What are the control methods for gray mold on hydrangea?
In Zhejiang, Shanghai, Jiangsu, Hebei, Beijing and other hydrangea native areas and introduction areas, it occurs to varying degrees. It harms the flowers, flower buds and young shoots of hydrangea, Chinese rose, pomegranate, ornamental peach and many other flowering trees and shrubs, causing the affected parts to soften and rot and reducing their ornamental value.
Symptoms The lesions occur mainly on the flowers. At first, water-soaked irregular small spots appear on the petals, then gradually expand and can spread over the entire corolla and inflorescence. When flower buds are affected, irregular water-soaked small spots also appear, which can expand to the entire flower bud, and finally the flower bud softens and rots and cannot open. After young shoots are affected, water-soaked irregular small spots first appear, gradually expanding until the new shoot and young leaves rot. Under warm and humid environmental conditions, in the later stage a large amount of gray mold develops on the affected parts.
Occurrence pattern The pathogen is a fungus, Botrytis cinerea. The pathogen mainly overwinters as sclerotia and conidia on diseased flower, shoot, leaf and other diseased tissue residues. The following spring when the temperature rises, or when rain occurs or humidity is high, conidia are produced from the sclerotia, or conidia produced on other infected host parts are spread by airflow to hydrangea and germinate quickly to infect it. For hydrangea in greenhouses and plastic tunnels in the north, the pathogen mainly comes from diseased tissue residues from the previous year, and the disease begins during the flowering period in early to mid-May. Planting too densely, rainy and humid and cool weather, as well as excessive application of nitrogen fertilizer or insufficient light and weak growth, all make the disease more likely to occur and spread. High temperature and dry conditions are unfavorable to the occurrence of the disease.
Control methods
(1) Clean the flower nursery. At ordinary times, pay attention to maintaining hygiene in the protected area. When diseased flowers and diseased shoots are found, prune them off promptly, sweep up plant residues on the ground at any time, and bury them deeply in a centralized place. After winter begins, thoroughly clean up fallen leaves and residues in the protected area and nearby areas, and bury them deeply in a centralized place; they must not be discarded at will.
(2) Strengthen cultivation management and enhance disease resistance. Keep planting density appropriate to facilitate ventilation and light penetration. Pay attention to applying more phosphorus and potassium fertilizer and avoid excessive application of nitrogen fertilizer. In sheds and rooms, pay attention to maintaining suitable temperature and humidity. When the temperature is low, close the shed to raise the temperature, increasing it to 31-33°C; when humidity is high, vent air to remove moisture and create conditions unfavorable to the occurrence of the disease.
(3) Chemical control. In sheds and rooms with a history of the disease, spray chemicals 1-2 times before flowering for prevention. You may choose 50% iprodione wettable powder at 1500 times dilution or 70% thiophanate-methyl wettable powder at 1000 times dilution, etc. During the flowering period, spray 1-2 times depending on the disease condition. You may choose 65% procymidone wettable powder at 1500 times dilution, 50% dimethachlon wettable powder at 1800 times dilution, 36% thiophanate-methyl suspension concentrate at 800 times dilution, etc.