Usually, this will only affect the tree’s growth that’s at least 1 year old. Its needles will start turning brown and eventually start to fall off. The symptoms will start at the bottom of the tree and move outward towards the tips of the branches. This will continue until the tips of the branches on the top only have green foliage. Rain and irrigation can cause this to happen more on one side of the tree by dripping the fungus to lower limbs. The portion of the tree that gets more sun may not be affected as much by drying out faster.
In cases of severe disease, all needles (except current year’s growth) turn brown, resulting in green needles being present only on branch tips. Spores develop during late spring to summer. They are spread primarily by rain, overhead irrigation, and wind, but also by tools.
Passalora needle blight symptoms somewhat resemble symptoms seen in a Leyland cypress that is responding to severe environmental stress, such as drought, in which its lower, interior needles turn yellow and drop.
Prevention and Treatment
When planting, space trees to allow adequate airflow. Leyland Cypress trees should be planted 12-15 feet apart. If you’re trying to use them as an immediate buffer you may choose to stager them. To minimize the spread of spores, avoid overhead irrigation or restrict it to early morning hours. Preferably, use drip irrigation and make sure that enough water is being applied during drought situations. Drip irrigation hoses should be no more than 75 feet long as pressure drops significantly after that point. Prune out diseased limbs, disinfecting pruning tools between cuts using 10 percent bleach solution (1 part chlorine bleach to 9 parts water). A professional tree service can easily help you prune your trees. If you choose to prune your own trees, remember to sanitize your equipment and oil them after each use to prevent rusting.
Fungicides such as thiophanate-methyl and myclobutanil are recommended for use against needle blight. However, to be effective, these sprays need to begin in late spring and continue through summer until the cooler, less humid months of fall. In addition, when applying these materials, it is essential that needles, including those on the inside near the trunk, are thoroughly sprayed to run-off. Once a tree is tall, adequate coverage by a homeowner is generally not feasible.