My hydroponic green radish has been growing well. Recently, a white powdery substance has grown on the surface of the leaf neck, and it will be rubbed for a few days. What's the disease? how

Without the real map, it is difficult to confirm, and there are two possibilities for personal guess:

1. Powdery mildew is caused by pathogenic bacteria or fungi, especially orchids. Poor ventilation is easy to breed. It can be treated by spraying broad-spectrum bactericidal drugs such as carbendazim and thiophanate methyl once a week or so.

2. The pests and diseases of the mealybug, commonly known as scale insects, attach to the stems of plants and suck the juice, which is slightly like white floc. When you pinch it with your hands, there will be reddish blood flowing out. You can buy two or more special killing drugs from pesticide stores or flower shops and use them at intervals to prevent drug resistance. These drugs are toxic and have a strong pungent smell.