Cec1985-3101.Pdf by Guest on 23 September 2021

ASME 1985 Citrus Engineering Conference CEC1985 March 28, 1985, Lakeland, Florida, USA CEC1985-3101 Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021

Jodie D. Whitney

FLORIDA CITRUS FREEZE LOSSES AND RECOVERY IN THE FIELD BY Jodie D. Whitney IFAS, University of Florida Citrus Research and Education Center 700 Experiment Station Road Lake Alfred, Florida 33850

INTRODUCTION Freezes have had and will continue to have a significant impact on the conduct of the Florida citrus industry. A viable industry and all its associated suppliers and services depend very heavily on the consistent and continued production of fruit in the field. The main reason that fruit production has been inconsistent is the fruit and tree losses associated with damaging freezes. This paper will discuss a brief history of the freezes, the economics of several options of rehabilitating freeze-damaged trees, and cultural practices, etc. in the field which can minimize freeze losses. HISTORY OF FREEZES There have been many freezes that have affected the Florida citrus industry and the ultimate concern is their effect on fruit production. Citrus production had reached an all time high of more than 5 million boxes when the Great Freeze of 1894-95 almost wiped out the industry (5)*. It was not until 1909-10 that this level of fruit production was again reached, after which the production began to steadily increase. Figure 1 shows Florida citrus production and bearing acreage from 1919-20

Acknowledgement - The author wishes to thank Jane Wilson for her assistance in preparation of the figures in this paper. *Numbers in parenthesis refer to appended references.

Published with permission. through 1983-84 (3, 4, 5, 6, 7). Production increased fairly steadily from 13.9 million boxes to a peak of 283.6 million boxes in 1979-80, and then declined to 166.1 million boxes in 1983-84. Bearing acreage increased from about 80,000 in 1919-20 to a peak of over 849,000 in 1970-71, and decreased to under 643,000 in 1983-84. Most of the significant interruptions in the upward trend in production and bearing acreage have been the result of 7 damaging freezes in the past 3 decades. In chronological order, these freezes occurred on December 13,1957; December 13, 1962; February 26, 1967; January 18, 1977; January 13, 1981; January 12, 1982; and December 25, 1983. The January 21, 1985 freeze could certainly be classified as damaging, but will not be discussed here because of Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 inadequate information at the time this paper was written. The 7 freezes prior to 1985 caused substantial reductions in fruit production while only the 1957,1962, and 1983 freezes caused what might be termed substantial reductions in bearing acreage. Some of the losses in acreage between 1970-71 and 1982-83 could be attributed to freeze damage, but were also due to commercial development, tree declines, and other factors. Why were the losses associated with freezes so different? Was it the minimum temperatures? Figure 2 shows a brief history of the daily minimum temperatures recorded just prior to and including the freeze dates at Lake Alfred 48). These temperature records are not meant to represent the average of those expe- rienced by the entire Florida citrus industry, but represent temperatures near the center of the citrus producing area, and will suffice for this discussion. Based on minimum temperature, the 1962 freeze should have caused the greatest losses with the lowest minimum temperature of 16°F. This was 4" below any of the other freezes. Acreage lost during 1962-63 from the 1962 freeze was only slightly more than half that lost during 1983-84 from the 1983 freeze with a 22°F minimum temperature. Fruit loss in 1962-63, however, was about50°/~more than that in 1983-84. These losses or reductions are in each case with reference to records from the previous season. These 2 freezes were the worst in terms of tree or acreage loss. A comparison of 7 freezes is made in Figure 2. Note the horizontal line at 50°F. This temperature is accepted by many as a threshold for citrus tree cold hardiness (conditioning which enables the tree to withstand colder temperatures without damage). Temperatures below 50°F are required to develop cold hardiness. In the 12 days prior to the freezes, 10 and 1 days were below 50" F in 1962 and 1983, respectively. Thus, the trees in 1983 were probably much more susceptible to cold damage than those in 1962. Also, damage from the 1981 and 1982 freezes which will be discussed later, may have weakened the trees, making them more susceptible to damage in the 1983 freeze. Fruit losses in 1962-63 were 50°/0 greater than in 1983-84 for several reasons. The capacity and knowledge of the industry to salvage freeze-damaged fruit in 1983-84 was better than in 1962-63. The temperature-time durations necessary to freeze the fruit were more widespread throughout the citrus-producing area in 1962 than in 1983. In addition, a higher proportion of the area in 1983 was situated farther south than in 1962. By comparison, the 1957 freeze with a 22°F minimum temperature was somewhat less