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Subtropical Frost and Freeze Hazards - PowerPoint PPT Presentation


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Subtropical Frost and Freeze Hazards. Freeze Damage in Citrus. Trunk . Fruit damage. Leaf damage. Freeze damage on citrus production . Complete lost of citrus groves. Frost Hazards. Ranks with pest control, nutrition, and irrigation. May be most limiting factor

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slide2

Freeze Damage in Citrus

Trunk

Fruit damage

Leaf damage

slide3

Freeze damage on

citrus production

Complete lost of citrus groves

frost hazards
Frost Hazards
  • Ranks with pest control, nutrition, and irrigation.
  • May be most limiting factor
    • 1962-63 entire Northern Hemi.
    • Texas from 10 M boxes in 1961 to 740,000 boxes in 1964.
wind machines
Wind Machines
  • Only for frosts
  • Most effective in hill and valley topography - California
  • Mixes inversion layers (upper warmer air with lower colder air)
  • Increase temp 0.5 to 1.5o C
  • One machine / 5 to 8 acres
damage continues
Damage Continues
  • Frost and Freeze losses in winter of 1983-84. Loss of 100,000 Ha.
  • Brazil seldom has loss from frosts and freezes.
  • Mediterranean area protected by Alps (Oriented east - west).
  • Rockies are North - South.
frost or freeze
Frost or Freeze?
  • Frost - Wind is light to none (Radiation)
  • Freeze - Wind over 10 mph (advective).
  • Since damage occurs by ice formation - term freeze hardiness fits what happens in fruit.
freeze avoidance supercooling
Freeze Avoidance (Supercooling)
  • Citrus species supercool threshold:
    • Fruit - - 5o C
    • Mature leaves - - 7o C
    • Stems - - 8.9o C
    • Non-acclimated < - 2o C
    • Flower -4.3oC
intercellular ice formation
Intercellular Ice Formation
  • Citrus tolerates some ice formation between cells.
    • Watersoaking at - 3o C may not cause leaf abscission.
freeze acclimation
Freeze Acclimation
  • Function of
    • Soil temperature
    • Tissue temperature
    • Day length
      • Better under long days
        • Increased metabolites
freeze tolerance
Freeze Tolerance
  • Is defined as the ability of plants to survive ice formation in extracellular tissues without significant damage to membrane or other cell components (Thomashow, 1993).
    • decrease of water potential in tissues due to sugar accumulation in vacuoles.
    • a significant increase in the abscisic acid levels which result in modification of protein synthesis.
  • The process of adaptation to low temperatures may cause changes in the function of genes and proteins.
tolerance of freeze damage
Tolerance of freeze damage
  • Citron < limes & lemons < grapefruit & pummelo < sweet oranges < tangerines & hybrids < sour orange < satsuma < kumquats < cintranges < Trifoliate orange.
maximum acclimation
Maximum Acclimation
  • Daytime temps/ 20 to 25o C
  • Night- time air & soil temp/ less than 12o C for 2 weeks or more.
  • Causes quiescence (not dormancy).
  • Loss of hardiness > 12.5o C.
biochemical changes
Biochemical Changes
  • Sugar content increases with acclimation.
  • Lowers freezing point and acts as a cryoprotectant for cell membranes.
  • Critical are minimum temp. and duration below minimum.
passive protection methods
Passive Protection Methods
  • Site selection
    • Weather Records
    • Avoid low places (Frosts)
    • Wind breaks N & NW (Freezes)
      • Trees
      • Shade cloth.
more passive methods
More Passive Methods
  • Clean cultivated, packed soil absorbs more net radiation from sun, thus more radiant energy at night than sod covered or newly cultivated orchard floor.
  • Orangeries- since Roman times.
  • Tree cover-Today near Sorrento, Italy.
  • Tree wraps
still more passive methods
Still More Passive Methods
  • Japanese grow citrus in greenhouses
    • Frost protection
    • Hastens fruit maturity
  • Taiwanese grow peaches under cover. (prevents frost & leaf curl)
active methods university return stack heating
Active Methods - University Return Stack Heating
  • Protection against both frosts and freezes.
    • Initial $40 x 48 = $1920/A
    • Annual operating 5 gal diesel x $0.65 x 48 x 4 nights + $50 labor = $674
    • Total = $2594/A first year
return stack specifications
Return Stack Specifications
  • Best of oil heaters
  • One hole setting uses 0.3 gph
  • Three hole setting uses 1 gph
  • 30,000 BTU / hr (20 - 70% radiant)
  • Energy directed horizontally
  • Rain in stack - blow over
other heaters
Other Heaters
  • Large Cone - slightly more radiant energy less blow over
  • Short Stack Heater - Smoke
  • Open Pots - Don’t even think about it.
slide21

FREEZE PROTECTION METHODS

Soil banking

Heaters

pressurized oil systems
Pressurized Oil Systems
  • Diesel delivered though underground plastic tubes
  • Efficient
  • Must keep nozzles cool
  • Problems - high pressure oil, filter clogging
propane heaters vapor pressure of propane
Propane HeatersVapor Pressure of propane
  • Temperature PSI
    • 70o F 109
    • 32o F 54
    • - 44o F 0
    • 130oF 257
  • 30,000 gal tank / 60 acre orchard
solid fuel blocks
Solid Fuel Blocks
  • Once cost effective - but not now
  • Four blocks under grapefruit canopy raised temp 13o F
  • Unique for LGRV
    • Fewer frosts / season
    • Store under trees all year
irrigation frost protection
Irrigation - Frost Protection
  • Provides Sensible Heat
    • Warm water source
  • Heat of Fusion
  • Only for frosts
    • Evaporative cooling removes 7.5 times as much energy from irrigated area than provided by Heat of Fusion.
slide26

WRAPS

Fiber-glass wrap

Foam wrap

Polyurethane wrap

overhead irrigation
Overhead Irrigation
  • Heavy foliage accumulates ice which breaks limbs.
  • Works better on strawberries and blueberries.
  • Primarily used on citrus nurseries.
microsprinklers
Microsprinklers
  • At ground level elevates 1 to 2o C to lower canopy
  • No help for fruit and upper canopy
  • Elevated about 1 m give some protection of scaffold limbs - quicker re-establishment.
elevated microsprinklers
Elevated Microsprinklers
  • Excellent results 12.5 gph / tree
  • Hardie Microsprinkler III
  • Protected peach buds when air temp dropped to 18o F (- 8o C)
  • Rieger, Mark and S. C. Myers. 1990. HortScience 25:632-635.
microsprinkler limitations
Microsprinkler Limitations
  • One 5HP pump for 5 A
    • Same pump irrigates 20 A
  • LRGV Irrigation Districts - water not available on demand.
insulators and tree wraps
Insulators and Tree Wraps
  • Soil banks effective
    • Expensive but saves trunk.
    • Remove in spring.
  • Polyurethane foam wrap banded with metal strapping.
  • Plastic bag of water between wrap and trunk???
slide32

Sprinklers

Overhead sprinklers

Under tree micro-sprinkler