Tree Diseases - Rhizosphaera Needle Cast
We started getting many calls about Blue Spruce browning out in 2010. In the following years we got more calls. We now average more than 20 + calls a year on Blue Spruce trees browning beginning on the bottom needles and working its way up the tree.
Rhizosphaera spores require water to germinate. Water must be present on the needles for 48 hours for the spores to breach the epidermis of the needle. Warm temperatures at 77 degrees during wet periods will enhance the spread of spores. Trees with poor drying conditions, shaded trees, trees with dense foliage and trees with areas of poor air circulation are the most susceptible. Most infection begins at the bottom needles. Irrigation heads that keep lower needles on Spruce and Fir trees wet constantly will speed up the amount of damaged needles.
Needles infected in the Spring will not show signs of symptoms until late summer when they will brown out. The browning will continue through the Winter. It takes about one year from infection of the needle to the time the needle drops to the ground. Cast needles will spread new spores in the Spring when activated with water. Dead needles that drop to the ground should be remove off of the property or burned. This will reduce the amount of spores in the Spring.
Rhizosphaera Needle Cast Trees
Rhizosphaera Needle Cast Tree closeup
Control is not simple. It will take 3-4 spray applications in the Spring as the needle elongate. The applications need to take place about every two weeks. Its all about the rain fall. Fungicides are protectant sprays. They cover the foliage and stop spores from infecting. We might go over the two week time frame to do a spray application if there is no rain in the future. We may do an application in 10-12 days apart is there is a lot of natural rain.