I’m hoping that someone in your group could give us some advice. Our blue spruce trees (7-8 years old in zone 5 just north of Toronto) have been affected by Rhizosphera (black spots on needles detected with a loupe).
We have Daconil fungicide (Chlorothanolil) that we want to use on infected trees but we’re not sure if we should wait for the next Spring or spray now. All information we found on the Internet indicates that critical time for fungicide application is in the Spring when the buds break. We missed that opportunity this year and are wondering if spraying trees now is waste of time, effort and money (Daconil) or if it would still protect this year’s growth to some extent.
We had a quote from an arborist (very expensive) who recommended that they spray in August and again in September this year and then continue 3 times per year over the next 3 years. Since our trees have been showing signs of disease for few years now we’re afraid that this year’s growth is already infected and that spraying with won’t help (not sure if we can trust the arborist company or not).
Please let us know what course of action you would recommend.
Thank you and best regards.
Thank you for contacting Toronto Master Gardeners regarding your spruce trees that have been affected by Rhizosphaera needle cast. While spring may have long passed, it might not be too late for your trees to benefit from fungicide treatment this year, as it may still provide some reduction in the spread of the fungus to healthy parts of the trees. Various online sources, including the ones cited below, suggest that appropriate fungicides can be applied every 3-4 weeks whenever conditions favour the spread of fungal spores – i.e. wet weather. If you are concerned that your arborist suggested an overly aggressive treatment schedule for this year, it would be best to seek the opinion (and quote) of at least a few other ISA-certified arborists to ensure that the advice is consistent and that you are paying a reasonable price for the service.
Agriculture and Agri-Food Canada – Rhizosphaera needlecast
University of Wisconsin Extension – Rhizosphaera Needle Cast
International Society of Arboriculture (ISA) – Ontario Chapter (‘Find an Arborist’ resource coming soon)