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Group Title: Circular
Title: Thinning practices in Florida citrus groves
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Full Citation
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Permanent Link: http://ufdc.ufl.edu/UF00084282/00001
 Material Information
Title: Thinning practices in Florida citrus groves
Series Title: Circular
Physical Description: 14 p. : ill. ; 23 cm.
Language: English
Creator: Norris, Richard E ( Richard Earl ), 1926-
University of Florida -- Agricultural Extension Service
Publisher: Agricultural Extension Service, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1962
 Subjects
Subject: Citrus -- Thinning -- Florida   ( lcsh )
Citrus fruit industry -- Costs -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: R.E. Norris.
General Note: Cover title.
General Note: "May 1962."
 Record Information
Bibliographic ID: UF00084282
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 80382311

Table of Contents
    Front Cover
        Page 1
        Page 2
    Main
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
    Back Cover
        Page 15
Full Text






IINNING Practices
in Florida Citrus Groves
R. E. NORRIS






























Cover shows a newly hedged 21-year-old Hamlin orange grove growing on
rough lemon rootstock on Lakeland fine sand.









Thinning Practices in Florida

Citrus Groves

R. E. NORRIS
Lake County Agricultural Agent

Citrus growers, confronted with ever increasing costs of
land, taxes, materials, and services, must maintain the highest
possible production and quality potential on each acre.
Citrus fruit growers know that close spacing of trees in-
creases fruit production during the early years of growth. Most
growers plan to remove certain trees when they become suffi-
ciently large to interfere with the normal growth and develop-
ment of others. Unfortunately, the thought of removing healthy
trees induces severe mental anguish among many growers.
Therefore, growers seek less painful measures for overcoming
the thinning problem.

THINNING METHODS

There are numerous methods of managing closely set trees.
Four methods used by citrus growers are hedging, topping or
"buckhorning," thinning by tree removal, and close spacing and
subsequent thinning.
Hedging is one means of alleviating the crowded condition
in citrus groves. It was used by a few growers in the early 50's
and has gained popularity in recent years. Hedging is especially
advantageous in tangerine plantings. The percent of tangerine
packout can be substantially increased because fruit size increases
after the first year of hedging. See Table 1, Grove A.
Hedging is also popular in orange and grapefruit plantings.
Although production is generally reduced from one to three
years following hedging in these varieties, the practice results
in better sizes, better rind color, higher solids, and cleaner fruit.
See Table 2, Grove C.
Hedging opens tree middles, enabling more effective oper-
ation of tractors, spray equipment, fertilizer distributors, discs,
and picking crews. Hedging allows more light in the tree mid-
dles, which results in better cover crops.







TABLE 1.-EFFECT OF HEDGING ON PERCENT OF PACK-OUT IN A
REPRESENTATIVE TANGERINE GROVE.
Grove A: Tangerine on rough lemon rootstock, 30 years old at beginning
of study, planted 26 x 26 on Lakeland fine sand.
I I [
Season Boxes Picked I Boxes Packed I % Pack-out


1949-50 .................... 6087 2207 36.25

Hedged on 2 sides in Feb. '50

1950-51 ................... 3564 3005 84.31
1951-52 ....................- 7908 6588 83.31
1952-53 ........... --........ 3970 3570 89.92
1953-54 ..................... 8634 5024 1 50.81

Hedged on 2 sides April '54

1954-55 ............... ..- 3992 3366 84.31
1955-56 ...................... 6171 5073 82.20

Hedged on 2 sides Jan. '56
-L
1956-57 ...................... 3422 2373 69.34
1957-58 ................... 816 478 58.57
(Freeze)
1959-60 ..................... 5349 3790 70.85

