What Is Rhododendron Leaf Spot? Symptom Identification and Control Methods
What is rhododendron leaf spot? How to control it. Please introduce rhododendron leaf spot: Symptoms: It mainly infects the leaves. In the early stage of the disease, small reddish-brown spots appear on the leaves and gradually expand into round lesions, or irregular polygonal lesions, dark brown, 1mm-5mm in diameter. In the later stage, the tissue in the center of the lesion turns grayish white...
What is rhododendron leaf spot? How to control it. Please introduce
Rhododendron leaf spot:
Symptoms: It mainly infects the leaves. In the early stage of the disease, small reddish-brown spots appear on the leaves and gradually expand into round lesions, or irregular polygonal lesions, dark brown, 1mm-5mm in diameter. In the later stage, the tissue in the center of the lesion turns grayish white. When the disease is severe, the lesions connect with one another, causing the leaves to turn yellow and fall early. Under humid environmental conditions, many small brown mold spots grow on the underside of the leaf spots, namely the conidia and conidiophores of the pathogen.
Pathogen and disease status: It is Cercospora rhocdodendri Fer., Deuteromycotina, Hyphomycetes, Moniliales, Cercospora. The pathogen overwinters on plant residues, and the following year forms conidia as the primary infection source. The conidia are spread by wind and rain and invade through wounds. In Jiangxi, the disease begins to occur in mid-May, and August is the peak period of occurrence. In the Guangzhou area, the peak period of occurrence is from April to July, and rhododendrons cultivated under greenhouse conditions can develop the disease year-round. Abundant rain, heavy fog, and heavy dew favor the disease, because conidia can germinate only in water droplets. Poor ventilation and light transmission, and poor plant growth, can aggravate the occurrence of the disease.
Control methods:
1. In autumn, thoroughly remove fallen leaves and dispose of them, and promptly remove diseased leaves during the growing season.
2. The planting density of potted flowers should be appropriate so as to provide ventilation and light transmission and reduce leaf surface humidity. In summer, place potted flowers in a shade shed outdoors to reduce wounds caused by sunscald and mechanical injury.
3. Immediately after flowering, spray 65% zineb wettable powder at 500-600 times dilution, or 50% carbendazim wettable powder at 500-800 times dilution, or 70% thiophanate-methyl wettable powder at 1000 times dilution. Spray once every 10-14 days, for 2-3 consecutive sprays.
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