Needle Drop naturally occurs seasonally in blue spruce. Some browning and shedding of inner needles in autumn normal. While in most years, the browning and needle fall is barely noticeable. When the inner needle browning is significant, however, a fungal disease may be the cause. Knit Cytospora Rhizosphaera cancer and are common causes of inner needle browning in blue spruce.
Cytospora cancer is caused by the fungus Cytospora kunzei which can enter the tree through wounds or penetrations. Browning of the inner needles on the tree is an early symptom. The brown needles eventually fall off leaving bare branches. Blue spruce trees are also prone to knit Rhizosphaera, caused by the fungus Rhizosphaera.
The disease begins on the lower tree branches and works its way up. Needles turn purple or brown and fall off eventually. Occasionally, the disease begins earlier in the tree with internal browning needles in the upper branches.
Symptoms and damage
Blue spruce trees that are infected with Cytospora have cancer death usually a branch, which often starts in the lower branches of the tree. An examination of the dead branches may reveal the presence of a sticky white sap that infected trees produce as a defense once infected with Cytospora cancer. Finally, the fungus can encircle branches resulting in death. Can cast with Rhizosphaera needle small black dots, the fruiting bodies of the fungus are structures that appear in rows on the needles of blue spruce. These are visible with a magnifying glass. Rhiszophaera knit can kill a tree in a few years, if not treated.
Pruning diseased branches is the main method of treating trees with Cytospora cancer. Prune 4 to 6 inches below the visible cancers. You may need a couple of branches back to the trunk. Prune in dry weather to prevent spread of the disease, as the spores can spread in wet conditions. While fungicide sprays are not effective for controlling canker disease, they can cast suitable for combating Rhizosphaera needle. Infected trees should be sprayed with a fungicide in late spring and early summer. Read the product label for specific rate and timing instructions.
The best control of fungal disease is prevention. Plant the tree in a well-drained site, which allows for unlimited growth. Add mulch around the tree overall vitality by moisture retention and weed control increase. Water is to prevent the drying out of deep blue spruce in dry conditions. If you plant a lot of trees, space for them to promote good air circulation.