What disease causes azalea flowers to turn black
1. Brown spot disease
Cause: In the early stage of the disease, small brown spots appear on the leaf surface, then gradually develop into irregular large spots. Many black or grayish-brown small dots form on the lesions, causing the affected leaves to turn yellow and drop. This disease often occurs during the plum rain season when humidity is high.
Control method: At ordinary times, pay attention to ventilation and light transmission, apply more organic fertilizer and mixed nitrogen-phosphorus-potassium fertilizer to enhance the plant's resistance to infection and growth ability. Apply more organic fertilizer and mixed nitrogen-phosphorus-potassium fertilizer to enhance the plant's resistance to infection and growth ability.
2. Red spot disease
Cause: In the early stage, small rust-red spots appear on azalea leaves, mostly on the edges or tips of the top leaves. The lesions gradually expand into round or irregular rust-red spots. In the later stage, the diseased leaves become brittle and easily crack, spreading to most of the azalea leaf and causing the leaves to drop prematurely.
Control method: First, promptly remove diseased leaves. In the early stage of the disease, spray 0.5% Bordeaux mixture or 0.4 degrees Baume lime sulfur mixture, and add 4% flour to increase adhesion.
Alright, the above are the methods for dealing with blackened azalea leaves. We hope this helps everyone identify the cause in time and save the plant.
What to do when azalea leaves turn black and how to prevent azalea leaves from turning black
Azaleas are one of the most common indoor plants, but during cultivation, improper care and other reasons may cause azalea leaves to turn black. What should you do when azalea leaves turn black? How do you prevent azalea leaves from turning black? Let's look at the answers below.
What to do when azalea leaves turn black
One: Greenhouse cultivation
Most azaleas are cultivated in greenhouses. They have relatively high requirements for soil moisture and temperature. In addition, forced flowering and fast-growing ones overdraft their lives, which can cause azalea leaves to turn black. This kind of azalea is basically impossible to keep alive unless you repot with new soil right after buying it, prune most of the branches and leaves, remove all the flowers, and grow it for one to two years. But that takes too much time and energy.
Two: Improper watering
Watering azaleas too much or too little can both cause azalea leaves to turn black. Do not water too frequently. Water thoroughly only when the surface of the potting soil is slightly dry. The watering interval should be determined by the substrate. Peat soil has strong moisture retention, so the watering interval is longer; pine needle soil has slightly weaker moisture retention, so the watering interval is slightly shorter. It is best to adjust flexibly.
Three: Improper fertilizing
Applying too much or too little fertilizer can also cause azalea leaves to turn black. Azaleas are not tolerant of heavy fertilizer. It is best to apply dilute fertilizer, and do not apply excessive or concentrated fertilizer. The fertilizing principle for azaleas is light fertilizer applied frequently, that is, put a little less at a time and apply it several more times.
Four: Humidity too low
Air humidity that is too low can also cause azalea leaves to turn black. This is also related to care and management. During growth, it is necessary to spray water frequently to keep environmental humidity stable, preferably between 60-80%. This symptom easily appears in dry environments.
Five: Improper lighting
Azaleas require semi-shade or scattered light. They should not be placed in a shady place. Strong summer light can also easily damage azalea leaves, cause them to turn black, and stop growth, and in severe cases kill the whole plant. After summer begins, place azaleas in a ventilated and cool place. In hot summer, use reed curtains, bamboo curtains, or shade nets for shading. Open the curtains before 8 a.m. and after 5-6 p.m.
Six: Brown spot disease
Azaleas may be infected with brown spot disease, which causes azalea leaves to turn black. In the early stage, brown lesions appear on the edges of azalea leaves. The boundary between diseased and healthy tissue is not obvious, showing a transition from light green to brown to rust-red. As the disease spreads, the lesions expand or the entire azalea leaf turns brown, causing the leaves to drop prematurely, and even the whole azalea to wither and die. The disease is most severe from July to August. During high temperatures, provide appropriate shading, strengthen azalea growth, apply more organic fertilizer, and improve disease resistance.
Adhere to the principle of prevention first, and spray the protective fungicide 80% Daconil wettable powder at 600 to 800 times dilution, or 75% Baijunxiao wettable powder at 600 to 800 times dilution. In the early stage of the disease, spray the systemic fungicide 12.5% Likejun wettable powder at 2500 times dilution, or 25% Diliketuo emulsifiable concentrate at 1500 to 2000 times dilution.
