Sequential applications of budbreak promoters in hail-netted apple trees in southern Brazil: a canopy stratification approachAbstract:
This work sought to evaluate sequential applications of budbreak promoters on hail-netted apple trees in southern Brazil, focusing on the effects at different canopy levels. One or two sprays were applied to ‘Baigent’ and ‘FujiKiku 8’ trees under black net in a commercial orchard in Vacaria/RS. Hydrogen cyanamide (0.34%) with mineral oil (3.5%) was the unique/first application. Mineral oil(3.5%) alone or with hydrogen cyanamide (0.17%, 0.34%), Erger® (1.5%), and Syncron® (1.5%) constituted the reapplications. During the 2017/18 and 2018/19 seasons, phenology, budbreak, fructification, and fruit production were assessed in the lower and upper halves of the canopy of treated and non-treated trees. The budbreak promoters anticipated blooming, generally increased and reduced budbreak and fructification, respectively, without changing production. The upper canopy exhibited delayed budburst/blooming compared to the lower one but showed higher fruiting and advanced harvest in ‘Baigent’. One and two sprays produced similar results and few were the differences among the sequential treatments. Little influences may be attributed to adverse weather conditions, such as water scarcity and low thermal accumulation. The second application is commonly used in the region’s apple orchards, as better outcomes than with just one have been reported. In this context, additional research is required to validate the schemes adopted for hail-netted ‘Baigent’ and ‘Fuji Kiku 8’ trees cultivated in southern Brazil.
Index terms
Malus domesticaBorkh.; dormancy overcoming; reapplication of chemical agents; canopy portions; protective netting
Resumo:
O presente trabalho teve como objetivo avaliar aplicações sequenciais de indutores de brotação em macieiras sob tela antigranizo, no Sul do Brasil, focando nos efeitos em diferentes porções da copa. Foram realizadas uma ou duas pulverizações em plantas das cultivares Baigent e Fuji Kiku 8, em pomar comercial em Vacaria-RS. A primeira ou única aplicação consistiu no uso de cianamida hidrogenada (0,34%) e óleo mineral (3,5%). As reaplicações foram feitas com óleo mineral(3,5%),isolado ou junto a cianamida hidrogenada (0,17%, 0,34%), Erger® (1,5%) eSyncron® (1,5%). Durante as safras de 2017/18 e 2018/19, foram avaliadas fenologia, brotação,frutificação e produção de frutos nas metades inferior e superior da copa de plantas tratadas e não tratadas. Os indutores de brotação anteciparam a floração, geralmente aumentaram e reduziram a brotação e a frutificação, respectivamente, sem alterar aprodução. A parte superior da copa apresentou atraso na brotação/floração, em comparação à parteinferior, mas ocorreram maior frutificação e antecipação da colheita em macieiras‘Baigent’. Uma ou duas pulverizações promoveram resultados semelhantes, com poucas diferenças entre os tratamentos sequenciais. Poucas influências podem ser atribuídas a condições climáticas adversas, como escassez hídrica e baixa soma térmica. A segundaaplicação é comumente utilizada na pomicultura da região, pois resultados melhores que aqueles de uma aplicação têm sido relatados. Nesse contexto, pesquisas adicionais são necessárias para validar os esquemas adotados em macieiras ‘Baigent’ e ‘Fuji Kiku 8’cultivadas no Sul do Brasil.
Termos para indexação
Malus domestica Borkh.; superação da dormência; reaplicação de agentes químicos; porções da copa; cultivo protegido
Introduction
The cultivation of apple trees (Malus domestica Borkh.) in the southern region of Brazil accounted for 99% of the national production in 2023, close to 1,2 million tons (IBGE, 2024). This species is a temperate climate fruit tree that, due to the reduction of photoperiod and temperature in the fall, begins to enter dormancy and does not show visible growth in winter until low and subsequently high air temperatures are accumulated.
In southern Brazil, the main cultivars, belonging to the ‘Gala’ and ‘Fuji’ groups, often do not receive the required chilling in some growing areas, exhibiting reduced and uneven budburst and flowering, increased apical dominance, and decreased fruit production and quality (MELKE, 2015; MARTIN et al., 2023).
The use of budbreak promoters, chemical agents, is a practice that can mitigate the issues arising from the lack of chill accumulation in Gala and Fuji cultivars, being well-established in the Brazilian apple production system.