severe in terms sf tree and fruit damage. Bearing acreagewas reduced by about 43,008 acres and production dropped almost 20 million boxes in 1957-58. Figure 2 shows that the daily minimum temperatures dropped below 50°F on 8 of the 12 days before the freeze. What about the February 1967 freeze? Figure2 shows a 54 million box increase in production from the 1965-66 to the 1966-67 season and a 50 million box decrease from the 1966-67 to the 1967-68 season. Bearing acreage was increasing at afast rate over thesame period, indicating no significant tree damage. Figure 2 shows that only4 out of the 12 days prior to the freeze were the daily minimum temperatures below 50" F. The minimum freeze temperature was 28"F, usually not low enough to cause wood damage in the tree. Fruit production was not significantly affected for the 1966-67 season because the freeze occurred near the end of the early-midseason harvest and the duration of minimum temperatures was not sufficient nor widespread enough to cause significant losses in late season fruit. The 1967-68 production dropped drastically because many of the trees had a bloom set for the 1967-68 crop when the freeze came, and much of it was destroyed. Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 The 1977 freeze reached a minimum of 23°F at Lake Alfred (Figure 2). This low temperature was widespread and of sufficient duration to freeze most all of the citrus fruit. Most of the early-midseason fruit was salvaged because of the late date of the freeze and cool weather conditions after the freeze minimized losses in processing the freeze-damaged fruit. The losses in freeze-damaged late season fruit were greater. Overall, however, citrus production increased over 5 million boxes from the 1975-76 season to the 1976-77 season. Tree damage was minimal in the 1977 freeze, even though minimum temperaures were as low as the devastating 1983 freeze. The main reason for the difference in tree damage was tree hardening prior to the freezes. Figure 2 shows that 10 out of the 12 days prior to the 1977 freeze had minimum daily temperatures below 50" F, compared to 1 day for the 1983 freeze. Some tree damage did occur in 1977, however, because bearing acreage, having stabilized somewhat at around 795,000 acres in 1975-76 and 1976-77, decreased to 766,000 by 1978-79. Fruit production also dropped from 254.5 million boxes to 230.2 million boxes from 1976-77 to 1978-79. The reduction in production was due not only to lower acreage but to lower yields per acre, which indicates the trees may have still been recovering from the 1977 freeze. The 1981 freeze reached a minimum temperature of 20" F (Figure 2). Only the 1962 freeze was colder (16°F). Trees were cold hardened with 12 days minimum daily temperatures below 50°F prior to the freeze. Minimum temperatures were generally lower and tree and fruit damage was generally greater in the northern part of the citrus producing area. Overall, the wood damage was negligible, though many trees were defoliated. Fruit production dropped from the record high of over 283 million boxes in 1979-80 to just over 238 million boxes in 1980-81, a reduction of 45 million boxes. Losses in processing the freeze-damaged fruit were somewhat higher in late season than in early-midseason. Many of the trees that were defoliated from freeze damage set a sparse crop for 1981-82. Then came the 1982 freeze with a minimum temperature of 22'F at Lake Alfred (Figure 2). Only 4 days out of 11 prior to the freeze were the minimum temperatures below 50" F. Yelenosky et al. (18), however, reported in a more extensive analysis of temperatures for 11 weeks before the freeze, that trees in the 1977, 1981, and 1982 freezes were exposed to similar cold hardening temperatures. During the 11 982 freeze, colder temperatures generally prevailed in the southern part of the citrus producing area than in the northern part. Most of the fruit was freeze-damaged. Production decreased from over 238 million boxes in 1980-81 to 189 million boxes in 1981-82, a reduction of 49 million boxes. Losses were substantial in both early-midseason and late fruit. Wood damage in trees was minimal, but was more prevalent in thesouthern producing areas where many trees were defoliated. In summation, all 7 freezes were quite different in their effects on production and bearing acreage. Freezes generally have substantially more effect on production than bearing acreage because fruit damage results at a higher minimum temperature than 'does wood damage in trees. Damage to wood in trees depends to a great extent on the cold hardening the tree has undergone prior to the freeze. All in all, the 1983 freeze has been called the "freeze of the century" because of the devastating tree losses (72,000 bearing acres), mainly in 11 northern counties of the citrus producing area. Bearing acreage losses from the 1983 freeze may be even greater as some of the freeze- damaged bearing trees which have been buckhorned or otherwise rehabilitated may be "pushed out" in the next few seasons because of poor regrowth. ECONOMICS OF REHABILITATING FREEZE DAMAGED TREES The Christmas 1983 freeze resulted in substantial tree damage, especially in the

