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Phyllosticta needle blight
Need to know:
- Symptoms include browning of tips.
- Stressors such as winter injury, drought stress, and crowding make trees more susceptible to disease.
- Alleviating stress is best treatment.
- Practices to reduce and slow further infection includes pruning and removing of dead/infected tissues, watering near base of tree, and proper spacing.
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.
Symptoms of phyllosticta needle blight
Symptoms of phyllosticta needle blight are typically browning tips.
Signs of phyllosticta needle blight
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.
Fungicide applications may be avoided by following good Integrated Pest Management practices like those listed in this encyclopedia article. Often, the only preventative application is effective to manage plant diseases. If the problem requires a fungicide, state law requires the user to read and follow all labels accordingly. For more information, read Proper fungicide use.
Dr. Lina Rodriguez-Salamanca is a diagnostician and extension plant pathologist with the Iowa State University Plant and Insect Diagnostic Clinic (clinic.ipm.iastate.edu), a member of the National Plant Diagnostic Network (NPDN, ...
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