Common diseases and insect pests of rhododendron

Rhododendron black spot, also known as brown spot, is a common multiple leaf spot disease of rhododendron. After the disease, the leaves formed black spots, which gradually dried up and fell off until the plant died. The disease mainly harms the leaves of rhododendron, which is infected by Cercospora rhododendron fungi, and several brown spots begin to appear. With the continuous expansion of the spots, the disease spots connect with each other and produce gray-brown fungal hyphae, and the damaged leaves start from the petiole and fall off early from green to brown, which seriously affects the growth, development and ornamental value of rhododendron. The pathogen overwinters on leaves or diseased plants, and the spores spread with the wind.

The recurrence period of the disease is usually in the high temperature and humid season, and the disease occurs in winter in the greenhouse. Generally, plants with weaker growth, seedlings, lower leaves, plants with poor ventilation and rhododendron (compared with rhododendron) have more serious disease. According to the law of the disease, the following prevention and control measures can be taken:

The main results are as follows: (1) to strengthen cultivation and management, rotten leaf soil should be selected in rhododendron cultivation basin soil, pH value of watering should be between 4.5 and 6.5, watering substrate should be dry and wet, and some mature thin organic liquid fertilizer should be often applied to promote plant health, leaf thickening and resistance. Potted cuckoos should be placed in ventilated places and shaded, moisture-proof and water-proof in summer. Diseased leaves should be removed and burned in time, disease-resistant varieties should be selected, and quarantine of plant diseases and insect pests should be strengthened.

(2) Pesticide control: spray 70% topazine wettable powder 800 times or 50% carbendazim 300 times immediately after anthesis. In addition, preventive agents can be sprayed regularly, and protective fungicides and fungicides can be mixed, such as Poly Anga M Dasheng 45 and Kesha 45 alternately, or 1 ∶ 1 ∶ 150 Bordeaux solution is sprayed twice a week. Spray 1 ∶ 1 ∶ Bordeaux every 10 days in the rainy season for 3 to 4 consecutive times.

Rhododendron chlorosis

Rhododendron chlorosis is not only a non-infectious disease, but also a common disease in rhododendron cultivation. After the plant has pathological changes, the leaves become thinner, chlorotic and pale, so the disease is also called chlorosis, and the new leaves lack green obviously. When the leaves of the new shoots become lighter and the mesophyll turns yellow, the veins are still green. At this time, the symptom of iron deficiency is generally diagnosed. This phenomenon often occurs in alkaline soil and areas where alkaline water is used to water flowers. After the appearance of diseased leaves, photosynthesis can not be carried out normally, which will affect the growth and development and ornamental value of the plant in light cases, and lead to plant death in severe cases. Prevention and control measures: to strengthen cultivation management, combined with irrigation, ferrous sulfate solution can be irrigated, and 0.5% ferrous sulfate solution can be sprayed on the leaf surface, which can gradually restore the green leaf surface of the plant.

Rhododendron red spider

The female adult is about 0.3 mm long, dark red, nearly oval, the back of the body is raised, 4 pairs of dark red; the male adult is 0.25 mm long, cuneate, flattened bright red. The adults overwintered in the root of the plant, mainly near the main vein of the petiole on the back of the leaf, propagated rapidly in high temperature, less rain and drought weather from June to July, and the damaged leaves were scorched and shedded when the damage was serious.

Prevention and control methods: manual control, regular inspection after April, when it is found that individual leaves have red spiders, insect leaves can be removed and burned in time. Conditional natural enemies such as ladybugs, lacewings and thrips can be released artificially for biological control. If more leaves are found to have red spiders, chemical control can be carried out, such as spraying 40% dicofol 800 to 1000 times, which has a strong killing effect on adults, nymphs, larvae and eggs, as long as the uniform effect of spraying is good.

Rhododendron net bug

Cuckoo net bug, also known as cuckoo army with worms, smelly sister. The adult body is about 3.5 mm long, dark brown, and the wings are covered with reticulated whiskers and the forewings are slightly rectangular. When at rest, the dark brown markings on the wings form an "X" shape. The nymph is similar to an adult, but the body is tender and wingless, about 2 mm long, the egg is 0.6 mm long, oval, milky white, produced in the midrib and larger leaf veins, light green at first birth, and then yellowish.

The insect has 3 to 4 generations a year. The adult overwinters in bark and land crevices in mid-late October, and begins to feed on the back of the leaves from April to May of the following year, and the damage is the most serious from July to August. Adult and nymph groups gather near the main veins on the back of the leaves, sucking the sap of the leaves, and their secretions form large yellowish-brown speckles, and in severe cases, the leaves are pale, causing early fall, affecting the growth and flowering of rhododendrons.

Prevention and control methods: (1) remove fallen leaves and weeds near flowers and trees after winter, bury or burn deeply to eliminate overwintering adults. (2) Pesticide control: in May, after the emergence of overwintering adults and the occurrence of the first generation nymphs, 80% dichlorvos EC or 50% borer pine emulsion was sprayed 1000 times, once every 7 to 10 days, 2 to 3 times continuously. 3% carbofuran can also be used to bury about 5 grams in each basin, and the effect is also very good.

Cuckoos and slugs mainly harm the roots. Sometimes slugs also harm leaves. The medium used in cultivation should be disinfected at high temperature, kill eggs, and find pests, which can be controlled by carbofuran and Tiemiake.