northern interior citrus producing area of the state. Grove owners in this area were Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 faced with difficult decisions concerning the future use of their land. If it was to be maintained for producing citrus, what was the best option to get the land back into production? I will discuss the economics of 3 scenarios over a 10-year period. Full details have been presented by Muraro et al. (14). The 3 scenarios are as follows: 1. "Buck horn" the freeze-damaged trees if they are judged salvagable (70 trees/acre). 2. "Buck horn" the freeze-damaged trees if they are judged salvagable and interset young trees within the tree rows for a total of 140 trees/acre. 3. Push out freeze-damaged trees and replant with young trees at 140 trees/acre.

The freeze damaged grove was assumed to be Hamlin oranges set at 25 x 25 ft. or 70 trees/acre, which is fairly common for older bearing orange groves. To exercise Scenarios 1 and 2, all of the freeze damaged trees must be salvagable. The assumptions common to all scenarios are shown in Table 1. The economic analyses for the 3 scenarios are presented in Tables 2,3, and 4. A11 scenarios assume the land is owned, an irrigation system would have to be installed, the 10-year period would be free of adverse weather conditions, and young trees would be readily available for replanting. InScenario 1 (Table 2), the operating expenses and the timeof negative cumulative cash flow are minimized, but the potential fruit yield peaks out at 330 boxes/acre in year 7 (Fig. 3). The cumulative net cash flow at the end of the 10-year period is $4721.00/acre. By comparison, Scenario 2 (Table3, Fig. 3) has a shorter time of positive cumulative net cash flow, but the magnitude of this flow at the end of the 10-year period is $9612.00/acre. This results mainly from thesuperior fruit yields (gross revenue) during the last half of this period. Fruit yield is maximized in year 10 at 688 boxes/acre. Scenario 3 (Table 4, Fig. 3) results in the longest time of negative cumulative cash flow. However, the positive cumulative net cash flow in year 10 is $3965.00/acre and slightly less than Scenario 1. Fruit yield at year 16) is maximum for the period at 658 boxes/acre. In summation, Scenarios 2 and 3 are the most and least desirable options, respectively, over the 10 year period. It should be pointed out, however, that Scenario 1 would replace Scenario 3 as the least desirable economic option in another year or two. CULTURAL PRACTICES AND OTHER INFLUENCES ON FREEZE PROTECTION The Christmas 1983 freeze was an advective (windy) one and developed conditions in the northern part of the citrus production area which made it difficult to prevent freeze damage by any feasible means. Many damaging freezes, however, are the radiation-type that develop on calm nights and seriously damage trees at temperatures around 22°F or less. Cultural practices can be used in many cases to provide some protection to prevent or minimize radiation-type freeze damage. Much of the inform- tion developed in this area has resulted from field observations and not precise experiments. Temperature and tree response measurements have been difficult to obtain because of the differences in freezes, and tree hardiness to cold temperatures changes with short periods of warm and cold weather prior to freezes. A knowledge of principles involved in the development of freezing temperatures, the microclimate of the space occupied by the tree and factors that induce maximum tree hardiness are helpful in understanding how cultural practices can be used to lessen or prevent damage. Much of the discussion on cultural practices was taken from thecold Projection Guide (13). Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 Freeze development - Freezes are generally divided into advective and radiation freezes. Advectivefreezes usually contain very dry air below freezing temperature and wind speeds of 3 mph or greater. Damage is usually greater on the north side of the tree and in grove areas on the top and north side of hills. In a radiation freeze, often called a frost, the air mass that moves into the state is usually not cold enough to damage citrus trees. During the daylight hours, the soil, trees, etc. absorb energy from thesun. At night, the wind is calm, and there is a loss of heat from the soil, trees, etc. to the cold sky by radiation. No heat is returned to the ground area unless a cover, such as clouds, which absorbs and radiates heat back, exists. Air in contact with the cold earth loses heat by conduction and a cold layer of air develops near the earth, with warmer air aloft if the air is calm. A light wind will mix the warmer air aloft with the colder air near the earth and prevent or delay damaging low temperatures. Cold air will drain off sloping terrain into lower areas which may be lakes or pockets of cold air while the slope stays relatively warm. If the layer of air near the earth continues to cool below the freezing point of water, this is termed a radiation freeze or a frost. A white frost is formed if plant part temperatures fall to the dew point temperature above freezing and then the air temperature drops below freezing. A damaging radiation freeze is much less likely to develop when the dew point is above freezing because a large amount of heat is released when water condenses and when the water freezes. Tree microclimate- In this discussion, tree microclimate concerns the temperatures within the tree canopy. During an advective freeze, the temperatures of the air and smaller parts of the tree are similar, whereas in a radiation freeze, the temperatures can be quite different. During a radiation freeze, exposed leaves lose heat to the sky by radiation and may be 3 to 4OF colder than the air temperature. Branches and leaves forming the tree canopy cover an area of soil underneath that is continuously radiating heat. The canopy absorbs this heat and in turn radiates heat back to the soil and to other parts of the tree. Inside the canopy, temperatures of the air, leaves, and twigs are similar. The larger limbs, trunk, and ground are warmer than the air underneath the canopy, which is warmer than air outside the canopy. Soil between the tree canopies also radiates heat into thesides of the trees as well as into the sky. Warmer tree parts radiate heat to cooler parts. Because the tree parts contain approximately 50% water, their heat capacity is substantial. Their drop in temperatures will lag that of the air, depending to a great extent on their size, that being the diameter of the trunk and limbs. Small young trees without much of acanopy have less mass and do not develop the microclimate described above for older, larger trees. Small trees thus are colder than larger ones. Tree hardiness - Dormancy and cold hardiness describe a tree's conditioning relative to withstanding cold temperatures as mentioned earlier in the "HISTORY OF FREEZES" section. Much research has been conducted to determine the reasons some trees withstand more cold than others and why the freeze damage temperature of a given tree or part of a treevaries within agiven winter. Our understanding of this is incomplete. It is recognized, however, that cool temperatures result in maximum dormancy, storage of carbohydrates and other metabolites, a process called hardening. Sun striking the bark sf trunks can cause thesunny side to become active and more susceptible to freeze damage. A relatively short period of warm weather at any time during the winter can result in a general loss of hardiness to cold just as cool weather can increase hardiness.

