The fungus Diplodia pinea is worldwide in distribution and importance. In North America, Diplodia causes shoot blight and stem canker of conifers in plantations, windbreaks, and ornamental plantings.
Most conifers are susceptible to infection, especially exotic species such as Austrian pine.
In the north-central United States, the most common hosts are red, jack, Scotch, and Austrian pine. Diplodia kills trees by killing the new foliage year after year or by initiating girdling stem cankers on stressed trees. Nursery seedlings are usually killed in the first year of infection. Peak spore production and infection usually coincide with host bud break and shoot and needle elongation. The fungus invades and kills succulent shoot tissue, and forms pycnidia on dead tissues.