Disease

Physiological needle droop of red pine.

Importance

Young trees growing in low areas, on droughty soils, with heavy competition, or with J-rooting are periodically severely affected in the north-central to northern Lake States area. Damage is greatest on the shoots towards the tops of the seedlings, but lower branches can also be affected. If many buds are damaged, very small seedlings may die. Surviving trees may have some growth loss and stem deformity.

Biology

Figure 12

Physiological needle droop is caused by an abiotic disease. Usually trees under 7 feet (2 m) tall are affected in July and August on sites that have limited water available on hot, sunny, and windy days when transpiration is rapid. It only takes a few hours for needle tissue under the sheath to collapse due to lack of sufficient water. The needles droop and die (fig. 12), but they remain green for awhile. They gradually fade to brown over winter and stay on the tree into the next summer. Usually the buds remain alive and will expand, but most of the buds on severely damaged shoots will die. The remaining live buds will develop, and the tree will develop a bushy appearance.

Management Guidelines

• Avoid planting red pine on droughty sites.

• Plant carefully to avoid J-rooting.

• Control weed competition.

• Correctively prune trees. This will be required during stand improvement operations on seedlings and saplings with severe stem deformity.

Bergdahl, D.R; French, D. W 197& Needle droop: An abiotic disease of plantation red pine. Plant Disease Reporter. 60: 472-476

Patton, P. F.; Riker, A. J 1954. Needle droop and needle blight red pine. Journal of Forestry. 52:412-418.