The following discussion on the relation of cultural practices to freeze damage Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 protection will generally be more applicable to radiation freezes than advective freezes. Soil management - A significant means of passive cold protection can be provided by managing the surface and moisture of the soil. The heat capacity and conductance of moist soil is better than dry soil. Compact soil is a better conductor than loose soil which has been fluffed by recent cultivation. Any types of vegetation (weeds, grass, etc.) are good insulators. They reduce both the amount of heat absorbed by the soil during the day and the amount released at night. High weeds between trees also impede air drainage down slopes. Thus, for maximum cold protection, soil should be moist, compact, and free of vegetative covering. Research work in Texas citrus showed that temperatures one foot above ground level over chemical weed control with no tillage averaged about 4 and 2°F warmer than over sod and clean mechanical cultivation, respectively. At five feet above ground, temperature differences wereslightly less. Temperature differences between sod and other weed control methods were smallest when the sod was closely mowed and greater when the height of the weeds was greater. Temperatures were lower on recently cultivated soil than on soil which had been allowed to covlpact after cultivation. Many Florida growers apply herbicides to a strip @fsoil either side of the tree row trunk line (underneath the tree canopies) but not the row middies between canopies; the middles are usually mowed or cultivated. Also, many growers are installing low volume irrigation systems which wet only a portion of the grove floor as compared to the older permanent overhead sprinklers which wet the entire grove floor. Although the low volume systems do not wet the entire grove floor, they can provide cold protection for small young trees (discussed under Irrigation). Werbiciding the entire grove floor and using an irrigation system that wets a high percentage sf the grove floor should improve protection from a radiation freeze. Air drainage- Good air drainage is recognized as one of the major factors determin- ing the warmth of a grove area. This is particularly true in the Ridge area of Florida which tends to be quite hilly and often with lakes at the bottom of the slopes. Anything that slows air drainage in such a grove makes it colder. Dams of debris (dead trees, etc.) at the bottom of these slopes can alter the natural drainage of cold air to the lower elevations. Removing this debris or cutting paths through it to allow for better air drainage will help alleviate the problem. Landsite location -When evaluating a land site for natural cold protection features, high ground is best for good air drainage, but as discussed earlier, the cold air must have an avenue and a place to drain off. Land sites immediately adjacent to the south side of large lakes are warmer than other areas. The amount of temperature advantage depends on the size of the lake, the distance from the lake, the water temperature, windspeed and wind direction (9). In a 1976 study by NASA using thermal scanners, temperatures on the south side of Lake Apopka were found to be as much as 10°F warmer than on the north side (10). Tree spacing and row orientation -A given land site will be coldest as a pasture or meadow and warmest as a forest. This is due to the canopy effect of trees that intercepts radiant heat from the ground, blocks radiation to the cold sky, and main- tains a microclimate warmer than that outside a tree. A citrus grove is similar to a forest and the more land area covered by canopy, the warmer it will be. Citrus tree plantings with wide spacings between canopies are colder than those at close spacings because there is more tree mass per acre and more canopy to intercept radiant heat from the soil. Recent work in California (1) and Florida (16) citrus suggests higher density Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 plantings (more treeslacre) are warmer and damaged less by cold temperatures than lower density plantings. Trees planted on a slope should have their rows up and down the slope. Row middles should be hedged to maximize air drainage. This may at times be in conflict with the benefits of running rows North and South to provide maximum light on tree sides. The cold hazard usually outweighs any benefits of the added light. Running hedgerows (solid canopy row) perpendicular to the slope would slow the drainage of cold air. Removing an occasional tree in each row would provide a path for air drainage down the slope. Lifting of low tree limbs (skirts) would improve air drainage in this situation, but may reduce the beneficial microclimate under the canopy. Pruning - A hedged or topped grove is probably slightly colder than a completely canopied one, but most growers have no choice but to occasionally hedge tree sides and top to facilitate harvesting, pest control, and other cultural practices. Severly topping trees just prior to a freeze can cause major tree damage because the inner tree structure is exposed to cold sky radiation from above and the tree microclimate will be less favorable. Hedging just prior to afreeze also removes part of the canopy side and develops canopy conditions for a less favorable tree microclimate, but to a lesser extent than topping. If hedging and topping are completed in time for substantial canopy regrowth before a freeze, then conditions for a favorable tree microclimate are good. Pest and disease control -The objective of the pest and disease control program in minimizing freeze damage is to maintain afairly dense canopy and avoid weakening of the tree. Any pest or disease that causes defoliation will reduce the protective cover of the canopy and reduce the warmth of the microclimate. back of control of greasyspot disease and mites are the primary reasons for defoliation. Mineral nutrition - Most evidence shows that mineral nutrition does not influence freeze damage in a tree except as deficiencies cause defoliation or the lack of a thick canopy. Application of nitrogen fertilizer just prior to a freeze may cause excessive growth and delay the development of winter dormancy, thus reducing cold hardiness, and should be avoided. Irrigation - lrrigation systems are used in many groves to provide supplemental water to the trees during dry periods. It has been shown that reducing the application of irrigation water to maintain the soil moisture somewhat below field capacity (maximum water holding capacity of soil) in the fall and early winter induces dormancy and increases cold hardiness. However, water deficiency sufficient to cause defoliation and weaken the tree reduces cold hardiness. Water stress in the treeshould not be developed to the point that a rain would force new growth and destroy dormancy. Later in the winter, if cool temperatures induce dormancy and cold hardiness in the tree, irrigation water should be applied to keep the soil near field capacity for a maximum reservoir of heat and conductance of heat into the soil during the day and out at night. Low volume microsprinkler irrigation systems which are properly designed and installed can provide some degree of cold protection to the trunk, bud union and lower scaffold limbs of young trees (15). Various tree trunk wraps used in combination with microsprinkler irrigation have been shown to be better than microsprinkler irrigation alone (2). Wraps and soil banks - Soil banks provide the greatest protection for young tree trunks of all the tree wrapping materials (fiberglass, polyurethane foam, rigid polysty- rene foam, closed cell polyethylene foam) (12). However, cost