Controlling Cytospora Canker

Asked June 22, 2018, 7:58 AM EDT

The needles on my decorative blue spruce are turning brown. Based on research I believe it is cytospora canker. If it is this disease how can I treat it? Is it possible it’s something else?

Sussex County Delaware blue spruce

3 Responses

Hello,

Colorado blue spruce is most commonly susceptible to fungal needlecast from both Rhizosphaera and Stigmina. There may some scale insects present too, that probably don't warrant control. Cytospora canker would cause large areas to turn brown from the center of the tree and there would be a lot of sap or resin on the main trunk. There is no cure for Cytospora. Control of the Rhizosphaera and Stigmina need an application of fungicide. Chlorothalonil (Bravo Weatherstik) should be applied, but timing is critical. Fungicides are best applied in May when new needles are elongating, because the fungicides are protectant. Two or three applications are usually needed, and control usually requires treatment for two years. Affected needles will still drop, fungicides will not sure the tree, merely protect the new growth.

Thank you for contacting Cooperative Extension,
Nancy

Thanks for your response. You say that the fungicide needs to be applied in May. So what do I do now that it’s July? Do I apply it anyway? If I do nothing now will it die?

Hello,

You could still apply the fungicide chlorothalonil, but apply when the weather is a little bit cooler at the end of the week. The fungicide will protect the new growth from infection by the fungus. Affected needles will not improve, and will probably drop. If you do nothing the tree will probably die in a year or two. You will need to put the treatment on your calendar for next year to apply in early May and mid-May for continued control. It will take at least two years to gain control on the disease. Reduce stress on the tree by watering if we get into a period of drought. Water once a week, deeply.
Thanks again for contacting Cooperative Extension.

Nancy