What can we do to stop the spread of disease on our spruce trees? We really do not want to loose them.
Livingston County Michigan
There are three principle types of diseases that affect blue spruce trees: needlecasts, tip blights and canker diseases. All of these diseases are caused by fungal pathogens. I am assuming you are asking about needlecast diseases .
As the name implies, trees with needlecast diseases shed needles. Needlecast fungi often infect needles on the current year’s shoots. As the disease progresses, the needles die, usually the year following the infection. As a result, trees affected by needlecasts often have an outer “shell” of live needles on current shoots and dead needles on older shoots. The two most common needlecasts we find in spruce are caused by the fungal pathogens Rhizosphaera and Stigmina/Mycosphaerella.
Fungicides that are available are preventative. Well-timed sprays can prevent new infections. Time your first application next spring after the new growth has expanded to 0.5 to 1.5 inches in length. New growth typically appears in May. Follow-up with 1-2 additional sprays as indicated on the fungicide label. Fungicide applications will need to be applied for at least 2-3 consecutive years and maybe more. Fungicides that are labelled for control contain the active ingredients of either chlorothalonil, mancozeb or copper. Remember to read and follow the instructions on product labeling.
In addition minimizing tree stress can also help. What the trees during hot,, dry weather. One important factor when watering evergreens is to apply water to soil under the dripline, Mulching around the trees can also help with soil moisture.
For more information –
What is spruce decline? http://msue.anr.msu.edu/news/what_is_spruce_decline_and_what_should_you_do_about_it