of construction and removal, possible insect and disease problems, and advantages offered by certain Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 types of wraps have caused many growers to choose wraps over soil banks. While wraps do not provide the same degree of protection as soil banks, some of the advantages they offer include a degree of permanency, ease of installation and removal, sprout inhibition and protection from mechanical damage. On the negative side, wraps offer less protection than soil banks and some wraps must be removed following freeze damage to the trees while others may be adjusted to allow for new growth to develop. Wind machines - During radiation freezes when a temperature inversion (temperature increases with height above ground up to about 50 ft.) exists, wind machines can be used to increase the temperature around the trees near ground level (1 1). This is done by mixing the higher, warmer air with lower, colder air. Wind machines are generally a permanent installation with a high initial investment. They are subject to vandalism because of their permanent location in a grove. It has been found that approximately 10 horsepower per acre is required to achieve adequate air mixing. Under calm wind conditions, ground level temperature increases from wind machines can range from 2 to 5OF when a temperature inversion of 8 to 10°F exists between ground and 30 to 50 ft. above ground. Managing freeze-damaged trees - How should freeze-damaged trees be managed? Where the extent of damage is moderate and is sufficiently limited that an effective canopy develops by the following winter, emphasisshould be placed on repairing the canopy through optimum water, fertilizer, and pest and disease control during the summer, enhancing development of dormancy by withholding late applications of fertilizer and by restricting water use as much as is feasible in the fall. Weed control, maintenance of adequatesoil moisture, and removal of debris at the bottom of slopes should be emphasized during the winter. Tree damage is severe if they are killed back to the main limb framework; tree mass is substantially reduced and the protective canopy no longer exists. No pruning practices will develop an adequate canopy by the winter following the freeze. Empha- sis on those factors described for moderately damaged trees holds as well for those severely damaged. However, one cannot expect to keep a severely damaged tree as warm or as dormant as one with a good canopy. Large limbs with sparse foliage absorb a considerable amount of heat from the sun during the day. The bark can reach high temperatures which causes the limbs to be more active (growth) and thus more susceptible to freeze damage than limbs shaded by a good canopy. Little attention has been given to this situation in citrus. Deciduous fruit growers, however, recognize the problem and refer to freeze damage of exposed bare trunks as "winter sun scald," even though dead tissues or cankers that develop are due to freeze damage. Spraying white wash or white paint on citrus trees has been, used to prevent sun damage to bare citrus limbs in the spring and summer but not to induce or maintain dormancy and cold hardiness in the fall and winter following a freeze. In Florida, whitewashing delays new growth and canopy development as much as 2 weeks if applied in thespring. Applying whitewash sprays to bare limbs in fall and winter should enhance dormancy; however, this has, to the best of our knowledge, not been investigated in citrus. White latex paint applied to the trunks of peach trees during the winter has both lowered trunk temperatures during the day and reduced freeze damage at night. Modification of cultural practices to maximize tree warmth and cold hardiness may be contrary to other management objectives. For example, small to medium sized trees might be subject to damage from blowing sand if soil is completely bare from tree to tree, making it desirable to leave strips of vegetative cover periodically to minimize the movement of sand. Irrigation water can also be used to minimize the movement of sand in high winds. Such factors must always be taken into account to reach an Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 appropriate compromise. If freeze-damaged trees are judged not salvagable as discussed in Scenario 3 of the previous section of the paper, then rootstocks and scions must be selected for replanting. The available scion and rootstock cultivars do have a range of tolerances to cold temperatures and should be considered when selecting young trees for replanting. Numerous exeriments and field observations have established the relative cold tolerance among citrus cultivars. Among scion cultivars, relative cold tolerancevaries (in order from least to most) as follows: lime, shaddock, lemon, grapefruit, sweet orange, mandarin, calamondin, and kumquat (17). Recent work (18) at the USDA A.H. Whitmore Foundation Farm near beesburg has demonstrated the relative cold tolerance of 8-year old Valencia orange and Marsh grapefruit trees on 12 different rootstocks. These trees were2years old when the 1977 freeze came, and were also exposed to the 1981, 1982, and 1983 freezes. The trees were rated for freeze injury after each freeze. The results areshown in Tables 5 and 6. The 1983 Christmas freeze was devastating. Many of the trees that survived the 1977, 1981, and 1982 freezes did not survive the 1983freeze.Forty-fiveout of the 165 Valencia trees which survived the3 earlier freezes were killed (Table 5). This was a27% tree loss in 1983 and represented 60% of the total trees lost prior to the 1983 freeze. The combined loss of 120 trees or 50% of the original planting, plus a5 rating (76 to 100% kill) in 3-inch diameter wood kill was too severe to consider rehabilitation efforts. The least number of Valencia trees lost during the past 8 years that had 4 major freezes were on the more cold-hardy type rootstocks. These were Sour Orange No. 2, Swingle citrumelo, diploid Rubidoux trifoliate orange, and an experimental citrangor. Two of the rootstocks, tetraploid Rubidoux trifoliate orange and diploid Carrizo citrang, had 40 to 50% tree loss. Each of the remaining 6 rootstocks had more than a 50% tree loss. Rootstock differences were not evident after the 1983 freeze based on injury up to and including 3-inch diameter wood. Trees were uniformly rated a 5 (76 to 100% kill) regardless of rootstock. Trees which survived the low of 8°F near Leesburg in 1981 with little or no kill in 3-inch diameter wood lost more than 75%of that wood during the 19' F advective freeze in December 1983. Extensive damage was also found in the Marsh grapefruit planting (Table 6). Sixty-four grapefruit trees were killed which was 1.18 times greater than all of the trees lost prior to the 1983 freeze and represented 34% of the 186 trees going into the 1983 freeze. These losses are somewhat greater than those in the Valencia planting, but similar in a combined loss of about 50% for the entire planting of 240 trees. The least number of grapefruit trees lost was on the same rootstock as in the Valencia planting. Only 1 tree was lost on Swingle citrumelo, 2 on diploid Wubidoux trifoliate orange, 3 on sour orange No. 2, and 5 on citrangor. Two rootstocks had 30 to 40% tree loss, and 6 rootstocks were similar in amount of damage up to and including 3-inch diameter wood of Marsh grapefruit trees. The information presented in Tables 5 and 6 is useful for selecting rootstocks for tolerance to cold temperatures. However, it should be pointed out that many other rootstock characteristics (disease resistence, etc.) should be considered before making a selection. Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021

