Efficiency of Fruitlet Thinning in Granny Smith Apples by Use of Metamitron

Efficiency of fruitlet thinning in ‘Granny Smith’ apples by use of metamitron

RadivojevicDragan1,Milivojevic Jasminka1, Oparnica Cedo1and Zabrkic Goran2

1University of Belgrade, Faculty of Agriculture, Belgrade, Serbia

2 PIK „Južni Banat“, Bela Crkva, Serbia

Abstract

Here are reported the results of chemical fruit thinning in apple cv. ‘Granny Smith’ carried out withthe herbicideBrevis® containing150 g kg-1 of metamitron as the active ingredient. In two treatments, effect of this compound was enhanced by NAA (1-Naphthaleneacetic acid). This study was conductedin commercial apple orchard of PIK „Južni Banat“ located in BelaCrkva (Serbia), in two consecutive years (2013, 2014). The planting distance of 3.3m × 0.8 m (3878 trees per ha) and slender spindlegrowing system were applied. Brevis®was used for spraying when central fruit in a cluster were 12-14 mm in diameter.Applied treatments in cv. ‘Granny Smith’ were as follows: control, 150 mgL-1, 188 mgL-1, 225 mg L-1, 150 mgL-1of metamitron + 5mg L-1 NAA and 225 mg L-1 metamitron + 5mgL-1 NAA. Spraying volume was 800 L ha-1 in all applied treatments. Metamitron expressed a positive influence on crop load in both investigated years. Treatments contained metamitron alone providedlarge yield consisted of high percentage of the first quality fruit. The effect of metamitron could beenhanced by mixing with NAA.

Key words: brevis, chemical thinning, yield, fuit quality.

INTRODUCTION

Fruit thinning of apples is essential for achieving adequate fruit size and quality. Hand thinning continues to be widely practiced, but increasing costs and decreasing availability of labour accentuate the appeal for chemical thinning agents (Lafer, 2010). Although ‘Granny Smith’ apple belongs to the group of cultivars which are “easy to thin”, regular and high yield and good fruit size may be achieved only by using reliable chemical thinners. Several chemical thinning agents are currently available but not all may remain on the market.Since Carbaryl, as the only effective fruit-thinning chemical, is not currently available in Europe because of its toxicity to bees, an alternative carbaryl-free strategy based on the tankmix of NAA and BA is mainly used (Dorigoni and Lezzer, 2007). Effect of these two chemical thinning agents can be erratic due to the high dependence on temperature in the moment of spraying. Recent studies have revealed that metamitron, a commonly used herbicide that at low dosage reduces photosynthesis, may be an effective thinner(Clever, 2007; Basak, 2011;Greene, 2014). Therefore, the aim of this study was to evaluate the thinning capability of metamitronapplied to ‘Granny Smith’ appleat low concentration alone or in combination with NAA.

Materials and methods

This study was conducted in commercial orchard of ‘Granny Smith’ apple located in Bela Crkva (Serbia), in two consecutive years (2013, 2014). The orchard was established in 2009 with planting distance of 3.3 m × 0.8 m (3878 trees per ha). Slender spindle growing system was applied. Brevis®(ADAMA Agricultural Solutions Ltd.),containing150 g kg-1 of metamitron as the active ingredient, was used for spraying when central fruit in a cluster were 12-14 mm in diameter.The following treatments were applied:

control (untreated trees),
150 mg L-1 of metamitron (M150)
188 mg L-1of metamitron (M188)
225 mg L-1of metamitron (M225)
150 mg L-1 of metamitron + 5mg L-1of NAA (M150+NAA5)
225 mg L-1of metamitron + 5mg L-1of NAA (M225+NAA5)

Spraying volume was 800 L ha-1 in all applied treatments. The experimental design was completely randomized with 5 repetitions and 5 trees per treatment. In both years of investigation the same trees were used for spraying. The following data were collected: number of fruit per tree, yield per tree (kg), flowering index (index 1-9), fruit distribution in size classes, fruit weight (g), fruit diameter (mm), firmness (kg cm-2), iodine starch index (scale 1-5) and soluble solids content (%). Yield (kg per tree), number of fruits per tree and average fruit weight were collected at harvest.Flowering index was estimated at full bloom in the year after the treatment using an arbitrary scale (1 = no flowers, 9 = abundant flowering). Size grading was performed in 4 classes using fruit diameter data. Evaluation of fruit quality parameters were done on random sample of 10 fruits per replication (50 fruits per treatment).

