Freeze Protection Practices for
Florida Blueberries
Gary K. England
Multi-county Extension Agent –Fruit
Crops
Freeze Protection Practices for Florida
Blueberries
• BMAPs and BMPs
• Florida Automated Weather Network (FAWN)
– Cold Protection Toolkit
• Critical Temperature
• Types of Freezes
• Freeze Protection Management
– Wet Bulb Temperature
BMAP
• Basin Management Action Plan
• “Blueprint" for restoring impaired waters by reducing
pollutant loadings to meet the allowable loadings
established in a Total Maximum Daily Load (TMDL).
• It represents a comprehensive set of strategies--permit
limits on wastewater facilities, urban and agricultural
best management practices, conservation programs,
financial assistance and revenue generating activities,
etc.--designed to implement the pollutant reductions
established by the TMDL.
BMPs and Freeze
Protection
Effects of freezing temperatures on
blueberries
Michigan State University
Effects of freezing temperatures on
blueberries
Michigan State University
Types of freezes
• Advective
– Windy
– Evaporative cooling
• Radiation
– Low/No wind
– Inversion
Blueberry freeze protection methods
Blueberry freeze protection methods
• Dormancy
• Cultivar
– Flowering time
• Site selection
– Windbreaks
– Hilltops
– Cold air drainage
• High tunnels & row covers
• Overhead irrigation
– Pre-freeze
– During freeze
Blueberry freeze protection methods
No!
Is it always advisable to apply water
for freeze protection?
Wet bulb temperature
Dr. Dorota Hamon
How to determine wet bulb
• FAWN
• Kestrel or sling psychrometer
Dr. Dorota Hamon
There is always a risk when using irrigation
systems - micro-sprinkler or conventional
sprinkler - for cold/frost protection. Low
humidity and wind can produce weather
conditions that result in a wet bulb
temperature - the lowest temperature to
which air can be cooled by evaporating water
into it - 5°F to 6°F lower than the air
temperature.
This may result in plant damage if the
wet bulb temperature is below the
critical minimum temperature (CMT)
for your particular crop.
‎ uesday, ‎January ‎03,
T
2012, ‎10:18:10 AM
(pre-freeze: cold air moving in)
According to Avalon
FAWN Station:
•Temp - 40.5 F
•Wind - 11 MPH
•Wet Bulb – 31.4 F
•Dew Point – 11.3 F
•Does this make you
a believer in
evaporative cooling?
‎
What happened on February
11-13, 2012?
Okahumpka FAWN Station
Time
Air Temp.
Wind
Wet Bulb
2/12/2012 2:00
39.29
36.12
33.56
31.95
30.51
30.04
8.84
12.24
10.25
8.75
7.13
7.56
32.75
29.7
27.74
26.68
25.91
25.31
2/12/2012 3:00
2/12/2012 4:00
2/12/2012 5:00
2/12/2012 6:00
2/12/2012 7:00
Morning of February 12; advective freeze
Insufficient coverage on northern margin of
a blueberry block
Evidence of freeze damage noted in areas of
insufficient freeze protection
Evidence of freeze damage noted in areas of
insufficient freeze protection
Morning of February 13; radiation freeze
with a low of 25 F
Fruit well protected by ice
Conclusions
• Monitoring the wet bulb temperature
before turning overhead freeze
protection on worked well for growers
• Evaporative cooling caused by
insufficient water coverage will result in
the temperature “crashing” to the wet
bulb and potentially damage blueberry
crop if below the critical mean
temperature
Resources
• Overview of Florida s Commercial Blueberry
Industry Florida’s – Jeff Williamson PPT. 2008
• Protecting Blueberries from Freezes in Florida
– HS968
• Michigan State University Blueberry Growth
Stages
http://blueberries.msu.edu/growing_blueberri
es/growth_stages_table
• Florida Automated Weather Network
Questions?
gke@ufl.edu