Flower Treatments: Annual Vinca Flower, Phytophthora Stem Blight &Pythium Root Rot


Annual Vinca

Annual vinca (Catharanthus roseus) is commonly used as summer color in our annual flower beds and landscapes. It thrives in sunny areas and is fairly drought tolerant. A perfect flower for our hot and dry region.  It is also called Madagascar periwinkle or just vinca.  While vinca can normally withstand blazing heat, there are times that the flower looks like it is under drought stress.  This is NOT drought stress.  It is a fungal disease called Phytophthora or Root Rot.  Root rot’s symptoms look like drought stress which causes most of us to rush out and water or irrigate the flowers in hopes that they’ll bounce back like most other annuals.  Unfortunately, watering only makes the symptoms worse.  Read below…

Phytophthora Stem Blight, Pythium Root Rot

Aerial stem blight and root rot are caused by Phytophthora nicotianae and occasionally other species. Stem and branch blight frequently occurs without root rot, but root rot is involved in some cases. Dark brown to black lesions form on stems and branches, causing the portions above to wilt and die back. Symptoms of root rot include yellowing and scorching of leaves, poor growth and stunting of plants, wilting and death. Plants with root rot have reduced root systems and individual roots tend to slough off the outer tissue, leaving the inner core behind.

Prevention & Treatment: Water management is the main preventative measure. Frequent watering, even in moderate to dry sites, can make things worse.  Annual vinca and Vinca species are fairly drought tolerant, so water only as needed. When rainfall is insufficient to supply an inch of water per week, apply deep supplemental irrigation once, or possibly twice per week, depending on soil type, exposure and weather conditions. Avoid excessive amounts of fertilizer as well. 

Plan of Action: Throughout the month of July, we will be removing infected plants as we see them. We will treat remaining plants with a fungicide if cultural practices are failing to prevent new infections from occurring.  Please resist the urge to water these plants and if you have any questions, feel free to give us a call and we will be happy to discuss in detail this POA if necessary.