Many growers in Florida face challenges propagating and growing Viburnum species. Leaf spots, defoliation, shoot dieback and potential death of plants can occur if the environment, weather conditions, and diseases are in the right alignment to favor fungal outbreaks. Over the last few years our research team (Dr. Gary Vallad and his pathology lab, Dr. Wael Elwakil, and myself) have been working on the identification of disease pathogens and their fungicidal control with the help of an FNGLA Research Endowment Grant. So, what have we learned from our work? Here is a summation of the important lessons we have learned.
We thought that downy mildew was the main culprit causing leaf spots blotches and defoliation. This might be true when the weather is slightly cool, for instance in early spring. When weather turns to hot and rainy, there are a whole host of other fungal pathogens we identified that cause very similar symptoms on the leaves and shoots. These fungi are hard to distinguish from downy mildew and require a different approach to which fungicides should be used to control them.
Our efficacy studies have had mixed results due to the fact we were initially targeting downy mildew with very specific fungicides. We learned that the other fungal pathogens were better controlled with non-downy mildew, general foliar spot type fungicides.
We presented this work at our last Grower and Landscape Field Day. We have also presented these results to the FNGLA in a research report as well as conveying the findings to our colleagues at various scientific and extension meetings.
For a closer look at which fungicides we used and the results, here is a link to a video we made to better explain our results. https://www.youtube.com/watch?v=8omLE9yu6q4
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