Disease causes of blackening of rhododendron

1. Brown spot disease

Cause: at the initial stage of the disease, small brown spots will appear on the leaf surface, and then gradually develop into large irregular spots, and many black or grayish brown spots will be produced on the disease spots, which will make the damaged leaves turn yellow and fall off. This disease often occurs during the rainy season when the humidity is high.

Control methods: usually pay attention to ventilation and light transmission, increase the application of organic fertilizer and nitrogen, phosphorus and potassium mixed fertilizer, enhance the plant anti-infection and growth ability. Increase the application of organic fertilizer and mixed fertilizer of nitrogen, phosphorus and potassium to enhance the plant resistance to infection and growth.

two。 Redspots

The reason: the rusty red spots were produced on the rhododendron leaves at the initial stage, which were mostly on the edge of the top leaves, and the disease spots gradually expanded into round or irregular rusty red spots. In the later stage, the diseased leaves were brittle and easy to break, which extended to most of the rhododendron leaves, causing the leaves to fall off ahead of time.

Prevention and treatment: first of all, diseased leaves should be removed in time. At the initial stage of the disease, 0.5% Bordeaux solution or 0.4 Baume stone sulfur agent was sprayed, and 4% flour was added to increase the adhesion.

Well, the above is the treatment of rhododendron leaves blackening, I hope to help you find the cause in time and save the plant.

How to prevent rhododendron leaves from blackening?

Rhododendron is one of the most common indoor plants, but in the process of breeding, it may be due to improper maintenance and other reasons, resulting in rhododendron leaves blackening, rhododendron leaves black how to do? How to prevent cuckoo leaves from blackening? Let's take a look at the answer next.

What if the leaves of azaleas turn black?

One: greenhouse cultivation

Rhododendron is mostly cultivated in greenhouse, which requires high soil moisture and temperature. coupled with the promotion of flowers, rapid growth and overdraft of life, the cuckoo leaves will be blackened. This kind of cuckoo is basically unable to live, unless it is bought back to change the soil, trim most of the branches and leaves, take off all the flowers, and grow for a year or two, but it takes too much time and energy.

Second, improper watering

Too much or too little watering can lead to blackening of cuckoo leaves. Watering can not be too frequent, the basin soil surface can be watered thoroughly when slightly dry, the interval of watering should be determined according to the matrix, the moisture retention of peat soil is strong, the watering interval is longer, the moisture retention of pine needle soil is slightly worse, and the watering interval is shorter. It is better to be flexible.

Third, improper fertilization

Too much or too little fertilization can also lead to blackening of cuckoo leaves. Rhododendron is not resistant to fertilizer, fertilization had better be light, not too much or too thick. The principle of cuckoo fertilization is to apply more thin fertilizer, that is, a little less at a time, can be applied several times.

Four: the humidity is too low

If the air humidity is too low, it will also lead to the blackening of rhododendron leaves, which is also related to maintenance and management. it is necessary to spray water frequently in the growth process to maintain the stability of environmental humidity, which is suitable for 60-80%, which is easy to occur in dry environment.

Five: improper lighting

Rhododendron light is required to be semi-overcast or scattered light, can not be placed in the shade, strong light in summer is also easy to cause rhododendron leaf injury, blackening, growth stagnation, serious death of the whole plant. After the beginning of summer, the cuckoo should be put in a cool and ventilated place. in hot summer, Reed curtains, bamboo curtains and sunshade nets should be used to shade, and the curtains should be opened before 8 o'clock in the morning and after 5: 00 p.m. to 6 p.m.

Six: Brown spot

Cuckoos may be infected with brown spot, which leads to blackening of cuckoo leaves. In the early stage of the disease, brown disease spots appeared on the edge of rhododendron leaves, and the junction between disease and health was not obvious, showing a transition of light green, brown and rust red. with the expansion of the disease, the disease spot expanded or the whole rhododendron leaves turned brown, causing the leaves to fall off ahead of schedule. Even the whole cuckoo withered and died, and the disease was the most serious from July to August. Proper shading at high temperature can enhance the growth of rhododendron, increase the application of organic fertilizer and improve disease resistance.

Adhere to the principle of prevention first, spray 80% of Dasheng wettable powder 600 to 800 times, or 75% of chlorothalonil wettable powder 600 to 800 times. At the initial stage of the disease, 12.5% of the internal absorbent fungicide can be sprayed with 2500 times of the limonium wettable powder, or 25% of the enemy demulsifiable oil 1500 times to 2000 times.

