Causal Agent

Mycosphaerella pini (perfect), Dothistroma pini (imperfect) 
Hosts: Over 30 species of pines, including Austrian, ponderosa, mugo, slash, Japanese black, and loblolly pines.

 

Symptoms

Symptoms develop in the fall of the year in which the infection was initiated. Early symptoms consist of yellow and tan spots, and water-soaked bands on the needles. The bands and spots may turn brown to reddish brown and may be surrounded by yellow bands. The tip of the needle beyond the red band eventually turns brown while the needle base remains green. The dead portion of the needle may break off leaving a blunted tip. Dothistroma needle blight looks similar to winter injury. When needles are damaged by winter injury, all of the needles will exhibit tip browning back to the same point on the needle. With Dothistroma needle blight, the length of tip dieback varies as shown in the image and a striping pattern may also be observed. In some cases, fruiting bodies of the fungus are visible on needles infected with Dothistroma.Extensive damage may occur on the needles within 2-3 weeks on the initial symptoms. Within a few weeks after the needles die, small black fruiting structures of the fungus break through the outer needle tissue. Infected needles drop prematurely, with the lower branches usually showing early loss of needles first.

 

Control

Dothistroma needle blight is controlled mainly through the application of protective fungicides.  Two applications are recommended, the first in mid-May to protect the previous seasons' needles and the second in mid-June to July to protect the current year needles.  Depending on the size of the tree, it may be possible for a home owner to treat their own trees or they may need to contact a pesticide applicator.  Products that contain copper will help control Dothistroma needle blight.  Additionally, the grower should rake up and discard fallen needles.