Vickie, thanks for your question.

  It’s hard to ensure that new plants will thrive, be Ok if there’re planted there. And there aren’t practicable soil sterilizers for this sitution. Knowing what caused to three viburnum to decline would help, buy in lieu of that there are several steps to take.

First, are any of the other viburnums showing the same symptoms? If not, that’s a good sign.

  The symptoms you described could be caused by a disease, pest or environmental factors. But from the description it is most likely a disease. Likely disease pathogens are fungal and bacterial. Either pathogen could be on any viburnum material (leaves, bark, twigs) lying on the soil around the plants. Also fungal or bacterial spores could be in the soil itself. Removing the viburnum material around the plants will eliminate these as a source of new infections. But, short of replacing all the soil, there is no practical way of getting rid of spores in the soil. But there are proven septs to reduce the chance of the new plants getting a disease.

General Tips for Preventing Disease

• Proper Watering: Avoid overwatering, which can promote fungal diseases. Water deeply and infrequently, allowing the soil to dry slightly between waterings.
• Air Circulation: Good air circulation around the plant helps prevent moisture buildup and discourages fungal growth. Prune away any branches that crowd the center of the shrub. Allow sunlight to enter the inside of the plant to reduce the chance of a disease getting started.
• Sunlight: Korean viburnums prefer full sun to partial shade. Adequate sunlight helps keep the foliage dry and reduces the risk of disease.
• Avoid Overhead Watering: Watering the leaves directly can spread fungal spores. Water at the base of the plant instead. Disease can also be spread when watering or rain causes the soil to be splashed up onto the plant. A layer of mulch, about two inches deep, under the plants will help stop the transfer of spores from the soil unto the plants.
• Diseased Plant Material: Remove and dispose of any fallen leaves, branches, or debris around the plant to prevent the spread of disease.
• Look for disease resistant cultivars and follow good cultural methods for viburnums, see the link.
• Fungicide Application (as a last resort): In some cases, applying fungicides specifically labeled for viburnums can be helpful as a preventative measure or to control an existing outbreak. However, this should only be done following proper safety guidelines and according to the specific product instructions on the label.

Clemson

  You're welcome Vickie, good luck your viburnums.