Healthy green pine needles.
A variety of conditions cause pine needles---particularly those on the lower branches---to die off. This rarely kills the tree, but may reduce its overall health and vigor. According to North Dakota State University, in most cases such problems can be solved by cutting back overgrown plants, a suitable fertilizer in the spring and plentiful watering during dry spells. The Plant Pathology Extension of North Carolina University stresses the correct choice of pine species for the planting location. White Pine for instance, is best-adapted to mountain regions.
Diplodia Tip Blight
This fungal disease causes stunted, brown needles at the tips of pine branches. Affecting the current season's growth, it is usually confined to the lower branches. Careful inspection with a hand lens will reveal tiny black specks---the fruiting bodies of the fungus---at the base of the brown needles. The condition may progress to stunt and distort the tree. Affected twigs should be cut off and destroyed. To prevent transferring fungal spores, this should be done in dry weather. Pruning equipment should be wiped with alcohol after each cut. Fallen needles, twigs and cones should be removed and destroyed. Fungicides such as chlorothalonil, thiophanate-methyl or propiconazole may be effective on severe infections.
Cyclaneusma Needle Cast
This fungal disease is more prevalent in spring and starts with small bright-green dots, which lighten and merge over time to leave the needles bright yellow. In the end, the condition will cause the needles to drop.
Dothisroma Needle Blight
This fungal disease may become apparent from late summer, with the development of dark green bands that gradually turn red-brown, giving this infection its common name of "red band disease."
Brown Spot Needle Blight
This fungal disease tends to affect longleaf pines and the Japanese Black variety. The brown spots gradually extend, to become bands that circle and kill the needles.
Lophodermium Needle Cast
This fungal disease begins with brown-yellow spots or bands on the needles, producing dead needles on which black oval fruiting bodies then develop.
Pine Needle Rust
This can take hold in early fall, as the white pustules of fungal fruiting bodies break out on the needles. It is an unsightly condition, but rarely causes severe damage. It can be controlled by removing nearby weeds---such as goldenrod or aster---that can act as alternative hosts to the disease.
Countering Fungal Diseases
Diseases caused by fungi tend to occur on the lower parts of the pine and on the north side. These conditions can be countered by thorough watering and ensuring good air circulation around the tree, through cutting back other crowding plants. For very bad infections, a fungal spray may be used. When buying pine seedlings, check them carefully for signs of infection. If in doubt, do not purchase such plants.
Other Causes
If the all the needles begin to wilt on Scots, Japanese Black, or Austrian pine trees, this may be an indication of serious damage caused by a microscopic worm, the Pine Wood Nematode, bursaphelenchus xylophilis. Where this is confirmed, affected trees should be removed and destroyed at once, as the condition can quickly spread. The atmosphere gas ozone may cause the tips of new needles on White Pine to turn bright red, but this produces few long-term problems. Needle browning or needle drop may also be caused by long periods of cold, by drought conditions, or simply by the aging of the tree.
