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Subtropical Frost and Freeze Hazards

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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Subtropical Frost and Freeze Hazards

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  1. Subtropical Frost and Freeze Hazards

  2. Freeze Damage in Citrus Trunk Fruit damage Leaf damage

  3. Freeze damage on citrus production Complete lost of citrus groves

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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

  9. Intercellular Ice Formation • Citrus tolerates some ice formation between cells. • Watersoaking at - 3o C may not cause leaf abscission.

  10. Freeze Acclimation • Function of • Soil temperature • Tissue temperature • Day length • Better under long days • Increased metabolites

  11. 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.

  12. Tolerance of freeze damage • Citron < limes & lemons < grapefruit & pummelo < sweet oranges < tangerines & hybrids < sour orange < satsuma < kumquats < cintranges < Trifoliate orange.

  13. 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.

  14. 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.

  15. Passive Protection Methods • Site selection • Weather Records • Avoid low places (Frosts) • Wind breaks N & NW (Freezes) • Trees • Shade cloth.

  16. 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

  17. Still More Passive Methods • Japanese grow citrus in greenhouses • Frost protection • Hastens fruit maturity • Taiwanese grow peaches under cover. (prevents frost & leaf curl)

  18. 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

  19. 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

  20. Other Heaters • Large Cone - slightly more radiant energy less blow over • Short Stack Heater - Smoke • Open Pots - Don’t even think about it.

  21. FREEZE PROTECTION METHODS Soil banking Heaters

  22. Pressurized Oil Systems • Diesel delivered though underground plastic tubes • Efficient • Must keep nozzles cool • Problems - high pressure oil, filter clogging

  23. 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

  24. 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

  25. 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.

  26. WRAPS Fiber-glass wrap Foam wrap Polyurethane wrap

  27. Overhead Irrigation • Heavy foliage accumulates ice which breaks limbs. • Works better on strawberries and blueberries. • Primarily used on citrus nurseries.

  28. 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.

  29. 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.

  30. Microsprinkler Limitations • One 5HP pump for 5 A • Same pump irrigates 20 A • LRGV Irrigation Districts - water not available on demand.

  31. 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???

  32. Sprinklers Overhead sprinklers Under tree micro-sprinkler

  33. Damage of citrus trees by sprinkler system

  34. THE END

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