Diplodia Tip Blight Diagnostic Guide
Diplodia tip blight (Diplodia sapinea) is a fungus that infects more than 20 pine species throughout the Central and Eastern United States, as well as California and Hawaii. It is most often found on Austrian pine and can be quite severe on mature trees that are stressed. Diplodia tip blight kills current year’s shoots, which means that infections year after year can weaken and eventually kill large trees.
Trees at Risk
Over 20 pine species are infected by Diplodia, but it is most severe on 2 and 3 needled pines including Austrian (Pinus nigra), scots (Pinus sylvestris), ponderosa (Pinus ponderosa), and mugo (Pinus mugo).
Signs of Damage
- Brown needles at the tip of the current year's growth are the first symptoms.
- Symptoms occur on lower branches first and work their way up the tree.
- Shoots do not develop to full maturity and needles turn brown in mid to late summer.
- Resin oozes from cankers at the base of new shoots in spring.
- Small, black fruiting bodies (pycnidia) may be seen at the base of the diseased needle, when using a hand lens.
- The fungus overwinters in infected cones, shoots, and needles.
- During wet conditions, spores travel to and penetrate newly emerging needles and quickly cause necrosis.
- Second-year seed cones are infected in late May or early June and serve as a reservoir of future inoculum.
Diplodia tip blight causes the most damage to mature trees that are stressed. Keeping trees in good vigor with deep watering during droughts, nutrition with fertilization or compost and wood mulch, and control of insects can improve the vigor of pines and decrease susceptibility to tip blight. However, over-fertilization can make trees more susceptible.
Fungicides can assist with the control of Diplodia tip blight. It is very important to protect the new growth in the spring. Applications should start just prior to bud break and continue every 10-14 days until full candle extension.
Other Treatment Practices
- Avoid planting susceptible pine species.
- Applications of Cambistat to improve drought tolerance and tree health. Studies have also shown that Cambistat can reduce the latent stage of diplodia tip blight.
- Prune off infected branches during dry periods in early spring or fall. Disinfect pruning tools between cuts with 70% rubbing alcohol.
- Reduce stress with proper watering and nutrition.
- Rake up and remove fallen needles, twigs, and cones.
Applications later in the growing season do not work. If using CuPro™ 5000, the 2nd and 3rd applications will also overlap and provide protection vs. dothistroma.
A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org