Hedged on 2 sides Jan. '60

1960-61 ....... ........... 6013 4924 81.88

Ten-year average after hedging ......-............... ...... ..- 75.55


Hedging generally costs from 10 cents to 1 dollar a tree,
depending on the type of equipment used, size of trees, amount
and size of brush waste and how brush disposal is handled.
For more information on hedging see Florida Agricultural
Extension Service Circular 115 and Agricultural Experiment
Stations Bulletin 519.
Topping or "buckhorning" is a type of rejuvenating pruning.
It is used primarily to revert an old block of low production
seedlings to much greater production without removing any trees.
Topping involves the removal of all wood from about 5 to 51/2
feet above the ground, although some trees are cut at ground
level because of an unsound trunk. This severe pruning stimu-
lates new growth over the remaining portion of the tree.







TABLE 2.-EFFECT OF HEDGING ON PERCENT OF PACK-OUT IN
REPRESENTATIVE ORANGE AND GRAPEFRUIT GROVES.

Grove B: Hamlin orange on rough lemon rootstock, 21 years old at beginning
of study, planted 20 x 20 (diamond pattern) on Eustis fine sand.

Season I Boxes Picked Boxes Packed % Pack-out
II i

1949-50 .................... 2307 All cannery 0
1950-51 ......-........- ...... 2125 1197 56.33
1951-52 ...................... 2663 1800 67.59

Hedged on 2 sides Feb. '52

1952-53 ...................... 2518 657 26.09
1953-54 ......... ........ 2763 1672 65.13

Hedged on 2 sides Jan. '54

1954-55 ................... 1995 1338 67.06
1955-56 ...................... 1445 1068 73.90
1956-57 .................. 1971 1132 57.43
1957-58 ...................... 2609 1280 49.05
(Freeze)
1959-60 ..................... 1346 571 42.42
1960-61 ...................... 1397 947 67.78


Eight-year average after hedging ................. ................... 56.10


Grove C: Duncan grapefruit on rough lemon rootstock, 19 years old at
beginning of study, planted 28 x 28 on Lakeland fine sand.


Season Boxes Picked Boxes Packed % Pack-out


1953-54 ............ 1142 | 259 22.66
1954-55 .......... ........ 1997 1166 58.39
1955-56 ............ .... 2975 1451 48.77

Hedged on 3 sides Feb. '56

1956-57 .................. 2497 1284 51.42
1957-58 ..... .............. 3006 1680 55.88
1958-59 ............-..... 2904 1079 37.22
1959-60 .................. 2427 1725 71.07
1960-61 ..-....... ....... | 1863 1332 71.49


Five-year average after hedging ................................ 57.21

Figures courtesy Lake Region Packing Association.
5


































Figure 1. A newly hedged Marsh grapefruit grove. The trees are on
rough lemon rootstock and are 19 years old. The grove is on Lakeland
fine sand.


Figure 2. A scene typical of that found in many old canopied groves
growing in Florida. These trees were cut back to shoulder height.








In many seedling blocks limbs have overlapped. Insect and
disease pests, together with a lack of sunlight in the lower por-
tions of the trees, have caused a gradual dying of the lower limbs.
Because of this, in some old seedling groves the first limbs are
10 to 15 feet from the ground. The tops are sparse, foliage is
small, production is down, and picking costs (usually from a
40-foot ladder) are decidedly up.
Table 3 indicates the expected yield for seedling trees that
are "buckhorned" in solid blocks. A power saw is used and cuts
are made at a height most convenient for the saw operator,
generally in the 5- to 51/2-foot range. All cuts are treated with
a heavy coat of water emulsifiable asphalt paint. The trunks are
whitewashed immediately with a durable, waterproof cement
paint. Then the pruned material is removed from the grove
and burned.

TABLE 3.-PRODUCTION RECORD OF A 10-ACRE SEEDLING BLOCK CUT BACK
TO WAIST HEIGHT.