Seven: erythema

Rhododendron infected with red spot disease can also cause cuckoo leaves to blacken. Rusty red spots appeared on the rhododendron leaves at the initial stage, mostly at the edge or tip of the top leaves, and the disease spots gradually expanded into nearly round or irregular rusty red spots, showing dark brown at the junction of the disease and health. In the later stage, black dots appeared in the diseased part, and the damaged leaves were brittle and easy to break. finally, the disease spots extended to most or the whole leaves of the rhododendron leaves, causing the rhododendron to fall off in advance. The peak period is from late June to August. Cut off the diseased leaves and burn them, and at the initial stage of the disease, spray 70% methyl topiramate wettable powder 1000 times, or 12.5% Lecrobacter wettable powder 2500 times, or 25% enemy emulsifiable concentrate 1500 times to 2000 times.

How to prevent cuckoo leaves from blackening

Cuckoos like a warm and humid semi-overcast environment and require good ventilation. Usually can be placed in bright light maintenance, summer and early autumn high temperature season to shade, avoid hot sun exposure, otherwise the strong light will burn leaves, but also can not be too shaded, lest rhododendrons grow too long, affect flowering, can be placed in the shade or tree shade maintenance. Keep the soil moist during the growing period, but do not accumulate water. Pay attention to drainage in the rainy season. When the air is dry, you can sprinkle water to the cuckoo and the surrounding ground to increase air humidity and prevent cuckoo leaves from drying up. The surface of the basin soil can also be covered with a layer of soft grass to prevent the scorching sun from burning the fine fibrous roots on the surface of the basin soil. The mature thin liquid fertilizer is applied every 15 days or so. In order to prevent the occurrence of chlorosis, a small amount of black alum can be added to the fertilizer solution to make the leaves green and bright. The application of phosphate fertilizer such as bone powder and calcium superphosphate at the bud stage can promote the rhododendron to be colorful.

What are the common diseases of rhododendron? How to prevent and cure?

The main diseases of rhododendron are root rot, brown spot, black spot, leaf blight, iron deficiency chlorosis and so on. After the rhododendron suffered from root arm disease, the growth was weak, the leaves wilted and withered, the surface of the root system appeared water-stained brown fields, serious soft rot, gradually rotted and peeled, and the xylem blackened. The disease is most likely to occur in an environment with high temperature and high humidity. The prevention and control method is to strictly disinfect Pei 10 soil before turning the basin, and keep the soil condition sulfur loose, moist, make it have good permeability, and avoid stagnant water. If the plant is found to be sick, the diseased plant and basin soil should be dealt with in time. During treatment, the diseased plant can be eluted with 0.1% potassium permanganate aqueous solution or 2% ferrous sulfate, then rinsed with clean water and put on the basin again. The basin soil can be cured by spraying basin soil with a solution of 70% topzine wettable powder and 1000 times water. Brown spot is a major disease of rhododendron. At the beginning of the disease, small brown spots appeared on the leaf surface, which gradually developed into irregular spots, and many black or grayish brown spots were produced on the disease spots, which made the damaged leaves yellow and fall off, affecting the flowering of the current year and the development of flower buds in the coming year. This disease often occurs during the rainy season when the humidity is high. The treatment method is to pay attention to make the plant ventilated and transparent, not to make the humidity too high, and to increase the application of organic fertilizer and nitrogen, phosphorus and potassium mixed fertilizer to enhance the plant resistance to infection and growth. If diseased leaves are found, they should be removed in time and burned centrally. At the initial stage of the disease, 0.5% Bordeaux solution or 0.4 Baume stone sulfur agent was sprayed, and 4% flour was added to increase the adhesion. Leaf spot and black spot can also be treated with the same method. Iron deficiency chlorosis often occurs in alkaline soil areas, when the disease is mild, only the plant late green phenomenon; in severe cases, the leaf tissue can all turn yellow and the leaf edge scorched. When the disease occurs, it is most obvious in the leaves of the top tip of the plant, which is generally caused by internal iron deficiency. The control method is to change the property of iron deficiency in soil and reduce soil alkalinity. Apply more organic fertilizer to transform clayey soil. 0.2%-0.3% ferrous sulfate liquid can be directly sprayed on iron-deficient plants. You can also poke several holes about 15 cm deep in the soil around the plant with chopsticks and slowly inject them with liquid ferrous sulfate solution at 1:30 to fill the holes to increase soil acidity and reduce alkalinity. The incidence and environmental conditions of rhododendron black spot are similar to those of brown spot, and similar methods can be used for prevention and control.