What is killing our shrubs?
By Ralph E. Mitchell
You may have noticed a few types of shrubs in our area which are either suffering from dieback, or completely ending up dead. There has been a lot of debate about what is the root cause of this decline ranging from disease and herbicide damage to cultural issues including incorrect planting and, of course, drought. What might be going on here?
The noted problems seem to have been limited mostly to Ligustrum, Viburnum, and Podocarpus in hedges and as individual specimens There are several identified factors that could be at work. One is disease, primarily a fungal disease called Botryosphaeria. Symptoms may include dried leaves, cankerous areas, tip and branch diebacks, and sometimes the death of the entire plant. Sometimes you will see individual shrubs in a hedge randomly affected. This disease can be triggered and enhanced by stress as may come from droughty conditions. Some results from Plant Pathology Labs seem to show this problem being fairly common in our area. Another fungus called Phomopsis may also cause tip blight and dieback. Phytophthora and Pythium fungal infections could damage roots and cause dieback to occur as well. To manage dieback diseases such as Botryosphaeria , prune about four inches below dead portions. It is essential that your pruning tools are disinfected between cuts. This disease and others can be spread with contaminated tools. Fungicides may be available to apply as a preventative.
In addition, shrub dieback and death could be caused by something as simple as faulty irrigation during this really hot, dry weather – this is a cultural problem. Another possibility proposed was even exposure to certain herbicides where dieback and death of off-target plants has been noted.
One last thought was damage caused by improper planting and exposed root balls. In at least one case, root balls were exposed allowing drying and drought damage. A simple thing like improper planting can result in problems down the road.
Without a positive identification, we are only able to speculate. To help confirm or eliminate the cause as a disease, you could send off a sample to the UF Plant Pathology Lab in Gainesville for a fee. Having a positive identification is always the best route . A sample form can be found here – http://plantpath.ifas.ufl.edu/media/plantpathifasufledu/plant-disease-clinic/PDC_Submission_form_CC-1.19.16.pdf.
Plant damage and death is often a detective story complete with hunches backed with testing and analysis. For more information on all types of woody plant problems, please call our Master Gardener volunteers on the Plant Lifeline on Mondays, Wednesdays and Fridays from 1 to 4 pm at 764-4340 for gardening help and insight into their role as an Extension volunteer. Don’t forget to visit our other County Plant Clinics in the area. Please check this link for a complete list of site locations, dates and times – http://charlotte.ifas.ufl.edu/horticulture/Plant%20Clinics%20Schedule.pdf.
Brown, S. H. (2013) Botryosphaeria Dieback of Eugenia, Ligustrum, Oleander, Pittosporum, Viburnum ’Awabuki’ and Wax Myrtle. The University of Florida Extension Services , IFAS – Lee County.
Marble, C., Smith, J., Broschat, T. K., Black, A., Gilman E., & White C. (2016) Effects of Metsulfuron-Methyl-Containing Herbicides on Ornamentals. The University of Florida Extension Services , IFAS.
Popenoe, J. (2008) Podocarpus macrophyllus . The University of Florida Extension Services , IFAS – Lake County.