||Typical pattern (bottom up) of brown spot needle blight of pines, shown here on an Austrian pine (Pinus nigra). MN DNR Archives, MN DNR, Bugwood.org
Brown spot needle blight is a fungal disease of pines caused by Mycosphaerella dearnessii. It affects much pine in the Midwest including mugo, Japanese black, Virginia, eastern white pine, and most noticeably Scots pine. It is similar in appearance and can be confused with Dothistroma needle blight which is more commonly found on Austrian and ponderosa pine in the St. Louis area.
It generally starts on the lower branches and moves up the tree. It also favors the north side of the plant which is more humid. The blight is most damaging on small trees but over time can retard growth and weaken mature trees.
Symptoms and Diagnosis
Dead needles, which turn brown or a burnt red-orange and then drop is characteristic of the disease. The loss of 2nd and 3rd needles is accelerated and branches may look bare except for small tufts of needles at the tips. Damage usually begins on lower branches first. Yellow to tan spots first appear in May to September on current year needles. Brown spots appear mid to late summer and coalescing into bands encircling the needles and causing death of parts beyond the band. The bands may occur at any location along the length of the needle. Resin may appear on the spots. By fall the spots may appear resin-soaked. By late summer/autumn yellow halos may surround brown bands and spots. Straw-colored lesions becoming light tan with a dark border may appear raised as surrounding, uninfected tissue dies. Dead needles drop in fall.
In late spring to early summer spores on dead needles initiate new infections through stomata on the needles. June-July is the most active infection period. In late summer, fruiting bodies called pycnidia form on infected needles in the tree and on the ground. The spores spread by splashing rain to new infection sites. Infection is favored by warm, humid conditions.
Integrated Pest Management Strategies
1. Live with the disease. If damage is slight you may decide just to live with a few browning needles. The plant can easily survive light infections.
2. Sanitation. Remove and dispose of diseased needle on the tree if practical and most certainly those on the ground as these are the source of on-going infection.
3. Refrain from overhead watering. Since splashing water spreads the spores, limit overhead watering or do so only early in the day so the needles dry quickly.
4. Improve air circulation. High humidity and slow drying needles fosters infection so prune out dense foliage and evaluate nearby plants to see if pruning them might promote faster drying of the pine's needles. Provide ample spacing between plants.
5. Use fungicides. copper-based fungicides such as Bordeaux mixture are effective as a protectant. Other protectant fungicides include chlorothalonil (Daconil) and Mancozeb. Follow label directions for application.
6. Plant resistant pines or other plants. Consider replacing the pines with a species that is more resistant to the disease or an evergreen other than a pine, such as spruce, arborvitae, or juniper.
Strategies 1, 2, 3, 4, and 6 are strictly organic approaches. Of the fungicides listed in Strategy 5, consult the Organic Materials Review Institute (OMRI™) for appropriate organic copper products.
|Brown spots surrounded by yellow halos on Scots pine needles (Pinus sylvestris), typical late season lesions of brown spot needle blight of pines. D. D. Skilling, USFS, Bugwood.org
|Fruiting bodies of brown spot needle blight of pine on Scots pine (Pinus sylvestris). D. D. Skilling, USFS, Bugwood.org