Before Cutting During Years Trees After Cutting
Back Trees Were Cut Back Back Trees
Yield in Yield in Yield in
Year Boxes Year Boxes Year Boxes
1946 3017 1951 958 1954 722
1947 2652 1952 385 1955 1120
1948 2801 1953 397 1956 1503
1949 2399 1957 2926
1950 1862 1958 4872
1959 5713
1960 5121
1961 6071

Figures courtesy Lake County Grower.

Within six weeks the trunks are sprouting vigorously. All
sprouts except the uppermost three or four on each large branch
are rubbed off. This forces all growth into the top of the limbs
and reduces the amount of decay that would subsequently occur
if the lower suckers were allowed to grow.
All new growth is very thorny. Terminal ends of the new
growth are broken off by hand or cut by sickle at intervals. This
forces the new growth to branch out quickly to make a full
headed tree. Thorns continue to appear on the new growth and
are so severe that inside pruning or training is almost impossible.
However, nature provides her own pruning and many of these
branches are shaded out when the full tops block out the sun-


































Figure 3. Trees in this block cut back to shoulder height looked like
this 16 months after topping.


Figure 4. This picture was made 24 months after the old trees were cut
back to shoulder height.







light. As the new growth gets older and longer, thorns begin
to disappear.
Trees that are cut off at ground level grow out very rapidly
too. They are more "squatty" than those cut higher. These
trees, as well as those cut off at 5- to 6-foot heights, grow back
resembling budded trees. Trees cut from 10 to 15 feet above
the ground assume the appearance of seedlings. A reason for
not cutting trees at the ground surface is that when a large
stump diameter exists much of it will eventually rot out regard-
less of care and management of the stump after cutting.
The trees in Table 3 took five years after topping to reach
commercial production. Cost of topping was as follows:

Sawing twice (once with chain saw, then with
reciprocating action saw to finish cut), two
men, % hour .......................... .......................... 1 man-hour per tree
Whitewashing, one man, % hour .............................. % man-hour per tree
Dressing wound, one man, hour .......................... / man-hour per tree
Trees pruned twice a month for first year,
a2 man-hour per month .......................................-- 5% man-hours per tree
Cost of whitewash (durable cement) ...................... $0.50 per tree
Cost of wound dressing ............................... ........... $0.15 per tree
Hauling brush (500 feet from grove, four trips
per tree), man and tractor, 1 hour @ $2
per hour ................................ ................. $2.00 per tree

SUMMARY OF COST
Labor (at $1 an hour) .............--- -. ....... .............. $ 7.75
M materials ................................................................... ..... 0.65
Equipment (tractor) .-.....--. ..-- -.........-........................ 2.00
Total for tree ....................... ............................... $10.40

Thinning by tree removal can be handled two ways, either
by removing alternate trees all at once or by removing them over
a period of time.
Table 4 illustrates what happened where alternate trees were
moved all at one time.
These trees, 20 years old, had never been hedged or pruned
back. The limbs interlocked badly and were dying as the result
of shading. During the five seasons prior to thinning by tree
removal, fruit production decreased markedly. During January
and February 1956, alternate trees in the 15-foot row were re-
moved. All wood under 4 inches in diameter was run through
a chipping machine and the chips were incorporated into the
soil. The heavier wood was hauled away and burned, and the
stumps were removed with a bulldozer.
9






































Figure 5. Seedling orange trees in this block were cut back to shoulder
height 14 years ago as a grower experiment. Much additional acreage
in the grove was subsequently cut back because of the success of the
operation.


TABLE 4.-EFFECT OF TREE REMOVAL ON PRODUCTION OF A REPRESENTATIVE
ORANGE GROVE.
Hamlin orange on rough lemon rootstock, planted in 1937 on deep phase
of Lakeland fine sand. Alternate trees removed in January 1956.


Before Thinning

Planting Distance 15' x 25'

Tree Count 1170


Year Yield in Field Boxes


1950
1951
1952
1953
1954
1955


4476
5634
6400
6679
5084
2886


After Thinning

Planting Distance 25' x 30'

Tree Count 598


Year Yield


1956
1957


in Field Boxes


3858
4349
4255
4553
4645
6174


Figures courtesy Lake


County Grouwer.