A statistical analysis was performed using software Statistica 6.0 for Windows (StatSoft Inc., Tulsa, OK, USA). Data were analyzed by ANOVA for each year separately. Significant differences among the treatments were determined by LSD test at a level of P≤ 0.05.

RESULTSAND DISCUSSION

The results of metamitron effect on ‘Granny Smith’ productivity in 2013 indicate that number of fruits per tree canbe significantly decreased at higherrates of metamitron (188 mg L-1 and 225 mg L-1) applied alone as well as in combination with NAA (Table 1). Fruit harvested from trees receiving the only 150 mg L-1 rate were larger than fruit on control trees despite carrying the highest crop load. Other treatments with higher rates of metamitron decreased yield per tree despite carrying larger fruits than in comparison to control treatment (Table 2). The share of fruits with lower diameter than 70 mm in total yield was the highest in control (19.1%), whereas it was much lower in other treatments (below 7%) except for treatment of 150 mg L-1with share of 11.6% (Figure 1).The significantly higher flowering index was induced by higher rates of metamitron (188 mg L-1 and 225 mg L-1), as well as in both combined treatments with NAA, which consequently enhanced fruit set on the trees subjected to the same treatments in 2014. Fruit firmness and soluble solids content were the highest in the combined treatment (225 mg L-1 metamitron + 5 mg L-1NAA), while no differences were observed iniodine starch index among the treatments.

In 2014, metamitron treatment only at rate of 150 mg L-1 significantly decreased number of fruit per tree (Table 3). Conversely, trees receiving metamitron in combination with NAA had significantly higher number of fruit than control trees. Thisphenomenon could be related to much higher flowering index on the treesfrom these treatments. Besides that, effectiveness of metamitron can be related to temperature for 3 weeks post application (Stern, 2015). Due to larger number of fruits per tree obtained yield tree was the highest when metamitron was combined with NAA (26.5 and 27.7 kg per tree, respectively). However, only the lowest rate of metamitron (150 mg L-1) statistically increased fruit weight and this is the treatment that had the lowest crop load (229 g and 17.2 kg per tree, respectively).The highest share of fruits with diameter below 70 mm in total yield was recorded in the treatment with the highest rate of metamitron (17.1%) and in lower rate of metamitron combined with NAA (15.4%).There were no fruits with lower diameter than 70 mm in metamitron treatment at rate of 150 mg L-1 (Figure 2).Flowering index was significantly lower when metamitron was combined with NAA in comparison to other treatments that contained metamitron alone. This could be explained by higher yield per tree obtained in these treatments.No treatment affected fruit quality parameters, including firmness, iodine starch index and soluble solids content, which are indicators of the stage of the fruit ripeness (Table 4).

CONCLUSION

The thinning efficacy of metamitron depended upon the concentration applied and the year of trials. Metamitron expressed a positive influence on crop load control in both investigated years, but in the second year its effect was not apparent because of flowering index on the treated trees was different.In the first year, treatments contained metamitron alone provided larger yield consisted of high percentage of the first quality fruit. The effect of metamitronwas enhanced by mixing with NAA. However, in the second year metamitroncombinedwith NAA increased fruit yield without a loss of the fruit size. There was very little influence of the treatments on the fruit quality parameters in both experimental years.

Tables and figures

Table 1. The influence of metamitron on productivity of cv. ‘Granny Smith’ in 2013.

