Winter Desiccation

From: Field Guide to Diseases and Insect Pests of Idaho and Montana Forests, USDA Forest Service Northern Region, Publication Number R1-89-54

Hosts. – All conifers.

Distribution. – Occasional throughout Idaho and Montana but especially common cast of the Continental Divide in Montana.

Damage. – Desiccation and death of foliage with dieback of windward or southwestern aspects of crown. Tree death sometimes results.

Identification. – Winter desiccation damage is usually the result of abrasion from windblown ice crystals removing the waxy coating of leaves, solar warming of southwestern aspect of tree crowns causing leaves to transpire excessive moisture when roots are frozen and unable to replace moisture, or temperature inversions in mountainous terrain stimulating transpiration from foliage of trees while soil is still frozen. Owing to these causes,the patterns of foliage damage varies. Foliage damage from winter desiccation may be predominantly on the windward side of the crown, the southwest aspect of the crown, or more general in the crown of trees but in an clevational zone corresponding to the transition zone between warm and cold air in a temperature inversion (rcf erred to as redbeit). In any of these cases, the portion of the crown which is covered by snow in winter will not be damaged (fig. 146). Damaged leaves turn yellow, red-brown or dark brown in the spring following winter desiccation. They are usually shed that summer. Older damage can be identified as dead branches re- stricted to the windward or southwestern side of trees (fig. 147) or as dead trees in an clevational belt representing air inversion-caused desiccation. Ice abrasion-caused desiccation is generally restricted to exposed, timberline sites.

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Figure 146 - Winter Dessication causes reddening of foliage above the level of snow. Some species, such as pine, are more susceptible to Winter Dessication damage than are others.	Figure 147 - Chronic Winter Dessication can kill parts of the crown as seen in the dead branches of this tree with both old and recent damage.

Similar damages. – Needle casts also cause discoloration of foliage but are typically heaviest in the lower crown while winter desiccation damage generally has the opposite pattern. Insect feeding may appear similar from a distance.

Reference.

Bega, R.V. 1978. Diseases of Pacific Coast conifers. USDA For. Serv. Ag. Hndbk. No. 521, 206 p.

Boyce, J.S. 1961. Forest Pathology. McGraw-Hill Book CO., New York, NY. 572 p.

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