Garden Q&A: pachysandra susceptible to blight
Q: Our home for many years has been surrounded by various healthy, expansive pachysandra plantings. The main patch is on a hillside that gets lots of sun. It has regular watering from an underground spring (in some areas). Another area with similar problems is very dry. Some leaves have turned yellow with brown spots, and, in some cases, sections appear to be slowly dying. We have applied Hollytone fertilizer and raked the fall seasonal leaves out of the patches. Our sister has a similar problem in Churchill and was told by a landscape person that the “disease is fatal and is similar to problems with alfalfa.” Your recommendations would be greatly appreciated.
Answer: The most common issue with pachysandra here in the East is volutella blight, a pathogen that causes tan to brown blotches on the leaves that gradually enlarge and kill the leaves. During wet weather, you also can find pink to orange spore clusters along the stems as well as on the leaves. This is a distinct feature of volutella blight.
This fungal disease thrives in moist conditions, and its spores are spread by rain and overhead irrigation. The disease often starts in patches and spreads. Volutella blight is most damaging when plants already are stressed by drought, insect infestations and full-sun conditions (pachysandra prefers full to partial shade).
Never work in pachysandra when the foliage is wet, and thin it every few years to increase the air circulation. Older plantings tend to be most susceptible because the plants are so dense. Never mulch pachysandra plantings because heavy mulches can trap moisture against the stems and increase its propensity for developing this disease. Mowing the plants down in early spring and raking up (and destroying) the clippings will encourage new, unblemished growth. Applications of an organic biofungicide such as Serenade are effective, especially when used early in the season on the new growth.
Unfortunately, pachysandra also has fallen prey to another pathogen in recent years. Alfalfa mosaic virus affects about 600 types of plants and is spread by an aphid. It is not common on pachysandra but is increasing in frequency here in Pennsylvania. Alfalfa mosaic virus is most often found near where farmers are growing alfalfa (which itself shows no symptoms) and causes rings or a yellow mosaic-pattern on the foliage. This virus is fatal, and infected plants should be removed and destroyed immediately.
Most gardeners will have a very difficult time telling alfalfa mosaic virus and volutella blight apart. Before doing anything, you should confirm which pathogen is at work in your pachysandra patch. Cutting off a few stems and putting them in a plastic baggie with a wet paper towel may cause the plants to develop the distinctive pink or orange spore clusters typical of volutella blight.
If the spores appear within a week or so, consider that confirmation of this common disease. If no spores develop, send a plant sample to the Plant Disease Clinic at the Penn State Extension Service. Their website is at plantpath.psu.edu/facilities/plant-disease-clinic. Only a pathology lab can properly confirm the identification of alfalfa mosaic virus.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.” Her website is www.jessicawalliser.com.
Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.
