Phyllosticta needle blight
Phyllosticta needle blight, caused by the pathogen Phyllosticta thujae, is one of the few foliar diseases we see on arborvitae in the clinic. Pathogens of the genus Phyllosticta can also infect fir trees, junipers, and spruce.
Signs and Symptoms
Symptoms of phyllosticta needle blight are typically browning tips. Under magnification, you can sometimes observe fruiting bodies of the fungus (signs), but this often requires putting a sample in a humid chamber.
Phyllosticta needle blight is usually observed in situations where there is a major stress event that has reduced a trees ability to fight off infection. Some common stressors include; winter injury, drought stress, crowding etc.
When we see phyllosticta needle blight infections, there is typically an underlying stress issue. Whatever the stressor is, it is typically more important than the infection of the pathogen. As an example, if the trees are experiencing drought stress, water during periods of drought. Alleviating stress to a tree should be the number one goal for this disease.
There are however, some cultural practices can help to reduce and slow further infection. These practices include; pruning and removing dead/infected tissue, watering trees near the base (avoiding getting the foliage wet) during periods of drought, and insuring that trees are spaced properly at the time of planting. Pruning can provide two benefits, the first of which is removing fungal bodies from the plant therefore reducing the amount of the fungus that can re-infect the plant later. The second benefit is greater ventilation, which helps foliage to dry more quickly, reducing the pathogen’s ability to infect. Since this disease is not very well studied, there are no chemical management recommendations at this time.