What is this white powdery substance on my plants and rockwool?
This white powdery substance is more than likely white powdery mildew, which can grow on your plants and rockwool due to a combination of lack of airflow, high humidity, overcrowded plants, lack of light, and/or mishandling.
White powdery mildew is a common fungus. While it is not directly harmful to humans, it will negatively affect your plants' health. The goal is to prevent it from growing, and when it does occur, the steps below should inhibit the fungus from growing any further.
If you see fuzzy white or grey growth on the rockwool, that may be a variety of mold. Mold grows similarly to white powdery mildew, as it prefers humid and wet conditions that lack airflow. However, it also prefers slightly warmer temperatures of 60-80 degrees Fahrenheit.
A good rule to follow is that if the leaves look healthy to the eye without any sign of disease when harvesting, they are suitable for consumption!
We recommend checking your plants at least twice weekly for signs of sick or weak leaves, trimming them back, and discarding them (following the rule of never trimming more than 1/3rd of the leaves). This way, the plant can put its energy towards creating more healthy leaves 🌱🥬 more suitable for consumption 🙂
How can I resolve the powdery mildew and mold on my plants and rockwool?
When white powdery mildew and mold do occur, we recommend the following steps:
Wipe down the rockwool with a clean cloth and 3% hydrogen peroxide (be careful not to wipe the plants as they are sensitive to such a high oxygen concentration). This a great step to remove mold as well.
You can wipe down infected leaves with a dish soap solution of 1 drop of dish soap for 1 cup water. You may notice this dries out your leaves, if your leaves are getting too dry reduce the ratio of dish soap. We find castile soap works best for plants. You can repeat this soap step every 10-14 days.
If the mold and/or mildew is only affecting parts of the plant you can trim off those portions. Remember to follow the rule of never trimming more than 1/3 of your plant at a time.
If a plant is fully covered by mildew or mold and you think there is a risk of it spreading, we would recommend removing the whole plant and using a soft rag with 3% hydrogen peroxide to clean the planting space.
How can I prevent white powdery mildew and mold in the future?
To prevent mold and mildew on your Flex Farm plants, check out our comprehensive article on Food Safety, Pest & Plant Disease Prevention.