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Cold Damage to Fruit Trees at the Sub-Tropical

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Cold Damage to Fruit Trees at the Sub-Tropical LEDIN: COLD DAMAGE 341 thousand boxes of Lulas and a smaller quan cultivation of young groves, and keeping all tity of other varieties were salvaged. trees in healthy condition, there are not many This did not apply in equal measure to things to do. In young groves, if the plants every variety, and it most certainly does not are small enough to be covered by hampers apply to the fruit we harvest earlier in the this should be done. It will prevent injury season. Observations in freezes occurring from mild freezes and will save the life of earlier in other winters show definitelv that the plants at temperatures as low as 27 de while Lula fruit will stand the cold well even grees. Older trees can be protected by firing, early in the season, many varieties cannot be as in citrus groves, but this is not often done salvaged at all if the temperature drops as as the need for it is not frequent and the ex low as 28 degrees. The damage is not always pense is great. The few groves that were pro manifested in the way just described, either. tected by oil heaters last February came Fruit which appears perfectly good on the through with little damage, but where old outside may "cut black" around the seed. And automobile tires were burned, as is frequently some varieties will drop badly after a cold done for truck crops, I could not see that they spell which did not even damage the leaves. afforded much protection. Whether or not Oddly enough, some of the varieties which oil-firing is economically justified as a general are quite susceptible to cold damage in No practice would require a careful cost study; vember or December came through this cold the answer is not available to us now. as well as the Lula. I have in mind particularly We have no experience with wind machines, the Booth 1, which will rain off the trees after but it seems to me that this device may prove temperatures no lower than 29 or 30 degrees to be a valuable aid in protecting from most early in the season; the fruit of this variety of our freezes. stood the cold in February as well as did the I will conclude with the sober observation Lula. There may be a change in the fruit that except for what we have learned about associated with full maturity which makes it keeping the trees healthy, the value of keeping able to stand more cold. the groves clean, and the possibility of sal Any discussion of cold injury should in vaging fruit from injured trees, we are in clude the subject of protective measures. Ac about the same position that we were 25 tually, in Dade County, aside from the clean years ago, when it gets cold. COLD DAMAGE TO FRUIT TREES AT THE SUB-TROPICAL EXPERIMENT STATION, HOMESTEAD R. Bruce Ledin for 13 hours and an official low of 26.5° F. Sub-Tropical Experiment Station was recorded at the Station. Except for one warm week the end of December and a few Homestead warm days during January, cool weather pre The numerous cold spells of the winter of vailed until February 22. 1957-58 provided an opportunity to evaluate In most cases damage by the February 4-5 the hardiness of some tropical and subtropical freeze was more severe than that of January fruit plants. At the Sub-Tropical Experiment 14-15, 1956, when temperatures below 32° Station, Homestead, the December 9-12 cold F. lasted for 8 hours and an official low of spell reached a low of 32° F. but did very 27° F. was recorded. Some plants, however, little damage except to sensitive plants and received more damage in 1956 than in 1958. those still in active growth. During the Janu Susceptibility of plants to cold damage de ary 8-9 cold spell two hours below 32° F. pends on several factors. caused no damage. The February 4-5 cold 1. The nature of the species—some species spell, on the other hand, did considerable are extra tropical, such as the bread damage; temperatures below 32° F. lasted fruit, Malay apple, and cashew, and will 342 FLORIDA STATE HORTICULTURAL SOCIETY, 1958 sometimes be damaged by cold even with irrigation ditches between. During cold without freezing temperatures. spells water was run into the ditches and al 2. The general condition of the plant from lowed to flood the beds. Unfortunately we a nutritional standpoint — if chlorotic, do not have any temperature records in the lacking fertilizer, especially nitrogen, or flooded area, but the official temperature on weakened by insects or diseases, the higher ground February 5 was 27.5° F. with plants will be more susceptible to cold 6 hours below 32° F. It was quite evident injury than those in good healthy con