Seven: Red spot disease
If azaleas are infected with red spot disease, it can also cause azalea leaves to turn black. In the early stage, small rust-red spots appear on azalea leaves, mostly on the edges or tips of the top leaves. The lesions gradually expand into nearly round or irregular rust-red spots. The boundary between diseased and healthy tissue is obvious and dark brown. In the later stage, small black dots appear on the diseased parts. The affected leaf parts become brittle and easily crack. Finally, the lesions expand to most of the azalea leaf or the entire leaf, causing azaleas to drop prematurely. Late June to August is the peak period of the disease. Cut off diseased leaves and burn them. In the early stage of the disease, spray 70% thiophanate-methyl wettable powder at 1000 times dilution, or 12.5% Likejun wettable powder at 2500 times dilution, or 25% Diliketuo emulsifiable concentrate at 1500 to 2000 times dilution.
How to prevent azalea leaves from turning black
Azaleas prefer a warm, humid, semi-shaded environment and require good ventilation. At ordinary times, they can be kept in a bright spot. In summer and early autumn, shade them during high-temperature seasons to avoid direct sun exposure, otherwise strong light will scorch the leaves. However, they should not be kept too shady, lest the azaleas grow leggy and flowering be affected. They can be kept under a shade shed or under tree shade. During the growing season, keep the soil moist, but do not let water accumulate. Pay attention to drainage during the rainy season. When the air is dry, sprinkle water on the azaleas and the surrounding ground to increase air humidity and prevent azalea leaves from drying out. You can also cover the surface of the potting soil with a layer of soft grass to prevent the strong sun from scorching the fine fibrous roots on the surface of the potting soil. Apply a dilute decomposed liquid fertilizer about once every 15 days. To prevent chlorosis, add a small amount of black alum to the fertilizer liquid so that the leaves become dark green and glossy. During the bud stage, apply phosphorus fertilizer such as bone meal or superphosphate 1 to 2 times to promote larger and more colorful azalea flowers.
What common diseases do azaleas have? How to control them?
The main diseases of azaleas include root rot, brown spot disease, black spot disease, leaf blight, and iron deficiency chlorosis.
After azaleas suffer from root rot, growth weakens, leaves wilt and dry up, and water-soaked brown patches appear on the root surface. In severe cases, soft rot occurs, gradually rotting and peeling, and the xylem turns black. This disease occurs most easily in environments with high temperature and high humidity.
The control method is to strictly disinfect the culture soil before repotting, and keep the soil loose, moist, and well aerated, avoiding water accumulation. If a plant is found to be diseased, promptly deal with the diseased plant and potting soil. For treatment, wash the diseased plant with a 0.1% potassium permanganate aqueous solution or 2% ferrous sulfate, then rinse with clean water and repot. A solution made with 70% thiophanate wettable powder plus 1000 times water sprayed on the potting soil can cure it.
Brown spot disease is one of the main diseases of azaleas. When the disease first appears, small brown spots appear on the leaf surface and gradually develop into irregular large spots. Many black or grayish-brown small dots form on the lesions, causing the affected leaves to turn yellow and drop, affecting flowering that year and the development of flower buds the following year. This disease often occurs during the plum rain season when humidity is high.
The treatment method is to pay attention at ordinary times to giving the plant ventilation and light, not letting humidity become too high, and applying more organic fertilizer and mixed nitrogen-phosphorus-potassium fertilizer to enhance the plant's resistance to infection and growth ability. If diseased leaves are found, remove them promptly and burn them in a centralized manner. In the early stage of the disease, spray 0.5% Bordeaux mixture or 0.4 degrees Baume lime sulfur mixture, and add 4% flour to increase adhesion. Leaf spot disease and black spot disease can also be treated with the same method.
Iron deficiency chlorosis often occurs in areas where the soil is alkaline. When the condition is mild, only delayed greening of the plant appears; when severe, the leaf tissue can all turn yellow, and the leaf edges become scorched. When the disease occurs, it is most obvious on the leaves at the top shoots of the plant, generally caused by internal iron deficiency.
The control method is to change the iron-deficient nature of the soil and reduce soil alkalinity. Apply more organic fertilizer to improve clayey soil. For iron-deficient plants, directly spray 0.2%-0.3% ferrous sulfate solution. You can also use chopsticks to poke several holes about 15 cm deep in the soil around the plant, slowly inject a 1:30 ferrous sulfate aqueous solution, and fill the holes to increase soil acidity and reduce alkalinity.
The occurrence situation and environmental conditions of azalea black spot disease are similar to those of brown spot disease, and similar methods can be used for control.