Frost
Injury
Distribution: Throughout
B.C., particularly in areas of poor air drainage (frost pockets) or
cold wet soils.
Tree Species Affected:
All trees of all ages are susceptible. Interior varieties are more tolerant than coastal varieties of the same species. Douglas-fir is most commonly affected in central BC.
What to Look For: Unhealthy appearance of foliage or
buds; vertical cracks and cankers in bark. Signs & Symptoms:
Conifers Frost injury results when unusually cold temperatures freeze sensitive new growth or older tissues not yet sufficiently hardened off for winter. Late spring frost affects buds just breaking dormancy and succulent new growth. Injury is visible within two days of frost incidence when foliage becomes limp and fades to yellow. After approximately one week, killed buds turn dark brown and soft. Affected foliage of the branch tips becomes red-brown and droopy. These symptoms are often most pronounced in the upper crown of smaller trees on the emerging succulent foliage.
Frost lesions are rough, callused patches on the main stem created by frost-killed cambium. Necrotic bark eventually sloughs off to expose the sapwood. Raised lateral woody folds, called frost ribs, surround older cankers. This type of injury generally occurs on young to pole-sized trees. Subsequent freezing of these lesions can cause internal radial shake, seen as brownish, resin-soaked rings of disrupted wood.
Frost cracks are usually seen in older trees, especially with true fir species. This type of damage is characterized by long, dark vertical cracks in the main stem. Frost heaving is almost exclusively restricted to first-year seedlings in cold, poorly drained soils. Affected seedlings are ejected from the soil and their roots are generally broken within several
centimeters of the root collar. For
Broadleaves: Frost damage can occur in spring with a
late frost, or in winter but with different effects. Spring
frost affects new leaves and causes wilting, discolouration, puckering
and premature dropping of the young and succulent leaves. The
foliage is patchy and not uniform when the trees foliate again after
damage. Aspen and birch leaves may grow abnormally large.
Older leaves can normally withstand frost despite marginal
discolouration. Winter
frost may cause stem and trunk damage in the form of cankers cracks,
and scabby (discoloured and scaly) bark. Damage most often
occurs on the sun-exposed side of the tree. Cracks may be closed
over by adjacent living bark, or may form cankers that bridge the
wound with burls and ridges (frost ribs). On trunks, bulging
frost cracks run vertically and start at wounds or branch stubs.
The cambium can be cut between dead and live stem zones and examined
for dark brown discolouration. Bud damage causes central tissue
mortality and reduced bud viability. Damaged terminal buds may
produce forked stems or multiple-leaders. Frost damage to buds
can be diagnosed by the discoloured, or green, and water-soaked
appearance. Root damage causes cankers and girdling.
Cankers may bridge over with new bark unless the tree is completely
girdled.
Damage: Conifers - Late spring frosts are usually more injurious than early fall frosts. Reduced lateral and leader growth or tip dieback are common. Frost heaving is also caused by late spring frosts, and can result in significant seedling mortality on newly planted sites at higher elevations. Internal radial shake can adversely affect growth rates and wood quality. Frost lesions or frost cracks act as entry points for canker and decay fungi or can lead to stem breakage. Several canker fungi act as weak pathogens following frost damage, and cause substantial dieback and branch flagging injury.
Broadleaves
- Frost can cause tree mortality if the tree is girdled with
cankers. Reduced growth from terminal bud damage and top damage
can also occur. The main concern is the introduction of diseases
through cracks and cankers. Cumulative effects of periodic
frosts produce poor quality stands of red alder. Young or recently
planted trees are most susceptible to damage. Low-lying
depressions and slopes oriented towards the sun experience more severe
frost. Frost cracks are especially common on large black
cottonwood trees and other thin-barked trees.
Similar Damage: A variety of biotic and abiotic agents can cause damage resembling frost damage. Repeated frost injury resembles damage caused by animal browsing. Consider climatic conditions, and look for signs of animal activities to distinguish between these agents. Frost cracks may be confused with lightning hits. However, lightning injury leaves a more jagged furrow in the bark, and may have an accompanying broken top. Shoot damage by insects such as the terminal weevil can be similar to late spring frost damage. Look for signs of insect feeding and activity to identify the causal agent. Sunscald
appears more as an elongated canker than a split in the bark.
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