(sp u os no 41) S3 U3V 111111111~~~~~~~

Figure 1. Bearing Acreage and Production of Florida Citrus. Approximate Dates of Major Freezes are indicated. 60 . .--- 40 ./ DECEMBER 13, 1957

20 - i 60 - Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021

DECEMBER 13, 1962

FEBRUARY 26, 1967

JANUARY 18, 1977

40. JANUARY 13, 1981 I--\-/--.*- -_--- --. \-, 20 - --.. 60 .-----T ..--7 --> i

'eL--.~-- 40 - "-, \. ----. 1 JANUARY 12, 1982 '*\/ 20 - I-.-- ,..------40boo] \ 1 DECEMBER 25, 1983 20

1210 86 420

DAYS BEFORE FREEZE

Figure 2. Minimum Daily Temperatures Recorded For Freezes at the Lake Alfred Citrus Research and Education Center. Freezes shown chronologically top to bottom. FRUIT YIELD Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021

CUMUlATIVE NET CASH FLOW

Figure 3. Fruit Yield Assumptions and Cumulative Net Cash Flow for 3 Freeze Recovery Scenarios. YEAR 4 YEAR 5 YEAR 6 YEAR 7 YEAR 8 YEAR 9 YEAR 10 YEAR------1 YEAR------2 YEAR------3 ------AVERAGE -----YIELD ---PER ----TREE: "BUCKHORN" TREES 0.00 1.00 1.75 RESET AND INTERSET/SOLIDSET TREES 0.00 0.00 0. 50

HARVESTING COST/BOX (PROCESSED FRUIT): ------0.00 1.65 1.70 AVERAGE------POUND ------SOLIDS ---PER ---BOX: "BUCKHORN" TREES RESET AND INTERSET TREES FRUIT----- PRICE----- FOR--- ANALYSIS:------PRICE PER POUND SOLIDS

(ALL--- COSTS----- ARE------INFLATED 5%-- PER--- YEAR---- WITH---- YEAR---- Y1-- BEING------THE BASE---- YEAR)---- GROVE----- CARE---- COSTS----- PER--- ACRE:------ITEM YEAR------1 ------YEAR 2 YEAR------3 YEAR------4 YEAR------5 YEAR------6 YEAR------7 YEAR------8 YEAR------9 YEAR------10

CULTIVATE, now & HERBICIDE SPRAY INQ FERTILIZATION HEDQ INO IRRIQATION MISCELLANEOUS SUPERVISION & OVERHEAD OTHER COSTS

TOTAL GROVE CARE COSTS

YOUNO TREE CARE COSTS PER TREE: YEAR Yl YEAR Y2 YEAR M3 YEAR Y4 ------NOTE: THE RESET COSTS ASSUMES THAT EACH YEAR ANOTHER RESET TREES:(ACCUMULATIVE COST) ---- TREE WILL BE PLANTED1 THUS, YEAR Y4 REPRESEKTB ------RESET TREES WHICH ARE 1,2,3. AND 4 YEARS OLD. YEAR Y4 = COST OF 4 TREES 6.25 8.90 12.25 15.80 AFTER FOUR YEARS, THE RESET TREE WOULD NOT NEED ANY ADDITIONAL CARE ABOVE THE RLQULAR OROIIE INTERSET/SOLIDSET PLANTED TREES: CARE PROORAM. THE RESET COSTS FOR THE INTER------SOLIDSET PROGRAMS ARE REDUCED APPROXIWTELY COST PER TREE FROM YEAR OF TWO THIRDS OF THE SAM€ PER TREE COST OF THE PLANTINQ 3.80 2.45 3.00 3.25 BUCKHORN TREE PROGRAM DUE TO THE SIMILARITY OF TREE SIZE AND GROVE CARE PROGRAM OF THE TWO COST OF PLANTINQ TREES 6. SO HIQHER DENSITY PLANTINOS. THE GROVE CARE COSTS FOR THE INTER-SOLIDSET PROQRAMS REPRESENTS THE PER TREE COST REQUIRED EACH YEAR UNTIL TREES ----COST ---PER ----TREE ---FOR -----OROVE ------REHABILITATION: ARE UNDER A PRODUCTIVE QROVE CARE PRQORAM.

*BUCKHORN' PRUNINO--YEAR Ul: 2.75 BRUSH REMOVAL: 1.45 TREE REMOVAL- SOLID: 2.25 SCATTERED: .6.00 Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 September 23 on guest by http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf from Downloaded "BUCKHORN" HAHLIN ORANGE GROVE -- IRRIGATED - - - - .------. ------

SCHEDULE------OF-- CASH------BUDGET ANALYSIS------YEAR 1 YEAR 2 YEAR 3 4 5 6 YEAR 7 YEAR 8 YEAR 9 YEAR 10 ------YEAR------YEAR------YEAR------ADJUSTED GROSS REVENUE 0 486 788 1 zoo 1496 153s 1639 I605 1576 1553

OPERATINO------EXPENSES: COST TO "BUCKHORN" DAMAOED TREES 193 0 0 0 0 0 0 0 0 COST TO REHOVE TREES OR BRUSH 102 13 13 14 15 24 25 27 28 GROVE CARE COSTS 276 357 485 509 535 590 619 650 683 YOUNG TREE CARE - RESETS 0 13 20 28 38 42 44 47 49 - INTER-SOLIDSET 0 0 0 0 0 0 0 0 0 PLANT RESET/INTER-SOLIDSET TREES 0 14 14 15 16 17 18 19 20 PROPERTY TAXES 13 19 25 3 1 38 4 1 43 46 48 ------.-.--- TOTAL OPERATING EXPENSE 390 4 1 5 557 598 64 1 7 15 751 788 828

NET OPERATINQ INCOflE -390 71 23 1 602 855 924 854 788 725

LESS: INSTALL IRRIGATION SYSTEM 800 0 0 0 0 0 0 0 0 ------

ANNUAL NET CASH FLOW 602 855 924 854 788 725 ======I== *==-=-= --===-- --=-=-- --=----

ACCUHULATIVE NET CASH FLOW -1190 -1118 -887 -286 569 2355 3209 3996 4721 =-P-=-= PI=PPPI IIPP-PI ======P=-EIC======-i-P=-S =101--z ------=