that the water kept the temperature above dition. freezing, as very little damage occurred to these plants, except for some that were situ 3. The stage of growth—a tree in active ated at the ends of the beds which were not growth with tender leaves is more sus flooded. One star-apple in this location was ceptible to cold than a tree in dormant injured severely, but star-apples that were condition. flooded showed little injury. This was also true 4. The age of the tree—a well established of Kent and Zill mangos planted in this same plant 4 years or more of age can tole area. At the Sub-Tropical Station in Home rate more cold than young plants only stead, many of the fruit plants were protected 1 to 3 years in the field. by fire pots and the trunks of young plants 5. Overhead protection — plants growing were wrapped with straw. under large spreading trees or protect In the following lists the plants are grouped ed by nearby trees or buildings will according to the amount of injury. In most not be hurt as much as trees in exposed cases both old and young plants are repre situations. sented; if there was any injury to young plants Cold protection can be provided in several and not to the older ones, this is noted. ways: 1. Species showing little or no damage. 1. Clean cultivation—exposed rock or sand Averrhoa carambola, carambola will permit more accumulation of heat Butia capitata, jelly-palm during the day and allow more radia Carissa grandiflora, Natal-plum. Mature heal tion of heat from the ground during thy plants were uninjured, but a row of the night than ground covered with Gifford carissa that were slightly chlorotic, mulch or weeds. 2. Wrapping the trunks of young plants infested with scale insects, and overgrown with weeds, showed some leaf burn and with straw or some other material that twig injury. is loose enough to allow circulation of air and to prevent accumulation of Casimiroa edulis and C. tetrameria, white-sa- moisture will provide sufficient insu pote. Old plants were unaffected, but 1- lation to protect the trunks even if the year old seedlings at Ft. Lauderdale had a top above the wrap is killed. little leaf-burn and twig injury. 3. Planting sensitive plants where they Ceratonia silique, carob will be protected by large trees. Clausena lansium, wampi 4. Use of fire pots to raise the temperature Dovyalis caffra, kei-apple a few degrees. Dovyalis hebacarpa, Ceylon-gooseberry 5. Covering small plants with hampers or Dovyalis hebacarpa X D. abyssinica, hybrid similar containers. dovyalis 6. Irrigation may be used to raise the air Elaeagnus philippensis, lingaro temperature; overhead irrigation or Eriobotrya japonica, loquat running water into ditches are both Eugenia aggregata, cherry of the Rio Grande effective. Eugenia dombeyi, grumichama Most of the notes on cold damage to the Eugenia luschnathiana, pitomba fruit plants were made at the Experiment Eugenia uniflora, Surinam-cherry Station in Homestead, but some notes were Feijoa sellowiana, feijoa made on plants in our fruit planting at the Macadamia ternifolia, macadamia nut Ft. Lauderdale Field Laboratory. At Ft. Lau- Myrica rubra, strawberry tree derdale the plants are set out on 50 foot beds Prunus persica, red Ceylon peach LEDIN: COLD DAMAGE 343 Psidium cattleianum, strawberry guava Achras zapote, sapodilla. Old trees were un Rhodomyrtus tomentosa, downy myrtle affected and grafted trees 4 years in the Ruhus albescens, Mysore black raspberry field were riot injured. Small plants in ex Triphasia trifoliata, lime-berry posed situations were killed to the ground Zizyphus mauritiana, Indian Jujube or to the straw wrap. 2. Species showing only slight injury. Artocarpus hypargyrea, kwai muk. Large trees Antidesma dallachyanum, Herbert River-cher had only a little leaf injury; smaller plants ry. This species proved to be hardier than A. showed considerable leaf burn and twig bunius; young plants in exposed places in injury. the same vicinity showed very little dam Artocarpus integrifolia, jackfruit. Very large age. Young plants at Ft. Lauderdale had trees were not hurt except for some exposed more leaf and twig damage. branches on one side of tree were killed; Diospyros discolor, mabolo. Old plants were one and two year old seedlings were killed. unaffected, but young plants had leaf burn Blighia sapida, akee. Large trees had some and some twig injury. leaf burn and twig injury but this was not Eugenia pimenta, all spice. Old plants were as severe as the cold damage in 1956. not damaged but young plants were in Carissa carandas, karanda. Both old and young jured. plants in exposed situations had consider Litchi chinensis, lychee. Old plants in dormant able leaf and twig injury.
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