Tree shading: an efficient method to control alternate bearing?

310 Archived at http://orgprints.org/13737/i Tree shading: an efficient method to control alternate bearing? Markus Kelderer1, Ewald Lardschneider1, Claudio Casera1 Abstract Conventional and integrated fruit growers, but not organic producers, have the possibility to use thinning agents (e.g. benzyl adenine), which allow crop regulation at a relatively late stage (10-16 mm fruit size). A few surveys have shown that by reducing net photosynthesis after blossom, June fruit drop increases. This could be an interesting new approach for organic apple orchards. Since 2003, different trials have been carried out at the Laimburg Research Station on the variety Golden Delicious rootstock M9 to devise a method for practical use by fruit growers. Unfortunately, there are still several constraints to the practical application of the shading method, not least because it does not sufficiently reduce alternate fruit bearing in the following year. Keywords: apple, June drop, organic orchards, photosynthesis, thinning. Introduction With the exception of hand thinning, there are no available thinning measures in organic fruit growing after blossoming (Kelderer et al., 2003). Further, in the near future even conventional and integrated fruit producers in South Tyrol will lose a thinning agent (Carbaryl) which currently enables them to regulate production at a relatively late point in time (at 10-16 mm fruit size, depending on variety; Waldner 2003). As it is still difficult to evaluate the progress of pollination at earlier time-points, these “late” thinning agents are very popular with producers. Several studies (Corelli, 1994; Bertschinger, 1997; Lafer, 2007) have proven a positive response of June drop to targeted short-term shading of the fruit trees in the post-bloom period. This knowledge could offer a new possibility of thinning for organic apple production and offer a substitute for Carbaryl to conventional producers. Between 2003 and 2006, various field experiments were carried out with the goal of increasing June drop through varying methods. Principally shade nets and various bentonites were used, which in pre-tests were shown to be effective in reducing net photosynthesis for a few days. Material and Methods Test area. – Randomized blocks with quadruple repetition of the treatments were used in all experiments. Each block contained 5 trees (Golden Delicious/M9). The evaluation was made using comparable trees with strong and uniform bloom intensity. Test preparations and treatments. – The nets used were customary black shade nets. These were laid over the trees and secured to the trunk with wire. In the sprays, various bentonites were used. In order to strengthen the shading effect, active charcoal was added to some sprayings. An overview of treatments and conditions is given in Table 1. Evaluation. –To record the thinning effect, the number of fruits per bunch of 100 blossoms was counted. Russet evaluation was recorded by determining the percentage of heavily russeted fruit, i.e. fruits with surface russeting exceeding 30%. The flower bud evaluation was made by a visual estimation of the percentage of flower buds. 1 VZ-Laimburg, 39040 Post Auer, Südtirol, Italien; [email protected] (corresponding author) Table 1: Details of fruit-thinning treatments employed in the experiments. YYrr 22 00 00 33 2 20 0 0 5 0 5 2 0 20 6 0 0 6 Bentcharcoal onite + ac t. c harc onet al Shade Shade net SShade hade nnet et SShade hade nnet et ShControl ade net SShade hade nnet et Shade Contronet l SShade hade nnet et Shade n+etact. Bentonite Scharcoal hade net Bent oControl nite + ac t. c harc oal Control TType/Name ype /Na m e artex BBartex SSurround urround rgilla rrossa SSurround urround ++ AArgilla os s a % ght % ooff llght e duction rreduction 9900 M a ufa cture r Maufacturer A rtes -Politec nic a Artes-Politecnica Engelhard E ngelhard Molinà EEngelhard ngelhard + M olinà Da te of of treatment tre a tme nt Date 09 -- 20.05.2003 20.05.2003 09 09.05.2003 09.05.2003 09.05.2003 09.05. 