Spruce tree rhizosphaera needle cast diease treatment
We have approximately 36 spruce trees with various degrees of needle loss and discoloration. We have been told by a licensed arborist that they are suffering from rhizosphaera needle cast diease and spider mites. We are looking for a product to treat this diease and improve the overall health of the spruce. My questions are: 1. What can we use to rid and prevent this? 2. Where can I purchase it? 3. How do I apply the product? (And how often?) 4. What is the best time of year to do this? Thank you for your help wth this.
The arborist's diagnosis may be correct, but before spraying fungicide, confirm that rhizosphaera is the fungal pathogen causing damage by sending a lab sample to the University of Minnesota plant disease diagnostic clinic. Several other fungi result in symptoms very similar to rhizosphaera.
If rhizosphaera is present, chlorothalonil can be sprayed twice in the spring to protect new needles. The first spray should be applied when new needles are half the length of the mature needles. A second spray should be applied 3-4 weeks later or as prescribed on the fungicide label. Read and follow all instructions on the label when applying a fungicide!
Go here for reliable information about this disease and its life cycle.
By the way, any trees as seriously affected as the one in the center of the photo should be removed because they are beyond recovery.
Spider mites are difficult to control with chemicals readily available to home owners, but this bulletin suggests steps that can be taken to reduce their numbers.
Products containing chlorothalonil and those mentioned that can be used to control mites are available at some hardware and farm stores and most full service garden centers.