Agriculture Reference
In-Depth Information
PROTECTING AGAINST FROST
Most commercial orchards now use large fans mounted on towers to
stir up the air in the orchard and help offset inversion layers during ra-
diation frost events. Inversion layers commonly develop when cold air
is trapped near the ground. You can see inversions when smoke from
chimneys rises 100 feet or so in the air and then spreads out in a ho-
rizontal layer as if it has hit a glass ceiling. That ceiling is the boundary
between cold and warm air layers. Mixing the cold layer with warmer
air layers above it can help prevent frost damage in orchards.
Propane- or kerosene-fired heaters are sometimes used alone or in
combination with fans to keep orchard temperatures above freezing
during bloom. Specially designed orchard heaters called “salaman-
ders” are available. On a small scale, one of my friends who has a home
orchard places a portable barbecue grill under each blooming tree
during frosty periods. The idea is to add just enough heat to the canopy
area to keep temperatures at about 32 to 34°F (0 to 1°C) or above.
When sprinkler systems are not intended to provide protection against
frosts, it is usually best to use sprinkler designs that keep the water close to
the ground. This practice keeps the foliage and fruit dry and greatly reduces
disease problems. When you use sprinkler irrigation, apply water early in the
morning to allow the understory of the tree to dry before nightfall. This prac-
tice keeps the humidity level lower and helps reduce disease problems. Keep-
ing the sprinkler pattern low also protects the kaolin clay film that is applied
to the foliage, fruit, and branches as part of some pest and disease control
programs. Sprinklers quickly wash the clay film off, leaving the crops sus-
ceptible to pests and diseases. We'll discuss kaolin use in chapters 10 and 11.
