TRUNK WRAP EVALUATIONS1

Transcription

1 of endomycorrhizae. Phytopathology : Maggs, D. H., and D. E. McAlexander. 69. The quantitative growth of young seedlings of the citrus rootstocks Citrus sinensis (L.) Osbeck, Poncirus trifoliata (L.) Raf. and their hybrid Carrizo citrange. Ann. Bot. : Martin, J. P., R. C. Baines, and A. L. Page. 63. Observations on the occasional temporary growth inhibition of citrus seedlings following heat or fumigation treatment of the soil. Soil Sci. 95: Mehraveran, H. 77. Mycorrhizal dependency of six citrus cultivars. Ph.D. Thesis, University of Illinois. 67 pp. 14. Menge, J. A., E. L. V. Johnson, and R. G. Platt. 77. Mycorrhizal dependency of several citrus cultivars under three nutrient regimes. New Phytologist 77: (in press). 15., H. Lembright, and E. L. V. Johnson. 77. Utilization of mycorrhizal fungi in citrus nurseries. Page, Vol. I, in W. Grierson, ed. Proc. Int. Soc. Citricullure, 77. Orlando, FL (Abstr.) 16., S. Nemec, V. Minassian, and R. M. Davis. 77. My corrhizal fungi associated with citrus and their possible interactions with pathogens. Page, Vol. I in W. Grierson, ed. Proc. Int. Soc. Citriculture, 77. Orlando, FL. (Abstr.) 17. Monselise, S. P.. Growth analysis of citrus seedlings, II. Palestine J. Bot., Rehovot Series 8:1-1.. Mosse, B.. Growth and chemical composition of mycorrhizal and nonmycorrhizal apples. Nature 179: Advances in the study of vesicular-arbuscular mycorrhiza. Annu. Rev. Phytopathol. 11: Nassery, H.. Phosphate absorption by plants from habitats of different phosphate status. II. Absorption and incorporation of phosphate by intact plants. New Phytologist 69:7-3.. Newcomb, D. A. 75. Mycorrhiza effects following soil fumiga tion. Int. Plant Propagat. Soc. : Ross, J. P. 71. Effect of phosphate fertilization on yield of mycorrhizal and nonmycorrhizal soybeans. Phytopathology :10-., and J. A. Harper.. Effect of Endogone mycorrhiza on soybean yields. Phytopathology : Schenck, N. C, and D. P. H. Tucker. 74. Endomycorrhizal fungi and the development of citrus seedlings in Florida fumigated soil /. Amer. Soc. Hort. Sci. 99:4-7.. Tucker, D. P. H., and C. A. Anderson. 72. Correction of citrus seedling stunting on fumigated soils by phosphate application Proc. Fla. State Hort. Soc. 85: Proc. Fla. State Hort. Soc. 91:14-.. CITRUS Andrew J. Rose Florida Citrus Groves Corporation, Rt. 2, Box 104, Clermont, FL 711 George Yelenosky Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Camden Rd., Orlando, FL 803 Additional index ivords. Citrus sinensis, cold protection. Abstract. Tests, during the last 3 winters, to evaluate temperatures of citrus tree trunks protected with insulating materials in contrast to soil banks and unprotected trees during different freeze conditions were made. Evaluations were made under field conditions and in a freeze chamber. Fiberglass wraps were not as effective in moderating low temperatures as were soil banks. On some freeze nights, wraps provided 4-5 F ( C) protection, and on others none, while soil banks provided F ( C) protec tion. Temperature drops under wraps lagged several hours behind the air temperatures during some freezes. Daytime maximum temperatures were not moderated by wraps, and exceeded ambient air temperatures under direct sunlight. Fiberglass wrapped trees adequately survived 77 freeze conditions. Trunk wraps for citrus resets have been tried by several people in Florida over the years, but data are not readily available on wraps as a means of cold protection in this area. In 69 a large scale commercial observation was started in Lake County using both fiberglass and foam rubber wrapping materials. After 3 years and 1 major freeze, the wraps were rated equal to soil banks from a freeze protec tion standpoint. Continued use of wraps over 8 years show ithis paper reports the results of research only. Mention of a brand name does not constitute a recommendation for use by Florida Citrus Groves Corporation or by the U.S. Department of Agriculture nor does it imply registration under FIFRA, as amended. 