Treatment / Number of fruit per tree / Yield
(kg per tree) / Yield (t ha-1) / Flowering index
(1-9)
Control / 124.5±13.91ab / 20.4±1.09abc / 77.3±4.14 / 4.0±0.41b
M 150 / 151.0±9.13a / 25.9±0.81a / 97.9±3.08 / 4.25±1.11b
M 188 / 107.5±10.66bcd / 18.9±1.98bc / 71.5±7.49 / 6.8±1.11a
M 225 / 86.3±13.43cd / 16.2±1.93bc / 61.3±7.30 / 7.3±0.75a
M 150+NAA 5 / 122.8±17.25abc / 21.9±3.28ab / 83.0±12.43 / 7.8±0.63a
M 225 +NAA 5 / 71.8±8.72d / 15.1±2.10c / 57.1±7.94 / 8.0±0.41a
F test / * / * / * / *

Data are means of 5 replications ± standard errors. Values within column followed by the same letter are not significantly different at 95% (LSDtest). * Statistically significant differences at P ≤ 0.05; ns, non significant.

Figure 1. Fruit distribution in size classes of cv. ‘Granny Smith’ in 2013. (Kg per tree)

Table 2. The influence of metamitron on fruit characteristics of cv. ‘Granny Smith’ in 2013.

Treatment / Fruit weight (g) / Fruit diameter (mm) / Firmness
(kg cm-2) / Iodine starch index (1-5) / Soluble solids content (%)
Control / 163.3±8.18c / 72.5±1.43c / 8.00±0.11b / 3.95±0.24 / 12.7±0.30c
M 150 / 176.3±9.80bc / 74.4±1.72bc / 8.39±0.12ab / 3.55±0.13 / 13.1±0.02abc
M 188 / 189.6±7.06bc / 76.2±1.08b / 8.32±0.19b / 3.44±0.12 / 13.0±0.09bc
M 225 / 195.3±6.63b / 77.6±0.73ab / 8.38±0.25ab / 3.65±0.21 / 13.1±0.23abc
M 150 +NAA 5 / 190.1±8.92b / 76.8±0.87ab / 8.06±0.26b / 3.50±0.23 / 13.3±0.18ab
M 225 +NAA 5 / 224.4±12.26a / 80.3±1.21a / 8.93±0.15a / 3.50±0.13 / 13.7±0.15a
F test / * / * / * / ns / *

Table 3. The influence of metamitron on productivity of cv. ‘Granny Smith’ in 2014.

Treatment / Number of fruit per tree / Yield
(kg per tree) / Yield
(t ha-1) / Flowering index
(1-9)
Control / 110.4±12.4b / 20.6±2.39bc / 78.1±9.04bc / 7.6±0.68ab
M 150 / 72.4±11.0c / 17.2±2.23c / 65.1±8.44c / 9.0±0.55a
M 188 / 111.0±7.7b / 20.4±1.52bc / 77.1±5.75bc / 8.0±0.66a
M 225 / 112.0±12.8b / 19.7±2.21c / 74.5±8.39c / 8.2±0.77a
M 150 +NAA 5 / 140.4±12.6ab / 26.5±2.64ab / 100.3±9.98ab / 5.2±0.58c
M 225 +NAA 5 / 147.0±6.7a / 27.7±1.51a / 105.0±5.71a / 5.8±1.02bc
F test / * / * / * / *

Figure 2. Fruit distribution in size classes of cv. ‘Granny Smith’ in 2014. (kg per tree)

Table 4. The influence of metamitron on fruit characteristics of cv. ‘Granny Smith’ in 2014.

Treatment / Fruit weight (g) / Fruit diameter (mm) / Firmness
(kg cm-2) / Iodine starch index (1-5) / Soluble solids content (%)
Control / 190±2.56b / 78.5±2.24 / 7.0±0.16 / 2.38±0.11 / 10.7±0.37
M 150 / 229±4.11a / 80.4±0.91 / 7.1±0.08 / 2.48±0.13 / 11.2±0.52
M 188 / 196±7.14b / 76.6±1.25 / 7.1±0.10 / 2.60±0.05 / 11.1±0.23
M 225 / 179±11.44b / 74.2±0.98 / 7.3±0.06 / 2.63±0.15 / 10.9±0.23
M 150 +NAA 5 / 193±7.15b / 76.8±1.20 / 7.1±0.07 / 2.54±0.07 / 10.6±0.58
M 225 +NAA 5 / 181±4.47b / 75.0±0.65 / 6.9±0.05 / 2.48±0.07 / 10.5±0.24
F test / * / ns / ns / ns / ns

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