Chemical thinning of ‘Fuji’ apples in Southern Brazil with consideration of economic aspects

Chemical thinning of ‘Fuji’ apples in Southern Brazil with consideration of economic aspects

Scientia Horticulturae, 34 (1988) 21-32 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands 21 Chemical thinning of 'Fuji' Ap...

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Scientia Horticulturae, 34 (1988) 21-32 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

21

Chemical thinning of 'Fuji' Apples in Southern Brazil with Consideration of Economic Aspects A. EBERT and C.L. KREUZ

Research Station of Cacador, EMPASC, C.P. D-l, 89.500 Caqador, SC (Brazil) (Accepted for publication 18 May 1987)

ABSTRACT Ebert, A. and Kreuz, C.L., 1988. Chemical thinning of 'Fuji' apples in Southern Brazil with consideration of economic aspects. Scientia Hortic., 34: 21-32. Experiments were carried out using the apple cultivar 'Fuji' and the thinning agents NAA, NAAm, carbaryl and ethephon in single and combined sprays, adding either a non-ionic wetting agent or an emulsifiable mineral oil as an adjuvant. Economic analyses were included to select the most profitable treatments. In most thinning treatments the use of mineral oil as an adjuvant improved thinning intensity and mean fruit weight. Ethephon sprays increased fruit set in the light-crop year 1983/84, but had no thinning effect in the heavy-crop year 1984/85. However, taking into account fruit set in both years as well as potential profit, the best treatments proved to be the single sprays NAAm and NAA, applied at 8 days AFB using mineral oil as an adjuvant, and a combination spray of NAAm at FB plus 8 days followed by a later spray (FB + 21 days ) of carbaryl. Both thinning agents were applied at low concentrations and with mineral oil as an adjuvant. All three treatments effectively reduced fruit set in the heavy-crop year to a fruit load density similar to that of hand-thinned trees. From an economic point of view the same treatments were superior to hand thinning when considering both years of observation. Keywords: carbaryl; chemical thinning; ethephon; hand thinning; Malus domestica; mineral oil; naphtaleneacetamide; naphthalene acetic acid. Abbreviations: AFB=after full bloom; F B = full bloom; NAA=naphthaleneacetic acid; NAAm = naphthaleneacetamide; TCA = trunk cross-sectional area.

INTRODUCTION

The Japanese apple 'Fuji' recently became the most planted apple in the state of Santa Catarina, South Brazil. It is a late-season cultivar with a long growing period; about 180 days between FB and harvest. It is harvested about 20 days after 'Golden Delicious'. Thinning in this cultivar is essential because of the high percentage of small-sized fruit, mainly due to its alternate bearing 0304-4238/88/$03.50

© 1988 Elsevier Science Publishers B.V.

22 behaviour and the predominating weak spur and lateral buds, which develop only a few small rosette leaves. Due to insufficient chilling during the mild winter, the prolonged flowering period of apple trees in Southern Brazil makes it difficult to establish optimal application dates for thinning agents. Early applications of NAA and its amide salt are necessary to get satisfactory thinning results without growth inhibition of part of the remaining fruit (Marsh et al., 1960; Link, 1967, 1969; Flore, 1978). However, such applications frequently do not affect weak flower buds which were formed late in the previous season resulting in delayed bud break. Therefore, these buds escape thinning and result in small fruit at harvest. Moreover, the normally dry, warm weather in the post-bloom period causes rapid drying of the applied thinning agents, frequently resulting in reduced thinning. Previous experiments had shown that 'Fuji' is difficult to thin chemically (Ebert and Bender, 1984). The same observations were made by Tiscornia and Iuchi (1984) under comparable climatic conditions. Combining chemicals to improve thinning, as suggested by several workers (Horsfall and Moore, 1964; Unrath, 1978, 1979; Grauslund, 1981; Looney and McKellar, 1984), led to good results in 'Fuji' (Ebert and Bender, 1984). Furthermore, favourable results were obtained in 'Gala' and 'Fuji' (Ebert and Bender, 1984) with the use of mineral oil as an adjuvant for carbaryl, as recommended by Byers (1978) as well as by Comai and Widmann (1980). This also led us to test other thinning agents like NAA, NAAm and ethephon, in single and combination sprays, together with this spray additive. Economic analyses were included in these experiments in order to select the most profitable treatments. MATERIALSAND METHODS The experiments were conducted during the growing seasons of 1983/84 and 1984/85 in a commercial apple orchard at Fraiburgo/Santa Catarina, South Brazil, using 9-year-old apple trees of 'Fuji' on M 7 rootstocks. The experimental design was a randomized block with 4 replicates per treatment. The thinning agents were applied with either a non-ionic wetting agent (chemical name, nonyl phenol polyethylene glycol ether; commercial name, ADESIN BR) at a concentration of 0.8 ml 1-1 or an emulsifiable mineral oil (commercial name, ASSIST) at 2500 mg 1-1. Trees were thoroughly wetted using a hand lance. Size-selective hand thinning was carried out 30 days AFB. The treatments were applied as detailed in Table I. Treatments 5 and 7 were only carried out during 1984/85. The weather conditions during application are given in Table II. In 1983/84 mean fruit size reached 12.6 mm diameter at 21 days AFB with 65.5% of the fruit reaching a diameter of 10 mm or more. In 1984/85, mean fruit size was