14 TRUNK WRAP EVALUATIONS1 good results in tree freeze survival. Observations over this period of time indicate wraps have decreased foot rot, (Phytophora parasitica Dastur), reduced labor for desprouting trees, and reduced physical damage to trees from animals, chemicals, and sun burn, with no increase in freeze damage over the conventional soil bank. Trunk damage from banking and unbanking was eliminated. Some tree injury was observed if excessive fertilizer was caught on the top of wraps. Other work at this time showed increased foot rot apparently from moisture in fiberglass wraps (3). Unpublished reports from California indicate that wraps of corn shuck and foam rubber provided very little tempera ture moderation and increased the incidence of foot rot. Other California researchers, reported that similar wraps as well as white paint provided some cold protection of citrus, pecans, and peaches (unpublished). It was specu lated that this was due to reduced temperatures on hot winter days, thus increasing dormancy. Wraps have been tested (1, 2, 4) and are currently being used successfully in citrus in Texas. This report is a continuation of evaluating citrus tree wraps during different freeze conditions. Data include the results of 7 separate experiments during 3 winters, through 77-. Experiment 1: Materials and Methods Resets of 'Hamlin' (Citrus sinensis (L.) Osb.) orange on Cleopatra mandarin (C. reticulata Blanco) in a com mercial grove in Lake County, on Astatula sand, 5-12% slope, were used. Thermistors were taped on the north side of the trunks, 4 inches (10.2 cm) above the scion-rootstock union or 6 inches (15.2 cm) above the ground. Trees were banked with soil or wrapped with 4 inch thick (10.2 cm) fiberglass insulation inches (.5 cm) high and inches (50.8 cm) long with other trees left exposed. Treatments were replicated 6 times. Temperature readings were made manually each hour, during February 8-9, 76, with a Cole-Palmer electronic thermistor thermometer. Proc. Fla. State Hort. Sac, 91;.

2 Experiment 2: Resets of 'Hamlin' on Poncirus trifoliata (L.) Raf. rootstock, were planted in a cold pocket located in a producing grove in Lake County. Thermocouples were taped 6 inches (15.2 cm) and 12 inches (.5 cm) above the ground and covered with a 16 inch (.6 cm) high fiberglass wrap. Thermocouples were also used to measure leaf and air temperatures on each reset. Treatments were replicated 6 times. Temperatures were measured and recorded auto matically every 2 hours during November 8-10, 76, and January 17-, 77. Experiment 3: Greenhouse container grown, 1-year-old budded trees were wrapped with fiberglass as described above and others were left exposed. The trees were subjected to temperature fluctuations of the Texas freeze simulated in a freeze chamber. Experiment 4: Resets of 'Hamlin' on Cleopatra mandarin rootstocks in a commercial grove on Astatula sand in Lake County were used to compare wraps of Corning 4 inch fiberglass roll insulation, Rubberlux urethane foam, 1 inch ( mm) thick, and inches (1.1 m) long, wrapped to approxi mately 4 inch (10 cm) thickness and Aerolite generated foam in a roofing paper mold approximately 8 inches ( cm) in diameter. temperatures were also taken at each tree. Thermistors were placed and temperatures re corded as in Experiment 1 during the period from February 10-11,. Treatments were replicated 5 times. Experiment 5: Two-year-old budded 'Marsh' grapefruit (C. paradisi Macf.) trees planted at the U.S.D.A. farm in Lake County, were used to compare fiberglass wraps with soil banks. Tem perature was measured with the use of -gauge copper constant thermocouples taped to the trunks at 3 (7.6 cm) and 12 inches (.5 cm) above the ground, then covered with 15 inch (.1 cm) fiberglass tree wraps or soil banks. Untreated trees were also monitored. Thermocouples were attached to a point recorder as in Experiment 2. Treat ments were replicated 2 times. Measurements were made January -, 77. oak ladder rungs were wrapped with each insulating material and weighed. Three wraps of each material were wetted with 0 ml of water each, while the other 3 were saturated with water and weighed again. The 16 inch (.6 cm) wraps were wrapped around the center of each ladder rung to en able them to be stood on end by forcing one end of the run into the soil. Each wrap was placed in firm contact with bare soil. Weights were taken at and hours to determine percent water retention. The trunks of all wrapped treatments were treated with a fungicide and insecticide immediately prior to wrapping. Experiment 1: Results and Discussion On the morning of February 8, 76, temperature checks were begun at 1: A.M. and continued until the air temperature began to warm up after sunrise. After the first check there was no significant difference in temperature throughout the night between the wraps and the air, and the soil banks were significantly warmer (Table 1). On the following night temperature checks were started in the afternoon before the air temperature started to fall. Until 9:00 P.M. temperatures under wraps were warmer than the air and cooler than under banks (Table 2). From that hour the temperature comparison was similar to the previous night. The 9:00 A.M. check shows that wrap temperatures increase rapidly, but not as rapidly as that