Your plant suffers from this disease when you discover a white, powdery and washable cover on top of the leaves. Later on, leaves change their colour to brown and wither. Pathogen of the disease is a fungus. Its spores fly through the air, sit down on leaves, germinate there and build up a mycelium. Most fungi require moisture in order to germinate, but not the Powdery mildew fungus. It germinates only on dry leaves. This is the reason why it is also called “The fair-weather fungus”. Powdery mildew infects plants like cucumber, carrots, black salsify, fruit trees, roses and other ornamental plants.
In contrast to the Powdery mildew, the Downy mildew loves moisture. Its spores swim on moist leaves and penetrate into the plant tissues through the stomas. Whereas Powdery mildew settles on top of the leaf, Downy mildew infects the backside of the leaf. Here, the fungus builds a grey-violet mycelium. Plants this mildew infects are radish, horseradish, lettuce, peas, spinach, onions and grapevines.
This is an illness without uniform symptoms because the pathogens can be different fungi species. The pattern of damage ranges from yellow, red and brown to black areas on top of the leaves. At the beginning, there are small spots which get bigger and bigger. When these spots start to flow together, the leaf starts to wither and dieback. Often affected plants are celery, tomatoes, marguerites, parsley and chrysanthemums. The disease spreads out rapidly. We recommend, from the beginning that you set your plants at larger distances apart, this way after rain the leaves are able to dry very fast which reduces the risk of infection. Most spores are in the soil therefore they can be washed up by the rain and also get into the leaves. You can prevent this by covering the ground with straw. Another tip is to water plants not from above but from below.
If your plants are infected with fungi it is important to remove the withered parts. Do not throw these parts into the compost because the fungi are able to spread further. You can get rid of them by throwing them into the domestic refuse. Strengthening plant broths are often effective when combatting unwelcomed parasites. A strengthening remedy is very simple to make. You take an onion or a bulb of garlic and heat it up with water. After that you water your plants with this broth. You can also spray infected parts with this liquid. This process, however, should be done regularly. Otherwise it has no effect. You should only use chemical pesticides if the infection is very serious or appears perennially.