23 TABLE I Thinning treatments and application dates Treatments

Concentration (mg l - 1)

Application time (days AFB )

1 = NAAm + wetting agent 2 = NAAm + mineral oil 3 = NAAm + mineral oil + carbaryl + mineral oil 4 = NAA + wetting agent 5 = NAA + wetting agent 6 = NAA + mineral oil 7 = NAA + mineral oil 8 = NAA + carbaryl + wetting agent 9 = NAA + carbaryl + mineral oil 10 = NAA + ethephon + wetting agent 11 -- Carbaryl + wetting agent 12 -- Carbaryl + mineral oil 13 = Carbaryl + wetting agent 14 = Ethephon + mineral oil 15 = Ethephon + carbaryl + mineral oil 16 = Ethephon + carbaryl + wetting agent 17 = Harvarde + wetting agent 18 = Hand thinning 19 = Control (no thinning)

6O 6O 35 450 15 15 15 15 7.5 + 450 7.5 + 450 7.5 + 30O 850 850 1700 300 300+450 300+450 400

8 8 8 21 8 16 8 16 16 16 16 21 21 21 21 21 21 21 3O

TABLE II Weather conditions during the application of the thinning treatments Year

Application time (days AFB) 8

1983/84

Temperature ( ° C) Relative humidity (%RH)

19-24 55-65

1984/85

Temperature (°C) Relative humidity (%RH)

23-29 55-65

16

21 22-27 45-55

22-25 65-75

15-24 60-75

10.8 m m d i a m e t e r a t 21 d a y s A F B w i t h 65.2% o f t h e f r u i t r e a c h i n g a d i a m e t e r o f 10 m m o r m o r e . For economic analyses, partial costs were calculated taking into account the costs of the t h i n n i n g a g e n t s a n d the l a b o u r costs of s p r a y a p p l i c a t i o n a n d h a n d t h i n n i n g . A s t h e l a b o u r n e e d e d for h a r v e s t o f t h e f r u i t v a r i e s w i t h c r o p load, t h e s e v a r i a b l e c o s t s b e t w e e n t r e a t m e n t s w e r e also c o n s i d e r e d .

24

TABLE III Effect of thinning treatments during the light-crop year 1983/84 on fruit load density (number of fruit at harvest cm -2 TCA), mean fruit weight, yield, fruit size distribution (percentage values were arcsine transformed) and return bloom (number of flower clusters per cm limb circumference ). Mean separation within columns by Tukey's procedure (Steel and Torrie, 1981 ) at the 5% level

Treatment

Fruit

Mean

Yield

Yield

load density

fruit weight

(g c m - 2 TCA )

(tons h a - ~)

