Pine needle blight symptoms appearing

Needle blight disease is showing up in pine trees. With all the information we hear about pine wilt killing Scotch pine, and some Austrian pine, it is important not to confuse needle blight for pine wilt and cut down trees. Unlike pine wilt, needle blight can be controlled fairly easily with timely fungicide sprays.

Dothistroma needle blight is one of the most common fungal diseases of pine trees in Nebraska. The fungus causes the greatest amount of damage on Austrian and Ponderosa pine. Scotch pine is usually not severely damaged.

Wet weather promotes the spread of fungal disease. With our above average rainfall last summer, infections increased, and we are now seeing the damage caused by infections that occurred last summer. If control is warranted, fungicides need to be applied beginning in mid-May to prevent new infections this year.

Symptoms of needle blight begin in the fall as yellow or tan spots on needles of current year or older growth can be seen. These spots become brown or reddish-brown then spread to form a band around needles. Early symptoms often go unnoticed until needles are killed from the tip back to the lesion.

Initially, needle tips die while their base remains green. As the disease progresses, the base of needles also die and entire needles drop off trees. Lower branches of trees are most severely infected although the entire tree can be affected.

The greatest amount of browning and needle drop is seen in late spring or early summer following the infection year. What we are seeing now is the result of last year’s infections. Fungicide sprays will not cure last year’s infections. Fungicides applied this spring will protect new and older growth from becoming infected this year.

Fungal spores infect pine needles during rainy periods from May to October. Infections can be reduced by applying liquid (Tenn-Cop 5E or Black Leaf Liquid Copper Fungicide) or fixed copper formulations (Basic copper sulfate or Tribasic Copper Sulfate) or Bordeaux mixture twice during the growing season. Read and follow all label directions before application.

Make the first application in mid-May to protect existing needles from infection. Make a second application around mid-June after new growth has occurred. New growth is initially resistant to infection and does not become susceptible until midsummer.

In some cases, control can be achieved with a single application of fungicide made in early June.

However, there is considerable risk with this timing since older needles could be infected before the early June application is made.

Annual fungicide applications are not always needed to control this disease. Monitor susceptible pines for symptoms each year. If infections occur during a year in which a fungicide has not been applied, and is severe enough to warrant control, then a fungicide can be applied the next year. If little or no infections occur during a year when a fungicide is not applied, then spraying can be skipped for another year.

Source: extensionhorticulture.unl.edu

Contact Kelly Feehan, Extension Educator, at 563-4901 or e-mail her at kfeehan2@unl.edu.