THE USE OF CALCIJJM FOR CONTROL OF

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1 GERALDSON: USE OF CALCIUM to 7.5. Of various crops tried, only celery has grown on this field without being iron chlorotic. The release of copper from the soil com plex studied in these samples may or may not be comparable to other soils having high cop per content. The copper extractable with ammonium nitrate, or with water in soils with high soluble salt content, is offered here as a method for studying available copper. In the Sanford area such determinations may be indicative of the copper availability in the soil which has been in vegetable production. Summary and Conclusions Copper extractable from soil with water or dilute reagents such as one-tenth normal ammonium nitrate gives an estimate of copper availablity which is reasonable on the basis of crop requirement. In the Sanford area, soils having one pound of available copper jper acre exhibited copper-induced iron chlorosis in several crops. The level of water-extractable copper increased from about one-tenth of a pound per acre, for soil in celery production 25 years or less, to several tenths on land used 35 years or more. Crop productivity lias declined on these older areas. Lower vahjes of water-extractable copper were found in samples taken below the surface six inches of soil. Such extractable copper was very much less than the total copper in the soil. Tne copper extracted was apparently independent of the magnitude of the major nutrients ex tracted and of ph in the range 5.5 to neutral ity. Although the soil regulates the availability of rather large amounts of copper, caution is advisable in the use of this element, particular ly where large amounts formerly have been applied. LITERATURE CITED 1. A Handbook on Pesticides and their Use in Flor ida Agriculture Compiled by Fla. Agr. Exp. Sta., Fla. Agr. Extension Service, Fla. Ind. Org. Com mittee, U. S. Fish and Wild Life Service. 2. Beeson, K. C. The mineral composition of crops with particular reference to the soils in which they were grown. U.S.D.A. Misc. Pub. 369: , Blue, W. G. Unpublished data. Soils Dept., Fla. Agr. Exp. Sta., Gainesville, Fla. 4. Bryan. O. C. Malnutrition symptoms of citrus with practical methods of treatment. State of Fla. Dept. of Agr. Bull. No. 93: pp , Cheng, K. L. and R. H. Bray. Two specific methods of determining copper in soil and plant ma terial. Anal. Chem. 25: Eno, C. F. The effect of copper on nitrification in some Florida soils. Proc. Fla. State Hort. Soc. 66: Forsee, W. T., Jr. Recent plant responses to some of the micro elements on Everglades peat. A symposium, State of Fla., Dept. of Agr. Bull. No. 115: pp Jamison, V. C. Adsorption and fixation of copper in some sandy soils of Central Florida. Soil Sci. 53: , Leonard, C. D. and I. Stewart. Chelated iron as a corrective for lime-induced chlorosis in citrus. Proc. Fla. State Hort. Sod. 66: Mayo, N. and J. J. Taylor. Annual Report, State Chemist of Florida, pp Peech, M. Availability of ions in light sandy soils as affected by reaction. Soil Sci. 51: Peech, M. Chemical studies on soils from Flor ida citrus groves. Fla. Agr. Exp. Sta. Bull. 448: pp. 13, 31-33, Reuther, W. and P. F. Smith. Iron chlorosis in Florida citrus groves in relation to certain soil con stituents. Proc. Fla. State Hort. Soc. 65: Reuther, W., P. F. Smith and G. K. Scudder, Jr. Relation of ph and soil type to toxicity of copper to citrus seedlings. Proc. Fla. State Hort. Soc. 66: 73-8, Rhoads, A. S. and E. F. DeBusk. Diseases of citrus. Fla. Agr. Exp. Sta. Bull. 229: 213 pp Smith, P. F. and W. Reuther. Mineral content of oranges in relation to fruit age and some fertiliza tion practices. Proc. Fla. State Hort. Soc. 66: S Smith, P. F. and A. W,. Specht. Heavy-metal nutrition in relation to iron chlorosis of citrus seed lings. Proc. Fla. State Hort. Soc. 65: Smith, P. F. and A. W. Specht. Mineral Com position of Valencia orange seedlings grown in solu tion with varying amounts of copper, zinc, manganese and iron. Pro. Fla. State Hort. Soc. 65: Westgate, P. J. Preliminary report on copper toxicity and iron chlorosis in old vegetable fields. Proc. Fla. State Hort. Soc. 65: S THE USE OF CALCIJJM FOR CONTROL OF BLOSSOM-END ROT OF TOMATOES C. M. Geraldson Gulf Coast Experiment Station Bradenton A physiological disorder of the tomato fruit known as blossom-end rot is common in all Florida Agricultural Experiment Station Journal Series, No. 41. the tomato-producing areas of the United States and most of the important countries of the world (1, 3, 4). The development of blossom-end rot in the Ruskin area of Florida during the spring crop season of 1954 was especially severe. Virtually all fields were af fected and losses up to more than 5 percent were attributed to the disorder.