SCHEDULE------OF-- GROVE----- DESCRIPTION,------ACREAGE------AND--- FRUIT----- PRODUCTION------YEAR 1 YEAR 2 YEAR 3 YEAR 4 YEAR 5 YEAR 6 YEAR 7 YEAR 8 YEAR 9 VEAR------10 ------.------TOTAL GROVE ACRES 1 1 1 1 1 1 1 1 1 1 TOTAL PLANTED ACRES 1 1 1 1 1 1 1 1 1 1 "BUCKHORN" TREES PER ACRE 70 68 66 6 4 62 60 58 56 5 4 52 INTERSET/SOLIDSET TREES PER ACRE 0 0 0 0 0 0 0 0 0 0 .? TREES LOST (REMOVED) PER YEAR 2 2 2 2 2 2 2 2 2 & TOTAL BOXES FROM "PUCKHORN" TREES 0 68 116 192 264 300 3 19 308 297 206 TOTAL BOXES FROM INTERSET/SOLIDSET 0 0 0 0 0 0 0 0 0 0 TOTAL BOXES FROM RESET TREES 0 0 0 1 3 6 11 18 7 6 3 6

TOTAL BOXES PER ACRE 0 68 116 193 267 306 3 30 326 --T>L> 522 Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 September 23 on guest by http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf from Downloaded "BUCKHORN' HAMLIN ORANGE GROVE WITH INTERSET TREES -- IRRIGATED ------

SCHEDULE------OF-- CASH---- BUDGET------ANALYSIS------YEAR------I YEAR------2 ------YEAR 3 ------YEAR 4 YEAR------5 YEAR------6 YEAR------7 YEAR------8 YEAH------9 YEAR------10 ADJUSTED GROSS REVENUk 0 486 788 1372 1833 2054 250 1 2820 3138 3319 OPERATING------EXPENSES: COST TO "BUCKHORN" DAfiAGED TREES COST TO REMOVE TREES OR BRUSH GROVE CARE COSTS YOUNG TREE CARE - RESETS - INTER-SOLIDSET PLANT RESET/INTER-SOLIDSET TREES PROPERTY TAXES

TOTAL OPERATING EXPENSE

NET OPERATING INCOME -390 -60 1 108 619 1016 1345 1744 2025 2303 2447

1000 0 0 0 0 0 0 0 it LESS: INSTALL IRRIGATION SYSTEM ------0 ------

ANNUAL NET CASH FLOW

ACCUMULATIVE NET CASH FLOW -1390 -1991 -1883 -1264 -248 1097 2841 4866 7169 96 12 =====I= LIIPIPI ======I ===I======I====-= =C=Z=-- I-==-===1===01 =====a=

SCHEDULE------OF-- GROVE----- DESCRIPTION.------ACREAGE AND--- FRUIT----- PRODUCTION------YEAR 1 YEAR 2 YEAR 3 YEAR 4 YEAR 5 YEAR 6 YEAR 7 YEAR 8 YEAR 9 YEAR 10 ------TOTAL GROVE ACRES 1 1 I 1 1 I 1 1 1 1 TOTAL PLANTED ACRES 1 1 1 1 I 1 1 1 1 1 "BUCKHORN" TREES PER ACRE 70 68 66 64 62 A0 58 56 5 4 5 2 INTERSET/SOLIDSET TREES PER ACRE 0 70 69 68 6 7 66 65 64 63 62 TREES LOST (REMOVED) PER YEAR 2 3 3 3 *- 3 3 3 5 3 TOTAL BOXES FROM "BUCKHORN" TREES 0 60 116 192 264 300 319 308 297 286 TOTAL BOXES FROM INTERSET/SOLIDSET 0 0 0 34 67 106 163 21 1 268 295 TOTAL BOXES FROM RESET TREES 0 0 0 3 9 19 34 5 3 79 107

TOTAL BOXES PER ACRE 0 68 116 229 540 424 515 575 644 688 Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 September 23 on guest by http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf from Downloaded SOLIDSET HAMLIN ORANGE GROVE -- IRRIOATED ------

SCHEDULE------OF-- CASH---- BUDGET------ANALYSIS------YEAR I YEAR 2 YEAR 3 YEAR 4 YEAR 5 YEAR 6 YEAR 7 YEAR B YEAR 9 YEAR 10 ------ADJUSTED GROSS REVENUE 0 0 0 334 646 983 1614 2246 2850 3177

OPERAT------ING ------EXPENSES: COST TO "BUCKHORN" DAMAGED TREES 0 0 0 0 u 0 COST TO REMOVE TREES OR BRUSH 5 5 6 9 10 10 GROVE CARE COSTS 0 0 562 619 650 683 YOUNG TREE CARE - RESETS 10 15 20 22 23 2 4 - INTER-SOLIDSET 465 518 0 0 0 0 PLANT RESET/INTER-SOLIDSET TREES 23 24 25 27 29 Ju PROPERTY TAXES 3 1 38 39 43 46 4 8 ------TOTAL OPERATING EXPENSE 535 599 652 722 758 796

NET OPERATING INCOME -170 -1538 -428 -200 47 33 1 1524 2092 238 1

LESS: INSTALL IRRIGATION SYSTEM 1000 0 0 0 0 0 0 0 0 ------

ANNUAL NET CASK FLOW -200 47 33 1 1524 2092 2781 ======------= = =PC======a==== =--=a======

ACCUMULATIVE NET CASH FLOW -1170 -2708 -3136 -3336 -3290 -2959 -508 1584 3965 =====PI ==PCP-= ====PIP ==PIE======-== =PlailEE ======i=lP======-