386 ab 362 ab

Size classes

Return bloom

< 60 mm

60-69 mm

>~70 mm

21.6 abed 21.5 abed

28.6 bed 31.0 bcde

39.6 ab 38.8 abed

37.1 ab 35.5 b

2.6 abed 2.1 cd

526 a

30.4 a

28.0 abe

36.4 abed

40.6 ab

2.6 abcd

(g) 1 2

3.74 abe 3.37 ab

3

4.65 abe

103.8 ede 108.8 abcde 113.0 ab

4 6

2.74 a 3.43 ab

110.6 abed 107.0 bcde

304 b 366 ab

14.6 d 19.9 bed

29.5 bcde 31.0 bcde

36.2 bed 35.2 bed

39.4 ab 38.9 ab

1.8 d 2.4 abcd

8 9 10

4.03 abe 3.18 ab 4.82 abe

107.2 bcde 111.6 abc 103.2 de

437 ab 353 ab 490 ab

20.2 bed 18.2 cd 28.0 ab

29.3 bcde 32.6 cde 30.8 bcde

39.0 abe 34.8 cd 39.1 abe

36.8 ab 38.3 ab 35.3 b

2.2 cd 1.8 d 3.0 abed

11 12 13

3.75 abe 4.03 abe 3.52 ab

102.0 ef 114.0 ab 107.0 bcde

377 ab 458 ab 377 ab

17.2 cd 21.0 abcd 20.1 bcd

30.7 bcde 22.6 a 30.1 bcde

38.8 abe 38.9 abc 37.4 abed

35.8 ab 42.1 a 37,9 ab

3.6 a 3.1 abe 2.6 abed

14 15 16

5.80 c 3.16 ab 5.05 bc

106.2 bcde 104.7 cde 106.8 bcde

435 ab 331 b 538 a

25.4 abe 17.1 cd 27.8 ab

27.9 abe 34.0 de 31.9 bcde

37.7 abed 36.6 abed 35.2 bcd

39.2 ab 35.0 b 38.4 ab

2.3 bed 2.5 abed 3,4 ab

17

4.23 abe

104.6 cde

439 ab

24.0 abed

31.6 bcde

34.1 d

39.6 ab

2.6 abed

18

3.14 ab

116.6 a

365 ab

17.6 cd

26.7 ab

41.0 a

37.2 ab

2.4 abed

19

3.89 abe

94.4 f

367 ab

22.1 abcd

34.4 e

36.6 abed

34.4 b

2.0 cd

The price of apples varies considerably according to size. These differences were taken into account when calculating the income from each treatment on a per hectare basis. The partial costs mentioned above were subtracted from this income, resulting in partial profit. The partial profit is given in the Brazilian currency, "Cruzado", where 13 cruzados and 80 cents were equivalent to one US-dollar in June 1986. RESULTS L i g h t - c r o p y e a r 1983/84. - - Treatment 4 (see Table I) resulted in the lowest

fruit load density (Table III ). It was the only treatment which presented overthinning. Treatments 14 and 16 substantially increased fruit load density. The use of mineral oil as an adjuvant in the combination spray of ethephon plus carbaryl (Treatment 15) resulted in similar fruit load density to hand thinning, whereas the use of a wetting agent in the same combination spray (Treat-

25 MEAN 1983/84 CZ$1000

1983/84

1984/85

1

1984/85

I

D

::fllI1ill ii HillIliiilB (

2

3

4

5

6

7

8

9

I()

II

12

13

14

15

16

17

18

19

TREATMENTS

Fig. 1. Partial profit ( CZ$1000) of two consecutive crops after different thinning treatments. The horizontal line in the graph marks the mean of both years of observation of hand-thinned trees (Treatment 18). m e n t 16) increased fruit set in c o m p a r i s o n with u n t h i n n e d trees ( T r e a t m e n t

19). As a result of Treatments 3, 4, 9, 12 and 18 (see Table I), relatively high mean fruit weights were obtained (Table III). Only Treatment i i showedno significant increase in mean fruit weight comparedto control trees. Surprisingly,the combinationsprays of Treatments 3, 10 and 16 resulted in significant improvement in mean fruit weight in comparisonwith unthinned trees, even though fruit load density was considerablyincreased. The highest yields in gcm -2 TCA and in tons ha -I (Table III) were obtained with Treatments 3, 10 and 16 (see Table I). Treatments 4 and 15 showed unacceptablylow yields. Treatment 12 (see Table I) was the most effectivein reducing small-sized fruit ( < 60 mm) and increasingpercentage fruit with a diameter of >~70 mm (Table III). Treatments I, 3, 14 and 18 also significantlyreducedthe percentage fruit with diameter < 60 ram, but did not present significantdifferencesin comparison with the control (Treatment 19) in the size-class >~70 mm. OnlyTreatments 11 and 16 (see Table I) significantlyincreasedreturn bloom in comparisonwith Treatment 19 (Table Ill). SurprisinglyTreatment 4, with the lowestfruit load density, also resulted - - together with Treatment 9 - - in the lowest return bloom. From an economicpoint of view Treatments 3, I0 and 16 - - combination sprays of chemicals (see Table I) - - were, together with Treatment 14, the most profitable (Fig. I). Most chemical treatments were superior to hand thinning (Treatment 18). Only Treatments 4 and 15 showed lower partial profit than Treatment 18. While Treatment 18 was less profitable than the control (Treatment 19), this was not the case with the chemicalTreatments 3, 8, 10, 14, 16 and 17.

