380 FLORIDA STATE HORTICULTURAL SOCIETY, 1974

INCREASING YIELD OF 'PARVIN' AND '' ON LAKEWOOD SAND BY INCREASED NITROGEN AND POTASSIUM FERTILIZATION1

T. W. and R. C. J. Koo variations, data for a greater number of years are desirable for tree crops. Therefore, in 1969, a NK I FAS Agricultural Research and Education Center fertilizer rate experiment was started in adjacent Homestead and Lake Alfred blocks of Tarvin' and 'Kent' trees in the same grove. This is a report of the results for 4 Abstract Mature Tarvin' and 'Kent' mango years. ( indica L.) trees on Lakewood fine sand were fertilized for 4 crop years with 2 levels each of N and K in factorial combinations. In Materials and Methods creasing N fertilization 3X increased yield sig The soil in the experimental grove was Lake- nificantly on both varieties the fourth year and wood fine sand with a reddish brown horizon start for the 4-year average. Increasing K fertilization ing at about 40 inches depth. Shortly before ex 3X increased yield of Tarvin' significantly in the perimental treatments were started, the plots were second and fourth years, and for the 4-year av limed with Aragonite at the rate of 12 tons per erage. Highest yields on Tarvin' were obtained acre. This was a precaution against excessive with high rates of both N and K fertilization. K breakdown in flesh of fruit while still on the tree, rates had no significant effect on yield of 'Kent'. especially on trees fertilized heavily with N (6). There was no readily measurable difference among The pH and Ca content of the soil at 0-6 and 6-12 treatments in incidence of physiological break inch depths in 1969, 10 months after liming, and down in the flesh of fruits. Correlation between at termination of the experiment in 1973, about treatment and leaf concentration of N and K was 4% years after liming, are given in Table 1. generally good. A heavy crop tended to decrease The Tarvin' trees were 16 and 'Kent* trees 20 the level of N and K in leaves, but crop size or years old at the beginning of the experiment. They treatment had no consistent effect on Ca concen were planted at a spacing of 25 by 25 feet. For the tration in leaves. 3 years just prior to the experiment, they were fertilized with mixtures which supplied approxi Light N fertilization has been suggested for mately 0.6 pound of N and 0.8 pound of K20 per fruit production on '' mango in Florida on tree per year to Tarvin' trees and 0.9 pound of N calcareous rock soil (1, 2). Yield of 'Haden' man and 1.2 pounds of K2O per tree per year to 'Kent' gos in Florida on well drained, acid, sandy soil was trees. There was no irrigation or cultivation. Weeds not affected by increasing ratesof fertilizer (3). were controlled by mowing. On the other hand, substantial increases in yield Experimental fertilizer treatments were 2 of 'Kent' mangos on similar soil resulted from in levels each of N and K in factorial combinations. creasing N fertization to around 4 or 5 pounds per These treatments were made on single-tree plots, tree per year (4, 7), with a smaller increase in buffered on all sides, and the4 treatments repli yield from increasing K2O fertilization to about 5 cated 10 times in randomized blocks. Application pounds per tree per year (7). The first of these of other nutrients (P and Mg in fertilizer and Mn, studies with 'Kent' was a short-term exploratory Cu, Zn, B, Fe and S in foliar sprays) was held test with a small number of trees (4). The second constant. Top height and width of the trees were study, in the same grove at Boynton, was termi measured and trees selected so as to have uniform nated with only 4 years of yield data because of top size within each replicated block of 4 trees. storm damage to the trees. Because of seasonal All trees in the experimental blocks were fer tilized once a year with mixed fertilizer in late summer or fall after harvest. This basic over-all lFlorida Agricultural Experiment Stations Journal Series No. 5650. treatment (NjKJ was at a slightly lower rate on The authors areindebted to Mr. James T. Miner of Tarvin' trees than on 'Kent' trees. It was supple Boynton Beach for use of trees, labor, equipment and sup plying fruit necessary to conduct this investigation. Thanks mented with calcium nitrate and potassium chloride and appreciation are extended to him for his helpful advice and suggestions during course of the work. (NL,K2) in 2 equal applications in early fall and in YOUNG & KOO: INCREASING MANGO YIELD 381

