Prevention and control of main diseases and insect pests of rhododendron

(1) ① brown spot of rhododendron: it is the main disease of rhododendron. At the beginning of the disease, small brown spots appeared on the leaf surface, and then gradually expanded into large dark brown patches, and many black or grayish brown spots were scattered on the disease spot. The damaged leaves turn yellow and fall off easily, which affects not only the flowering of the current year, but also the development of flower buds in the coming year. The disease is more serious in the rainy season. After the onset of the disease, the diseased leaves should be removed in time, and 50% topiramate 800 times solution should be sprayed for prevention and treatment.

② rhododendron leaf swelling disease: mainly occurs on tender leaves, buds and stems. After the injury of the tender leaves, the disease was obviously enlarged, the back was concave, and the front was raised, showing a hemispherical shape. The disease spot is light red at the beginning, and then becomes yellowish brown, with a white powder on the surface. In the later stage, the plaque turns brown to black. The lesions healed each other, the whole leaf was swollen, or malformed and curled, and finally withered and fell off. It's a fungal disease. The disease occurs twice a year, one at the end of spring and early summer, the other at the end of autumn and the beginning of winter, and the disease is the most serious in spring. Prevention and control method: remove the diseased leaves and destroy them before the white powder is produced in the disease department, and spray 65% Dysen zinc 600 times solution for prevention and control.

In addition, there are flower rot, leaf blight, soot and so on.

(2) insect pests

Mountain army parasite: the adult is small and flat, 3.5-4.0 mm long, dark brown. The front wing folds to form an "X"-shaped pattern, and the wing surface is densely covered with reticulate patterns. The nymph is dark brown with obvious spines on its body. Adults and nymphs swarm near the dorsal host and lateral veins of the host leaves. Yellow and white spots appeared on the injured leaves, and at the same time, a lot of dark brown insect droppings and husks could be seen on the back of the leaves. It can be sprayed with 50% carbaryl wettable powder 500 × 700 times, 50% phoxim or 50% fenitrothion emulsion 1000 / 1500 times.

② short beard mite: mainly prick and suck juice near the main vein of the back of the leaf. The peak period is from July to September, which often causes a large number of deciduous leaves of rhododendron, which seriously affects the growth and ornamental.

In addition, there are leaf wasps, shell insects, coir moths and so on.

(3) physiological diseases

Rhododendron chlorosis is a physiological disease, the main causes are: alkaline soil; rhododendron likes acidic soil, if planted in alkaline soil will make rhododendron leaves yellowing, or even withered. Iron deficiency, lack of iron in the culture soil, chlorophyll synthesis was affected, and the leaves became smaller and yellowish-white, especially in the young leaves. There is a related relationship between them, and alkalinity often leads to iron deficiency. Improper maintenance, excessive or insufficient light, excessive watering, excessive or insufficient fertilization, and soil viscosity will cause physiological obstacles, resulting in poor growth of rhododendron, yellowing and shedding of leaves, and so on. Chlorosis should be aimed at the above causes and prescribe the right medicine to the case. If the yellowing caused by iron deficiency can be sprayed or irrigated with 0.2% ferrous sulfate solution, once every 7 days, continuously for 3 times for 4 times, the leaves will change from yellow to green; for the yellowing caused by soil alkalinity, the soil quality should be acidified and can be replaced with acid culture soil dominated by rotten leaf soil; if the yellowing caused by improper maintenance, comprehensive maintenance measures should be taken.

Prevention and control of main diseases and insect pests of rhododendron

1. Diseases of rhododendron

① brown spot is the main disease of rhododendron. At the beginning of the disease, small brown spots appeared on the leaves, and then gradually expanded into large dark brown patches, and many black or grayish brown spots were scattered on the disease spots. The damaged leaves turn yellow and fall off easily, which affects not only the flowering of the current year, but also the development of flower buds in the coming year. The disease is more serious in the rainy season. After the onset of the disease, the diseased leaves should be clear in time, and 50% topiramate 800 times solution should be sprayed to prevent and cure the disease.

