Title: Vegetarian
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00087399/00552
 Material Information
Title: Vegetarian
Physical Description: Serial
Language: English
Creator: Horticultural Sciences Department, Institute of Food and Agricultural Sciences
Publisher: Horticultural Sciences Department
Place of Publication: Gainesville, Fla.
Publication Date: October 2010
 Record Information
Bibliographic ID: UF00087399
Volume ID: VID00552
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Full Text

Vegetarian Newsletter

A Horticultural Sciences Department Extension Publication on Vegetable and Fruit Crops

Eat your Veggies and Fruits!!!!!

Issue No. 562 October 2010

Cold Protection by Sprinkler Irrigation for Vegetable and Berry Crops

By: Richard Tyson, University of Florida Orange County Extension

Cold protection from frosts and freezes are often needed to protect high value vegetable and
berry crops in Florida. Active cold protection methods can come in various forms such as using
row covers, high tunnels, or overhead sprinkler irrigation. Wetting the soil the day before a cold
front has also been shown to provide a modest 1-2 o F protection up to a height of 1 foot as wet
soil absorbs more radiant heat during the day for subsequent release at night compared to a dry
soil. Of these choices, sprinkler irrigation has the potential, if used properly, to provide the
largest degree of protection from cold temperatures (Figure 1). For example, tomatoes where
protected against temperatures of 19 o F when sprinkler irrigation was used at the rate of 0.26
inches/hour in a 5 mph wind.
The highest tissue freezing points for many fruits and vegetables range between 29 and 31 o F
(Table 1). Properly designed and managed sprinkler irrigation systems can maintain tissue
temperatures near 32 o F on a freeze night. There are some important principles to consider
when using irrigation for cold protection since used incorrectly, sprinkler irrigation can
potentially cause more crop damage than using no irrigation at all. These principles are:

1. Sprinkling protects by the release of heat as water turns to ice. As long as there is a
uniform mixture of water and ice present on the plant, the surrounding temperature
remains at 32 o F. If insufficient water is applied or if distribution is poor, plant damage
will be more severe than if water had not been applied.

2. As expected low air temperatures decline and wind speeds increase the irrigation
application rate must increase to obtain adequate levels of plant protection (Table 2).
Irrigation for cold protection is considered not feasible at wind speeds greater than 8mph.

3. Leaves should be rewetted with an irrigation pass at least once every minute to keep a
constant film of water present.

4. Irrigation risers should be spaced at 50% of their effective diameters so that the water
discharge from one riser touches the base of the next riser for best results.

5. Irrigation should begin when falling temperatures reach about 34 o F and should operate
continuously until the air temperature increases above 32 o F and ice begins to melt.

I " ^ ,- .

Figure 1. Florida blueberry crop protected from freezing conditions
with overhead sprinkler irrigation.

Table 1. Freezing points of selected vegetables and fruits.*
Variety Range in Freezing Points Highest Freezing Point
Avocado 29.0 to 31.5 F 30.0 to 31.5 F
Lime, Persian 28.0 to 28.5 F 29.5 F
Lime, Key 28.0 to 28.5 F Not available
Mango 29.0 to 30.5 F Somewhat Higher
Papaya 30.0 to 30.5 F 30.5 F
Tangelo, Orlando 27.0 to 30.1 F 30.1 F
Tangerine, Dancy 28.3 to 30.1 F 30.1 F
Beans, Snap 29.8 to 30.7 F 30.7 F
Cabbage, J. W. 29.8 to 30.4 F 30.4 F
Eggplant, B. B. 30.2 to 30.6 F 30.6 F
Lettuce, Iceberg 30.8 to 31.3 F 31.3 F
Okra 28.3 to 28.7 F 28.7 F
Tomato, Homestead 29.9 to 30.5 F 30.5 F
Squash, Yel. Cr. 30.1 to 30.8 F 30.8 F

Table 2. Application rates recommended for cold protection under
different wind and air temperature conditions.*

Temperature WIND SPEED IN M.P.H.
Expected 0 to 1 2 to 4 5 to 8
Application Rate (inches/hour)
270F 0.10 0.10 0.10
26 F 0.10 0.10 0.14
240F 0.10 0.16 0.3
22OF 0.12 0.24 0.5
20 F 0.16 0.3 0.6
180F 0.20 0.4 0.7
150F 0.26 0.5 0.9

*Adapted from: Harrison, D.S., J.F. Gerber and R.E. Choate. 1997. Sprinkler irrigation for cold
protection, University of Florida Cooperative Extension Service Circular 348, Gainesville, FL.

Richard Tyson, PhD
Orange County Extension Director
6021 S. Conway Rd
Orlando, FL 32812-3604

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