2 198 FLORIDA STATE HORTICULTURAL SOCIETY, 1955 Blossom-end rot first becomes apparent as a water-soaked area under the fruit wall on the blossom end of the fruit. The lesion usual ly develops rapidly, eventually resulting in a blackened, dry, sunken leathery tough spot. Another form of the disorder occurs as an in ternal browning or blackening and may be present without the characteristic end rot be ing visible. Many investigators (4, 7), over a period of more than 6 years, have studied the problem and the resultant evidence frequently appears to be contradictory. Unfavorable moisture re lationships (low, high or fluctuating) have been associated more often with blossom-end rot than any other one factor (4, 6, 15, 16). High levels of both nitrogen (2, 4, 12, 15) and potassium (4, 12) have increased the in cidence, and additions of fertilizers that did not contain superphosphate accentuated the injury (4, 6). Robbins (13) showed that blossom-end rot was definitely associated with high osmotic pressures of nutrient solutions. Raleigh and Chucka (12) found that any nutrient variable that resulted in production of fruit with less than.2 percent calcium increased the incidence of the disorder. It was produced at relatively low osmotic values and by high nitrogen, high sulphur, high mag nesium, high potassium, high chloride and low calcium. Evans and Troxler (5), checking the possibility that calcium nutrition may be an important consideration found that blossomend rot could be controlled by injection of calcium gluconate into the fruits. Control of blossom-end rot in the past has never been successful, although in some cases it has been reduced by avoiding or correcting practices or conditions which have been as sociated with its prevalence. Rolfs (14) in 1913, at a time when blossom-end rot was believed to be caused by bacteria or fungi, recommended Bordeaux spray as preventative. Most recent information indicates that what ever control was attained by this treatment could have been due to calcium nutrition pro vided by the spray. In field trials, Evans and Troxler (5) reduced the incidence of blossomend rot from 17 to 13 percent by use of highcalcium fertilizers. They also reported that in pot tests the incidence was reduced from 38 to 26 percent by use of a weekly calcium chloride spray. The purpose of this paper is to describe a method of controlling blossom-end rot that is proving completely successful. It is based on the concept that the fundamental cause of blossom-end rot is deficiency of calcium. Results and Discussion Results of a number of greenhouse experi ments indicated that blossom-end rot, induced by maintaining a low calcium level in the nutrient culture, could be prevented by utiliz ing periodic calcium chloride sprays. Calcium nitrate sprays were not utilized in these ex periments because previous results had in dicated that the nitrate sprays caused blossom drop. Excess nitrogen when calcium levels are low appears to be associated with blossom drop. It should be emphasized that blossomend rot was also prevented when an adequate supply of calcium was available in the nutrient culture. Florida soils often contain inadequate sup plies of calcium. Virgin, sandy flatwood soils generally have a ph of 4.5 or lower. Most of these soils contain varying amounts of a natural source of calcium in the subsoil such as marl or shell. The standard practice is to supply 2 or 3 tons of liming material per acre. This usually raises the ph of the plow layer above 5.5 and increases the calcium content of the soil as determined by an available cal cium test. Despite the above practices, many cases of probable calcium deficiencies have occurred. This indicates that the ph and available calcium tests were not always ade quate for determining the calcium-supplying potential of the soil. A measurement of the percentage calcium in the total soluble salts contained in the saturated soil extract has been found to be an excellent indicator of the calcium-supplying potential as shown by crop responses (8). The calcium is reported as percent of the total soluble salt contained in the soil solution. This method measures the portion of the nutrients maintained in the soil solution at equilibrium which, in the case of calcium, varies inversely with the content of the other cations. The proportion of specific cations contained in the soil solution is dependent on a number of factors, many of which have been associated with blossom-end rot. Some of these factors are: fluctuating moisture, low

3 GERALDSON: USE OF CALCIUM 199 or high moisture levels, high soluble salts, low ph, and excesses of potassium and nitrogen. All of these factors adversely affect the per centage of calcium in the soil solution. In an effort to determine the effects of liming materials, fertilizers, and moisture levels on the occurrence of blossom-end rot, a potculture experiment was conducted using Leon fine sand. Results of this experiment are pre sented in Table 1. From the data presented in Table 1 it is evident that blossom-end rot can be correlated with additions of fertilizer which furnish potassium, sodium and ammonium as cations competitive with calcium. Fluctuating mois ture did not appear to be a factor, except as it might effect the movement of nutrients to and from the root zone and thus alter the cation ratios. It is also evident that the percent cal cium, based on total salt content and not the total ppm calcium in the soil solution, is the correlating figure. At a later date when plants were growing relatively slowly, blossom-end rot was not pro duced when the above-described treatment was repeated. However, some blossom-eiid rot was produced by holding moisture levels high. It was found that most of the nitrogen contained in the soil solution from these soils was present as ammonium. As a result of many soil analyses, the pre valence and severity of blossom-end rot r^as generally been found to vary inversely with the percent calcium as it fluctuates below 2 percent of total salts in the soil