2003 D. after a fte r D. bloom Fruit Fruit size siz e bloom 27 15,7mm 27 15,7mm 27 15,7mm 27 15,7mm 27 15,7mm 27 15,7mm D. of of D. sha ding shading 11 11 BBartex artex Bartex Bartex Bartex Bartex Bartex BBartex artex Bartex 4400 90 90 90 90 60 6900 90 Artes-Politecnica A rtes -Politec nic a Artes-Politecnica Artes -Politec nic a Artes-Politecnica Artes -Politec nic a Artes-Politecnica A rtes -Politec nic a Artes-Politecnica Artes -Politec nic a 10 10 -- 19.05.2004 19.05.2004 10 - 13.05.2004 10 - 13.05.2004 19 - 22.05.2004 19 - 22.05.2004 19 - 22.05.2004 19 -- 29.05.2004 22.05.2004 26 21 21 21 21 30 30 30 30 37 12 12 mm mm 12 mm 12 mm 15 mm 15 mm 15 mm 15mm mm 23 10 10 3 3 3 3 3 33 Bartex BBartex artex BBartex artex BBartex artex 60 6900 9600 6900 Artes-Politecnica A rtes -Politec nic a Artes-Politecnica Artes-Politecnica A rtes -Politec nic a Artes-Politecnica A rtes -Politec nic a 06.- 09.05.2005 06.- 09.05.2005 09.05.2005 06.016-19.05.2005 6.- 09.05.2005 16-19.05.2005 16-19.05.2005 15 15 15 22 15 22 22 6 mm mm 66 mm 12 mm 6m m 12 12 mm mm 3 33 33 33 Süd-Chemie + Molinà + Engelhard + IBA S.p.a. Süd-Chemie + Molinà + Artes-Politecnica Engelhard + IBA S.p.a. Artes-Politecnica A rtes -Politec nic a Artes-Politecnica A rtes -Politec nic a Artes-Politecnica 20.05.2005 29 15 mm Bartex Edasil + Argilla rossa + Surround + Carbopal Edas il + Argilla ros s a + Bartex Surround + Carbopal Bartex BBartex artex BBartex artex Bartex BBartex artex Bartex BBartex artex Bentonite Bartex montmorillonitica + Bartex Carbopal Bentonite montmorillonitic a + Carbopal 90 60 90 6600 9900 60 9750 90 7905 90 90 Artes -Politec nic a Artes -Politec nic a A rtes -Politec nic a Artes-Politecnica Artes-Politecnica Artes-Politecnica A rtes -Politec nic a ArtIBA es -PS.p.a. olitec n+ic a ArDonau tes -PolCarbon itec nic a IBA S.p.a. + Donau Carbon 26 - 29.05.2004 16-19.05.2005 20.05. 2005 37 22 29 23 mm 12 mm 15 mm 3 29 29 29 36 29 36 15 mm 15 mm 15 mm mm 23 15 mm mm 23 3 3 33 33 15.-17.05.2006 22-24.05.2006 15-18.05.2006 36 22 22 29 22 23 mm mm 15 15 mm 22 15 mm mm 33 2 23 26 20 mm 26 20 mm 15.-17.05.2006 2219.05.2006 -24.05.2006 19.05. 2006 36 22 29 23 mm 15 mm 22 mm h l / ha hl/ha Tre a t##Treatm e nts ments 10 10 kg kg 55 ++ 55 kg kg 20 20 20 20 55 55 Bentonite 4,5kg + 4,5kg + 1kg act. charcoal 3 kg 15 5 15 5 10kg Benonite+ 3kg act. charc. 15 5 10k g Benonite+ 3k g ac t. c harc . 15 5 3 20-23.05.2005 20-23.05.2005 20-23.05.2005 27.-30.05.2005 20-23.05.2005 27.-30.05.2005 27.-30.05.2005 215-18.05.2006 7.-30.05.2005 Dosa ge /hl Dosage/hl Bentonite 4,5k g + 4, 5k g + 1kg ac t. c harc oal 3 k g 3 2 2 Archived at http://orgprints.org/13737/i 2 2 0 0 0 04 4 re a tme nt TTreatment et SShade hade nnet BBentonite entonite 11 BBentonite entonite 22 CControl ontrol SShade hade nnet et Shade net Shade net Shade net Shade net Shade net SShade hade nnet et ShControl ade net Contronet l Shade SShade hade nnet et SShade hade nnet et hade nnet SShade et Shade n+etact. Bentonite 311 312 Archived at http://orgprints.org/13737/i Table 2: Thinning effects, russeting, and flower bud formation in the following year: Year Year 2 2 0 0 0 0 3 2 0 0 0 4 4 2 2 0 0 0 0 5 5 2 2 0 0 0 0 6 6 Treatment Treatment Shade net net Shade Bentonite 11 Bentonite Bentonite 22 Bentonite Control Control Shade net net Shade Shade Shade net net Shade Shade net net Shade Shade net net Shade Shade net net Control Control Shade Shade net net Shade Shade net net Shade Shade net net Shade Shade net net Bentonite Bentonite Shade Shade net net Shade Shade net net Shade Shade net net Shade Shade net net Control Control Shade Shade net net Shade Shade net net Shade Shade net net Bentonite Bentonite Control Control %light light % Fruit size reduct. Fruit size reduct. 90 15,7mm mm 90 15,7 15,7mm mm 15,7 15,7mm mm 15,7 Daysofof Days shading shading 11 11 40 40 90 90 90 90 60 60 90 90 12mm mm 12 12 12mm mm 15 15mm mm 15 15mm mm 23 23mm mm 10 10 33 33 33 33 60 60 90 90 60 60 90 90 66mm mm 66mm mm 12 12mm mm 12 12mm mm 15 15mm mm 15 15mm mm 15 15mm mm 23 23mm mm 23 23mm mm 33 33 33 33 15 15mm mm 15 15mm mm 22 22mm mm 20 mm 20 mm 33 22 22 60 60 90 90 60 60 90 90 75 75 90 90 90 90 33 33 33 33 % heavy Thin. Thin. Stat.* % heavy russeting effect%%Stat.* russeting effect 97,1 36,9 97,1 aa 36,9 15,2 18,2 15,2 bb 18,2 28,8 25,3 28,8 cc 25,3 65,2 65,2 7,64 24,1 7,64 aa 24,1 21,7 abab 21,1 21,7 21,1 64,6 cc 29,2 64,6 29,2 36,0 bb 24,7 36,0 24,7 34,6 bb 20,8 34,6 20,8 18,6 18,6 -8,50 aa -8,50 8,70 abab 8,70 19,7 bcbc 19,7 66,8 dd 66,8 30,8 cc 30,8 12,9 bcbc 12,9 84,3 ee 84,3 4,80 abab 4,80 62,6 dd 62,6 39,1 39,1 57,0 57,0 43,6 43,6 26,9 26,9 Statistics: One-way ANOVA, Tukey’s Post-Hoc repeated comparison bcbc dd cc abab 10,1 10,1 9,18 9,18 4,73 4,73 1,10 1,10 3,30 3,30 flower %% flower Stat.