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Hoppe Tree Disease Alert: Dothistroma Needle Blight

Written by John Sepulveda, Certified Arborist WI-1454A

Dothistroma needle blight is a fungal disease caused by Dothistroma pini. The fungus affects Austrian and ponderosa pines, while Scots and red pines are least susceptible. The fungus is not usually deadly in mature trees, but can be in younger trees or trees that have over 40% needle infection. The disease is most prevalent in the commonly planted Austrian pine species.

Recognizing Dothistroma Needle Blight

Needle blight symptoms are browning needles that eventually fall off. The needles first show

reddish brown spots that eventually spread and create a band that cuts off the tip from the base of the needle. This kills the tip and eventually the infection spreads and kills off the base. Needles that are closer to the trunk are more likely to become infected and die than newer needle growth, but they too eventually will become infected. The lower six feet of the tree is usually the area most affected because there is lower air flow and so needles take longer to dry. The tops of trees or needles above 20 feet are less likely to be infected.

Spreading of the fungus occurs when the weather is wet and cool for several days in a row. The spores are formed as small black structures that appear on the dead needles and spread by rain and wind. Infections may take five weeks to up to six months to show symptoms, but usually appear in late summer to fall.

Steps You Can Take

While it may not be deadly for older trees, dothistroma needle blight will make them look less attractive and can still be harmful to new tree plantings. If you have a concern about your pine trees, contact Hoppe to schedule a visit by a certified arborist who can diagnose the problem correctly and recommend a treatment plan. Some options may include pruning the lower branches to increase air flow inside of the canopy, and a fungicide treatment that can be helpful in slowing down spread.

Hoppe performs dothistroma needle blight treatments in a series of two or three applications of a fungicide that can protect new needles from infection. Fungicides will only protect new growth and will not fix any damaged needles. The timing is critical: our certified pesticide applicators perform the first foliar spray around late-May or early-June just after the buds open in the spring. A second application happens roughly a month later after new needles have grown to their full length. A third application may be applied later in summer.

We can also explore new plantings of resistant pine species in your yard. For help with your existing trees or to plant new ones, give us a call or request a quote today.

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