The Value, Propagation, and Pest and Disease Control Techniques of Western Azaleas
What values do Western azaleas have? Western azalea belongs to the order Ericales, and was developed in the Netherlands and Belgium through complex hybridization of Rhododendron indicum, Rhododendron simsii, and Rhododendron mucronatum. The flowers are brilliantly colored and diverse, producing buds and blooming multiple times a year, with flowers in all four seasons, possessing three major values: ornamental, ecological, and medicinal. Therefore, it has attracted widespread attention from all sectors of society, and its application fields continue to expand.
1 The Value and Characteristics of Azaleas
1 The Ornamental, Ecological, and Medicinal Value of Azaleas
(1) The ornamental value of Western azaleas: Western azaleas come in many colors and are very brilliant, so they are relatively common in courtyards, alleys, and landscaping projects. Among them, the "Hundred-Mile Western Azalea" scenic area is relatively famous and has become a well-known tourist destination.
(2) The ecological value of Western azaleas: The flowers of Western azaleas can not only effectively absorb O3 and SO2 components in the air, but also effectively purify the air, playing an important role in improving the environment to a certain extent. At the same time, Western azaleas are also important acid soil indicators, and can play an important role in improving the ecological environment on the basis of maintaining and conserving water sources.
(3) The medicinal value of Western azaleas: The rhizome part of Western azaleas can be used as medicine, mostly for treating symptoms such as cough and excessive phlegm, mainly because the quercetin in them has a very important effect of relieving cough and calming asthma.
2 Cultivation Techniques for Western Azaleas
2.1 Propagation Techniques for Western Azaleas
Seed propagation, cutting propagation, grafting propagation, and layering propagation are all relatively common methods for propagating Western azaleas, and the specific method should be determined according to the actual variety of Western azalea during propagation. (1) Seed propagation: commonly used for evergreen Western azaleas. (2) Cutting propagation: relatively common for deciduous Western azaleas. (3) Softwood cleft grafting propagation: for some valuable varieties that are relatively difficult to survive. (4) Cutting propagation: conventional Western azaleas, with a relatively high propagation coefficient and a relatively high survival rate.
2.2 Cultivation Techniques for Western Azaleas
In cultivating and planting Western azaleas, the basic pH value of the growing medium should be controlled between 4.5 and 6. In addition, attention and control should also be given to the fertilization process during cultivation, and fertilization management should be carried out in an orderly manner according to standardized procedures. During cultivation and planting, attention should be paid to soil nutrients to ensure that the soil is loose and has good overall aeration and water permeability. If the soil fertility is insufficient, fertilization should be applied to meet the needs of Western azaleas. During cultivation, the balance and efficiency of fertilization should be fundamentally maintained. When applying fertilizer, the fertilizer must be fully fermented and composted, and concentrated water control operations should be carried out before composting the fertilizer.
2.3 Flowering Period Management Techniques for Western Azaleas
(1) Light conditions: Western azaleas like light, so good light conditions must be ensured.
(2) Temperature conditions: The optimal temperature is controlled at 12 degrees C, while for cutting-propagated Western azaleas, a temperature of 20 degrees C is better.
(3) Humidity conditions: Humidity should be controlled between 70% and 90%. In spring and autumn, water once every 2 to 3 days; in summer, ensure watering once in the morning and once in the evening every day.
3 Pest and Disease Control of Western Azaleas
3.1 Disease Control of Western Azaleas
(1) Damping-off: Before propagation, disinfect the soil with formalin; use a 500-fold solution made from 70% thiophanate-methyl or 70% chlorothalonil for irrigation control.
(2) Black spot disease: In winter, promptly remove diseased leaves and strengthen routine management; in the early stage of black spot disease, use a 1:1:100 Bordeaux mixture for disinfection treatment, or use 70% thiophanate-methyl made into a 1000-fold solution for irrigation control.
3.2 Pest Control of Western Azaleas
The common pest problems are red spiders and lace bugs.
(1) Red spiders: Handle by removing diseased leaves and burning them in a concentrated manner, and concentrated spraying with 40% dicofol.
(2) Lace bugs: In July and August, use 50% phoxim made into a 0.0067% to 0.01% solution for spraying control.
Cultivation Methods for Western Azaleas
Western azaleas are considered relatively difficult for beginners to grow, because the climate varies from place to place, especially in the north. When purchased, they look very good, but before long they drop leaves and buds. As long as you learn more about the habits of Western azaleas, it is not that difficult to grow them well.1. Growth Habits of Western Azaleas
They prefer warm, humid, cool-air, well-ventilated, and semi-shaded environments. The soil is required to be acidic, fertile, loose, rich in organic matter, and well-drained. In summer, direct sunlight should be avoided, shading should be provided, water should be sprayed frequently, and air humidity should be maintained. A loose, fertile, well-drained acidic sandy loam soil is good. For potted soil, use a mixed soil of leaf mold, culture soil, and coarse sand, with a pH of 5 to 5.5 being suitable.