② rhododendron leaf swelling disease mainly occurs on tender leaves, buds and stems. After the injury of the tender leaves, the disease was obviously enlarged, the back was concave, and the front was raised, showing a hemispherical shape. The disease spot is light red at the beginning, and then becomes yellowish brown, with a white powder on the surface. In the later stage, the plaque turns brown to black. The lesions healed each other, the whole leaf was swollen, or malformed and curled, and finally withered and fell off. It's a fungal disease. The disease occurred twice a year, one in late spring and early summer, and the other in late autumn and early winter, with the Spring Festival being the most serious. Prevention and control method: remove the diseased leaves and destroy them before the white powder is produced in the disease department, and spray 65% Dysen zinc 600 times solution to prevent and cure.

In addition, there are flower rot, leaf blight, soot and so on.

2. Insect pests

①: the adult is small and flat, 3.5 to 4.0mm long, dark brown. The front wing folds to form an x-shaped pattern, and the wing surface is densely reticulated. The nymph is dark brown with obvious spines on its body. Adults and nymphs are all sucked near the dorsal host and lateral veins of the host leaves. Yellow and white spots appeared on the injured leaves, and at the same time, a lot of dark brown insect droppings and husks could be seen on the back of the leaves. Spray 50% carbaryl wettable powder 500 times 700 times, 50% phoxim or 50% fenitrothion emulsion 1000 times 1500 times.

② short beard mite: mainly prick and suck juice near the main vein of the back of the leaf. The peak period is from July to September, which often causes a large number of deciduous leaves of rhododendron, which seriously affects the growth and ornamental.

In addition, there are leaf wasps, shell insects and decaying moths.

3. Physiological diseases

Rhododendron chlorosis is a physiological disease, the main causes are: alkaline soil; rhododendron likes acidic soil, if planted in alkaline soil will make rhododendron leaves yellowing, or even withered. Iron deficiency: the lack of iron in the culture soil affected the synthesis of chlorophyll, and the leaves became smaller and yellowish-white, especially in the young leaves. There is a related relationship among the patients, and alkalinity often leads to iron deficiency. Improper maintenance, excessive or insufficient light, excessive watering, excessive or insufficient fertilization, and soil viscosity will cause physiological obstacles, resulting in poor growth of rhododendron, yellowing and shedding of leaves, and so on. Chlorosis should be aimed at the above causes and prescribe the right medicine to the case. In the case of yellowing caused by iron deficiency, 0.2% ferrous sulfate solution can be sprayed or irrigated every 7 days for 3 times continuously, and the leaves will change from yellow to green; for the yellowing caused by soil alkalinity, the soil quality should be acidified and can be replaced with acid culture soil dominated by rotten leaf soil; if etiolation caused by improper maintenance, comprehensive maintenance measures should be taken.

Control methods of main diseases and insect pests of rhododendron

The main diseases of rhododendron:

(1) Brown spot is the main disease of rhododendron. At the initial stage of the disease, small brown spots appeared on the leaf surface, and then gradually expanded into large dark-exposed patches, with many black or grayish brown spots scattered on the disease spot. The damaged leaves turn yellow and fall off easily, which not only affects the flowering in the same year, but also has a great influence on the bud development in the following year. Plum rain season is more serious, after the disease should be timely removal of diseased leaves, and spray 50% topiramate 800 times solution for prevention and treatment.

(2) Leaf swelling disease of rhododendron mainly occurs on tender leaves, buds and stems. After the injury of the tender leaves, the disease was obviously enlarged, the back was concave, and the front was raised, showing a hemispherical shape. At the beginning, the plaque is reddish. It turns yellowish brown and produces white powder on the surface. In the later stage, the lesion became exposed to black. The lesions healed each other, the whole leaf was swollen, or malformed and curled, and finally withered and fell off. It's a fungal disease. The disease occurs twice a year, one is in late spring and early summer, the other is in late autumn and early winter, and the disease is the most serious in spring. The other time is the mildew arrow flying at the end of autumn and the most serious disease in spring.

Prevention and treatment: remove the diseased leaves and destroy them before the white powder is produced in the disease. Spray 65% Dysen zinc 60 times solution for prevention and control. In addition, there are flower rot, leaf blight, soot and so on.