Several of the most common leaf spot fungal diseases can affect this shrub. These diseases are so common that they can be called ubiquitous, just waiting for an opportunity to infest a susceptible host.

To prevent the spread of the diseases, avoid overhead watering, prune overhanging foliage to improve air circulation and sunlight penetration, clean up fallen plant debris, etc.

Fungicides can be used successfully to gain control and good housekeeping practices can help prevent it from starting up again. Look up any university based fact sheet on viburnum diseases to read the details and see fungicide recommendations.

Unless you change the environment, your plants will always have problems. Just a little bit of gardening will make a big difference.

Thanks Rhizo.