These compounds have historically been applied once a year in the combination of hydrogen cyanamide (HC, a highly toxic molecule) and mineral oil (MO) (PETRI et al., 2006). However, in response to the growing demand for less aggressive options, there is an increasing number of studies on the use of biostimulants in budbreak induction, some of which demonstrate the high efficacy of Erger® and Syncron® when applied alongside MO or calcium nitrate (PETRI et al., 2016; PASA et al., 2018).
The efficacy of budbreak promoters depends on factors related to the compounds themselves, their respective applications, the local climate, and the tree (PETRI et al., 2006; HAWERROTH, 2018). The longer the shoot length, the greater the chilling requirement of axillary buds and the acrotonic tendency (EREZ, 2000; PETRI et al., 2006).
Consequently, considering the various efficacy- related aspects of the chemicals, unsatisfactory results have been observed in some years, particularly in important cultivars Gala and Fuji covered by hail nets.
According to Bosco et al. (2017), using hail nets is the most effective alternative for producers against the increasing hailstorms in apple-producing areas of southern Brazil.
However, in addition to its protective benefits, hail netting also alters the microclimate in the orchard, including changes in the light environment, such as intensity (BOSCO et al., 2017). These events interfere with tree-environment interactions, according to net characteristics, cultivar/rootstock combo, planting density, orchard management, and climatic factors (LEITE et al., 2002; MIDDLETON; MCWATERS, 2002; MUPAMBI et al., 2018).
Hail nets influence the vegetative growth of apple trees, leading to increases in average or total shoot length reported worldwide (MUPAMBI et al., 2018). A possible explanation is that reduced photosynthetic active radiation (PAR) and other shading effects induce modifications in hormone levels and stimulate resource allocation into extending shoots (WIT et al., 2016; MUPAMBI et al., 2018). In this context, vigor-increasing conditions can be especially relevant in southern Brazil, where the upper canopy has sometimes displayed an increased proportion of verticalized structures, regardless of the presence of netting.
Many apple growers in southern Brazil adopt a sequential application of budbreak promoters, involving two applications aimed at enhancing their effects.
Improved results, such as increased budbreak, have been observed (FENILI et al., 2017; GOULARTE et al., 2018; PETRI et al., 2021a,b), but only Paim et al. (2020) tested responses under netting. Various application schemes can be defined based on the factors involved, including different compounds and combinations (HAWERROTH et al., 2018). Thus, this work sought to evaluate sequential applications for budbreak induction in the cultivars Baigent and Fuji Kiku 8 under hail netting in southern Brazil, focusing on the effects at different canopy levels.
Material and Methods
The study was conducted in a commercial orchard in Vacaria/RS, Brazil (lat. 28º30’S, long. 50º56’W, alt. 971 m), during the 2017/18 and 2018/19 seasons. According to Köppen’s classification, the climate in the region is Cfb, meaning it is constantly temperate and humid with mild summer.
The accumulation of low air temperatures, rainfall, and thermal sum during periods of interest in the respective growing seasons are presented in Table 1.
12-year-old ‘Baigent’ and ‘Fuji Kiku 8’ apple trees, grafted onto M.9 rootstock and trained as central leaders under black anti- hail netting, were subjected to the treatments.
The netting was installed in a fixed system in 2010, with no possibility of removal. Within the block, trees were planted in a pattern of three rows of ‘Baigent’ followed by one row of ‘Fuji Kiku 8’, with an overall spacing of 3.5 m between rows and 0.45 m within rows. Orchard management followed regional recommendations from planting onwards, without making distinctions between experimental units.
To assess the intrinsic characteristics of the treatments, different trees, each with canopies divided into lower and upper portions, were evaluated in the two growing seasons.
A randomized complete block was adopted as the experimental design, with four replicates of two useful trees per unit. The levels of budbreak promoter studied were: 1.Control (no spray); 2. HC 0.34% + MO 3.5%; 3. HC 0.34% + MO 3.5% (first application - FA) + MO 3.5% (second application - SA); 4. HC 0.34% + MO 3.5% (FA) + HC 0.34% + MO 3.5% (SA); 5. HC 0.34% + MO 3.5% (FA) + HC 0.17% + MO 3.5% (SA); 6. HC 0.34% + MO 3.5% (FA) + Erger® 1.5% + MO 3.5% (SA); 7. HC 0.34% + MO 3.5% (FA) + Syncron® 1.5% + MO 3.5% (SA). A non-ionic surfactant was added in all chemical treatments, Break-thru® at 0.05%.
