry up?
Solution: We can move the azalea to a place with diffused light, or adjust according to the season. In winter, light can be appropriately stronger; when the weather gradually warms and temperatures rise, move it again to a semi-shaded place.
3. Overwatering
For every plant, overwatering can cause a lack of oxygen in the soil, rot some fibrous roots, hinder normal respiration and the absorption of water and nutrients, and cause leaves to turn yellow and drop. Azaleas are no exception, and azalea leaf drying can also have this cause.
Solution: If azalea leaves dry up because of overwatering, we should promptly pour off the water or replace the potting soil, temporarily stop fertilizing, and frequently loosen the soil so that the soil is well aerated.
4. Improper fertilizing
Azalea is a plant that especially needs nutrients and requires fertilizer to supplement nutrient elements. If no fertilizer is applied for a long time, the soil will lack nutrients such as nitrogen, and the azalea will be malnourished and thus dry up. However, excessive fertilizing is also not acceptable, so flower lovers should pay attention in normal care.
Solution: For this kind of plant that needs nutrients, we cannot avoid fertilizing. If too much fertilizer has been applied, fertilizing should be stopped immediately, watering increased so that fertilizer flows out from the drainage holes at the bottom of the pot, or the pot should immediately be turned out, the root ball rinsed with water and then replanted in the pot.
5. Soil problems
Most plants have certain requirements for soil. For azaleas grown in the south and north, special attention must be paid. Most areas in the north have relatively high salt and alkali content in soil and water, while red soil in the south is on the acidic side and elements such as magnesium are easily lost. These are all causes of azalea leaf drying. Under such circumstances, what should be done if azalea leaves dry up?
Solution: If this happens in the north, we can choose acidic soil when planting and frequently water with alum fertilizer water during the growing period. In the south, calcium magnesium phosphate fertilizer can be applied or magnesium sulfate solution sprayed to solve this problem.