solution, other factors being equal. A method of control has been developed which utilizes supplementary calcium applications based on judgment of when the calcium requirement by the plant may exceed the supply in the soil. Control Method (1) The primary objective of the control method is to maintain a calcium level in the soil solution above 2 percent of total salts during the entire growing season. The addi tion of sufficient calcium before planting to obtain the desired level is the first step. It should be recognized that soils will vary in calcium-supplying potential depending on the amount, source and depth of calcium-bearing materials contained in the virgin soil. The calcium content of the subsoil of cropped soils generally increases with use. Any source of subsoil calcium is as available as a similar source in the surface soil, but utilized in pro portion to the subsoil-root development. Cal cium may freely move as calcium nitrate, chloride or sulphate and during leaching rains will move into the subsoil or even be lost in runoff water. Thus leaching of calcium in cultivated soils becomes important when con sidering the control method. When liming materials containing magnesium are utilized, less calcium as well as greater amounts of a competitive cation are being supplied per unit of liming material. (2) The second objective in the control method is to be able to recognize the factors that tend to repress the soil-solution calcium percent during the growing season. Certain Table l. Correlation of blossom-end rot of tomatoes with percent soil-solution calcium as affected by liming material, fertilizer, and moisture application*. Lime source 1. 6# dolomite Z. 3# dolomite +3# agri lime 3. 6# agri lime 4. Same as 2 +2# gypsum Ave. of 4 ph's During Season Before Appl. Total Sol. Salt (ppm) Soil of Fert. Solution Ca ppm Blos somend rot After appll. of. L# 4-8-8/A Soil Total Sol. Solution Ca Salt (ppm) ppm Blossoi ip#nd No spray rot OaClo spray *The JdigurjptK given are averages of 4 replications. Water was applied daily to plants main taining rapid growth in soil contained in-4 gallon crooks. No blossom-end rot was produced, although moisture levels fluctuated greatly, until fertilizer (plus water to leach it into the root zone) was applied. Blossom-end rot then developed within 24 hours. Plants sprayed with a.4m CaClg solution at the time of fertilizer application developed no blossom-end rot.

4 2 FLORIDA STATE HORTICULTURAL SOCIETY, 1955 practices can accordingly be altered or avoided and supplementary calcium added if necessary. The more insoluble sources of calcium are not generally satisfactory when applied as side or top dressings. The success of any soil ap plication of calcium after planting depends on how soon and how well it moves into the root zone soil solution. When the calcium supply is considered to be approaching inadequacy, the following steps are suggested: (1) Any subsequent addi tion of fertilizers should not contain soluble magnesium but should contain superphosphate, a source of calcium. (2) Many growers use nitrate of soda or nitrate of soda potash as top dressers at a time when plant requirement for calcium is high. This type of fertilizer supplies no calcium, but does supply other cations that reduce the percent calcium in the soil solution. It would appear especially de sirable to eliminate sodium because only limit ed quantities are taken up by the plant. (3) The addition of large amounts of such cations as ammonia or potassium should be avoided. Nitrogen becomes a special problem because it can exist as a cation or anion and excesses of either can accentuate a calcium deficiency. Nitrogen levels and ammonium-nitrate ratios can vary with the amount and rate of break down of organic matter, as well as with the amount added in fertilizers. The ammonianitrate ratio also varies with the ph and moisture level. (4) Supplementary calcium sprays should be applied when an approaching calcium inadequacy cannot be avoided or cor rected in other ways. The requirement of the plant in conjunction with all the factors that affect the calcium supply must be considered in the timing of the sprays. Rainfall, tem perature, irrigation and fertilizers can all be called contributing factors if the primary ob jective of the control method has been neglect ed. When it is not neglected such factors are generally not associated with blossom-end rot. Using the Control Method Field experiments conducted in several commercial tomato fields during the spring crop season of 1955 were designed to test the degree of control of blossom-end rot by use of soluble calcium salts applied to the soil or to the plants. Two replicates of singlerow plots, each 2 ft. long, were treated in each field. The soil applications were made at least a month before blossom-end rot was expected to be a problem. Sprays were ap plied as often as twice weekly if need was indicated (as described in the control method). Spray treatments were continued from 2 to 6 weeks, also depending on the indicated need. Sufficient blossom-end rot eventually develop ed in three of these fields to yield the data presented in Table 2. It is evident that applications of soluble calcium to the soil, if made in time, were partly successful in controlling blossom-end rot. Spray applications, provided they were properly timed, were highly effective. Sprays should hot be applied indiscriminately because the spray burn can become serious. In the above field experiments when sprays were used properly, no injury was detected. In a separate experiment in which blossom-end rot was not a factor, yields of tomato plants re- Table 2. Effect of soluble calcium salts applied to the soil or as foliage sprays on the amounts of blossom-end rot produced by tomatoes grown in commer cial fields. Treatment* 1. Check 2. 5# Ga 3. 25# OaCl 4. 4# g/ 5. Same as4 LSD number of Blossom-end Rotted Fruits per 4 ft, row Field 1 Field 2 Field 3 (staked) (unstated) (staked) Total Treatments 2 and 3 were applied to the soil; 4 and 5 were foliar sprays.