* buds Stat.* buds 92,5 92,5 dd 13,0 13,0 bb 18,5 18,5 cc 1,6 1,6 aa 4,0 4,0 aa 16,0 bb 16,0 52,7 cc 52,7 13,5 bb 13,5 8,0 aa 8,0 2,0 aa 2,0 11,5 abab 11,5 11,1 abab 11,1 27,4 cc 27,4 64,0 ee 64,0 3,5 aa 3,5 25,8 cc 25,8 76,5 f f 76,5 19,5 bcbc 19,5 48,0 dd 48,0 10,0 abab 10,0 14,8 bb 14,8 29,3 cc 29,3 13,8 bb 13,8 1,67 aa 1,67 3,8 aa 3,8 p=0,05 Results A summary of all results discussed below is given in Table 2. In 2003, the first data regarding the shading method were collected, using nets with a 90% reduction of light transmission. These nets were left in the orchard until the first fruit began to fall. This period of shading was clearly too long and resulted in nearly 100% thinning. The darker of the two bentonite combinations showed better thinning effects. All shading treatments seemed to lead to reduced russeting. As expected, the degree of blossoming in the following year was very high with the net method (almost 100%). At 13% and 18% flower buds, the other treatment variations provided at best modest results, which were nonetheless an improvement over the unshaded control (1.6%). In 2004, various shading intensities and treatment periods were tested, whereby a light reduction of less than 60% resulted in almost no thinning effect, in spite of an extended period of shading (10 days). The best thinning effect was obtained when the shading was carried out at a fruit size of 15 mm (up to 64% thinning effect). Using 90% light reduction, the thinning effect was twice as high (64%) as when using 60% light reduction (36%). There were no noticeable differences in russeting between the variations. At the next blossoming, only the 90% light reduction treatment showed an entirely satisfying flower bud share of 52%. In 2005, different shading dates and shading intensities were again tested. The best thinning effect was obtained between 12 and 23 mm, whereby the highest effectiveness was shown at 15 mm fruit diameter. 313 Archived at http://orgprints.org/13737/i The variation with 60% light reduction showed a maximum thinning effect of 19.7% which was unsatisfactorily low. When active charcoal was added to the bentonite variation to improve shading, a satsfactory thinning effect of 30.8% was obained. The following year’s blossoming was very good using all variations of 90% light reduction except for the first date. In contrast, variations with 60% light reduction were barely satisfactory, giving flower bud shares between 19.5 and 25.8%. The bentonite variation resulted in a very low flower bud share of 3.6%, in spite of satisfactory thinning effects. In 2006, all net variations showed strong thinning effects (39-57%). The bentonite variation also gave satisfactory results with 26.9% thinning. The net variation caused a slight increase in russetting. In the following year, only the net variation with the heaviest thinning effects (57%) also brought satisfactory results with respect to alternate bearing (29.3% flower buds). The bentonite variation again performed poorly with a flower bud share of 3.8%. Discussion In the experiments described here, net shading consistently yielded promising thinning effects. Duration of shading, shading intensity and the period of treatment had a decisive influence over the resulting thinning effect. The best thinning effect was achieved at 15 mm fruit size. Noteworthy thinning effects could not be achieved below 60% light reduction. The effect on blossoming in the following year was mostly unsatisfactory when using the net variations. Applications of bentonite gave partially sufficient thinning results, yet had no positive effect on the alternate bearing in the following year. Also, soiling of the fruit was still visible at the date of harvest. At the moment, shading with nets is therefore the only possibility to selectively promote June drop and thereby achieve thinning. It is, however, questionable if this method will find its way into practice. High costs of acquisition and expenditure of time in application as well as the poor influence on alternate bearing are surely solid arguments for questioning the advantages of this method. 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