Winter injury and south-west injury
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This disorder affects:
Identification
Buds
Uneven or lack of bud break in the spring
Brown or black dormant bud tissue compared to green tissue of
healthy buds
Scorching or drying of leaves
Trunk & Limbs
Injury occurs in the lower trunk, crown or roots near the soil
surface
Large vertical cracks or splits on bark that may leak visible sap
near the ground or snow line
Development of suckers at base of the tree
Damaged inner bark will turn brown, while healthy bark will appear
greenish yellow
Injury become more apparent during the growing season; as the
cambium dies, flattened, dark coloured areas will be apparent on the
damaged portion of the trunk
Winter injury may cause tree death within one year. These trees may
actually bloom and start to leaf out in the spring. Depending on the
severity of the injury and the health of the tree the previous year, trees
may die at any point during the first part of the growing season. Less
severely injured trees may recover or they may decline for the next few
years before dying.
Bending, splitting or breaking of limbs due to heavy snow or ice
load
Often Confused With
Rootstock-scion incompatibility bark tissue is discontinuous between
rootstock and scion
Girdling physical injury that prevents trunk growth
Poor drainage (water stress) most severe in low-lying areas or where a
tile is broken; puddling of water after rains
Nutrient deficiencies confirm with tissue analysis
Drought- follows hot dry weather
Biology
Frequency and severity of winter injury depend on a combination of planting
site, tree species, tree health and ultimately the severity of the winter.
Winter injury can be caused by a number of factors, including excessive
winds (desiccate trees), bright sun or high mid-winter temperatures when
ground is frozen, alternate freezing and thawing of ground in late winter,
heavy snow and ice cause bending and may snap roots, ice damage to trunks
and branches, and mammalian feeding.
Buds and cambial tissue of fruit trees are the most sensitive to cold
damage. Frequently, the damage is observed first in low-lying areas of the
orchard or where natural airflow is restricted. Trees of low vitality,
induced by poor cultural practices, inadequate insect pest and disease
control, or heavy cropping are more susceptible to low temperature injury.
Desiccation occurs when water leaves the plant faster than it is taken up.
Other cell contituents, like sugars, become more concentrated within the
cell during dormancy, also contributing to dehydration. In severely cold
weather, the ground may freeze to a depth beyond the extent of the root
system, cutting off the supply of water. If the previous fall had been dry,
there may be insufficient ground moisture to supply roots with adequate
water. The risk of desiccation is greatest during periods of strong winds
or sunny weather.
Freezing injury may occur when new growth is stimulated by late summer or
early fall fertilization or pruning and may not have had time to harden off
sufficiently to survive sudden drops to below freezing. Ice crystals form
and rupture cell walls. This injury to the cells inhibits the movement of
nutrients and water in the tree, causing damage, such as death of branch
tips. If only some of the cells are killed, the tree will be able to
survive in the spring when demands for water and nutrients are relatively
low. In the summer, when such demands increase, the tree may show signs of
delayed winter injury, because its damaged cells cannot move enough
nutrients and water. Water may be plentiful at this time, but the plant
will not be able to take it up as quickly as required. Symptoms of delayed
injury include browning of leaves, flower and fruit loss. Freezing injury
can also occur in the spring when sun or mild temperatures cause flower or
leaf buds to break dormancy early. Freezing nights may kill these buds.
Roots of cherries, peaches and nectarines are most susceptible to
injury from soggy, wet soils.
Pears, apples and plums are somewhat more tolerant but also can be
injured by extended periods of wet soil conditions.
Southwest injury, or winter sunscald, occurs in the winter in, peach, pear,
cherry, plum and apricot. Injury is usually confined to the southwest sides
of the trunk and main scaffold branches due to mid-afternoon sun exposure
when temperature is often highest.
Living cells just inside the outer bark (mostly phloem and cambium) are
damaged by day to night temperature fluctuations during the winter months.
Exposed bark warms up on sunny days and previously dormant cells within the
tree become active in response to the warmth. These cells lose some of
their cold-hardiness and are injured when temperatures drop below freezing
during the night.
Generally, as the tree matures, it develops thicker bark and becomes less
susceptible to injury. However, thin, dark colored bark like that of stone
fruit may remain susceptible or even become more sensitive to southwest
injury with age.
Period of Activity
Dormant peach trees start to be seriously damaged (shoot death)
when the temperature drops below -29°C, and fruit bud injury occurs once
the temperature falls into the -23 to -26°C range.
In pears, dormant freezing resistance of most cultivars is -30°C .
