Spruce trees are a common feature found in our urban landscapes. Usually species such as Colorado Blue, White, and Norway Spruce. Blue Spruce being the most common as landscape designers and homeowners enjoy its blue foliage. Unfortunately, owning these trees may come at an extra cost in Southern Ontario.
Rhizospharea Needlecast
Rhizosphaera Needlecast is a fungal disease that targets the foliage of Spruce trees. Colorado Blue Spruce is the most susceptible to the disease. Infection usually begins in the lower, central portion of the tree. Symptoms of Rhizosphaera Needlecast appear in the spring; turning needles yellow, then purplish-brown by end of summer, with black fruiting bodies appearing in lines on the needles. The infected needles will eventually shed off the tree, causing branches to look sparse. Spore dispersal from infected needles occurs during wet weather in spring, spreading by rain from needles infected the previous season to newly emerging needles. Unless controlled, infection will continue to spread each season, decreasing the aesthetic value of the tree and potential fatality of the host.
Control and Suppression
If identified in the early stages, treatments for Rhizopharea Needlecast are simple and quite successful. Fungicides are available that are applied topically to the foliage during the spring / early summer months. Applications need to take place as soon as the buds break and the new foliage is exposed. In Southern Ontario, Spruce buds break sometime in the month of May, depending on the weather. The fungicide applied to the new growth will ensure the spores don’t spread from the already infected needles from previous seasons. It is highly recommended multiple applications are conducted for 2–3 seasons to ensure that all infected needles are completely removed from the host tree.
Helpful Tips
There are some other methods that can be done to help prevent the diseases and limit the spread. Consider planting different kinds of species of trees in your landscape. Avoid monocultures (the cultivation or growth of a single species of tree). The more of the same species of tree in your landscape, the more difficult and costly treatments can be. Elevate and remove the lower branches. This will allow better airflow on the dampest area of the tree. This is where spore development usually starts. If your tree is already infested, rake up and remove infested needles that have fallen off the tree. Even after the needles have fallen and died off, the spores still remain.