Commercial products Dormex® (HC 49%), Assist® (MO 75.6% - 2017/18), and Agefix® (MO 92% - 2018/19) were used as sources of the respective active ingredients.
All applications were conducted when buds were between stages A (dormant) and B (swollen), according to the phenological scale in Iuchi (2006). In the 2017/18 season, the first application took place on 08/25, followed by the second one on 09/04, 10 days later.
In the subsequent season of 2018/19, applications were carried out on 08/28 and 09/13, respectively, with a 16-day interval between them. All treatments were made using a motorized trailed sprayer at the volume of 1,000 L ha-1, when air temperature, relative humidity, and wind speed ranged from 20- 25ºC, 70-80%, and 1.5-2.4 km h-1, respectively.
In the 2017/18 season, dates of budburst and flowering stages: beginning, full and end of blooming of ‘Baigent’ trees were visually assessed in the lower and upper portions of the canopy.
Budburst was recognized when buds reached between green tip and half-inch green (C-C3), while the beginning of blooming (F) was marked by the presence of 5% open flowers. Full blooming (F2) was noted when more than 70% of flowers had opened, and the end of blooming was determined by the appearance of the last flowers - scale in Iuchi (2006).
The period (days) between the first application and the start of blooming, as well as flowering duration, were calculated. Because of the significant chilling accumulation during the winter of 2018 and the resulting homogenization observed among the treatments, phenological recordings were not conducted in this season.
Budbreak intensity was evaluated for axillary and terminal buds and expressed as a percentage. Axillary budbreak was obtained by the ratio of burst to the total number of buds in five one-year-old shoots (brindles of similar vigor) previously selected in both lower and upper parts of the canopy. A scaffold branch was also marked in both portions to estimate terminal budbreak.
The assessment of budbreak intensities was conducted at 24 and 62 days after the first application (DAFA) in the 2017/18 season, and at 29 and 63 DAFA in 2018/19.
At approximately 85 DAFA in both 2017/18 and 2018/19 seasons, all clusters with fruit and fruits per tree were counted to attain their total number and mean number of fruits per cluster.
Harvest was always performed when fruits reached commercial maturity, with ‘Baigent’ apples being picked on 02/26/18, 03/07/18 and 03/16/18, and 02/05/19, and ‘Fuji Kiku 8’ apples on 04/11/18 and 04/02/19.
Immediately after harvesting, they were counted and weighed to calculate mass of fruits per tree (kg) and average fruit mass (g). In cases where multiple pickings were conducted, the relative contribution to the total mass per tree was determined. All evaluations were taken in the lower and upper portions of the canopy.
Data were subjected to analysis of variance (p≤0.05) in response to budbreak promoter, canopy portion and their interaction.
Percentages were previously transformed using square root (x+1). Orthogonal contrasts were also tested. All statistical analyses were performed using the Sisvar software, version 5.6 (FERREIRA, 2014).
Results and Discussion
Budburst was initially recorded on 09/10 in all lower portions of the canopy during the 2017/18 season (Table 2). Variations persisted until 09/13 in the upper part, when buds in control (no spray) reached this stage.
The start, full, and end of blooming occurred on 09/16, 09/20, and 09/24, respectively, in the lower portion of treated trees, happening 2-3 days earlier than in untreated ones. Notably, differentiated dates were discerned in the upper part due to chemical intervention.
While Syncron® or Erger® 1.5%+ MO 3.5% as a sequential application usually caused a delay of 1-3 days, the start, full and end of blooming occurred on 09/19, 09/22, and 09/26, respectively, for the other trees, 2-8 days earlier than in the untreated group.
Phenological stages (budburst, start, full and end of blooming) dates and subperiods duration of hail-netted ‘Baigent’ apple trees submitted to a single application of budbreak promoters and different sequential ones. Data from the lower and upper canopy in the 2017/18 season. Vacaria-RS, Brazil, 2024.
Anticipations of budburst and blooming induced by budbreak promoters are well reported in non-netted medium to high-chill cultivars Gala in southern Brazil (PETRI et al., 2016; FENILI et al., 2018).
Nevertheless, despite the benefits of these compounds, temporal and spatial differences regarding budburst and flowering are often observed at the shoot-level, especially in years with low chilling (PERTILLE et al., 2021).
In this context, this study evaluated potential disparities throughout the canopy and identified significant influences related to canopy level.
The upper portion exhibited delayed phenology, especially in flowering, compared to the lower one, defining vegetative and flowering gradients (Table 2). However, they generally occurred at shorter intervals in response to the chemicals.
