Group Title: Agricultural economics mimeo report
Title: Citrus tree loss survey in twelve northerly counties of Florida
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 Material Information
Title: Citrus tree loss survey in twelve northerly counties of Florida
Physical Description: 6 leaves : ; 28 cm.
Language: English
Creator: Kelly, B. W.
Donor: unknown ( endowment )
Publisher: Department of Agricultural Economics, Florida Agricultural Experiment Stations
Place of Publication: Gainesville, Fla.
Publication Date: November, 1959
Copyright Date: 1959
Subject: Citrus -- Losses -- Florida   ( lcsh )
Citrus -- Climatic factors -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: by B.W. Kelly.
General Note: Cover title.
General Note: "November 1959."
General Note: Agricultural economics mimeo report - University of Florida ; 60-4
 Record Information
Bibliographic ID: UF00094242
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 320779171

Full Text

November 1959

Agricultural Economics
Mimeo Report 60-4

Marston Science

OCT 10 1996
S 29
University of Florida -




B. W. Kelly
Associate Agricultural Economist

Department of Agricultural Economics
Florida Agricultural Experiment Stations
Gainesville, Florida



B. W. Kelly

The freeze of 1957-58 came just one year after the completion of the citrus tree

count in December 1956 by the State Plant Board. There was considerable damage to

existing trees and a number of trees were killed outright. The U. S. Department of

Agriculture made a rough estimate of this damage in March 1958 by classifying the first

three trees in rows on both sides of a 1,500 mile route which ran through the 19 most

important citrus producing counties of the State. These counties are Polk, Lake, Orange,

Hillsborough, St. Lucie, Pasco, Highlands, Volusia, Pinellas, Indian River, Marion,

Hardee, Brevard, Seminole, DeSoto, Osceola, Manatee, Putnam, and Sarasota.

According to this survey, about 76 percent of orange trees and 80 percent of

grapefruit trees escaped with no appreciable damage, about 7 percent of the orange and

6 percent of the grapefruit trees suffered a less than 50 percent loss of bearing surface,

16 percent of the orange and 12 percent of the grapefruit trees suffered more than 50 per-

cent loss of bearing capacity, and about 1-1/2 percent of both orange and grapefruit

trees appeared to be dead. As might be expected, tree losses were much greater in the

more northerly counties. This route survey furnishes the only basis available at present

for adjusting the Plant Board tree census numbers for losses.

On the northern fringe of the citrus belt there are seven more counties which con-

tain commercial citrus groves and through which there are no routes. These counties are

Alachua, Citrus, Duval, Flagler, Hernando, St, Johns, and Sumter. An investigation of

tree losses in these counties seemed in order. When a survey for this purpose was being

planned, it was decided to extend the coverage to five of the northern counties that had

been included in the route survey. These counties are Marion, Pasco, Putnam, Seminole,

and Volusia. Cold damage, as estimated by the routes, was greatest in these counties and

there is always some question as to just how well a route sample represents a universe.

The sample survey was conducted in July 1959. Its purpose was to provide sample

estimates of tree losses since the 1956 citrus census in the seven northern counties and in

all twelve counties, to compare tree losses with the route estimates in the five common

counties, and to provide a frame for subsampling yields. The sample was not designed to

estimate the number of trees planted or reset since the 1956 census.

The sampling unit used was the same unit that was used by the Plant Board in making

the tree count. This unit was the property. A property is the area of land planted to

citrus under one ownership within a single section of land. A sample of 200 properties

was allocated to two strata based upon size and was drawn with equal probabilities. The

sampling rate in Stratum I was three times that of Stratum II. Both sample size and stratum

allocations were determined largely by the need for enough sampling units for yield work.

The allocation of the sample to the two strata is given in Table 1.

A sample of 100 units was thought to be sufficient for our purpose; thus, only the

hundred even numbered sampling units were enumerated during the survey. The odd numbers

were held in reserve. Copies were obtained of the census schedule for each sample property.

Likewise, property maps were also photostated for ease in finding and identifying sampling

units. Enumerators were instructed to count the number of trees in each block within a

property and to record the information on a form devised for this purpose. On this same

form was entered the number of trees in each corresponding block as counted by the Plant

Board during the census. A block consists of a group of trees within a property that has the

same varietal, age group, and root-stock characteristics. It was decided to subsample each

property in order to obtain an estimate of trees according to present bearing surface area.

The center row of trees in each block was classified according to observed fraction of normal

bearing surface. Four classes of bearing surface areas delineated were: (1) Tree dead or

missing, (2) two-thirds or more bearing surface destroyed, (3) less than two-thirds but

more than one-third gone, and (4) a loss of less than one-third.