2. Common Problems in the Cultivation Process of Western Azaleas
1. Plants are prone to withering and dying after flowering.
Key to the solution: Air humidity must be moderate.
Western azaleas have relatively strict requirements for air humidity. For Western azaleas cultivated in greenhouses, as long as no water accumulates on the greenhouse floor, under normal circumstances the air humidity can fully suit azalea growth. It should be pointed out that in rooms equipped with air conditioning, the air humidity is far lower than the physiological needs of azaleas. Therefore, the phenomenon of yellowing leaves and most plants withering and dying after flowering occurs. This is precisely the crux of the difficulty in cultivating Western azaleas. As long as clean water is sprayed on the leaves of the azaleas every day during cultivation to increase the air humidity around the plants, this problem is readily solved.
2. Uneven growth on both sides of the plant
Key to the solution: Daily watering and fertilization must be uniform.
Since the culture soil for Western azaleas must be a loose and breathable substrate, most of what is actually used in cultivation is pine needle soil, which has quite strong water permeability. During watering, water will seep straight down, and some nutrients will also be lost with the water. However, we often habitually water from the side that is convenient to operate, so the culture soil remains in a state of being dry on one side and wet on the other, and fertile on one side and poor on the other. Over time, this causes the plant's fibrous roots to be well-developed on one side and shrunken on the other, thus making the plant appear uneven in growth on both sides. Therefore, when watering and fertilizing Western azaleas, you must start from all around the flowerpot and operate evenly.
3. Plants bloom sporadically, and the flowering period is inconsistent
Key to the solution: Pinch back centrally at the right time.
From the perspective of operators, flowers can win maximum profit only when they bloom during peak flower-consuming periods such as holidays. Therefore, centralized and timely blooming of Western azaleas is crucial. Pinching back is an important means of adjusting the flowering period. Experience has proven that for Western azaleas to reach full bloom during the Spring Festival, a centralized pinching back should be carried out once from late July to early August. During the pinching process, each branch tip of the plant must be thoroughly pinched, and the length removed should be appropriate to ensure the overall plant shape is neat. Throughout the entire process of cultivating Western azaleas, this step is extremely critical and must not be ignored.
4. Plants develop "little leaf disease"
Key to the solution: Control mites.
Western azaleas themselves have relatively strong resistance, but under improper operation, pests and diseases can still occur. In addition to the common brown spot disease and iron deficiency, there is another common symptom, which generally first appears on the new shoots of the plant, with leaves in clusters, not spreading out, and leaf color tending toward yellow, very similar to the symptoms of little leaf disease in fruit trees, so it is habitually called azalea "little leaf disease."
Most flower growers also naturally believe that the "little leaf disease" of Western azaleas is also a physiological disease caused by zinc deficiency, and they try every method to supplement zinc to the azalea plants but with poor results. In fact, this disease of Western azaleas is caused by mites. When we bring plants into the greenhouse or purchase them, we should remove diseased plants. During the bud-breaking period, 1 to 3 degrees Baume lime sulfur mixture can be sprayed, or 40% omethoate 5 to 10 times solution can be applied to the trunk for prevention. Once the disease occurs, choosing 20% dicofol emulsifiable concentrate 500 to 600 times solution can achieve very ideal results.
Common Pests and Diseases of Azaleas and Their Control
Azalea (scientific name: Rhododendron simsii Planch.): also known as yingshanhong or mountain pomegranate, it is an evergreen or semi-evergreen shrub. Legend has it that in ancient times there was a cuckoo bird that cried mournfully day and night until it coughed blood, dyeing the flowers all over the mountains red, hence the name. Azaleas generally bloom in spring, with 2-6 flowers per cluster, funnel-shaped corollas, in colors such as red, light red, apricot red, snow blue, and white, with lush and brilliant flower colors. They grow in mountain open thickets or under pine forests at altitudes of 500-1200 (-2500) m, and are typical acid soil indicator plants in central-south and southwest China. Common Pests and Diseases of Azaleas and Their ControlAzalea Black Spot Disease
Azalea black spot disease, also called brown spot disease, is a common and frequently occurring leaf spot disease of azaleas. After onset, black spots form on the leaves, which gradually dry up and fall off until the plant dies. This disease mainly damages azalea leaves and is caused by infection by the fungus Cercospora rhododendri. The pathogen first appears as several brown small spots. As the small spots continue to expand, the lesions connect with each other into patches, producing gray-brown mold hyphae. The affected leaves start from the petiole, turn from green to brown-yellow, and fall off early. In severe cases, it affects the growth and development and ornamental value of azaleas. The pathogen overwinters on leaves or diseased plants, and spores spread with the wind.
