In many places these days, hanging petunias are competing with geraniums as balcony plants, as they grow quickly in a sunny location and are available in a variety of attractive colors. However, petunias can also be attacked by a number of diseases that can severely limit the blooms without countermeasures.
What diseases can affect petunias and how do you treat them?
Petunia diseases include powdery mildew, root rot and chlorosis (deficiency symptoms). Prevention and treatment include removing infected plant parts, changing location, fertilizing or replacing the plant substrate.
Powdery mildew on petunias
Powdery mildew is a fungal disease that can spread quickly in dense petunia stands without treatment. The occurrence of powdery mildew is more likely when petunias are exposed to wet, rainy weather without a protective roof. If persistently wet weather means that plants are permanently moist and are not easily dried by the wind and sun due to their growth, powdery mildew usually doesn't take long to appear. It can be recognized by the white coating that can cover all parts of the petunia like a flour-like layer. Possible prevention and treatment options are:
- the regular removal of wilted flowers and plant parts
- Setting up in a rather dry location
- spraying with a water-milk mixture (9 parts water, 1 part milk)
- cutting out affected plant parts
Unlike downy mildew, powdery mildew only thrives on living plants, so removed petunias can be safely composted.
The root rot
The so-called root rot is a disease that is transmitted with the plant substrate used. The upper root area and the base of the stem turn black or brown before the entire plant wilts and dies. In such a case, there is no longer any salvation for the petunias. However, you should replace the potting soil and dispose of the old substrate if possible (not in the compost). In this way you can ensure that newly purchased plants or young plants grown from seeds are not affected by root rot again.
Chlorosis: A deficiency symptom
Chlorosis is the yellowing of leaves, which usually occurs on the young leaves of petunias. Strictly speaking, this is not a disease, but rather a deficiency caused by too few nutrients in the plant substrate. This often occurs when petunias are overwintered in the same balcony box for several years without significant fertilization. Since it is usually a case of chlorosis due to iron deficiency, foliar fertilization with a special iron fertilizer (€5.00 on Amazon) often helps.
Tip
Severity symptoms in petunias are often not necessarily due to illness, but can also be a symptom of persistent wetness in the root area. Petunias should only be watered very sparingly, especially in winter quarters, otherwise they can easily die due to root rot.