Dark blotches on leaves are sign of Volutella blight
Q: My bed of pachysandra has developed dark blotches on the leaves. I’mwondering what this problem is and what I can do to improve the health and appearance of this planting?
— Bob Gordon, PrairieView
A: Your description indicates that your plants are suffering froma disease called Volutella blight, which can be a very destructive disease affecting pachysandra in the Chicago region.
Volutella is a fungus that can cause necrotic blotches on leaves and stems; the blotches range in color from brown to black. The blotches have lighter and darker zones that appear as irregular concentric rings, and they increase in size throughout the season until the entire leaf and stem turns black and dies. In verywet conditions, the fungus may kill large patches of plants.
A diagnostic feature to look for is pink-to-orange spore masses on the underside of leaves or on stems. Look particularly for Volutella blight in dense plantings where heavy mulch has been used and where conditions arewarm and moist. Pachysandra beds that have been stressed by winter, drought, insects or overcrowding are more susceptible to this fungal disease.
Late spring and early summer are the most common times to find active Volutella blight on pachysandra after winter stresses plants, followed by lots of moisture in spring and early summer at the optimal temperature range of 64 to 80 degrees Fahrenheit. These linked conditions can happen later during the season and incite active infection later in years like this year. The summer drought followed by rains may have caused the active Volutella blight you are finding in your garden. I have seen infections in other gardens recently, too.
Stressed plants are far more susceptible to this disease, so begin to control it by removing the stressors. Be sure your pachysandra getswatered during extended dry periods, but onlywater deeply and in the morning to allowthe foliage time to dry before nighttime. Avoidwatering frequently and shallowly, as this willworsen the condition.
Wetweather encourages nearly all fungal diseases, including stem and leaf blight. Do not mulch an established bed of pachysandra, as the mulches holdwater against the plant stems, which can promote fungal issues. On the other hand, if you are planting pachysandra this fall, then it is important to mulch the bed so the plants can establish. Remove fallen leaves and debris fromthe bed of pachysandra this fall and in subsequent years.
Youmaywant to treat your bed of pachysandra with a fungicide this fall to help mitigate the problem. Prune out any badly affected areas and discard the foliage. Soon itwill be too cool for the disease to proliferate, but the stage is set to have more problems next spring. Some chemical options include chlorothalonil, copper, Duosan, Fore, mancozeb and Zyban. Always followlabel directions when using any chemical product.