Needle cast is not a single disease but rather a collective term for a number of diseases caused by fungal infection and that can infect a wide range of tree species. As its name implies, symptoms are most noticeable in the needles of evergreen trees, but identification of parallel symptoms occurring alongside poor needle health will help identify the exact fungal species that is causing the needle cast disease in your tree and thus help design an approach to treatment that will protect the health and life of your evergreen trees.
Needle cast diseases are common problems in myriad species of evergreen trees, such as blue spruce, balsam fir and others. Needle cast disease agents include Rhizosphaera kalkhoffii, Lirula nervata, Lirula mirabilis and Isthmiella faullii as well as other fungi, and infection occurs when wind, rain or other natural forces distribute fungal spores onto a susceptible species of tree. Infection from needle cast diseases can cause cosmetic problems and even tree death if left untreated.
Symptoms of Infection
Symptoms of course vary depending on the species of infected tree and on the fungus species causing the infection. Needles begin to discolor, turning yellow, red, purple or brown. Leaves also discolor, turning yellow, brown, tan or straw, and eventually defoliate. On some species such as balsam fir, current-year leaves will remain a healthy color and discoloration will only be seen on leaves form the previous growing season or older. In its advanced stages, the disease will cause premature death of the trees.
Preventative measures are the first and one of the most effective ways to prevent needle cast in your trees. Carefully inspect trees for any signs of infection before planting them and avoid planting new trees next to ones that are already established. Ensure good air circulation between the trees and make sure to remove all mowing and grass debris from the area near the base of the trees. Even disinfecting pruning equipment with isopropyl alcohol can help prevent infection.
Treating an Infected Tree
Of course, if your tree is already infected, preventative measures won't be of much use to you. First and foremost, discard all needles and other defoliated foliage from an infected tree and remove it at once to prevent the disease spreading to other trees. A chlorothalonil fungicide or a 8-8-100 solution of hydrated lime, copper sulfate and water can be sprayed on infected trees as well. When fungicidal treatments are combined with the other control methods here described, healthy growth should be restored within two years.
- New Mexico State University Extension: Needle Cast Disease of Blue Spruce
- USDA Forest Service Northeastern Area State and Private Forestry: How to Identify and Manage Needlecast Diseases on Balsam Fir
- Ohio State University Extension Fact Sheet; Rhizosphaera Needlecast on Spruce; Nancy J. Taylor & Stephen T. Nameth
- Photo Credit Jupiterimages/Comstock/Getty Images
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