26 TABLE IV Effect of thinning treatments during the heavy-crop year 1984/85 on fruit load density (number of fruit at harvest cm -2 TCA), mean fruit weight, yield and fruit size distribution (percentage values were arcsine transformed). Mean separation within columns by Tukey's procedure ( Steel and Torrie, 1981 ) at the 5% level Treatment

1

Fruit load

Mean fruit

density

weight (g)

96.8 bcd 100.9 b

Yield (g cm -~ TCA)

Yield (tons ha-1)

690 abc 582 bcde

Size classes < 60 mm

60-69 mm

>/70 mm

43.2 abcd 39.7 bcd

38.8 bcdef 32.7 ab

40.3 cd 42.5 abcd

24.3 abcde 29.7 ab

550 cde

35.5 cd

33.4 abc

47.3 ab

23.0 bcdef

33.4 43.3 27.8 41.9

45.6 abcd 43.4 abcd 45.8 abc 42.1 bcd

25.2 abcd 13.8g 30.4 a 17.9 defg

2

7.3 bcdefg 5.8 abc

3

5.9 abc

94.2 bcde

4 5 6 7

6.0 abcd 8.6 g 4.7 a 5.6 ab

100.5 b 86.7 fgh 109.3 a 91.6 cdefg

604 abcde 730 ab 517 de 510 e

40.4 49.5 36.0 35.4

8 9 10

8.3 fg 6.6 bcdef 7.6 cdefg

87.9 efgh 94.0 bcdef 82.7 h

731 ab 614 abcde 626 abcde

51.0 a 44.5 abcd 50.5 ab

39.8 bcdef 35.3 abcd 39.4 bcdef

43.2 abcd 48.6 a 46.3 abc

18.9cdefg 18.3 defg 14.6 g

11 12 13

8.9 g 6.1 abcde 7.0 bcdefg

85.7 gh 89.5 defgh 87.3 efgh

754 a 545 cde 616 abcde

43.8 abcd 43.6 abcd 40.7 abcd

38.1 bcdef 39.4 bcdef 37.7 bcde

46.0 abc 43.7 abcd 45.4 abcd

17.6 efg 19.5cdefg 19.7cdefg

14 15 16

7.3 bcdefg 7.4 bcdefg 8.1 fg

83.8 h 86.4 gh 82.2 h

608 abcde 638 abcde 662 abcde

41.2 abcd 46.1 abcd 46.7 abc

43.8 ef 44.0 ef 40.8 cdef

42.4 abcd 41.4 bcd 44.9 abcd

14.6g 16.4 fg 15.6g

17

7.8 defg

82.5 h

638 abcde

42.1 abcd

45.6 f

39.5 d

16.3 fg

18

5.7 abc

98.6 bc

561 cde

41.3 abcd

33.3 abc

44.9 abcd

26.0 abc

19

8.0 efg

84.3 gh

669 abcd

44.5 abcd

39.5 bcdef

43.8 abcd

19.3 cdefg

abcd ab cd d

abc ef a def

H e a v y - c r o p y e a r 1984/85. - - While still not presenting over-thinning, Treat-

ment 6 (see Table I ) was the only chemical treatment which reduced fruit load density to a lower level than hand thinning (Table IV). Moreover, in comparison with the control (Treatment 19), a significant reduction of fruit load density to approximately the same level as hand-thinned trees (Treatment 18) was obtained with Treatments 2, 3, 4 and 7. With late NAA sprays at 16 days AFB, the addition of a wetting agent (Treatment 5) slightly increased fruit set, while the use of mineral oil as an adjuvant (Treatment 7) provided satisfactory thinning. The same behaviour of both additives was found in the com-

