Late frost occur always during the night with cloudless
sky and calm air !
Such late frost often is called "radiation frost"
because the warmth remaining from the previous day is given off into the cold and black sky
in the form of infrared radiation. This means that it is NOT the cold surrounding air which
does suck off energy, the plant tissue itself is giving it off.
Sometimes temperatures of plant tissue can be as low as - 7°C, which means a total loss
of the harvest.
With a cloud cover this situation cannot occur, because the
infrared radiation would be much lower. Therefore we can deduct that an insulating layer
which prevents radiation could protect the fruit cultures.
In earlier times farmers created such insulating layer by
lighting smoky fires with moist straw and other nasty things; the resulting smoke cloud did
insulate very effectively. However such methods are not possible anymore, if only for environmental
In established fruit growing areas (South Tyrol) mostly
Sprinkler-Systems are used.
This does not create an insulating layer, however a protecting ice-coating is deposited on
the blooms. As effective this process seems it has several setbacks :
- large amounts of water are needed
the amounts of clean drinking water used for sprinkling are not provided for easily...
- a large fraction of the distributed water simply does
not reach the twigs of the trees and wets the soil between the trees. This leads to a
compactification of the soil which needs later reworking
- part of the blooms are lost by broken twigs which cannot
bear the additional weight of the ice coating
Application of Water-Fog
If a hovering fog is created and distributed across the orchard
an artificial insulating layer and a coating with water-ice can be achieved ( refer to remark)
This method provides serveral advantages -
- the thickness of the insulating layer can be easily regulated.
- water consumption is considerably lower than with sprinklers
- consumption of electrical energy is considerably lower
- soil compactification cannot occur because no water will
fall down directly
- broken twigs will occur only sparingly because the ice
coating is much thinner however more regular
Fogging as a successful method of prevention of hoar frost
is known for many years and is used regularly in fruit growing areas in North America; why
European fruit growers do not acknowledge this simple method is not known.
it is important to remark
that topographic issues are to be observed. Sloping plantations are not suited because the
fog will "run off". If public road cross the area an additional fact has to be
observed - dense fog creates accident-prone conditions.
Ideal locations are flat areas or
flat valleys. Fencing in the fog with hedges is only partly possible...