Q. Our Vinca minor is in its third year since planting. It looked great this spring … lively, lush, green, lots of small purple flowers. In fact, it never looked better. A month or so ago, we started noticing brown areas here and there, then more and more. Nothing that we have done has changed and we don’t any sign of pest. What might be the cause of this? — G. Carlin, Williamsburg
A. A number of fungal stem/root rot and leaf spots plague both annual and perennial vincas. One of these, Phoma blight, aka Phomopsis, is caused by the fungus Phoma exigua. The pathogen attacks the above-ground parts of the plant. The stems wilt, turn black and die. On closer examination, you will see black lesions, which girdled and killed the stem. Within these, the black, pin-size fruiting bodies of the fungus may be visible.
Both Phytophthora and Rhizoctonia stem/root rots, as well as Pythium root rot, present similar symptoms in that the plant begins to decline, accompanied by leaf and stem wilting, followed by death. In the case of root rot, the pathogen infects and kills portions of the roots, causing the above-ground symptoms. The root system is no longer able to conduct water and will be brown and mushy.
These pathogens can be problematic in planting areas that are poorly drained and remain consistently wet. Good water management is key to their control. Cultural practices that reduce the moisture on the foliage and/or time the foliage remains wet will help suppress foliage fungal infections. Those that prevent waterlogged soils will help prevent root rots. Be sure to water carefully and monitor irrigation systems.
Other cultural control measures include removing dead leaves and stems and completely removing diseased plants, including roots. These should be taken off-site and destroyed.
With respect to chemical control, a number of fungicides can be used with varying results. Copper sulfate products (such as Bonide Copper Fungicide) and chlorothalonil products (such as Fertilome Broad Spectrum Landscape & Garden Fungicide and Bonide Fung-onil Concentrate) may offer some control. Always read the label completely and follow the directions.
Despite these treatments, the pathogen may persist in the soil. In this case, bed solarization or replacement with non-host species may be necessary.
And one more thing
The Tidewater Daylily Society is affiliated with the American Daylily Society. Its mission is to promote, encourage and foster the development and improvement of the daylily in Southeastern Virginia. For the past 14 years, the group has sponsored the Daylily Festival at Norfolk Botanical Garden. But because of the pandemic, this and other society events and fundraisers have been canceled.
In an effort to move their inventory of daylilies, the society will hold a “driveway sale” at 3612 Manchester Lane, Virginia Beach, next Saturday, July 18 from 8 a.m. to 2 p.m. This is your chance to pick up some rare and unusual cultivars.
Send questions to wkspen@gmail.com or to Home + Living c/o The Virginian-Pilot, 703 Mariners Row, Newport News, VA 23606.