The grower estimates his labor cost for removing these trees
at $1.50 per tree, which is probably conservative.
Another grower removed trees over a period of time to
avoid a serious reduction in his crop in any one year. This grove
was an 18-year-old Valencia block budded on rough lemon root-
stock, planted 15' x 30' on a good grade of Eustis fine sand.
Fifty trees were removed each year for several years until alter-
nate trees had been removed from the 15-foot spacings.
Comparative yield data, before and after thinning, are not
available for this grove, as trees were removed from the block
every year from 1953 to 1959. The trees in rows where alternate
trees were removed in 1953 and 1954 thus far have not increased
production. However, the limbs of the trees were becoming
interlocked, and had trees not been removed, crowding might
have seriously hampered production by this time.
The trees that were removed were all replanted in other
parts of the grove. First they were "buckhorned" and then
lifted out of the grove with a bulldozer equipped with a rake
blade. A tractor equipped with a crane immediately took the


Figure 6. Alternate trees were removed from this 20-year-old Hamlin
orange grove planted 15' x 25'. The trees are on rough lemon rootstock.
The stumps were later removed with a bulldozer.








tree and suspended it while all ragged roots were pruned. Five
trees were loaded on a tractor-trailer and taken to the new loca-
tion. The trees were set using 175 gallons of water to settle
them into the soil. Immediately after planting they were white-
washed with a concrete paint-type durable whitewash. Trees
were watered once a week until they became established.
This planting operation has proved very successful. Here
is an explanation of the costs:

Move and set 15 trees, four men, 9 hours ................ 2.4 man-hours per tree
Dig tree and refill hole with bulldozer .................... 10 minutes per tree
Dig hole and set tree with bulldozer .................... 5 minutes per tree
Tractors ($2.00 per hour without driver)
4 2 hours .............................................. ........-- $0.60 per tree
Supply unit ($2.00 per hour with driver)
4 hours ........-- ........- .....- ...- .... ..................... $0.60 per tree
SUMMARY OF COST
Topping, etc., (from preceding section on Topping) ........$10.40
L abor ....................................................................................... 2.40
Equipment (tractor, supply unit and bulldozer) ................ 2.20
Total for tree ......... ... ............... .................... ..$15.00

Close spacing and subsequent thinning allows per acre pro-
duction of citrus fruits to increase almost directly in proportion
to the number of trees in the grove. When adequate fertilizer,
moisture, and pest control measures are provided, a close spacing
of 15' x 25' is satisfactory until trees begin to become too
crowded.
As the trees begin to crowd each other, the alternate trees
in the row are hedged just enough to leave a "frame of light"
around their edges. Each year this is done on the same alter-
nate trees. Half of the trees are never hedged.
By the time the alternate trees are hedged to their trunks,
they no longer have a bearing surface worthy of consideration.
Then there is less mental anguish for the grower in removing
them. Ultimately the spacing of the large trees is 25' x 30'.
During the years that the close spacing and subsequent thin-
ning operation is progressing, the grove is giving maximum
yields. Another advantage of the "frame of light" around the
alternate trees is improved air drainage throughout the grove.
Zach Savage, economist with the Agricultural Experiment
Stations, has compared probable yields of trees planted at 20'
x 30', 15' x 25' (alternate trees not hedged), and 15' x 25' with
alternate trees hedged. See Table 5.




