See:
Boxwood (Buxus spp.) - Boxwood Blight
Cause The fungus Calonectria pseudonaviculata (synonyms Cylindrocladium pseudonaviculatum or C. buxicola) can infect many plants in the boxwood (Buxus spp.) family including boxwood, Pachysandra and Sarcococca. Diseased pachysandra are usually found in landscapes in mixed plantings with infected boxwood. Both Pachysandra procumbens and P. terminalis are susceptible while P. axillaris is less so. There may be differences in susceptibility between various cultivars.
The fungus can survive in fallen leaves for up to 5 years and can produce spores in a sticky, slimy matrix when environmental conditions become suitable. Mild wet weather west of the Cascade Range is conducive for long-term survival and infection. Microsclerotia (long-lived survival structures) are formed within infected tissue, released into the soil when the tissues break down, and subsequently initiate new infections by producing infective spores or when splashed onto foliage directly. Short-distance dispersal occurs through water or rain splash (especially wind-driven rain) and human activities such as pruning. Long-distance dispersal can occur through the transport of infected nursery stock or infected plant debris. Spores are unlikely to travel long distances by wind alone.
Symptoms Leaf spots start as water-soaked spots that develop into small (up to a third of an inch), round to irregularly shaped, brown-to-black leaf spots. Blotches occur from coalesced lesions, and lesions in old leaves had a thin and darker margin. Sporodochia were observed on the undersurface of affected leaves after 24-hr incubation at 77°F. Leaf chlorosis and defoliation were also observed.
Cultural control To limit spread and movement of the pathogen, all confirmed infected plants should be destroyed including nearby boxwoods.
- Do not grow susceptible plants on ground that has been positive for this disease.
- Avoid overhead irrigation.
- Grow tolerant species or cultivars.
- Mulching with composted pine bark has helped reduce transmission to healthy plants in landscape conditions.
Chemical control Although chlorothalonil (group M5) is available in small, home packaging (from Bonide, Hi-Yield, Ferti-lome or Ortho) none are specifically labeled for this disease. It is suggested that home gardeners hire a reputable landscape company for management of high-value hedges and landscapes. Both cultural and chemical tactics must be used.
- Daconil Weather Stik at 1.38 pints/100 gal water. Do not use with a surfactant. Excellent control. Can be used in the landscape and many other sites. Group M5 fungicide. 12-hr reentry.
- Spectro 90 WDG at 1 to 2 lb/100 gal water. Many turf sites need to be avoided. Group 1 + M5 fungicide. Excellent control. 12-hr reentry.
Reference LaMondia, J.A. 2017. Pachysandra Species and Cultivar Susceptibility to the Boxwood Blight Pathogen, Calonectria pseudonaviculata. Plant Health Progress doi:10.1094/PHP-01-17-0005-RS