Table 1, Soil pH and Ca content

Parvin Kent 0-6" depth 6-12" depth 0-6" depth 6-12" depth lbs/A lbs/A lbs/A lbs/A Year PH Caz PH Ca PH Ca PH Ca

1969 6.0 2700 6.1 700 6.1 2200 5.7 400 1973 6.5 3000 6.3 1300 6.5 2200 6.3 1000

Z Extractable with 1 N ammonium acetate, pH 7,0. mid-winter each year. It has been demonstrated fruits in the field at harvest. Leaf samples for that fertilizer timing has no measurable effect on N, K and Ca determinations were taken in April yield of mangos on sandy soil in Florida (3), but 1971, 1972 and 1973 by treatments. supplemental fertilization was divided to reduce In general, weather conditions were favorable the possibility of significant leaching by excessively for mango production during most of the experi heavy rains that may occur. The total annual rates mental period. Rainfall was usually sufficient and per tree of N and K2O from the basic fertilization fairly well distributed. There was no severe cold. plus supplemental fertilization for the 4 treatments In 1970 and 1971 there were a few periods of short each year are listed in Table 2. duration of relatively low temperatures during Yields were taken by weight at harvest. Pick bloom that might have affected fruit set slightly. ing was done at intervals of 3 to 4 days as fruit In 1972 the season was unusually warm with ample matured. The number of pickings within a given rainfall. Trees of both varieties tended to remain season differed slightly with variety and considera vegetative at bloom time and bloom was generally bly among seasons because of variation in length light and scattered. The crop on each variety was of blooming period. The average was 10 pickings poor. Climatic conditions were near ideal for mango per season. Frequent inspections were made for production in the 1973 season. A heavy bloom set incidence of physiological breakdown in the flesh and matured a record crop on both varieties. of fruits by cutting representative numbers of

Table 2» Total annual N and K2O fertilization rates.

Pounds per tree per year NlKl N2K1 N]K2 N2K2 Variety Year N K20 N K2O N K2O N K2O

Parvin 1970 0.6 0.8 1.8 0.8 0.6 2.4 1.8 2.4 1971 0.9 0.9 2.7 0.9 0.9 2.7 2.7 2.7 1972 0.8 0.9 2.4 0.9 0.8 2.7 2.4 2.7 1973 0.8 1.0 2.4 1.0 0.8 3.0 2.4 3.0

Kent 1970 0.9 1.2 2.7 1.2 0.9 3.6 2.7 3.6 1971 1.0 1.0 3.0 1.0 1.0 3.0 3.0 3.0 1972 0.9 1.1 2.7 1.1 0.9 3.3 2.7 3.3 1973 0.9 1.2 2.7 1.2 0.9 3.6 2.7 3.6 382 FLORIDA STATE HORTICULTURAL SOCIETY, 1974

Results and Discussion quirement of 'Kent' may be lower than that of 'Parvin', and thereby the response to increased K Yields increased significantly with increased N fertilization was less marked. The higher leaf con fertilization on 'Parvin' the fourth year and for tent of K in 'Kent' than in 'Parvin' in the heavy the 4-year average, and tended to increase the sec crop years of 1971 and 1973 (Table 4) lends sup ond and third years (Table 3). Increasing K fer port to this hypothesis. It appears that the reduc tilization significantly increased yields the second tion in K content of 'Kent' leaves by a combination and fourth years, and for the 4-year average, with of moderate vegetative growth and heavy crop was a trend to increase yield the third year. Highest moderate, whereas on 'Parvin' with both heavy yields on 'Parvin' were obtained with high rates of vegetative growth and heavy crop the reduction in both N and K fertilization. leaf K was considerably greater. Increasing N fertilization on 'Kent' tended to increase yields each year, with the difference be Observations indicate that with temperatures below about 40 F but above freezing during bloom, coming significant the fourth year and for the 4-year average (Table 3). The increases in yield seed abortion and production of small, seedless on 'Kent' from increased N fertilization, especially fruits, which generally shed regardless of nutri for the first 3 years, were considerably smaller tion, are less likely in 'Kent' mangos than in some than obtained previously (7). These smaller yields other varieties, including 'Parvin'. If such tem may have been due partly to lower rates of fer peratures had occurred frequently during the 4 tilization used in the present than in the previous seasons of this study, the yield response of 'Par study. Another cause may have been that tree tops, vin', as compared with that of 'Kent', to increased reduced in size by the storm several years earlier, fertilization might have been less favorable. had not yet reached their original full size. It has been found that physiological breakdown A trend for yields to increase with increased K in the flesh of 'Kent' mangos while still on the tree fertilization occurred on 'Kent' the second, third is aggravated by heavy N fertilization on light and fourth years, and for the 4-year average, but sandy soils in Florida, but is alleviated to some it was not statistically significant. The low yield extent by a high level of Ca in the tree (6). In response of 'Kent'* as compared with 'Parvin', to cidence of physiological breakdown in fruits of increased K fertilization perhaps resulted from the both varieties in this experiment varied consid characteristically less vegetative activity normally erably from picking to picking and from season to found in 'Kent' than in 'Parvin'. Thus, the K re season. No correlation was found between in-