of the air. Bank temperatures increase much slower. Temperatures on both nights reached the same minimums whether under wraps or in the air, although average temperatures show a trend toward a time lag in decreasing temperature under the wraps. Therefore, durations of freez ing temperatures under wraps were shorter. Damage from cold temperatures during both nights was limited to tender growth. Consequently, resets were planted in a severe cold pocket and temperatures were monitored hours per day the following winter. Experiment 2: The first freeze of the winter in this cold pocket occurred on November 8, 76. Results appear to be very similar to the previous year (Table 3). Mean temperatures were 4-5 * ( C) warmer under lower portions of the wrap on the Table 1. Mean temperatures, F, of 'Hamlin' tree trunk surfaces for February 8, 76, Clermont. Experiment 6: Wrap Bank 52.8a.5b.0b.4a.3b.3b.8a.3b (A.M.) One-year-old budded 'Star Ruby' grapefruit trees in Treatment 1: 2: 3: 4: 5: 6: 7: containers were exposed to a controlled freeze chamber test to evaluate temperatures under wet and dry fiberglass wraps. Experiment 7:.3b.5a.5b.3b.5a.5b.2b.7b.0a.7a.8b.3b To determine water holding capacities of the fiberglass zmeans followed by the same letter are not significantly different at and urethane tree wraps tested previously, 6, inch ( cm) the 1% level. Table 2. Mean temperatures, F, of 'Hamlin' tree trunk surfaces for February 8 (P.M.) and February 9 (A.M.), 76, Clermont. Treatment 5:00 7:00 8:00 9:00 10:00 11:00 12:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 Wrap Bank.8abz 50.3b.3b 64.3a.8a.7a GO.Ob.3c.0c 0b 8b.5b.7b.7b.7b.7b 2a.0a 49.5a.8a.0a.2a.8a.0c.8b.8b.2b.5b.5b.5b.5b.3b.0b.0a.5a.0a.0b.8b.8b.2b.5b.2b.2a.0a.7b.8b.0b.0a zmeans followed by the same letter are not significantly different at the 1% level. Proc. Fla. State Hort. Soc. 91:. 15

3 Table 3. Mean temperatures, F, of wrapped and exposed tree trunks of Hamlin' resets during November 8 (PM), November 9, and No vember 10 (AM), 76, Clermont. Table 4. Mean temperatures, F, of wrapped and exposed tree trunks of 'Hamlin' resets during January 17 through January, 77, Clermont. Under fiberglass wraps 6" from 6" from top bottom of wrap of wrap Exposed trunk Leaf Under fiberglass wraps 6" from 6" from top bottom of wrap of wrap Exposed trunk Leaf November 8: November 9: 1 November 10: first night but about the same as air temperatures the second night. Temperature drops under the wraps lagged several hours behind those of the air as they did in previous tests 1 emperatures under wraps during the day of November y were, on the average, even warmer than air temperatures, failing to substantiate the theory that wraps cause cooler daytime temperatures which promote increased tree dormancy. As a result of this freeze, resets suffered severe leaf drop but only minor wood loss. During the week of January 17, 77, a series of major freezes occurred. Recordings continued throughout this period showed that temperatures in the upper part of the wrap reached air temperatures each night (Table 4) How ever, temperatures in the lower part of the wrap stayed wanner, sometimes significantly, during periods of more rapid drops m air temperature. Wrap temperatures once again lagged several hours behind air temperatures as temperatures fell. r On January 17 and, during periods of sunshine, maxi mum temperatures under wraps exceeded those of ambient all*. In each treatment, resets were killed to the ground at the lowest level of the cold pocket. Additional resets 90 ft ( m) up the slope froze to the tops of the wraps and banks. Cold-period temperatures averaged 4-5 F ( C) warmer on these trees with corresponding shorter durations of freezing temperatures. In this area, no difference in tree or wood loss was obtained where resets were soil banked. Experiment 3: Trunk temperatures were not recorded in this test. temperatures in the freeze chamber were regulated by a cam cut during the freeze in Texas where minimum temperatures reached 14 F (-10 C). Trees were about January 17: January : January : January : January : inches ( mm) in circumference, 4 inches (10.2 cm) above the bud union, and had received no cold hardening. During this test the untreated check trees froze to the surface of the potting media while the wrapped trees froze to the top of the fiberglass wrap. Experiment 4: Although air temperature did not reach freezing, the comparison of effectiveness of three wrap materials was made on February 10-11, 77, (Table 5). Fiberglass wraps performed as expected from past investigations. The fiber glass wraps protected best, Aerolite foam poorest, and the Proc. Fla. State HorL Soc. 91:.