5 i GERALDSON: USE OF CALCIUM 21 ceiving periodic sprays (every 5 to 7 days) over a 2-month period were reduced 17 per cent. During the spring crop season of 1955, the experimental control method as described in this paper was used by two commercial to mato growers who were concerned about pre vious annual losses due to blossom-end rot. The disorder was almost completely controlled in both fields. It was estimated by these grow ers that up to 3 percent or more of the fruits would have been lost if the control method had not been put into practice. In the preceding discussion, the possible role of calcium in the association of blosiomend rot with high osmotic pressures (caused by excessive amounts of soluble salts or' de creasing moisture levels) has not been men tioned. On a theoretical basis calcium uptake by plants becomes increasingly more difficult as soil solution osmotic pressures increase. Energy relationships in nutrient uptake (11), as affected by the relative activities of these nutrients, is an important factor when con sidering uptake of calcium from high salt solutions.! Any factor which causes a variation in up take of calcium regardless of whether it is basically a soils or a physiology problem is especially important, because calcium with in the plant is not translocated from older plant parts and must be obtained from the soil solution as needed by meristematic tissue. This helps to explain the often temporary na ture of the developments of blossom-end rot and the importance of timing in the control method. Rate of plant growth and variations in meta bolism are also important factors to be con sidered in connection with the control method and the timing of calcium sprays. Obviously, fast growing plants will be more sensitive to the effects of contributing factors because the requirement for calcium is increased per unit of time. However variations in the metabol ism, other than rate of growth, might also increase the requirement. A number of in vestigators (9, 1) have found that a nitrate source of nitrogen caused an increased pro duction of organic acids by the plant whiph in turn increased the calcium requirement. Evans and Troxler (5) indicated that certain organic acids could immobilize calcium within the plant, making it unavailable for transjocation or assimilation. The activities of the hydrogen ions in the root is considered an im portant factor in the cation uptake by plants (11). These activities would vary with the metabolism of the plant. In this paper, a combination of experi mental and theoretical evidence has been used to explain how calcium can be a fundamental cause of blossom-end rot and yet be in agree ment with the major conclusions of previous investigators. The successful control method is based on this evidence. Summary A method of control for blossom-end rot of tomatoes, which has been completely success ful in the field and greenhouse, is described. It is based on the concept that the funda mental cause of blossom-end rot is a calcium deficiency. Decreasing percentages of calcium in the soil solution have been correlated with the prevalence and severity of the disorder. All factors generally associated with blossom-end rot have been shown to adversely affect either the percent calcium in the soil solution or the uptake and movement of calcium by the plant. Such a condition as rapid growth tends to accentuate the effect of any causal factor. The primary objective of the control method is to maintain a calcium level in the soil solu tion which will remain above 2 percent (cal cium/total soluble salts) during the entire growing season. The second objective in the control method is to be able to recognize the factors that tend to repress the calcium percent during the growing season. Certain practices can accordingly be altered or avoided and supplementary calcium added if needed. Sup plementary calcium sprays (.4M Calcium chloride) can be successfully utilized when an approaching calcium inadequacy cannot be avoided or corrected in other ways. All the evidence presented supports the concept that the fundamental cause of blossomend rot is a calcium deficiency. LITERATURE CITED 1. Anonymous Blossom-end rot of tomatoes. Yearbook of Agriculture: Brooks, C Blossom-end rot of tomatoes. Phytopath. 4: Chamberlain, E. E Blossom-end rot of tomatoes. Jour. Agr. New Zealand 46:

