Diplodia tip blight is a disease of pines in the Midwest area and the treatment window will soon be upon us. This disease is caused by the fungus Sphaeropsis sapinea and highly effects two-needled pines such as Austrian, scotch, mugo and red, but can infect all evergreens. Here, our Austrian Pines are the most affected and are no longer planted here.
The disease will eventually kill the tree, but can take a long time, without treatment (5 years-ish). Although treatments can slow the process, careful thought is needed in a budgetary sense. The tree will begin to have die-back (larger branch death) and will require regular pruning to be aesthetically pleasing… if that’s even possible. Treatments can be costly, worse-case ineffective, if not applied correctly. The cost of removal will go up as the tree gets larger or becomes more hazardous to fell. In the end, depending where the tree is located, along with the ‘value’ placed on the tree, it may be more cost-effective to remove the tree and replace it as soon as diagnosed.
The Diplodia fungus overwinters on infected needles, cones, and within the bark of twigs. Spores are released from spring through late fall. New shoots are infected during the spring from bud break to the end of the growing season. The cones are infected during the spring of the second season, as it takes two years for cones to mature.
Spread of the disease is by the splashing of water, be it rain or over-head irrigation. Because this disease tends to overwinter and spread from infected cones, symptoms are first noticeable on the lower branches, as old cones collect under the tree. Symptoms of infected trees become visible in summer through fall and resemble stunted needle growth and yellowing. Spores can be seen on the needles & old cones as black dots. Because cones are more susceptible to infection, younger, non-cone bearing trees are often symptom-free.
Managing Diplodia tip blight focuses on tree health and sanitation. Providing proper care such as no overhead (and proper) watering, mulching, pest management and fertilization, helps suppress the disease. Removal of diseased cones from the ground helps, but is not practical in large stands of pines. Pruning of infected tips will aesthetically improve the tree, but will do little in the stop of the disease.
Severely infected trees should be removed. A fungicide spray program needs to be implemented in the spring and includes at least three applications. Make the first application just prior to bud break* (which will be soon) and make two additional applications at 10-day intervals. It is important to get the first application on the trees before any bud sheaths have broken (the papery tan cover). If the tree you’re trying to save is of high value, consult a licensed ISA arborist, as the chemicals available to professionals are usually more effective.
* Indicator plants to watch for blooming that coincide with bud break:
- Spiraea x vanhouttei – Vanhoutti Spirea
- Cercis canadensis – Eastern Redbud
- Chaenomeles speciosa – Quince
- Syringa vulgaris – Common Lilac
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