SCHEDULE OF GROVE DESCRIPTION. ACREAGE AND FRUIT PRODUCTION ------I 3 YEAR 4 YEAR 5 YEAR 6 YEAR 7 YEAR 8 YEAR 9 YEAR LO YEAR------YEAR------2 YEAR------TOTAL GROVE ACRES 1 1 1 1 I 1 I 1 I 1 TOTAL PLANTED ACRES 1 1 1 1 1 1 1 1 1 1 "BUCKHORN" TREES PER ACRE 0 0 0 0 ir 0 O 0 O (11 INTERSET/SOLIDSET TREES PER 4CHE 0 140 137 134 15 1 128 125 122 119 116 TREES LOST (REMOVED) PER YEAR 0 3 3 3 3 3 3 3 5 7 TOTAL BOXES FROM "BUCKHORN" TREES 0 0 0 0 0 0 0 0 O 0 TOTAL BOXES FROM INTERSET/SOLIDSET 0 0 0 67 1 3 1 205 313 403 506 55 1 TOTAL BOXES FROM RESET TREES 0 0 0 3 9 19 74 53 79 107

TOTAL BOXES PER ACRE 0 0 0 70 140 223 346 456 585 658 Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 September 23 on guest by http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf from Downloaded Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021

Table 5. Tree Loss and Damage In An 8-Yr.-Old Planting of "Valencia' Orange on 12 Different Rootstocks on USDA A.H. Whitmore Foundation Farm Near Leesburg, Florida, After the 1983 December freeze.= Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021

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Table 6. Tree Loss and Damage In An 8-Yr.-Old Planting of "Marsh' Grapefruit: on 12 Different Rootstocks on USBA A.H. Whitmore Foundation Farm Near Leesburg, Florida, After the 1983 December freeze.= References

1. Boswell, S.B., E.M. Nauer, and D.R. Atkin. 1982. Effect of Tree Density on Fruit Quality, Temperature, Light Penetration, Growth, and Production of Old-live 'Atwood' Navel Orange Trees. Journal of the American Society of Horticultural Science. 107(1):60-69. 2. Davies, F.S., L.K. Jackson, and L.W. Rippetoe. 1984. Low Volume Irrigation and Tree Wraps for Cold Protection of Young Citrus Trees. Proceedings of the Florida State Horticultural Society. 97. Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021 3. Florida Agricultural Statistics. Citrus Summary. 1965. Florida Crop and Livestock Reporting Service, Orlando, Florida. 4. Florida Agricultural Statistics. Citrus Summary. 1968. Florida Crop and Livestock Reporting Service, Orlando, Florida. 5. Florida Agricultural Statistics. Citrus Summary. 1983. Florida Crop and Livestock Reporting Service, Orlando, Florida. 6. Florida Agricultural Statistics. Commercial Citrus Tree Inventory. Preliminary Report. September 6, 1984. Florida Crop and Livestock Reporting Service, Orlando, Florida. 7. Florida Citrus Fruit. Annual Summary. 1950. Florida Crop and Livestock Reporting Service, Orlando, Florida. 8. Florida Climatological Data. United States Department of Commerce. National Climatic Center, Ashville, N.C., Volumes 61, 66, 71, 81, 85, 86, 87. 9. Gerber, J.F. and J.D. Martsolf. 1965. Protecting Citrus from Cold Damage. Florida Cooperative Extension Service Circular 287. 29 pages. 10. Jackson, J.L. 1984. The Role of Elevation in Lakes and Cold Protection Chapter. Cold Protection Guide. Central Florida Freeze Recovery Task Force, IFAS, Uni- versity of Florida, Gainesville, Florida. 11. Jackson, J.L. 1984. Wind Machines Chapter. Cold Protection Guide. Central Florida Freeze Recovery Task Force, IFAS! University of Florida, Gainesville, Florida. 12. Jackson, J.L. 1984. Wraps vs. Banks Chapter;. Cold Protection Guide. Central Florida Freeze Recovery Task Force, I FAS, University of Florida, Gainesville, Florida. 13. Krezdorn, A.H. 1984. Cultural Practices and Cold Protection Chapter. Cold Protec- tion Guide. Central Florida Freeze Recovery Task Force, IFAS, University of Florida, Gainesville, Florida. 14. Muraro, R.P. and J.L. Jackson. January 1985. Ten-Year Budget Analysis For Rehabilitation of Freeze Damaged Citrus Groves. Staff Paper No 170. IFAS. Food and Resource Economics Department, University of Florida, Gainesville, Florida. 15. Parsons, L.R. 1984. Microsprinkler Irrigation for Citrus Cold Protection. Fruit Crops Fact Sheet FC-69. IFAS, University of Florida Cooperative Extension Ser- vice, Gainesville, Florida. 16. Whitney, J.D. and T.A. Wheaton. 1984. Tree Spacing Affects Citrus Fruit Distribu- tion and Yield. Proceedings of the Florida State Horticultural Society. 97. 18. Yelenosky, G., C.J. Hearn, and D.J. Hutchinson. 1984. Non-hardening Tempera- tures - Major Factor in Freeze Damage to Citrus-Tree in December 1983. Proceed- ings of the Florida State Horticultural Society. 97. 17. Wiltbank, W.J. 1984. Hardening of Citrus Chapter. Cold Protection Guide. Central Florida Freeze Recovery Task Force, IFAS, Urliversity of Florida, Gainesville, Florida. Downloaded from http://asmedigitalcollection.asme.org/CES/proceedings-pdf/CEC1985/99724/1/2370541/cec1985-3101.pdf by guest on 23 September 2021