ISSUE 1 May 6, 2004
WINTER INJURY ON SPRUCE
Spruce trees are susceptible to many types of disease in ND, but the much more common injury symptoms on spruce are caused by environmental factors. This seems to be the case this year. The lab has seen several spruce samples this spring with brown needles. The pattern of symptom expression is atypical for both Rhizosphaera needlecast and Cytospora canker, the two most common, biotic spruce diseases.
The needle browning is typical of injury that occurs when needles on a spruce tree are not able to replace moisture lost due to respiration, winter desiccation. Several factors influence this condition, such as early fall frost, drought, spring freeze/thaw cycles. Damage from winter desiccation first becomes apparent in late winter or early spring. As temperatures warm up above freezing, spruce needles will essentially not recognize that winter is not over, and will instead begin to respire. As moisture is lost from those needles, it cannot be replaced either because it was not there in the first place or the roots are still in frozen soil and cannot move water up to where it is needed. This results in dried out, brown needles. This condition is not usually lethal or even seriously damaging to spruce; and unless the injury is significant enough to kill the new buds, it is primarily aesthetic. As new buds emerge and new green growth expands, the brown needles gradually become less apparent, and will eventually fall off.
Management for winter desiccation injury is straight forward, water trees when rainfall is not adequate to maintain sufficient hydration. This is particularly important in the fall as trees are getting ready for winter. This practice does not ensure that no injury will occur, but it maintains a more vigorous state of health in the tree and will minimize damage due to winter desiccation. Spruce with spider mite injury may be predisposed to winter desiccation so it will also be helpful to manage for that condition as well.