TABLE 5.-ORANGE PRODUCTION AT Two SETTING DISTANCES, 25' x 30' AND 15' x 25'.
I 1 -
Age of Tree Average Yield (boxes) Total Group Yield Cumulative Yield
(years) Age Group
25' x 30' 15' x 25' 25' x 30' 15' x 25' 25' x 30' 15' x 25'

5 to 9 79 158 395 790 5 to 9 395 790
10 to 14 135 270 675 1,350 5 to 14 1,070 2,140
15 to 19 178 310 890 1,550 5 to 19 1,960 3,690
20 to 24 221 310 1,105 1,550 5 to 24 3,065 5,240
25 to 29 264 300 1,320 1,500 5 to 29 4,385 6,740
30 to 34 299 280 1,495 1,400 5 to 34 5,880 8,140
35 to 39 341 255 1,705 1,275 5 to 39 7,585 9,415
40 to 44 386 220 1,930 1,100 5 to 44 9,515 10,515
45 to 49 434 180 2,170 900 5 to 49 11,685 11,415

Estimated orange production on setting 15' x 25' with alternate trees pruned to make room for remaining trees, with
stumps removed at approximately 40 years of age, leaving trees 30' x 25'.

30' x 25' Alternate All Total Cumulative Yield
Age of Tree Trees Trees Trees Yield Age Group
Combined 15' x 25' 25' x 30'

5 to 9 79 79 158 790 5 to 9 790 790 395
10 to 14 135 135 270 1,350 5 to 14 2,140 2,140 1,070
15 to 19 178 135 313 1,565 5 to 19 3,705 3,690 1,960
20 to 24 221 125 346 1,730 5 to 24 5,435 5,240 3,065
25 to 29 264 100 364 1,820 5 to 29 7,255 6,740 4,385
30 to 34 299 75 374 1,870 5 to 34 9,125 8,140 5,880
35 to 39 341 35 376 1,880 5 to 39 11,005 9,415 7,585
40 to 44 386 0 386 1,930 5 to 44 12,935 10,515 9,515
45 to 49 434 0 434 2,170 5 to 49 15,105 11,415 11,685
45-year average .......................................................... ............................................... 336 254 260
Deficit as compared to combined group, 5 to 49 years .............................................. 3,690 3,420
Relative yield over period with combined group as 100 ......................................... 100 76 77
Relative yield 5 to 39 years with combined group as 100 ............................................ 100 86 69
Deficit as compared to combined group, 5 to 39 years ........................... ............. 1,590 3,420

Data from studies of the Florida Agricultural Extension Service and Experiment Stations, Gainesville, Florida,
combined with estimates.








Brush Removal.-This is one of the most costly operations
encountered by growers in all forms of pruning. Recently a
number of production managers and operators of large acreages
have employed the use of rotary cutters, initially designed for
use in pasture clearing operations. Rotary cutters will chop
up and return to the soil brush that was cut by hedgers. A
cutter makes a 4- to 6-foot swath, covering as much area in
a day as is covered by either a single or double boom hedger.
Where these machines are used, they are available at about
$3.50 an hour. This operation greatly reduces the cost and
time involved in brush removal.

SUMMARY
1. Growers generally space trees closely to attain maximum
fruit production.
2. High production is attained only as long as the branches
of one tree are not interlocked with those of its neighbors.
3. Several thinning practices, including hedging, thinning
(by tree removal), and "buckhorning" have improved production
and quality of fruit in groves studied.
4. Hamlin groves recovered their production levels more
quickly than Valencias, following thinning operations in the
groves studied.
5. Twenty-seven year old Valencias on rough lemon root-
stock have been transplanted bare-rooted very successfully by
pushing and lifting the trees with a bulldozer and setting them
in a new location in similar soil. The procedure has not been as
successful where trees of the same age and variety on sour
orange rootstock were moved into sandy soil.
6. Recovery of transplanted budded Valencia trees is very
rapid, as is the recovery of "buckhorned" seedling trees, but
the budded trees resume fruit production much more quickly.
7. Although the data presented here are limited, they do
illustrate the trends observed by field study of groves receiving
the thinning treatments described.











































































COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Florida State University and United States Department of Agriculture, Cooperating
M. O. Watkins, Director




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