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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 regulations.
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 :
o large amounts of water are needed
the amounts of clean drinking water used for sprinkling are not provided
for easily...
o 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
o 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 -
o the thickness of the insulating layer can be easily
regulated.
o water consumption is considerably lower than with
sprinklers
o consumption of electrical energy is considerably lower
o soil compactification cannot occur because no water will
fall down directly
o 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.
remark )
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...
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