6 22 FLORIDA STATE HORTICULTURAL SOCIETY, Doolittle, S. P Tomato disorders. Year book of Agriculture: Evans, H. J. and Troxler, R. V Relation of calcium nutrition to the incidence of blossom-end rot in tomatoes. Proc. Am. Soc. Hort. Sci. 61: Foster, A. C Effect of environment on the metabolism of the tomato plant as related to the development of blossom-end rot of the fruit. Phytopath. 29: Galloway, B. T Notes on the black-rot of tomatoes. U.S.D.A. Rept Geraldson, C. M. Unpublished data. 9. Gilbert, S. G. et al Nitrogen form and base supply affect on organic acids of tung leaves. Plant Physiol. 26: Hoagland, D. R Organic Plant Nutrition (Prather Lectures at Harvard Univ.) Chronica Botanica Co. 11. Marshall, C. E. and Upchurch, W. J Chemical factors in cation exchange between root surfaces and nutrient media. Soil Science Proc. 17: Raleigh, S. M. and Chucka, J. A Effect of nutrient ratio and concentration on growth and composition of tomato plants and on the occurrence of blossom-end rot of the fruit plant. Physiol. 19: Robbins, W. R Relation of nutrient salt concentration to growth of the tomato and to the incidence of blossom-end rot of the fruit. Plant Physiol. 12: Rolfs, P. H Tomato disease. Pla. Agr. Expt. Sta. Bui Spencer, E. Lr. and Beckenbach, J. R Blossom-end rot of tomatoes. Fla. Agri. Exp. Sta. Circular S Weber, G. F Blossom-end rot of toma toes. Fla. Agric. Exp. Sta. Press Bui WEED CONTROL IN PEPPERS GROWN ON ORGANIC SOILS* V. L. Guzman and E. A. Wolf Everglades Experiment Station Belle Glade The experiments herein reported were con ducted in an attempt to find effective herbi cides for peppers growing on the organic soils of the Everglades. Screening herbicides for peppers was initiat ed in 1952 and has continued to date. The following chemicals selected from the screen ing trials were used in these studies: isopropyl- N (3-chlorophenyl) carbamate (CIPC); 2- methyl-4-chlorophenoxyacetic acid (MCP); 3-p-chlorophenyl-l-l-dimethylurea (K a r m e x W); sodium trichloroacetate (TCA); octachlorocyclohexenone (Oktone); sodium a, a- dichloropropionate (Dalapon); 2, 4-dichlorophenoxyacetic acid (2, 4-D); disodium 3, 6-endoxohexahydrothalate (Endothal 33); pentachlorophenol (PCP); oc -chloro-n, N- diallylacetamine (CDAA); oc-chloro-n, N- diethylacetamine (CDEA); and 2-chloroallyl diethyldithiocarbamate (CDEC). All herbi cides were applied in 3 gallons of water per acre except Oktone and pentachlorophenol, which were applied in diesel oil at the same rate per acre. Pre-emergence treatments were applied after the ground was well compacted by rolling. Mechanical cultivation followed the disappearance of the effect of a given herbicide where no post-emergence treatment was employed. * This work was made possible in part by grants from. B. F. Goodrich Chemical Company and Columbia Southern Chemical Corporation. Pre-Emergence Experiments Two experiments were carried out in the spring of 1954 in a commercial field. Treat ments used and results obtained from one experiment are presented in Table 1. The herbicides used were similar to the hand hoed and cultivated check in effects on weeds, stand of plants and yields of peppers, except in the case of CIPC, which killed the plants. Endothal 33 gave good control of weeds but its effect disappeared quite rapidly and consequently this herbicide does not appear worthy of further trial. Observations on the appearance and develop ment of the plants during the growing period indicated that Oktone was the most effective herbicide. Pepper plants in the Oktone plots were usually equal in appearance and some times better than those grown in the check plots, particularly during the first two months. TCA proved to be the second best herbicide, but it works chiefly as a grass toxicant. Pep per plants from the TCA plots were slightly smaller than those from the check plots dur ing the initial stages of growth. In this experiment, yields were not statis tically different from the check in spite of very low yields with some herbicides due to large variation within treatments. It should be noted, however, that the yield from the Oktone treated plots was similar to the check. The second experiment was designed to ob tain information on effectiveness of various rates of Oktone. Table 2 lists the rates used and their effects on weeds, stand of pepper plants, and yields of marketable fruit. While