Phoma blight in plants is particularly damaging to a number of crops and ornamentals, especially to vinca groundcover. There are some preventative measures you can take in the garden and things you can do if you already see the infection. These may help save your plantings.
What is Phoma Blight?
Phoma blight disease is a fungal infection caused by various Phoma species. Infections by this fungus are most common in wet and cool conditions. It survives in soil and in the old plant debris that is under your plantings.
The signs of a phoma infection include wilting, browning, and death of runners and entire plants. If it is phoma blight, you’ll also see dark brown to black lesions that girdle the stems. The lesions usually appear close to the soil line. Leaves will have dark colored spots as well.
Phoma blight spreads rapidly, and any health part of a plant that is touching infected soil is at risk of succumbing. Plants that are most likely to be infected are those with wounds or that are stressed by growing conditions, such as overwatering or nutrient-poor soil.
How to Stop Phoma Blight
Stopping the spread of the fungal disease is difficult. It tends to spread rapidly through beds, and it also persists for a long time because the fungi survive well in the soil and debris under the plants.
Preventative steps are important and include avoiding overhead watering and ensuring air flow in the bed. Remove overhanging plants that restrict air movement and thin plants whenever necessary. It is also important to remove debris from under the plants, although this is difficult to do. Pull out any diseased or dead plant material underneath healthy plants to prevent further spread of the disease.
Treating phoma blight with fungicides may have mixed results. Copper fungicides are generally recommended, but be sure to check with your local nursery to get the right chemical for use on specific plants like periwinkle. There may also be other fungicides that will help control the spread of the disease. If phoma blight does become a big issue in your beds, you may want to consider pulling out all of the plants and putting in alternative disease resistant ones.