Rosemary, diseases and treatments : what to do in case of rosemary with yellow leaves or if the tops turn black or with white dots. All the instructions for the correct cultivation of rosemary in pots or in the field.
Rosemary is an aromatic plant that is easy to grow, even for those who do not have a plot of land: potted rosemary grows well on the balcony or terrace of your home. Even though it is an easy plant to grow , rosemary is certainly not immune to diseases. On this page we will see the most common diseases that attack rosemary grown in pots or in open fields.
Rosemary, diseases and cures
Rosemary , botanically known as Rosmarinum officinalis , is a very robust species that rarely contracts diseases that require phytosanitary intervention. Generally, problems arise more easily in the case of cultivation in pots with excessive irrigation.
To prevent any type of disease or help the regression of symptoms, we invite you to take care of some aspects of rosemary cultivation such as:
- if growing rosemary indoors, lack of light. Make sure the plant gets the right amount of light.
- If growing in pots or in open ground, overwatering. Make sure the soil is dry between waterings.
- Check the soil conditions, avoid water stagnation. If growing rosemary in a pot, add a drainage layer (5 cm of expanded clay) on the bottom of the pot.
- Fertilize only if necessary (usually in spring), some diseases can occur due to a lack or excess of fertilization.
- If growing in open fields or if the pot is placed near the composter, check that there are no harmful nematodes in the soil.
It is not necessary to protect rosemary plants in winter because this very rustic species can tolerate temperatures down to -10 °C.
Rosemary with yellow leaves or leaves that dry up and fall off prematurely
Yellow leaves with spots that may be brown and that dry towards the tips may be the result of inadequate irrigation. Check the drainage of the soil, aerating it with a hoeing operation.
If the rosemary is grown in a pot, the operation is simpler because you will only have to repot it by changing the soil. When repotting, check the health of the root system (if there are black parts, cut them off! Black roots indicate necrosis , that is, dead tissue and root asphyxia). For the new pot, use a specific soil for aromatic plants and arrange 5 – 6 cm of expanded clay on the bottom of the container.
Fungal diseases of rosemary
When there are critical conditions such as yellow leaves or black tops, rosemary becomes more exposed to fungal attacks. Be careful of powdery mildew which can cause the death of the plant. If your garden has recently had powdery mildew infestations, perform a copper-based treatment.
Rosemary with white dots on the leaves
This is a fungal disease, powdery mildew, also known as white mold. As mentioned, powdery mildew can take root on rosemary when the plant is already fragile. In this case, it is possible to follow treatments with fungicides permitted in organic farming.
The copper sulfur-based fungicide is effective against powdery mildew and other cryptogamic diseases such as alternaria, anthracnose, diseases that can infest rosemary in case of deficiencies or inadequate irrigation. We reiterate this concept because, in addition to the use of the fungicide, it will be necessary to control the soil conditions as previously explained.
Rosemary with black leaves that dry
The discussion is similar to what was previously stated: black leaves, first on the tips and then on the entire leaf, are a symptom of excessive irrigation. Also in this case, proceed with repotting the rosemary grown in a container while restoring good drainage in the case of rosemary grown in the open field.
