This document discusses low temperature injury in plants. It explains that chilling injury occurs above freezing between 0-12.5°C, while freeze injury occurs below 0°C due to ice formation. Tropical plants are more susceptible to damage from slightly below freezing temperatures, while temperate plants can withstand colder temperatures. Hardening makes plants more tolerant of freezing through increased solute concentrations. Symptoms of winter injury include trunk splitting, darkened cambium, and tree decline or death. The document recommends techniques like trunk guards and pruning to mitigate frost damage.

1. JAWAHARLAL NEHRU KRISHI VISHWA VIDYALAYA

2. • Low temperature (e.g. chilling and freezing) injury can occur in
all plants, but the mechanisms and types of damage vary
considerably.
• Many fruit, vegetable and ornamental crops of tropical origin
experience physiological damage when subjected to
temperatures below about +12.5 °C, hence well above freezing
temperatures.
• However, damage above 0 °C is chilling injury rather than freeze
injury.
• Freeze injury occurs in all plants due to ice formation.
• Crop plants that develop in tropical climates, often experience
serious frost damage when exposed to temperature slightly
below zero, whereas most crops that develop in colder climates
often survive with little damage if the freeze event is not too
severe.

3. • Some exceptions are lettuce, which originated in a temperate
climate, but can be damaged at temperatures near 0 °C and some
subtropical fruits trees that can withstand temperatures to -5 to -8
°C.
• HARDENING- Species or varieties exhibit different frost damage at
the same temperature and phenological stage, depending on
antecedent weather conditions, and their adaptation to cold
temperatures prior to a frost night is called "hardening".
• During cold periods, plants tend to harden against freeze injury,
and lose the hardening after a warm spell.
• Hardening is most probably related to an increase in solute
content of the plant tissue or decreases in ice-nucleation active
(INA) bacteria concentrations during cold periods, or a
combination.
• During warm periods, plants exhibit growth, which reduces solute
concentration, and INA bacteria concentration increases, which
makes the plants less hardy.

4. SYMPTOMS
• Injury may appear in several ways. The most obvious damage is splitting
of the trunk.
• Vertical cracks may occur at the time of freezing.
• Less noticeable injury may appear as darkened cambial areas under the
bark.
• It will become more apparent during the growing season.
• As the cambium dies, flattened, dark colored 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.

5. • Less severely injured trees may recover or they may decline for the next
few years before dying.
• Trees weakened in such a manner are also more susceptible to insects
and diseases at either the injured site or throughout the tree than are
healthy trees.
• Flower bud survival can be checked by
dissecting a bud and observing the color inside
– green is healthy, while brown or black means
damage.
• A damaged bud could potentially bloom but
would not be reproductively viable and will
most likely brown quickly and fall prematurely
from the tree

6. • Winter injury is most severe when it
occurs in the lower trunk, the crown
(where the trunk transitions to roots)
and the upper region of the root system
(closest to the soil line).
• Damage in these areas usually results in splitting of the
cambium layer just under the bark, which disrupts the flow
of nutrients and can initiate wood rots or insect damage.
• Trees with this level of damage will often leaf out in spring,
since energy is stored in the buds themselves, but once that
energy is spent and the tree can't pull more resources from
the roots, affected areas will start to die back.

7. FROST PROTECTION TECHNIQUES
• The two most common methods of
protecting trees from winter injury are using
certain trunk guards or painting the tree
trunks.
• Trunk guards should be light-colored,
preferably white, and extend from about 2
inches below ground to about 16 or 18
inches above ground.
• The ideal guard should have holes in it to
allow for some air movement next to the
trunk and should be loose enough to prevent
girdling of the trunk as it increases in
diameter.

8. Other Protection Measures
• During wet weather, an outer covering of plastic film helps
keep the insulating materials dry, but plastic alone provides
very little frost protection.
• Cover the trunks from the ground level up to the main
branches. Keep the ground around the trees as clean and as
free from mulch, weeds, and ground cover as possible.
• Bare, moist soil radiates more heat than soil blanketed with
mulch or ground cover, and this radiated heat helps protect
trees from frost.
• Protect young frost-sensitive trees by wrapping
the trunks and branches with insulating material
such as palm fronds, cornstalks, cardboard, or
fiberglass.

9. • In cases where severe frosts are predicted, a 100-watt lamp (designed for
outdoor use) placed in the interior of the tree will emit enough heat to
reduce frost damage.
• Make sure your garden soil is moist. If the soil has good drainage, run a
sprinkler system slowly or furrow-irrigate through the night.
• The water gives off heat, and this can help protect the trees from freezing.
Also, damp soil retains heat better than dry soil, protecting roots and
warming the air near the soil.
• Commercial growers use large fans or wind
machines to protect citrus trees from advective
frosts caused by temperature inversions.
• The fans mix the layers of warm and cold air,
raising the temperature at the surface. Wind
machines, however, are seldom practical for a
backyard gardener with a few trees.

10. PRUNING
• If citrus trees sustain frost damage, do not prune away dead wood
or remove the trees in early spring. Wait several months in order to
assess the full extent of the damage and to allow the trees to
recover during warm weather.
• As new foliage begins to grow in the spring and early summer, frost-
killed twigs and branches will become readily apparent and can be
pruned out without removing viable portions of the tree.
• Postpone heavy pruning until the following year, so that the trees
are able to regain their full canopy.