Artificial Windbreaks

Windbreaks for Citrus

Florida’s winds and artificial windbreaks for citrus

L. Gene Albrigo and Mark Maliszewski, University of Florida, Citrus Research & Education Center

Instructions on how to determine wind vectors and strengths in your area using the Florida Automated Weather Network (FAWN).

Wind damage to citrus trees and fruit in California was recognized in the 1930s (Blanchard, 1934). The benefits of windbreaks were reported at about the same time in Florida (Newins, 1937). In Florida, average wind speeds are greatest in the spring (Fig. 1), which coincides with the greatest susceptibility of the fruit to windscar (Albrigo, 1976).

Some work using artificial windbreaks for citrus in Australia showed that this type of windbreak could be very effective (Freeman, 1976). Under central Florida conditions, citrus hedge-rows planted north-south provided substantial self protection (Albrigo, 1976). At that time it was proposed that in a hedge-rowed grove that outer rows and every 10th or 12th row could be grown taller to protect the tops of inner rows to improve fresh fruit pack-out (Fig. 2). While hedge-rows appeared very effective, a single windbreak in the center of a block of Hamlin orange trees provided only marginal protection (Rose, 1987).

Fig. 1.  Average wind speeds for Lakeland, Florida from 1941 to 1958.

Fig. 1. Average wind speeds for Lakeland, Florida from 1941 to 1958.

Fig. 2.  Citrus hedgerows as a self windbreak with outer rows taller than inner rows.

Fig. 2. Citrus hedgerows as a self windbreak with outer rows taller than inner rows.

With the advent of hurricanes and spread of canker to an endemic condition, additional benefits from windbreaks are envisioned. Previous studies indicated that wind speed should be reduced below 18 mph to minimize wind driven rain infection with bacterial canker (Serizawa and Inoue, 1975). The conditions associated with these events are quite different than those during the spring fruit windscar period (from petal fall for three months). During those three months, winds are primarily from easterly or westerly directions in Central Florida (Albrigo, 1976). Canker bacterial spread from high winds accompanied by rainfall is most likely to occur in the summer rainy season, particularly during hurricanes. The likely directions of those winds had not been evaluated previously. By using FAWN (Florida Automated Weather Network) data, it was determined that 84 to 97% of winds higher than 25 mph were from easterly or westerly directions for 4 rainy seasons, including the 2004 hurricane season, at three locations representing central, south and western citrus producing areas (Table 1). But the high winds at Ft. Pierce on the East Coast only came from these directions 19% of the time. Over 80 % of the winds above 25 mph occurred in the 2004 hurricane season. In respect to the 4 locations, direction of wind speeds between 15 to 24 mph came more uniformly from easterly or westerly directions, but overall these percentages were lower than for the higher wind speeds (67 to 86% easterly or westerly, Table 1).

An analysis of wind speeds and directions for another site near Clermont in the central region also indicates that during the rainy season less than half of the higher wind speeds, above 15 mph, come from easterly or westerly directions (Table 2). All this suggests that protection to decrease winds below 18 mph should be first from N-S running windbreaks, but E-W windbreaks will be necessary also, particularly on the East Coast. Rose (1987) concluded that all directions needed protection in a study location west of Clermont.

Table 1. Number of 15-minute intervals with wind speeds above 25 miles per hour or between 15 and 24 mph during the rainy seasons in 4 citrus producing areas between 1999 and 2005.

 
 
Number of observations 1999-2005
 
Wind direction
Lake Alfred
 
Ft. Pierce
 
Ona
 
Immokalee
> 25
mph
East
10
 
5
 
2
 
5
North
6
 
97
 
3
 
2
Northeast
17
 
20
 
0
 
0
Northwest
1
 
1
 
31
 
7
South
1
 
87
 
0
 
4
Southeast
9
 
18
 
2
 
6
Southwest
0
 
0
 
35
 
29
West
1
 
0
 
31
 
32
 
Total 15 min events
45
 
228
 
104
 
85
 
% of Easterly-Westerly
84.00%
 
19.00%
 
97.12%
 
93.00%
 
% events in 2004
100
 
98
 
86
 
80
 
 
 
 
 
 
 
 
 
15 to 24 mph
East
44
 
233
 
21
 
63
North
51
 
220
 
4
 
19
Northeast
19
 
261
 
0
 
15
Northwest
36
 
35
 
36
 
67
South
12
 
177
 
39
 
62
Southeast
30
 
126
 
30
 
115
Southwest
3
 
84
 
45
 
107
West
6
 
62
 
24
 
150
 
Total 15 min events
201
 
1198
 
199
 
598
 
% of Easterly-Westerly
69.00%
 
67.00%
 
78.00%
 
86.00%
 
% events in 2004
58
 
41
 
59
 
36

Table 2. Occurrence of high winds in a north central citrus location (Avalon, FL).