Table 3O Yield of 'Parvin1 and 'Kent1 mango trees for 4 years -

main effect means • Pounds of fruit per tree Parvin Kent Treat. 1970 1971 1972 1973 Avg 1970 1971 1972 1973 Avg.

Nl 97 518 85 630 332 308 709 78 873 492 N2 90 621 121 760 398 328 749 107 988 543

Kl 89 497 97 629 328 334 722 70 915 510 K2 97 642 110 761 403 302 737 116 945 525

Sigo N ns ns ns ** ** ns ns ns * *

K ns ns ** ** ns ns ns ns ns

.A. NXK ns ns ns ns ns ns ns ns

Statistical significance: ns not significant. * significant at 5% level. ** significant at 1% level. YOUNG & KOO: INCREASING MANGO YIELD 383 cidence of breakdown and treatment for either va light in 1972. The N and K levels in leaves in the riety. For the 4 seasons, Tarvin' had an average heavy crop years were lower in all treatment than of 14% defective fruits as compared with 9% for in the light crop year. Crop size had no consistent 'Kent*. While these defective fruits would not be effect on Ca level in leaves. The N, K and Ca con suitable for shipping, often a considerable portion centration of all samples were within the desirable can be used in local trade. range tentatively set for Florida mango leaves, ex It is possible that the difference between the 2 cept for K which often, especially in 'Kent', was varieties in incidence of the breakdown may be due higher than the suggested maximum (8). to an inherent difference in ability to absorb Ca Calcium nitrate was used as the source of sup from the soil. The Ca level in leaves of Tarvin' plemental N because it tends to increase the Ca trees in this study generally was lower than in level in the tree and thereby reduce physiological 'Kent' leaves (Table 4). Unpublished data by these breakdown in fruit (6). However, there was little authors indicate that 'Kent' generally has a higher difference in the Ca level of leaves from trees re level of Ca in leaves than several other commercial ceiving calcium nitrate (N2 treat.) and those that Florida mango varieties, including Tarvin'. did not (Nj treat.) (Table 4). Although K and Ca Correlation between treatment and leaf concen in the soil tend to retard absorption of each other tration of N and K generally was good (Table 4). by the plant, the levels of K and Ca in leaves from Crop size appeared to affect the N and K concen this experiment (Table 4) did not indicate that tration in the leaves. The crop on both varieties measurable interference in absorption of either was heavy in 1971 and 1973, and comparatively element resulted from the supplemental fertilizer

Table 4« N, K and Ca concentration in 'Parvin1 and 'Kent1 mango leaves - main effect means. Parvin Kent dry weight Year Treat. N K Ca N K Ca

Ni 1.12 0.80 2.45 1.19 0.87 2,68 1.11 0.72 2.51 1.28 0.87 2.86 1971 N2 Kl 1.10 0.73 2.54 1.23 0.81 2.63 K2 1.13 0.79 2.41 1.24 0.93 2.91

Nl 1.26 1.01 2.32 1«29 0.95 2.90 1.08 2.31 1.39 0.94 2.87 1972 N2 1.36 Ki 1.28 0.96 2.19 1.25 0.87 3o00 % 1.34 1.13 2.44 1.43 Io06 2.77