Scouting Notes
Injury will usually be more common in low spots in the orchard, areas of
tree stress or where natural air movement is restricted resulting in areas
where cold stagnant air accumulates.
Injured trees may become more susceptible to insect and disease during the
growing season. Proper pest management will help to reduce tree stress.
Evaluate the extent of cold injury to fruit buds that may have occurred in
their orchards. Dissect fruit buds vertically using a single-edge razor
blade, and examine for browning of the flower parts. Undamaged buds will be
uniformly 'greenish' throughout, while cold-damaged buds will be 'browned'
to varying degrees in the center. Sometimes slightly browned buds will be
OK, but more than likely, any significant browning indicates the flower bud
is damaged and will not set fruit upon bloom. (Although the flower may
actually 'bloom,' the reproductive parts are dead.) Usually, it is good to
wait until warmer temperatures arrive (above freezing) to evaluate the
damage, as the browning will be accentuated. Also, fruit buds should be
sampled throughout the canopy to get an accurate estimate of percent injury.
Cambium injury in the trunk or limbs is also visible soon after the tissue
thaws. Often trunk injury is most easily found near the ground or snow line.
Southwest injury is typically found on the portion of the tree with south
or west exposure. Young trees with thin bark are most susceptible to
southwest injury. Monitor closely when cold, still nights follow sunny days.
Management Notes
Make sure trees are fully hydrated in the fall before the ground freezes. A
layer of mulch around the base of the tree may also help conserve soil
moisture and moderate temperature.
Avoid heavy watering and fertilization in late summer or early fall as may
encourage continued growth and limit chance for trees to harden off for
winter survival.
Remove weak, narrow-angled, V shaped crotches.
Avoid late summer pruning as stimulates new growth and reduces supply of
nutrients available to plant through winter.
Remove broken or dead branches in the spring and prune to stimulate new
growth.
Carefully trim away loose bark at any crack until remaining bark is firmly
attached to the tree. This trimming helps improve wound wood formation or
callusing. Callus is cell tissue that forms to cover wounds.
Reduce stress on injured plants by fertilizing, watering during dry
periods, controlling weeds and insects, mulching, and generally increasing
plant vigour.
Southwest injury causes significant stress for trees and can make them
highly susceptible to pests and disease entering the damaged areas. In
stone fruit orchards, these injuries provide ideal sites for infection by
peach canker or other canker diseases or infestation by tree borers.
Paint the trunk, crotches and lower parts of main scaffold branches with
exterior white latex paint to minimize southwest injury. This helps to
reflect light away and keep surface bark temperatures cooler, ensuring
dormant cells remain inactive.
Do not use oil-based or latex paints that contain any oil. These
products contain toxic materials that may injure or kill fruit trees.
October is the best time to apply the paint. Best results are
obtained when trees are painted on days when the temperature is above 10°C
and when paint will dry rapidly.
Apply the paint by brush or by spray. If you choose spray, use 1-2
L of water/4.5 L of paint, depending on the thickness of the paint and the
air pressure available.
On young trees, paint the whole trunk. Only the south and southwest
sides of older trees require paint. The whiter the bark after you paint,
the greater the protection. Better quality paints are more durable.
Damage may eventually heal, but damaged areas should not be painted
or filled with any sealing substance, including paint or tar.
Protection from southwest injury can also be accomplished by placing light-
coloured spiral tree guards on newly planted, susceptible trees. Tree
guards should fit loosely around the trunk for good air movement and should
be periodically inspected for insects or excessive build up of moisture
inside the wrap. They should be adjusted annually to prevent the guard from
interfering with trunk expansion (growth).
Information included above excerpted from;
http://extension.usu.edu/files/publications/factsheet/NR_FF_021pr.pdf
http://mgofmc.org/docs/winterinjury.pdf
http://agbio.usask.ca/trees-winter
http://www.agriculture.gov.sk.ca/Agriview_Feb_09_7
http://www.umass.edu/fruitadvisor/clements/articles/peachfreeze.html
http://utahpests.usu.edu/IPM/htm/ornamentals/landscape-insects-and-
diseases/winter-injury/
http://pubs.ext.vt.edu/426/426-500/426-500.html
http://pubs.aic.ca/doi/abs/10.4141/cjps59-028
http://trace.tennessee.edu/cgi/viewcontent
http://ohioline.osu.edu/hyg-fact/1000/1409.html
>From Ontario Ministry of Agriculture Tender Fruit and Grape Newsletter
Jerome L "Jerry" Frecon
Professor Emeritus, Rutgers University
And Horticultural Consultant for
www:jerseypeaches.com
www.acnursery.com
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