Needle Blight Tree Disease - Identification and Control

This group of blight diseases - including Diplodia, Dothistroma and brown spot - attacks conifers (mostly pines) by girdling needles and killing branch tips. These needle blights are caused by the fungus, Dothistroma pini mostly on western pines and Scirrhia acicola on longleaf and Scots pine needles.

Needle damage can cause major commercial and ornamental damage to conifers in North America significantly affecting the nursery and Christmas tree industries.

Infected needles often fall from the tree creating a symptomatic scorched, denuded look. The blight usually results in dramatic browning and dropping of the foliage beginning on the lower branches. It rarely attacks upper branches on conifers so the tree might not immediately die.

Diseased Needle Identification

Early symptoms of a blighted needle would be deep-green bands and yellow and tan spots on needles. This deep green color banding is short-lived. The spots and bands quickly turn brown to reddish brown during the summer months. These bands tend to be brighter red and more numerous on pines in California, Oregon, Washington, and Idaho, where this disease is often referred to as the "red band" disease.

Needles may develop extensive leaf browning within several weeks of the first appearance of symptoms. Infection is typically most severe in the lower crown. Infected second-year needles usually drop before infected current-year needles. Needles that become infected the year they emerge often are not shed until late summer the following year.

Successive years of severe needle infection can result in tree death. In most cases, the disease makes pines in landscapes unsightly and pines in Christmas tree plantings unmarketable.

Prevention

Repeated annual cycles of disease infection can result in dead limbs and eventual loss of any meaningful ornamental or commercial value of the conifer. Breaking this infection cycle has to happen to effectively stop the fungus. Brown spot needle blight in longleaf pine is controlled using fire.

The use of genetic resistant pine strains or clones has been identified in Austrian, ponderosa, and Monterey pines. Seeds from Eastern Europe have shown high resistance and are currently used to produce Austrian pines for Great Plains plantings. Sources of ponderosa pine seed have been identified as having high resistance and collected for planting in endemic areas.

Control

High-value nursery and Christmas tree plantings can benefit from chemical fungal control. Early detection is important and high dollar trees may be sprayed as a preventative measure in locations where the fungus is active.

A copper fungicide spray program, repeated over several years, will eventually allow new, undamaged needles and branch tips to replace the diseased ones. Chemical applications should begin in spring where the first spray protects the previous year's needles and the second spray protects the current year's needles. When symptoms of the diseases have disappeared, you can discontinue spraying. Ask your local extension agent for recommended chemicals.