27 bination spray of NAA plus carbaryl (Treatments 8 and 9). However, Treatment 9 was rather less effective than Treatment 7. While carbaryl at 850 mg 1-1 with a wetting agent as additive (Treatment 11 ) increased fruit load density, the same thinning agent resulted in reasonable thinning when mineral oil was used as an adjuvant (Treatment 12). Carbaryl applied in double concentration at 1700 mg l-1 (Treatment 13 ) was less effective than Treatment 12. Treatments containing ethephon (Treatments 10, 14, 15 and 16) or harvarde (Treatment 17) hardly had any thinning effect. Treatment 6 (see Table I), giving the lowest fruit load density, presented the highest mean fruit weight (Table IV). Significant improvement in mean fruit weight to about the same level as that of hand-thinned trees (Treatment 18) was measured in Treatments 1, 2, 3, 4 and 7. Treatments 10, 14 and 16, containing ethephon, as well as Treatment 17, resulted in very low mean fruit weights; even lower than Treatment 19 (control). In general, the yields in g cm-2 TCA and in tons h a - 1were very high ( Table IV). Treatment 6 (see Table I) which gave the lowest fruit load density resulted in similar yield per cm 2 TCA as the most productive treatment in the light-crop year (Treatment 3; compare Table III). On a per hectare basis, the yield of Treatment 6 was superior to that of Treatment 3 in the light-crop year. Treatments 5, 8 and 10 presented unusually high yields of approximately 50 tons h a - 1. Treatments 2 and 6 (see Table I) provided the most pronounced reduction in small-sized fruit ( < 60 mm diameter) and the highest increase in fruit with diameter >~70 mm (Table IV). Unacceptably high levels of small-sized fruit and correspondingly low percentages of fruit with diameter >/70 mm were found with Treatments 5, 7, 14, 15, 16 and 17. Considering economic aspects, Treatments 1, 2, 8 and 10 (see Table I) were superior to Treatment 18 - - hand thinning - - (Fig. 1 ). Partial profits slightly inferior to those from hand thinning were obtained with Treatments 4, 9, 11, 16 and 19. Considerably lower partial profits (in comparison with hand thinning) were calculated for Treatments 7, 14 and 17. DISCUSSION In the heavy-crop year, good thinning was obtained with NAA in combination with a wetting agent only when applied early, i.e. 8 days AFB ( Treatment 4; Table IV). This is in contrast to the report of Pereira et al. (1984), who found good thinning in 'Fuji' with relatively late applications (15 or 20 days AFB). The use of NAA with mineral oil instead of a wetting agent as an adjuvant resulted in effective thinning with early ( 8 days AFB ) and late (16 days AFB ) applications (Treatments 6 and 7; Table IV). However, the improvement in

28 mean fruit weight was only satisfactory with early application, resulting in this case in the largest fruit of all treatments. The favourable responses obtained with mineral oil in combination with NAA and NAAm confirm earlier results reported by Ebert and Bender {1986) in the apple 'Gala' under the same climatic conditions. In Southern Brazil temperatures are relatively high during the post-bloom period, resulting in rapid drying of applied chemicals. The use of mineral oil as an adjuvant may keep the thinning agents in solution on fruit and leaf surfaces over a longer period of time, thus increasing the absorption period (Byers, 1978). This might explain the better thinning action of NAA and NAAm when combined with mineral oil. Under the climatic conditions of the Federal Republic of Germany the use of mineral oil as an adjuvant in NAAm sprays on 'Golden Delicious' also significantly improved thinning (Link, 1984 ). Carbaryl at 850 mg l- 1 applied in single sprays ( Treatments 11 and 12 ) only gave satisfactory results when mineral oil was used as an adjuvant, showing better thinning intensity and mean fruit weight than a double concentration ofcarbaryl with a wetting agent as an adjuvant (Treatment 13; Table IV ). The lack of increase in thinning activity of carbaryl when applied at double concentration, also observed by other workers (Tiscornia and Iuchi, 1984), may be due to the low solubility of this substance in water. The use of mineral oil as an adjuvant enhances the thinning activity of carbaryl on 'Golden Delicious', 'Starkrimson Delicious' ( Byers, 1978 ) and 'Starkspur Red' ( Comai and Widmann, 1980) as well as 'Gala' and 'Fuji' (Ebert and Bender, 1984). This effect of mineral oil could be due to an improvement in the solubility of carbaryl in the spray solution and/or a prolonged uptake period by the fruit. In the heavy-crop year, ethephon applied separately (Treatment 14) or in combination with carbaryl (Treatments 15 and 16) or NAA {Treatment 10) did not show any thinning effect or result in greater mean fruit weight compared to unthinned trees (Table IV). In the light-crop year there was only a slight thinning effect from a combination spray of ethephon plus carbaryl with mineral oil as an adjuvant (Treatment 15; Table III). The same combination and an ethephon-NAA combination using a wetting agent as an adjuvant (Treatments 16 and 10, respectively) resulted in increased fruit set (Table III ). The highest increase in fruit set was obtained with ethephon plus mineral oil (Treatment 14). Not only was fruit set substantially increased in these latter treatments, but mean fruit weight was also augmented compared to unthinned trees (Table III). These unexpected results meant that the ethephon spray (Treatment 14) and the ethephon-NAA (Treatment 10) and ethephon-carbaryl (Treatment 16) combinations (with a wetting agent as an adjuvant) in the light-crop year were the most interesting treatments from an economic point of view. These treatments might be used to increase fruit load in orchards with generally poor fruit set or in orchards with alternate bearing during the light-crop year.

