Infected foliage on Northern white cedar (Thuja occidentalis L.). Bruce Watt, University of Maine, Bugwood.org
Lorraine Graney, Bartlett Tree Experts, Bugwood.org
Up close view of symptoms on Japanese Cedar (Cryptomeria spp.). Lorraine Graney, Bartlett Tree Experts, Bugwood.org
Pestalotiopsis is a type of needle blight fungal disease that is primarily found on arborvitae (Thuja). It is usually considered a secondary disease that attacks foliage that has been injured or weakened by unfavorable weather or growing conditions. The disease may kill the smaller twigs where the infected needles died.
Symptoms and Diagnosis
The blight usually starts at the tip of the foliage and progresses towards the leaf base. The affected foliage color progresses from green to yellowish, then to a dark brown that looks almost black. Twig tips can also turn brown and have black, pimple-like, pinhead size, fungal fruiting structures dotting the surface. Usually, killed foliage is near the base of the plant where foliage is relatively dense. The plants may appear scorched.
Infections can occur at any time of year. However, spring is the most likely time because favorable weather conditions exist and plants are showing stress from winter conditions.
Integrated Pest Management Strategies
1. Avoid overcrowding plants to allow for sufficient sunlight and air circulation.
2. Keep plants healthy with good cultural practices. Follow proper watering and fertilization practices, and minimize any mechanical and snow/ice damage, etc. that could cause an entry point for the fungus.
3. Prune out dead foliage and twigs as soon as possible.
4. Application of fungicides should not be necessary. If necessary in certain circumstances (e.g. a nursery), copper fungicides are registered for this use as a preventative. Always read and follow product label directions before application to plants.
Strategies 1 and 3 are strictly organic approaches. Using an appropriate organic fertilizer would be a viable organic approach to Strategy 2. Of the fungicides mentioned in Strategy 4, consult the Organic Materials Review Institute (OMRI™) for appropriate organic copper products.