Prevention and control of rhododendron brown spot
1. Symptoms
Primary reddish-brown dots on diseased leaves, gradually expanding into subcircular, or polygonal spots limited by veins, 1-5 mm in diameter, dark brown; sometimes gray-white in the center, the margin is not obvious. The disease spot leaves are one-sided deep and the back color is light, and the disease spots on the leaf edge can be connected to each other, and most of them produce gray-black mildew spots on the surface of the disease part when it is wet.
2. Pathogen
The pathogen of rhododendron brown spot is CercosporarhododendriFerraris, which belongs to Trichoderma. The gray-black mildew spots on the disease spot are the conidia and conidia of the pathogen. Conidia light brown, 1-4 septum. The conidia are placed at the top of the conidiophores, whip-shaped, apical, slightly curved and segregated after maturity.
3. The law of occurrence and development
The pathogen overwintered with mycelium on diseased leaves or plant remains, and the suitable temperature in the second year was to produce conidia. The spores were transmitted by Rain Water or the wind, and the spores floated on the leaves. When they encountered dew or water droplets, they produced bud tubes and invaded the leaf tissue, which generally occurred more seriously from April to July.
4. Prevention and control methods
(1) strengthen the management of the nursery: remove the diseased leaves, remove the fallen leaves underground or in the basin and burn them centrally. Keep ventilated and transparent in summer to avoid excessive humidity.
(2) Pesticide control: spray 50% carbendazim wettable powder 500 times 800 times, or more than 50% topiramate 800 times 1000 times, or spray with 1 Bordeaux solution.
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Pay attention to changing pots after azaleas.
The pot should be selected according to the plant size, and the mud pot is better. The general pot diameter (inner diameter) should not exceed half of the crown diameter. Cuckoos like acidic soil and require a pH value of 4.25-5.5. If this acidity is not maintained, it is difficult for potted cuckoos to survive, and the potted soil requires loose drainage, rich in humus, and do not use sticky loess. When using soil, it is best to prepare according to the original soil quality of rhododendron. Previously, plants cultivated with pine soil should still choose loose soil, which can be mixed with a small amount of rotten horse dung and bone powder.
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Control of Root Rot of Rhododendron
Root rot is a serious threat to rhododendron. Although its incidence is not high, the mortality rate after infection is very high. Therefore, attention must be paid to the prevention and control of root rot in the cultivation and management of rhododendron. Root rot is a soil-borne disease caused by Fusarium oxysporum, which mostly occurs in the roots of rhododendron, because these parts are often moist, lack of sunlight, and Fusarium oxysporum fungi are active frequently. Once it invades the cortex, it will soon cause rot, watery brown spots and soft rot will appear on the roots, and the xylem will be black and brown.
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