4 Table 5. Mean temperature, F, of 'Hamlin* tree trunks for February 10 and 11,, Clermont. February 10: Treatment [ Foam Foam rubber Fiberglass.6NSz NS NS NS NS by.6b.8a.8b 52.2b 55.0a b 50.8ab 52.0a.0.4b 49.4ab 50.6a.0 February 11: Treatment 5 :00 AM Foam Foam rubber Fiberglass.8b.0ab 49.0a.0.2b.2ab.0a.0.4NS NS NS b.4ab.0a.0.2NS NS.2.0 zns = Means do ymeans followed not differ significantly, by the same letter do not significantly ' differ at the ; 5% level. temperatures were not included in the statistical comparison. urethane foam rubber intermediately. The Aerolite liquid foam also had the disadvantages of loosening from the trunk due to an apparent shrinkage when drying. In some cases it broke away with the rooting paper mold as weather loosened the tape holding it on, thus exposing the trunk. This, how ever, did not occur until several months after temperature measurements were completed. Experiment 5: In this study, temperatures at 2 levels under the tree wraps and soil banks were measured. During both nights treatments were in the same order of protection. The greatest protection was found in the bottom of the banks, followed by the bottom of the wraps, the top of the wraps, and then by the top of the banks (Table 6). The low temperatures 3 inches (7.6 cm) into the top of the banks can be explained by the opening produced by the movement of the tree trunk pushing the moist sand away from the trunk. The cold front bringing the freezing temperature was preceded by rain and windy conditions, Although the bud union temperatures under the wraps were 6-7 F ( C) colder than the banks, they were 4-6 F ( C) warmer than the air; however, tempera tures in the top of the wraps were 2-3 F ( C) warmer than the top of the banks. No differences in tree or wood loss were noted. Experiment 6: With field testing it was not practical to have an es tablished wrap completely dry for determining the influence of moisture in protection since most cold fronts are pre ceded by rain. A freeze chamber test was set up with fiber glass wraps to express the maximum effect that might be seen. Temperatures dropped at about the same rate until freezing occurred at about the 4-6 hours (Table 7). After that, temperatures dropped faster under the wet wrap but lagged behind the dry wrap at the 11th hour. By this time air temperatures would normally be increasing in the field. Experiment 7: The fiberglass insulation wraps held considerably less water at both the and hour period than did the ure thane foam. This was true whether the wraps were partially wetted or saturated. (Table 8). Both materials held approxi mately the same weight of water immediately after satura- Proc. Fla. State Hort. Soc. 91:. Table 6. Mean temperatures of 'Marsh' grapefruit tree trunks for January and, 77, Leesburg. January : 1: AM 2: AM 3: AM 4: AM 5: AM 6: AM 7: AM 8: AM 9: AM 10: AM 11: AM 12: AM 1: PM 2: PM 3: PM 4: PM 5: PM 6: PM 7: PM 8: PM 9: PM 10: PM 11: PM 12: PM January : 1: AM 2: AM 3: AM 4: AM 5: AM 6: AM 7: AM 8: AM 9: AM 10: AM Fiberglass wrap Topy Bottom* F Soil bank Top Bottom Exposed barkz Top Bottom ^Treatment not replicated. ytemperature 3 inches (7.6 cm) down from top of wrap or 12 inches (.5 cm) above soil. ^Temperature 3 inches (7.6 cm) above soil. tion but by the time they were placed against the soil, the fiberglass wraps were noticeably lighter. After 96 hours wraps were taken off the ladder runs. Runs under the ure thane wraps were darkened by water while those under the fiberglass showed no indication of moisture. 17