29 Child et al. (1986) suggested the application of ethylene inhibitors at flow: ering time to increase initial and final fruit set in apple. It is therefore difficult to understand why ethephon can result in increased fruit set. Ebert and Bangerth (1982) found a 6- to 13-fold increase in ethylene concentration in apple fruit within 24 h after the application of ethephon. One explanation might be that the inhibition of ethylene synthesis by sprays used for fruit-setting is a side-effect rather than the real mechanism by which these substances act (Dennis et al., 1986). The thinning effect of ethephon varies with the cultivar. Besides 'Fuji' there are cultivars like 'Golden Delicious' (Link, 1978; Ebert and Bangerth, 1982) and 'King of the Pippins' (Ebert and Bangerth, 1982) where ethephon sprays sometimes have no thinning effect. In 'Gala', ethephon applied alone or in combination with carbaryl and NAA results in good thinning but also inhibits growth of the remaining fruit (Ebert and Bender, 1986). There are several other cultivars, however, such as 'Jonathan' (Veinbrants and Hutchinson, 1976; Link, 1978), 'Belle de Boskoop' (Link, 1978), 'Glockenapfel' (Link, 1978), 'Laxton's Superb' (Knight, 1978; Wertheim et al., 1978), 'Winston' (Kustermans and Westerlaken, 1978), 'Delicious' (Unrath, 1978), 'Mantet' and 'Benoni' (Wertheim et al., 1978), where good thinning can be obtained without inhibition of fruit growth. An early spray of NAAm at a low concentration followed by a later spray of carbaryl at reduced concentration (Treatment 3) resulted in the most profitable treatment during the light-crop year (Fig. 1 ). In the heavy-crop year the same treatment gave a good thinning response, moderately improving mean fruit weight (Table IV). This combination spray offers some advantages to the growers: (1) the risk of overthinning is minimized due to the low concentrations applied; (2) the second application will eliminate flowers or fruitlets from weak buds, which often open late because of insufficient chilling, producing mainly small-sized fruit. Taking into account potential profit as well as effect on fruit set in both years and aiming at a reduction in the alternate-bearing behaviour of 'Fuji', there are two other treatments besides the NAAm-carbaryl combination spray (Treatment 3) which deserve attention; NAAm and NAA applied at 8 days AFB using mineral oil as an adjuvant (Treatments 2 and 6, respectively). The fruit from hand-thinned trees showed the highest mean fruit weight in the light-crop year ( Table III ), but the yield in tons h a - 1was so low that many chemical treatments were of major interest from an economic point of view (Fig. 1 ). It therefore seems advisable to avoid hand thinning in situations of poor fruit set, even though the fruit may not be ideally distributed over the whole tree. In common with hand thinning, chemical treatments 9, 11 and 15 also gave relatively low yields in the light-crop year (Table III). Treatment 4 - -