 
 
 
 
Number of 15-minute observations
 
 
Wind direction
 
2004
 
2005
25 mph and up
 
East
 
19
 
3
 
North
 
9
 
16
 
Northeast
 
64
 
1
 
Northwest
 
1
 
3
 
South
 
41
 
2
 
Southeast
 
45
 
5
 
Southwest
 
2
 
1
 
West
 
0
 
0
 
 
% of Easterly-Westerly
 
72.38%
 
41.94%
 
 
 
 
 
 
 
15-24 mph
 
East
 
59
 
25
 
North
 
183
 
219
 
Northeast
 
80
 
32
 
Northwest
 
6
 
13
 
South
 
179
 
123
 
Southeast
 
52
 
105
 
Southwest
 
6
 
36
 
West
 
1
 
47
 
 
% of Easterly-Westerly
 
36.04%
 
43.00%

Natural tree windbreaks can easily be established around the perimeters of grove blocks if sufficient space is available after leaving room for equipment turn-around at the ends of rows and block to block travel along the sides of blocks. Artificial windbreaks may be needed if external space is not available for wide tree windbreak bands or if internal block lengths or widths exceed the 10 or 15 times windbreak height down-wind protection that a windbreak can provide. Artificial windbreaks are an option because of the reduced width of these structures and the possibility to provide over the top artificial windbreaks within the block. Higher topping of internal citrus rows is no longer an ideal option because of canker susceptibility of citrus.

A typical artificial windbreak is shown in Figure 3. At least one such windbreak was constructed and evaluated in Florida (Rose, 1987). The basic construction of poles, wind restricting netting and strengthening guy-wires is presented by R. Ehsani and L. G. Albrigo in another paper in this short course. The principles of wind reduction for an artificial windbreak work very much the same as for natural windbreaks. A diagram of the effect in reducing wind speeds is presented in Figure 4. When constructing windbreaks in parallel, it is important to recognize that there is a wind reduction in front of as well as behind the windbreak. This effect easily allows for a 15 time response down-wind from the first windbreak in parallel.

Fig. 3.  Artificial windbreaks in Australia (from Freeman, 1976).

Fig. 3. Artificial windbreaks in Australia (from Freeman, 1976).

Fig. 4.  Wind reduction effect from artificial wind break (from Freeman, 1976).

Fig. 4. Wind reduction effect from artificial wind break (from Freeman, 1976).

To reduce interference of windbreaks with grove operations within grove blocks, a new concept is introduced at this time that calls for an above tree artificial windbreak to allow equipment travel under the windbreak if it is perpendicular to the rows. Alternatively, windbreaks could be placed parallel and over the row top (Fig. 5). Enough space would be left between the established topping height and the lower edge of the netting material to allow equipment to cut or pass under the windbreak. Topping and hedging equipment might require some modification Hedging equipment would need to tilt backward or forward enough to pass under the netting. This concept has not been tested, but appears to be a viable option that would allow long rows to minimize turn-arounds for equipment, especially for mechanical harvesting.

Fig. 5a

Fig. 5a

Fig. 5b. An artificial windbreak concept for over the row-top windbreaks side-view (Fig. 5a) and over-view (Fig 5b).

While the benefits of windbreaks for management of canker spread have been reported by Gottwald and Timmer from studies in Argentina (1995), comparable studies are not available for spread from hurricane force winds. Salvatore et al. (2005) reported that windbreaks and citrus hedgerows did reduce the amount of leaf loss, but no post hurricane canker development was assessed in that study. A preliminary evaluation of areas within hurricane spread vectors supplied by M. Irey, USDA, Fort Pierce is underway. One such comparison is shown in Figure 6 where more new canker finds occurred in an open area compared to a nearby area behind a windbreak. Several new canker outbreaks, found at this same time, were behind windbreaks suggesting that the windbreaks may have not been sufficient to protect from spread of canker when hurricane force winds are involved. Data from 2004 probably is too limited to make valid comparisons of canker spread to groves with natural windbreaks versus nearby unprotected areas, but so far it appears questionable if windbreaks can prevent canker spread in hurricane conditions. Further, artificial windbreaks may not withstand winds of those forces and appropriate tests are needed.

Fig. 6. Image of citrus area with new citrus canker finds after 2004 hurricanes.  Red points are affected trees and line indicates wind vector through a windbreak area.  Clump of red (infected) points in left corner of block on right are over a water area without a windbreak.

Fig. 6. Image of citrus area with new citrus canker finds after 2004 hurricanes. Red points are affected trees and line indicates wind vector through a windbreak area. Clump of red (infected) points in left corner of block on right are over a water area without a windbreak.

Literature Cited

Albrigo, L.G. 1976. Influence of prevailing winds and hedging on citrus fruit wind scar. Proc. Fla. State Hort. Soc. 89:55-59.

Blanchard, F. 1934. Depressing effects of wind on growth and yield of citrus trees. Calif. Citrogr. 19:206

Freeman, B. 1976. Artificial windbreaks and the reduction of windscar of citrus. Proc. Fla. State Hort. Soc. 89:52-54.

Gottwald, T.R. and L.W. Timmer. 1995. the efficacy of windbreaks in reducing the spread of citrus canker caused by Xanthomonas campestris pv. Citri. Trop. Agric. 72(3):194-201.

Newins, H.S. 1937. Windbreaks for prevention of damage to citrus trees. Proc. Fla. State Hort. Soc. 50:43-46.

Rose, A.J. 1987. Effect of an artificial windbreak on rind blemish and yield of Hamlin orange. Proc. Fla. State Hort. Soc. 100:122-126.

Serizawa, S. and K. Inoue 1975. Studies on citrus canker, III. The influence of wind blowing on infection. Bull. Schizuoka Pref. Citrus Expt. Sta. 11:54-67.

Salvatore, J.J., M.A. Ritenour, L.G. Albrigo and B. Scully. 2005. The effect of the 2004 hurricanes on citrus flowering potential for the 2005 season. Proc. Fla. State Hort. Soc. 118:75-79