Quick facts
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Dothistroma needle blight of pine trees causes needles to turn brown and fall off.
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Severe infection for several years in a row can cause tree death.
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Manage this disease by maintaining good air circulation, mulching and preventing sprinklers from spraying needles.
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Austrian pine and Ponderosa pine are most likely to be damaged by this disease.
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Red pine and Scots pine are mostly resistant.
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Fungicides can be used to protect trees from Dothistroma needle blight.
How to identify Dothistroma needle blight
Needle symptoms
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Reddish-brown spots scattered on green needles. These spots grow into a band, encircling the needle.
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Tip of the needle turns brown while the base of the needle remains green. These two sections are separated by a reddish-brown band. The transition from green to dead areas is abrupt.
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Eventually, needles turn completely brown and fall off.
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Older needles found close to the trunk are more severely affected compared to the younger needles that are found towards the ends of the branches.
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Within the spots and bands, you may see tiny bumps pushing through the surface of the needle. These black, pimple-like structures produce fungal spores.
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Needles on lower six feet of a tree are most noticeably affected. Needles over 20 feet high are rarely affected.
When do symptoms appear?
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New infections often appear in late summer to fall.
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Dead needles and spots may be seen at any time during the year on a plant with reoccurring disease.
Lab analysis is often necessary to distinguish Dothistroma needle blight from Brown spot. Submit a sample to the Plant Disease Clinic for testing.
Trees affected by Dothistroma needle blight in Minnesota
Trees most severely damaged
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Austrian pine (P. nigra)
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Ponderosa pine (P. ponderosa)
Tree less affected
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Mugo pine (P. mugo)
Mostly resistant
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Red pine (P. resinosa)
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Scots pine (P. sylvestris)
How does Dothistroma needle blight survive and spread?
- Dothistroma needle blight is caused by the fungus Dothistroma septosporum (syn. Mycosphaerella pini).
- Dothistroma needle blight is a slow-moving disease that takes over a full year to complete its life cycle. It takes several years of repeated infection to develop into a serious problem within the tree canopy.
- Spores are produced on infected needles throughout the growing season whenever cool, wet weather occurs.
- Spores are spread by wind or rain to needles within the same tree or in neighboring trees.
- Infection occurs if spores land on susceptible needles under favorable weather conditions.
- Second year or older needles are susceptible to infection anytime during the growing season.
- Young needles are resistant until they reach maturity in early to mid summer.
- Several consecutive days of cool (41-77°F), wet weather are needed for successful infection.
- Reddish brown spots or bands appear on needles in the fall.
- Needle spots eventually girdle the pine needle. The needle beyond the band then dies and turns brown leaving the bottom portion of the needle green.
- Tiny black fungal fruiting bodies called stromata appear in the bands or in dead areas of the needles. These fruiting bodies will release spores the following year.
- Infected needles may remain attached to the tree for one or two years depending on the age of the needle at the time of the infection.
- Eventually infected needles turn completely brown and fall off prematurely.
How to manage Dothistroma needle blight
Maintain good air circulation around trees
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Do not overcrowd plants. Use the mature size of the tree as a spacing guide when planting.
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Remove the bottom most branches from the trunk to help increase circulation around the tree canopy.
Mulch under trees
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Remove all weeds under the trees.
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Maintain a 3 to 4 inch deep, even layer of wood chip mulch around your tree to prevent weed growth.
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Leave at least a 2 inch space between the mulch and the trunk to allow for air movement.
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Do not mound the mulch around the trunk of the tree.
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Inspect the depth of the mulch layer each year. Add additional mulch only to maintain a 3 to 4 inch depth.
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Don’t allow sprinklers to spray needles
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If the tree is in a landscape with a sprinkler irrigation system, make sure that water is not spraying the needles.
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When setting out sprinklers, direct the water away from needles.
Plant disease tolerant pine trees
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In low lying or other areas with cool, moist air, where environmental conditions are favorable to Dothistroma needle blight, plant Scots pine or Red pine trees.
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Avoid planting Austrian or Ponderosa pines in areas with a history of Dothistroma needle blight or where environmental conditions favor disease.
Fungicides
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If trees have a history of Dothistroma needle blight, copper fungicides can be used to protect new needles from infection.
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Fungicides need to be applied:
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once just before buds open in the spring (typically in mid-May) to protect previous year’s needles.
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once after new needles have grown to their full length (in early to mid summer).
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CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.
Reviewed in 2019