30 N A A ÷ w e t t i n g agent at 8 days AFB - - yielded 14.6 tons ha -1, only 2.6 tons more t h a n is necessary to equal production costs ( E b e r t et al., 1987 ). No visible differences between t r e a t m e n t s were found concerning the number of flower clusters per tree in 1985/86. Differences seemed to exist, however, in terms of flower quality. As compared with adequately t h i n n e d trees, plants with a high fruit load density in 1984/85 formed a higher proportion of "weak" flower buds, leading to intensive abscission of flowers and fruitlets after pollination took place. Reduced flower quality, in part, might be related to delayed fruit harvest in the heavily cropping trees, as observed by Williams et al. (1980) in 'Bramley Seedling'. Recent reports indicate t h a t the addition of surfactants to t h i n n i n g agents may improve t h i n n i n g (Noga and Engel, 1986), especially where low concentrations of NAAm or carbaryl are used (Wertheim, 1986). Depending on the material used, surfactant sprays alone result in thinning, as observed by Noga and Bukovac (1986). Similarly, certain types of mineral oil could have a thinning effect on their own. T h e r e f o r e it seems advisable to include controls with only a wetting agent or only mineral oil in further experiments. ACKNOWLEDGEMENTS T h e authors express appreciation to Drs. Margaret and David Evans, Great Britain, for correction of the English manuscript.

REFERENCES Byers, R.E., 1978. Chemical thinning of spur 'Golden Delicious' and 'Starkrimson Delicious'with Sevin and Vydate. HortScience, 13: 59-61. Child, R.D., Atkins, H.A. and Rodriguez,A.F.R., 1986. Effects of suppression of ethylene biosynthesis with aminoethoxyvinylglycine(AVG) on fruit set in Cox's Orange Pippin apple. In: L.C. Luckwill (Editor), Fifth International Symposium on Growth Regulators in Fruit Production. Proc. Fifth Int. Symp. Growth Regulators in Fruit Production, 2-6 September 1985, Bologna-Rimini, Italy. Acta Hortic., 179 (I): 375-376. Comai, M. and Widmann, L., 1980.Diradamento chimicodei frutti di 'Starkspur Red'. Esperienze e Ricerche, 10: 27-34. Dennis, F.G., Jr., Ozga, J.A. and Xia, R.-X., 1986. Endogenous ethylene and apple fruit set. HortScience, Sect. 2, 21 (3): 765 (abstracts, 775 ). Ebert, A. and Bangerth, F., 1982. Possible hormonal modes of action of three apple thinning agents. Scientia Hortic., 16: 343-356. Ebert, A. and Bender, R.J., 1984. Raleio qulmico em macieira (Malus dom~stica Borkh.) cultivares Gala e Fuji. In: SBF/EMPASC (Editors), VII Congresso Brasileiro de Fruticultura. Anais do 7 Congresso Brasileiro de Fruticultura, 25-29 July 1983, FlorianSpolis, SC, Brazil, Vol. 3, pp. 891-902. Ebert, A. and Bender, R.J., 1986. Influenceof an emulsifiablemineral oil on the thinning effect of NAA, NAAm, carbaryl and ethephon in the apple cultivar Gala grownunder the conditions of Southern Brazil. In: L.C. Luckwill (Editor), Fifth International Symposiumon Growth Reg-