The severe outbreak period of this disease is generally mostly in hot and humid seasons, and in greenhouses there are also cases of onset in winter. Generally, weakly growing plants, small seedlings, lower leaves, plants with poor ventilation conditions, and Western azaleas (compared with Rhododendron mucronatum) are more severely affected. According to the disease occurrence pattern, the following control measures can be taken:
(1) Strengthen cultivation management. For azalea cultivation, leaf mold should be selected for the potting soil. The pH value of the water used should be between 4.5 and 6.5. The watering substrate should be dry before watering and wet after watering. Some fully decomposed dilute organic liquid fertilizer should be applied frequently to promote robust plant growth, thick leaves, and improved resistance. Potted azaleas should be placed in a ventilated place. In summer, shade, prevent moisture, and prevent water accumulation. Diseased leaves should be removed and burned in time, and attention should be paid to selecting disease-resistant varieties while strengthening plant pest and disease quarantine work.
(2) Chemical control: After flowering, promptly spray 70% thiophanate wettable powder 800 times or 50% carbendazim 300 times solution. In addition, fungicides can be sprayed regularly for prevention. Protective fungicides and fungicides can be mixed and applied, such as alternating Bailian plus M Daisheng 45 and Kocide, which can achieve good results, or use 1:1:150 Bordeaux mixture once a week for 2 consecutive sprays; during the rainy season, spray 1:1:100 Bordeaux mixture once every 10 days for 3 to 4 consecutive sprays.
Azalea Chlorosis
Azalea chlorosis is a non-infectious disease and is also a common disease in azalea cultivation. After the plant develops the disease, the leaves become thinner, lose green color, and become pale, so this disease is also called chlorosis. The lack of green in new leaves is obvious. When the leaf color of new shoots becomes lighter and the mesophyll turns yellow while the veins remain green, it is generally diagnosed as iron deficiency symptoms. This phenomenon mostly occurs in alkaline soil and in areas where slightly alkaline water is used to water flowers. After the leaves show symptoms, photosynthesis can no longer proceed normally. In mild cases, it affects the growth and development and ornamental value of the plant; in severe cases, it can lead to plant death.
Control measures: Strengthen cultivation management. Combined with irrigation, irrigate with ferrous sulfate solution. A 0.5% ferrous sulfate solution can be sprayed on the leaf surface, which can gradually restore the green color of the plant leaves.
Azalea Red Spider Mite
The female adult is about 0.3 mm long, dark red, nearly oval, with a convex back and 4 pairs of dark red legs; the male adult is 0.25 mm long, wedge-shaped, flat, and bright red. It occurs in multiple generations a year. Adults overwinter at the roots of the plant and mainly damage the underside of leaves near the main vein close to the petiole. During June and July, with high temperature, little rain, and dry weather, reproduction is fast and the number occurring is relatively large. When damage is severe, the affected leaves scorch and fall off.
Control methods: Artificial control. After April, check frequently. When red spider mites are found on a few leaves, promptly remove the pest leaves and burn them. If conditions permit, natural enemies such as ladybugs, lacewings, and thrips can be artificially released for biological control. If red spider mites are found on many leaves, chemical control can be carried out, such as spraying 40% dicofol 800 to 1000 times solution, which has strong killing power against adults, nymphs, larvae, and eggs. As long as it is sprayed evenly, the effect is good.
Azalea Lace Bug
Azalea lace bug, also called azalea army-arrangement bug or little stink bug. The adult is about 3.5 mm long, dark brown, with wings covered in net-like veins; the forewings are slightly rectangular, and when at rest, the dark brown markings on the wings form an "X" shape. Nymphs resemble adults, only tender and small without wings, about 2 mm long. Eggs are 0.6 mm long, oval, milky white, laid at the midrib and larger veins. When newly laid they are pale green, later turning pale yellow. It occurs in 3 to 4 generations a year. Adults overwinter in bark and soil crevices in mid-to-late October, begin activity in April to May of the following year, and feed and cause damage on the underside of leaves. Damage is most severe in July and August. Adults and nymphs like to gather near the main vein on the underside of leaves, piercing and sucking leaf sap. Their secretions form relatively large yellow-brown rust spots. In severe cases, the leaves become pale and fall early, affecting the growth and flowering of azaleas.
Control methods: (1) After winter begins, clear fallen leaves and weeds near the flowers and trees, bury them deeply or burn them, and eliminate overwintering adults. (2) Chemical control: In May, after overwintering adults appear and during the occurrence period of the first-generation nymphs, spray 80% dichlorvos emulsifiable concentrate or 50% fenitrothion emulsion 1000 times solution once every 7 to 10 days for 2 to 3 consecutive sprays. Alternatively, 3% carbofuran can be buried at about 5 g per pot, and the effect is also very good.
Azalea earthworms and slugs mainly damage the roots. Sometimes slugs also damage the leaves. The medium used for cultivation should be high-temperature disinfected to kill insect eggs. If pests are found, carbofuran or aldicarb can be applied in the pot for control.