Do you know a natural or herbal preventive fungicide for phytophthora in peonies?
The Gardener’s Answer
Hello, Anne: Phytophthora cactorum is a fungus that is actually commonly found in our soil. When we introduce certain plants such as peonies into this soil, they can become diseased. Of course, there are other factors that make the peonies more susceptible to this fungus. Peonies should be planted in full sun, with good air circulation and well-drained soil, which is key to protecting these flowering shrubs. The drainage can be improved by adding a product such as Permatill to your existing soil. Permatill is an expanded slate material and will help to break up clay and improve drainage as well as air circulation within the soil. The best natural defense is planting in an optimal environment. Phytophthora is spread by rain when it splashes from the soil onto the plant; this is especially true during cool springtime weather. This is why we water from the base of the plant and avoid watering the foliage. It is also a good idea to avoid watering mid-day into the evening before the sun goes down since there is not enough sunlight to allow the foliage to dry out. Morning watering is best. The fungus can also be spread through contaminated tools, so it is important to clean your gardening tools frequently. If the roots are infected on your peonies, you should remove the plants as well as the soil surrounding the roots. If the roots are still healthy, make sure to remove and dispose of all contaminated foliage/stems. They will be dark brown or black in color with a leathery texture. Fungicides will only be effective as a preventive measure if the plants are not yet diseased or to parts of the plant that are not yet affected. Neem oil is a natural product that can be used as a fungicide. As with any fungicide, natural or not, it will only be useful when used as a preventive treatment.