Nl lolO 0.52 2.86 1.09 0.57 3.06 1.19 0.46 2.55 1.10 0.60 2.69 1973 N2 K]_ 1.15 0.45 2.62 1.08 0.57 2.94 K2 1.15 0.53 2.79 1.11 0.60 2.81 384 FLORIDA STATE HORTICULTURAL SOCIETY, 1974

treatments with calcium nitrate and potassium Literature Cited

chloride. 1. Ruehle, Geo. D. and R. B. Ledin. 1960. Mango growing The production cost of additional fruit obtained in Florida. Fla. Agr. Ext. Serv. Bui. 174. 2. Wolfe, H. S. 1933. Variety Tests of Minor Fruits and by increased N and/or K fertilization would be Ornamentals. Fla. Agr. Exp. Sta. Ann. Rept. 201. 3. Young, T. W. 1959. Mango fruitfulness. Fla. Agr. Exp. only the cost of the extra fertilizer. This cost, Sta. Ann. Rept. 365. using ammonium nitrate and potassium chloride as 4. and James T. Miner. 1960. Response of 'Kent' mangos to nitrogen fertilization. Fla. State Hort. Soc. fertilizer sources for the extra N and K necessary Proc. 73:334-336. to obtain the maximum rates used in this experi 5. . 1961. Mango fruitfulness. Fla. Agr. Exp. Sta. Ann. Rept. 353. ment, would be about 50^ for N and 20^ for K per 6. , R. C. J. Koo and James T. Miner. 1962. Effects of nitrogen, potassium and calcium fertilization on tree per year at present prices. Based on fruit 'Kent' mangos on deep, acid, sandy soil. Fla. State Hort. prices for the past few years, 10 to 15 pounds of Soc. Proc. 75:364-371. 7- , , and . 1965. Fertilizer fruit easily would have covered the cost of both trials with 'Kent' mangos. Fla. State Hort. Soc. Proc. 78: 369-375. the extra N and K. In this experiment, increased 8. and R. C. J. Koo. 1969. Mineral composi yields from increased fertilization amounted to con tion of Florida mango leaves. Fla. State Hort. Soc. Proc 82:324-328. siderably more than this, except for increased K on 'Kent'.

TWO MAJOR PEST PROBLEMS OF PAPAYAS

D. O. Wolfenbarger and S. D. Walker High degrees of aphid repellency by aluminum delayed the onset of virus infections and increased IF AS, Agricultural Research and Education Center yields of squash and tomatoes (3, 6). Aluminum Homestead foil, aluminum scrap metal, aluminum paint, alum inum laminated with plastics and paper, clear, Abstract. Virus disease inocula vectors be white and black plastics were tested as mulches of lieved principally the green peach aphid, Myzus squash and tomato, then papaya plants. Although persicae (Sulzer), and the payaya fruit fiy, Toxo- there were varying degrees of aphid repellency and trypana curvicauda Gerst, are the two most im of delayed virus infections aluminum sheeting were portant insects affecting papaya production in the most effective. Some comparisons of papaya, Florida, the control of which is only partially squash and tomato plants are considered. Papaya achieved. plants are taller, wider, (except where runners are involved) and live longer than squash and to Papaya production in Florida is limited by two mato plants. Increased heights and areas of papaya insect pests. These are 1) the vectors of the virus plants require more aluminum (or other mulch) diseases (1) believed to be principally the green around them than smaller plants. These increased peach aphid, Myzus persicae (Sulzer), and 2) the coverings of mulch for longer time periods in papaya fruit fly, Toxotrypana curvicauda Gerst. creased the frequency of tearing, decaying (with Although papaya production is a crop of minor paper), rolling and destruction of the mulch which importance in south Florida it is a partial liveli impaired or eliminated its effectiveness. hood for some individuals and is a desirable prod A number of tests showed that on the younger uct in spite of the insect pests. No practical nor and smaller plants virus infections were delayed on facile method has been developed for control of the mulched plants. After the plants were about these problems. Attempts to control them are dis four months of age or four feet in height the in cussed briefly. cidences of virus symptoms became nearly equal on the mulched and the unmulched plants. Heights, Papaya Virus Diseases and Insect Vectors ages, requirements of plants and mulch disintegra tion forced abandonment of the mulch trials. Insecticides have not been effective for the con Heavy and repeated applications of balanced trol of aphid borne virus diseases. None was tested fertilizer with abundant watering produces plants on papayas. which grow and produce some fruit even though