This is actually one of the most common diseases affecting trees in cities, suburbs, and other urban environments. Most people do not know what they’re seeing when they notice it, however, and usually attribute it to poor irrigation or sun bleaching.
Diplodia can affect any needled pine tree, usually preferring two-needled pines such as Scots, Monterey, and Ponderosa pines. It’s a fungus that attacks mature trees under stress from drought, root restriction, or another infestation. It’s also not unusual in nursery and Christmas tree plantings where saplings have been placed too closely together or in containers that are too root-restrictive.
Plant Disease Symptoms
The most obvious symptom is the dead brown needles that have been infected and died. The first sign will be die-back of the tips of needles in little clusters in affected areas of the tree. These will eventually become large enough to be seen easily from a distance.
Over time, as the infection returns every year, more and more of the tree’s needles will be affected and if left unchecked, the tree will eventually die. The infection most often begins at the lower levels of the tree, nearest the ground.
This fungus, like most, begins as spores in the black pycnidia at the base of infected needles. As these needles are shed, they spread the disease by coming into contact with other needles. The pinecone-like fruits of the fungus, which are visible under microscope, spread very quickly, as the Diplodia pinea (the proper name for this fungus) develops. Like many flowering plants, the Diplodia fungus produces spores in the spring that spread rapidly and for the rest of the year attack the needles of the tree.
How This Disease Impacts the Plant
A Diplodia tip blight infection is aesthetically unpleasing at first. As it progresses, the tree will begin to stunt its growth as it loses exposure to sunlight from the dead needles. Eventually, more and more of the needles will be infected and killed, until the tree eventually succumbs and dies.
How to Prevent
The best prevention is proper watering and care for the tree. If the tree is not under stress, Diplodia will not likely take hold. Good aeration, plenty of root space for spread, and proper cleaning and management in the fall and spring to keep the tree well aerated are important safeguards.
Diplodia Tip Blight Control
Once it’s started, ridding an infected tree of Diplodia can become a multiyear-long process. If caught early, it can be destroyed in one year, but the longer it’s had to get established, the longer it will take to remove.
Single applications of fungicides will kill much of the infection if caught early. Multiple applications are nearly always required, however, and will take time to finally rid the tree of the infestation. Finding the root cause (drought, restriction, etc) is required if the tree is to be kept disease-free afterwards, however.