Control measures of common diseases of rhododendron

The common diseases and control measures of rhododendron can be classified into the following categories:

1. Botrytis cinerea

Symptom

Botrytis cinerea occurs in the leaves and flowers of rhododendron. Freezing injury is often the cause of leaf disease. In spring, cuckoos cultivated indoors and outdoors are often infected with Botrytis cinerea. In the early stage of the disease, necrotic spots appeared on the petals, expanded rapidly, and connected to each other to form large disease spots. Under the condition of high humidity, the disease produces a large number of gray conidium, hence the name Botrytis cinerea.

Pathogen

Botrytis cinerea [BotrytiscinereaPers.exFr.] It belongs to the subphylum of half-known bacteria. The fruiting body of the pathogen originates from the hyphae or sclerotia. Conidiophores tufted, gray, turning brown later, conidia ovate. Its sexual generation [Botryotinia****eliana (deBary) Whetze] belongs to the subphylum ascomycetes.

two。 Rhododendron brown spot

Symptom

Rhododendron brown spot is also known as leaf spot. At first, there were small yellowish round spots on the leaves, which gradually expanded in an irregular shape, turning into reddish brown in the middle and dark brown in the middle. The diseased leaves fall off prematurely, and the growth of the plant is hindered in severe cases. Examination of diseased leaves, you can find small black spots on the disease spot, which is the conidium of the pathogen. The disease of cuckoo planted in greenhouse is serious, especially when the humidity is high.

Pathogen

Cephalosporium [SeptoriaazaleaeVogl.] It belongs to the subphylum of semi-known bacteria. The pathogen overwintered with mycelium and conidia in the host plant tissue or on the fallen leaves, and a large number of conidia were transmitted on the diseased leaves in the coming year.

Prevention and cure method

Sweep and burn the fallen leaves in time in winter and spring. After leaf spreading, Bordeaux solution (1-1-1-100) was sprayed every half a month, which could be sprayed 2-3 times continuously to prevent the disease. 1000 times of 50% methyl topiramate wettable powder was sprayed 1-2 times in the early stage of the disease to inhibit the development of the disease.

3. Iron deficiency chlorosis of rhododendron

Rhododendron iron deficiency chlorosis, also known as yellow leaf disease, chlorosis, is a common disease of potted rhododendron.

Symptom

The disease often occurs on tender shoots and new leaves. At the initial stage, the mesophyll between the veins faded and lost its luster, and then gradually became yellow and white, but the veins remained green, making the green on the leaves reticulate. Then the yellowing degree increased gradually, except for the larger veins, the whole leaf turned yellow and white, and when it was serious, it scorched inward along the leaf and leaf edge.

Cause of disease

Rhododendron iron deficiency chlorosis is a physiological disease, mainly because soil iron deficiency or iron can not be absorbed and utilized, so it affects the synthesis of chlorophyll and makes the leaves turn yellowish green. In general, there are the following aspects: in calcareous alkaline soil, the soluble divalent iron that can be used is transformed into insoluble trivalent iron salt and precipitated, so that the roots cannot be absorbed; potted flowers are watered frequently, resulting in excessive leaching and loss of soluble iron in the soil. In the areas with heavy soil viscosity, poor drainage or high groundwater level, the root development is affected, the normal physiological activities of the roots can not be carried out, and the ability of the roots to absorb iron is reduced.

Prevention and cure method

Cuckoos like acid and alkali, should avoid planting in alkaline and calcium-rich soil; garden open field planting, do not go near cement, brick walls or places where lime has been used. Potted rhododendron should use acidic soil, which can be replaced by alkaline soil; when rhododendron is planted in nursery, compost, green manure or other organic fertilizers can be used, and the organic acid produced in these fertilizers can dissolve insoluble iron in the soil and make it easier for plants to absorb. Or mixed with ferrous sulfate in fertilizer, the preparation is: ferrous sulfate 2.5-3 cm, oil meal 5-7.5 cm, dung 10-15 kg, water 200-250 jin, mixed, after its maturity into black can be used. This method has a good effect. In the slightly alkaline soil, 0.1-0.2% potassium dihydrogen phosphate solution can be irrigated, and the pH value of this solution is 4.7, which can turn the alkaline soil into an acidic soil, and the yellowing of tender leaves can be treated. At the same time, there are phosphorus and potassium elements in potassium dihydrogen acid. conducive to flowering and increase the number of flowers.

Regular application of ferrous sulfate solution will cause too much sulfur and effective iron in the soil and poison plants. Disodium ethylenediamine tetraacetate 0.14 g, ferrous sulfate 0.1 g (chemically pure) can be mixed into 500 ml tap water and foliar sprayed, the leaves should be sprayed on the front and back, once every 3 days, several times, good results can be obtained.