Dealing with Powdery Mildew on Rosemary: Causes, Symptoms, and Remedies

Growing rosemary plants is common. Although it is easy to grow, but it does comes with some faults such as fungus.

If you are also struggling with this issue, then your plant is suffering from powdery mildew on rosemary. Continue reading the article to know what causes it, the symptoms and the effective remedies.

What is powdery mildew on rosemary?

Many different closely related fungi cause the common plant ailment known as powdery mildew on rosemary. This ailment appears as a white, fungus-like powder.

Powdery mildew is basically the most common problems with all the indoor infected plants and rosemary is of no difference.

Rosemary powdery mildew, though won’t kill the plant but reduces the strength of it. The powder is the little spores and can spread to other plants, if severe. However, this the most easiest plant disease to diagnose.

Rosemary with powdery mildew.

Causes of powdery mildew rosemary

The rosemary has rarely indoor issues. It survives the summers even without proper watering. However, as soon as you expose it to outdoor conditions or place it in a humid environment, the countdown begins. Let’s discuss the factors contributing to rosemary powdery mildew.

Environmental Situations

  • High Humidity: One of the primary factors that contribute to the onset of powdery mildew is high humidity.
  • Temperature: Mild temperatures, generally between 60-80°F (15-27°C), also favor the growth of powdery mildew.

Improper Air Circulation

  • Stagnant Air: Lack of air movement around the rosemary plant can create a microclimate that is conducive for the fungus to grow.
  • Plant Density: Overcrowding of rosemary plants can also lead to poor air circulation, making it easier for the disease to spread.

Weakened Plants

  • Nutrient Deficiency: Plants that are weak due to lack of essential nutrients are more susceptible to diseases, including powdery mildew.
  • Stress Factors: Other factors like overwatering or underwatering can also weaken the plant, making it more prone to infection. 

Spread and Infection Mechanism

Powdery mildew spores are primarily spread through wind and water splashes. The spores germinate on the leaf surface and penetrate the plant tissue, leading to the characteristic white, powdery spots, when the environmental conditions are favourable.

The spores can be transferred from one plant to another through direct contact or via gardening tools that have not been properly sanitized.

Symptoms of Powdery Mildew on Rosemary

Rosemary powdery mildew signs can be identified by various visual symptoms that includes white or grey powdery spots on leaves, stems, and on flowers. As the disease spreads, it leads to discoloration, turning the leaves yellow or brown. The new leaves grows twisted, proving that the plant’s growth is adversely affected.

However, the symptoms of rosemary powdery mildew goes beyond as it can affect the overall health of the plant. It hampers the plant’s ability to photosynthesize, reducing the growth. In addition, the plant’s ability to absorb nutrients may be compromised, making it more susceptible to other diseases.

Powdery mildew on rosemary.

Remedies for Powdery Mildew on Rosemary

There are several different species of fungi that causes powdery mildew. It is in best course to prevent it in first place and this could be the best remedies for rosemary powdery mildew.

The other ways of how to get rid of powdery mildew on rosemary is as follows:

  • The disease spreads if they are kept too near to one another. However, if your plant is kept indoors, an open window or light moving fan can assist with air moment and prevents the fungus from growing on the rosemary leaves.
  • As cold and flu viruses pose challenges to affected individuals, similarly, maintaining healthy plants reduces their susceptibility to illnesses. Thus, it is advisable to ensure that your plants are in good shape.
  • Rosemary grows better in drier, looser soils. Make sure that the soil is apt.
  • An alkaline baking soda solution. Is baking soda capable of doing anything else? But indeed, you can treat powdery mildew in a highly natural way using baking soda. You should mix three tablespoons of baking soda, one tablespoon of vegetable oil, and a few drops of dish soap with one gallon of warm water.
  • Trichoderma harzianum treating powdery mildew on rosemary.Trianum-V, with its active ingredient Trichoderma harzianum, is often considered environmentally friendly compared to chemical fungicides.  Trichoderma harzianum produces enzymes and secondary metabolites that can directly inhibit the growth of the powdery mildew fungus. These substances can break down the cell walls of the powdery mildew pathogen, disrupting its mycelial growth and preventing its attachment to the plant’s surfaces.


In conclusion, powdery mildew on rosemary is a common issue that can weaken your plant but is treatable. Interestingly, strawberry powdery mildew is another similar problem. You can manage both by implementing preventive measures and using natural remedies like baking soda and neem oil.

Don’t let your garden suffer; take action now. If you’re grappling with rosemary or strawberry powdery mildew, check out our range of organic products designed to tackle these issues.


1.Peres, Natalia, et al. “Biopesticides and Alternative Disease and Pest Management Products: VPH ch. 19, CV295, rev. 5/2022.” EDIS (2022).

2.Mahapatra, Sunita, et al. “Antimicrobial agents for wheat disease management: mode of action and its application.” New Horizons in Wheat and Barley Research: Crop Protection and Resource Management (2022): 179-214.

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