Diplodia Tip Blight of Pines
Diplodia tip blight is caused by the fungus Sphaeropsis sapinea.
It is a common disease of many pines such as Mugo pine, Scotch pine, Austrian pine, and red pine. White pines, spruces, and other evergreens are rarely affected.
The diplodia fungus infects and kills the current year's growth and symptoms appear as the browning, stunting, and twisting of the new shoots. A close inspection of the base of dead needles may show small, black fungal fruiting bodies. The presence of these fruiting bodies distinguishes this disease from winter kill and other environmental damage due to drought or drying winds.
Diplodia tip blight spreads by spores blown by wind or transported by birds or insects. The main source of spores is from fungal fruiting bodies on old cones still clinging to the tree or debris. These spores drop onto lower branches during periods of rainfall and the disease can be particularly bad during a wet spring. The new growth (candles) can only be infected while the needles are elongating in the spring. After the needles have fully expanded, the shoot is no longer susceptible to fungal attack. Though the fungus only kills the new growth, constant, repeated infections of the disease can weaken and eventually kill mature trees.
One of the best ways to avoid this disease is to plant resistant species. However, since many susceptible species are desirable for the landscape, certain measures can be followed to help control the disease.
- Keep your trees healthy and vigorous! Trees that are stressed from drought or nutrient deficiency are more susceptible to diplodia tip blight. Proper, deep watering and feeding will promote good vigor which goes a long way towards prevention of this disease. Andre's fertilizer recommendations.
- Practice good sanitation around your trees. Spores survive over winter in infected twigs, bark, cones, or needle litter under the trees. Rake up and dispose of any dropped needles, cones, or twigs. DO NOT compost.
- Prune out previously blighted shoots and branches. This does not control the disease but improves the overall health and appearance of the tree.
- Avoid pruning trees from late spring - early summer when they are most susceptible to the disease, since the disease can enter through wounded tissue.
- Do not prune infected trees during wet weather.
- Disinfect tools in a 10% bleach solution between each cut.
- Diplodia tip blight can be partially controlled with certain fungicides. Since the symptoms appear after infection, the only time to control this disease is during the period when infection is likely to occur.
- Timing of the fungicide application is critical! The first application must be made just prior to bud break when the buds begin to swell (before any bud sheaths have broken). Depending on where you live, this is usually late April or early May. After the bud sheaths have broken, spraying with fungicides is a waste of time and money!
- Two or more additional applications should be made at the label recommended intervals until the candles and needles have fully elongated.
- Recommended fungicides include Cleary's 3336, Mancozeb, copper fungicide, and Daconil.
As with all chemicals, always read and follow the label directions for dilution rates and proper methods of application.