TABLE 1 .--Allocation of Tree Loss Sample to Strata and Counties

Stratum No. No.
and County Properties Samples

Stratum I (1) (2)
Alachua 69 5
Citrus 118 8
Duval 66 5
Flagler 6 0
St. Johns 58 5
Sumter 119 8

Total Stratum I 436 31

Stratum II
Hernando 329 8
Marion 1108 27
Pasco 1830 44
Putnam 699 17
Seminole 1413 34
Volusia 1610 39
Total Stratum II 6989 169
Total Both Strata 7425 200

Estimates were computed from the data sampled of the ratios of the number of trees

by types that were found in the sample properties relative to the number present at the time

of the census. Sampling errors were computed for these ratios. Sample estimates were made

of the fractions in the different categories of tree damage. These estimates for the entire

group of 12 counties by type of fruit are given in Table 2.

TABLE 2.--Sample Estimates of Present Number of Trees Relative to Citrus Census Number
and of Fraction in Each of Four Damage Classes, 12 Florida Counties, July 1959

Relative No. Trees Fraction in Damage Class
Standard 2/3 or 1/3 Less Than
Kind Ratio Error Deador More to 2/3 1/3
of Ratio Missing Damaged Damaged Damaged
(1) (2) (3) (4) (5) (6)

Early Oranges .758 .063 .273 .270 .166 .291
Midseason Oranges .804 .044 .268 .232 .164 .390
Late Oranges .795 .036 .207 .365 .117 .312
Seedy Grapefruit .874 .091 .208 .180 .118 .494
Seedless Grapefruit .727 .037 .185 .172 .140 .504
Tangerines .683 .066 .264 .266 .145 .325
Temples .797 .017 .121 .197 .152 .529
All Oranges .774 .026 .230 .289 .148 .332
All Grapefruit .769 .086 .199 .176 .129 .496

According to the survey, about 77 percent of the census number of orange and grape-

fruit trees were still present at the time of th3 survey. The standard errors of the ratio are

about 2.6 percent for orange and 8.6 percent for grapefruit trees. Sampling errors for the

fraction in the different damage classes were not computed, but some notion of the error

may be obtained by noting the degree to which the ratio in column 1 and the dead or

missing trees in column 3 complement each other. As mentioned before, the survey did not

take into account resets or new plantings. The 23 percent disappearance of orange and

grapefruit trees is an estimate of the fraction of trees present at the time of the census that

are no longer living.

Similarly, the fraction dead or missing and its standard error were computed for the

current survey in each of the five counties common to both the current and route surveys.

Comparisons between the results of the two surveys are given in Table 3.

TABLE 3.--Fraction of Orange and Grapefruit Trees Lost in Five Northerly Counties as
Estimated by Route and Tree Loss Surveys

Orange Trees Grapefruit Trees
Route Sample Tree Loss Survey Route Sample Tree Loss Survey
County Fraction Fraction
Fraction Standard Fraction Standard
County Fraction Dead or Dead or
ead DError Dead Error
Missing Missing
(1) (2) (3) (4) (5) (6)

Marion .115 .395 .083 .212 .051 .031
Pasco .007 .172 .046 .066 .089 .102
Putnam .003 .234 .060 0 .321 .273
Seminole .043 .146 .109 .232 .495 .178
Volusia .051 .223 .091 .395 .210 .139
Five Counties .042 .209 .027 .167 .227 .094

For the five counties of Marion, Pasco, Putnam, Seminole, and Volusia, the fractions

dead or missing, as estimated by the current survey, were 21 percent for orange and 23 per-

cent for grapefruit trees. This compares with route survey estimates of 4 percent and 17 per-

cent, respectively. Sampling errors for the five counties are only slightly larger than for

the group of 12.

Sample estimates for individual counties were not computed for those in the small

county stratum because sampling errors of these estimates would have been prohibitively

large. However, for the six county group of Alachua, Citrus, Duval, Flagler, St. Johns,

and Sumter, estimates of the ratios of the present number of trees to census tree numbers

were .724 for orange and .641 for grapefruit trees. Standard errors of these ratios are

.250 and .192, respectively. WVhen Hernando County is added to this group, the orange

ratio becomes .706 with a standard error of .143 and the grapefruit ratio is .785 with a

standard error of .125,

This survey indicates that a sizable loss of trees has occurred in the twelve county

area in a period of about three years. It is surprising, judging by the comparisons of

Table 3, that only a relatively small portion of this disappearance can be ascribed to the

1957-58 freeze. Of course, it is realized that some of the trees now dead or missing may

have been so injured or weakened by the cold that they have since died. However, the

fact remains that, in the 12 northern counties of the citrus producing area, almost one-

quarter of the citrus trees counted three years ago now appear to be dead or missing. It is

hoped that the fraction of tree loss in the rest of the State is much smaller.

BV K: mfs 12/4/59
Exp. Sto., Ag. Ec. 250

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