As with any landscape garden, the best way to prevent pest and disease problems is to provide an environment needed to grow healthy plants. Most problems that attack Pachysandra terminalis (Japanese spurge) do so when the plants are under stress. Too much sun can make pachysandra appear diseased by causing leaves to yellow and burn. Thin out dense stands to ensure adequate air circulation. If optimum growth conditions are absent, certain pests and diseases may make their way into a pachysandra spread.
Volutella Leaf Blight
The fungal disease Volutella pachysandrae gets its name because it affects pachysandra alone. It mostly attacks dense patches of Japanese spurge in wet environments. The Plant Disease Diagnostic Clinic at Cornell University best describes the symptoms: "Irregular spots or lesions are first seen in the early summer. Infected leaves and stems exhibit brown blotches on leaves and/or brown shriveled stems. The planting of pachysandra may become thin as the disease progresses. The leaves may appear orange due to the presence of spores of the fungus." Help prevent infection by pruning to keep patches thin. Fungal diseases spread by moving water, so do this on dry days.
Volutella pachysandrae also causes cankers on pachysandra stems. The shoots will blacken and die, sometimes before symptoms are noticed on the leaves. Once a fungal infestation is noticed, dig out infected plants and remove the dead material from the garden entirely. Put them in a sealed bag in the trash. Apply fungicides according to label instructions for additional control. The Ohio State Extension Service recommends spraying every two weeks from early spring through mid-summer.
The University of Arkansas Cooperative Extension Service describes nematodes as "microscopic worms that live in soil and feed on the roots of many common garden crops." Nematode feeding causes swelling, or "knots" on roots, yellow, wilting leaves, symptoms similar to sunny or otherwise poor growing conditions. If the environment is right for healthy pachysandra, dig up a few plants and look for swollen, perhaps rotting roots. Chemical controls are available but not recommended. Dig out under-performing plants and fertilize the soil well to encourage vigorous root growth, despite nematode presence.
Pachysandra growing in sunny, drier conditions tends to be susceptible to scale infestation. Tiny bugs with armored bodies attach themselves to stems and the undersides of leaves and suck vital juices from the plant. Plants may yellow and will grow very little. Remove groups of infected plants and maintain a fertile, healthy growing environment. The armored bodies of adult scale protect the bugs from insecticides, so target newly hatched "crawlers" with frequent applications in late spring through midsummer.
Dry weather invites mites to feed on pachysandra. Heavy infestations are apparent when fine webbing clings to the undersides of yellowing leaves and stems. Mites are best controlled by frequent irrigation and shady growing conditions. Do not apply miticides to plants already stressed by dry weather.