5 Table 7. Mean temperatures of 'Star Ruby' grapefruit bud unions under fiberglass wraps in a controlled freeze. Hour Dry zwrap soaked with 0 i ml of water 3 hr before freeze started. Table 8. Water holding capacity New wraps. Material 3i/2" Fiberglass Bat 1" Urethane wrap op- Wet wrapz Exposed bark Percent Water Retention 0 ml Saturatedz Hrs. Hrs. Hrs. Hrs ^Fiberglass held of water at saturation, urethane Conclusions Fiberglass wraps provide some freeze protection, but wraps are not as effective as soil banks in moderating low temperatures. Except under extremely severe freeze conditions (very cold and long durations), fiberglass wraps are an effective means of freeze protection. Minimum temperatures under wraps may lag several hours behind those of ambient air and result in shorter freeze durations at any one temperature. Of the tree wrap materials tested, the 4 inch (10.2 cm), foil backed, fiberglass insulation batting was the most effec tive means of temperature moderation. Wet wraps moderate initial freeze temperatures and field observations indicate no apparent added freeze danger from wet wraps during freeze conditions. In summary, 8 years of field trials indicate less foot rot, less labor for de-sprouting trees, and less physical damage to trees from animals, chemicals, sun burn, and soil bank ing and unbanking with no increase in freeze damage over the conventional soil bank. Some tree injury results if excessive fertilizer is caught on the top of wraps during cultural practices. Literature Cited 1. Hensz, R. A. 69. The use of insulating wraps for protection of citrus trees from freeze damage. Proc. First Int. Citrus Symp. 2: Leyden, R. F. and P. W. Rohrbaugh. 63. Protection of citrus trees from cold damage. Proc. Amer. Soc. Hort. Sci. 83: Reese, R. L., 69. Soil banks or fiberglass wraps for young citrus trees. The Citrus Industry, January, p. 17,,. 4. Young, R. H., I. E. Fucik and R. A. Hensz. 67. Tests of insulat ing materials for citrus tree trunk freeze protection using controlled freezing conditions. Jour. Rio Grande Valley Hort. Soc. : Proc. Fla. State Hort. Soc. 91:-.. THE EFFECT OF WITHHOLDING WATER ON COLD HARDINESS OF 'VALENCIA' ORANGE AND 'STAR RUBY' GRAPEFRUIT TREES IN CONTROLLED FREEZES George Yelenosky Federal Research, Science and Education Administration, U.S. Department of Agriculture, Camden Road, Orlando, FL 803 Additional index words, citrus, water stress, freeze injury. Abstract. Withholding water increased the cold hardiness of -month-old potted trees of 'Valencia7 orange (Citrus sinensis (L.) Osb.) and 'Star Ruby' grapefruit (C. paradisi Macf.). Water-stressed 'Valencia' trees on C. volkameriana Wester rootstock and 'Star Ruby' on rough lemon (C. limon (L.) Burm. f.), C. miaray Wester, and Carrizo and Tryer citrange (C. sinensis X Poncirus trifoliata (L.) Raf.) rootstocks showed no wood kill at F (-6.1 C) for 3 hr. Wood was killed on all nonstressed trees and on water-stressed 'Va lencia' on C. miaray and C. macrophylla Wester rootstocks and 'Star Ruby' on C. macrophylla. It is generally accepted that frequent watering during the fall and early winter tends to stimulate new growth and increases the chances of freeze injury to citrus trees. In some instances, this does not happen and freeze recovery is helped with increased watering (7); usually, however, re duced watering is the better practice. Milliken and others found more freeze injury to citrus trees irrigated 2, rather than 6, weeks before a freeze (8). After the January 77 freeze in Florida, unreported data of the author indicated that -year-old 'Valencia* orange trees on rough lemon rootstock irrigated frequently during the fall suffered more freeze injury than did nonirrigated trees. However, 3-yearold grapefruit plantings were a total loss in nonirrigated areas with prolonged water stress. Cold hardiness in citrus trees is largely characterized by low temperature-induced cold hardening, and the effectiveness of water stress in in ducing cold hardiness in citrus trees is largely unknown. This study evaluates the cold hardiness of young citrus trees that were water stressed before controlled freezing tests. Materials and Methods Trees tested were 'Valencia' orange on C. miaray, C. macrophylla, and C. volkameriana rootstocks and 'Star Ruby' grapefruit trees on rough lemon, C. miaray, C. macrophylla, and Troyer and Carrizo citranges. Rootstock Proc. Fla. State Hort. Soc. 91:.