31 ulators in Fruit Production. Proc. Fifth Int. Symp. Growth Regulators in Fruit Production, 2-6 September 1985, Bologna-Rimini, Italy, Acta Hortic., 179: (II) 667-672. Ebert, A., Kreuz, C.L., Raasch, Z.S., Zaffari, G.R. and Bender, R.J., 1987. Capacidade de produq~o de macieiras. Florian6polis, EMPASC, Bol. Tec., 41, 23 pp. Ftore, J.A., 1978. Chemical thinning of Paulared and Jerseymac. Compact Fruit Tree, 11:115-119. Grauslund, J., 1981. Chemical thinning of the apple cultivar 'Summerred' with NAA and carbaryl. In: L.C.Luckwill (Editor), Symposium on Growth Regulators in Fruit Production. Proc. Fourth Int. Symp. Growth Regulators in Fruit Production, 21-24 June 1981, Ithaca, NY, Acta Hortic., 120: 77-82. HorsfaU, F., Jr. and Moore, R.C., 1964. Effect of 1-naphthyl N-methylcarbamate (Sevin) on thinning four varieties of apples. Proc. Am. Soc. Hortic. Sci., 82: 1-4. Knight, J.N., 1978. Chemical thinning of apple cultivar, Laxton's Superb. J. Hortic. Sci., 53: 63 -66. Kustermans, C.J. and Westerlaken, J., 1978. Chemische dunning op Winston. Fruitteelt, 68: 561-563. Link, H., 1967. Chemisches Ausduennen mit Pantrin und Geramid Neu. Mitt. Obstbau, 11: 96-101. Link, H., 1969. Vom Einfluss zweier Ausduennungsmittel auf den Bluetenknospenansatz und einige Qualitaetsmerkmale der Fruechte bei 'Golden Delicious'. Obst. Garten, 88:169-171. Link, H., 1978. Results of thinning apples with some chemical compounds. Acta Hortic., 80: 283-286. Link, H., 1984. Gibt es bei der Fruchtausduennung Fortschritte? Obstbau, 9: 222-225. Looney, N.E. and McKellar, J.E., 1984. Thinning of Spartan apples with carbaryl and 1-naphthaleneacetic acid: Influence of spray volume and combinations of chemicals. Can. J.Plant Sci., 64: 161-166. Marsh, H.V., Jr., Southwick, F.W. and Weeks, W.D., 1960. The influence of chemical thinners on fruit set and size, seed development and preharvest drop of apples. Proc. Am. Soc. Hortic. Sci., 75: 5-21. Noga, G.J. and Bukovac, M.J., 1986. Impact of surfactants on fruit quality of 'Schattenmorelle' sour cherries and 'Golden Delicious' apples. In: L.C. Luckwill (Editor), Fifth International Symposium on Growth Regulators in Fruit Production. Proc. Fifth Int. Symp. Growth Regulators in Fruit Production, 2-6 September 1985, Bologna-Rimini, Italy, Acta Hortic., 179 (II) : 771-777. Noga, G. and Engel, G., 1986. Chemische Ausduennung von Aepfeln mit Hilfe von Netzmitteln neue Ansaetze fuer die Praxis ? Erwerbsobstbau, 28 ( 5 ): 141-143. Pereira, A.J., Barradas, C.I.N., Koller, O.C. and Dittrich, R.C., 1984. ConcentraqSes e dpocas de aplicaq~o do ~icido naftalenoacStico na prodwfio e qualidade das maq~s. Pesqui. Agropecu. Bras., 19: 835-844. Steel, R.G.D. and Torrie, J.H. (Editors), 1981. Principles and Procedures of Statistics. International Student Edition 2. McGraw-Hill, Singapore, 633 pp. Tiscornia, J.R. and Iuchi, T., 1984. Raleio qufmico de maq~ no Rio Grande do Sul. In: SBF/EMPASC (Editors), VII Congresso Brasileiro de Fruticultura. Anais do 7 Congresso Brasileiro de Fruticuitura, 25-29 July 1983, Florian6polis, SC, Brazil, Vol. 3, pp. 878-890. Unrath, C.R., 1978. The development of ethephon's thinning potential for spur 'Delicious' apples. Acta Hortic., 80: 233-243. Unrath, C.R., 1979. Ethephon, carbaryl and NAA combinations for thinning spur 'Delicious' with the "tree row volume" technique. HortScience, Sect. 3, 14 ( 3 ) : 429 ( abstracts, 260 ). Veinbrants, N. and Hutchinson, J.F., 1976. Studies on the use of 2-chloroethylphosphonic acid (ethephon) as a thinning agent for Jonathan apples. Aust. J. Exp. Agric. Animal Husb., 16: 937-942. Wertheim, S.J., 1986. Chemical thinning of Golden Delicious apple with NAAm and/or carbaryl in combination with a spreader and the anti-russeting agent GA4+7. In: L.C. Luckwill (Edi-

-

32 tor), Fifth International Symposium on Growth Regulators in Fruit Production. Proc. Fifth Int. Symp. Growth Regulators in Fruit Production, 2-6 September 1985, Bologna-Rimini, Italy, Acta Hortic., 179 (II) : 659- 666. Wertheim, S.J., Scholtens, A. and Bootsma, J.H., 1978. Het chemisch dunnen van enkele beurtjaargevoelige rassen. Fruitteelt, 68: 558-560. Williams, R.R., Arnold, G.M., Flook, V.A. and Jefferies, C.J., 1980. The effect of picking date on blossoming and fruit set in the following year for the apple cv Bramley Seedling. J. Hortic. Sci., 55: 359-362.