On average, blooming occurred 3.7 days earlier in the lower part, but flowering duration did not differ between the two parts. A budburst and flowering gradient may be explained by a vigor one, formed or intensified by the hail net. For instance, increased shoot length tends to hamper total budbreak (EREZ, 2000; PETRI et al., 2006), and this effect has been shown to be more significant in the upper canopy.
An increased proportion of verticalized structures may be linked to inadequate winter pruning, the hail net itself, and the natural acrotonic growth habit of the apple species cultivated in mild winter regions (PERTILLE et al., 2021).
Hawerroth et al. (2018) highlighted the potential of sequential applications for greater anticipation of budburst and blooming.
Then, this approach could also provide homogenization between the canopy portions.
However, in this study, such effects were not observed, as the results were similar to those with HC 0.34% + MO 3.5% (Table 2). These findings differ from many reports by growers over the past few years in both netted and non-netted apple trees, which may be related to an increased relative contribution of terminal buds to flowering due to high chilling during the winter of 2016.
In the 2017/18 growing season, the vigor gradient indicated between the canopy portions of ‘Baigent’ trees could lead to lower axillary budbreak in the upper one.
Probably due to the uniformity of the evaluated one-year-old shoots and lower chill accumulation in 2018 (Table 1), there were no differences between them at 24 and 62 DAFA (Figure 1). For ‘Fuji Kiku 8’ trees, at 24 DAFA, the expected response was attained, which can be attributed to the inability to achieve the same degree of shoot uniformity due to a reduced number of brindles available.
In this sense, lower axillary budbreak is undesirable as it results in lower development of reproductive structures, such as brindles and spurs, for the following year.
Nonetheless, these initial differences were mitigated, as both canopy parts exhibited almost 65% budbreak at 62 DAFA.
At the end of the evaluation period in the 2017/18 season, percentages were lower in ‘Baigent’ trees (nearly 35%) compared to ‘Fuji Kiku 8’ (nearly 71%) (Figure 1).
These findings underscore the greater importance of using budbreak promoters to enhance axillary budbreak in cultivars Gala in certain situations, consistent with Fenili et al. (2018).
In the 2018/19 season, ‘Baigent’ trees exhibited expressively higher percentages, likely due to increased chilling during dormancy in 2018. In contrast, axillary budbreak in ‘Fuji Kiku 8’ did not differ significantly between the two seasons, suggesting that ‘Baigent’ trees are more responsive to chilling accumulation.
Axillary budbreak was affected by budbreak promoter at 24 and 62 DAFA in the 2017/18 season, and at 29 and 63 DAFA in 2018/19 (Figure 1). The application of budbreak promoters significantly enhanced budbreak in both cultivars, with variations among treatments.
In 2017/18, ‘Baigent’ trees treated with HC 0.17% and 0.34% + MO 3.5% as a sequential application showed higher percentages compared to those treated with MO 3.5%, especially at 24 DAFA. The same outcome was observed in ‘Fuji Kiku 8’ trees in 2018/19, particularly at 29 DAFA.
In this season, Erger® and Syncron® 1.5% + MO 3.5% induced higher axillary budbreak compared to MO 3.5%, but only in ‘Fuji Kiku 8’ trees. The responses of the two cultivars were not consistent across the two seasons.
Axillary budbreak of hail-netted ‘Baigent’ (a, c) and ‘Fuji Kiku 8’ (b, d) apple trees submitted to a single application of budbreak promoters and different sequential ones. Data from the lower and upper canopy in the 2017/18 (a, b) and 2018/19 (c, d) seasons. Vacaria-RS, Brazil, 2024.1 Break-thru® 0.05% was added in all chemical treatments. DAFA: days after the first application. HC: hydrogen cyanamide. MO: mineral oil.FA, SA: first and second applications, respectively. ns: not significant (p>0.05). **, *: significant at p=0.01 and p=0.05, respectively.
According to Petri et al. (2006) and Hawerroth (2018), the efficacy of budbreak promoters is related to the applied compounds, application conditions, pre- and post-application meteorological factors, and tree characteristics.
These aspects interfere with their effects, justifying different responses among studies.
Studying Erger® 1.5% + MO 3.5% as a sequential application 10 and 15 days after the first, Paim et al. (2020) reported increases in axillary budbreak of netted ‘Baigent’ trees almost exclusively following the same treatment.
Conversely, Goularte et al. (2018) found that two applications of HC 0.17% + MO 3.5%, spaced 7 days apart, increased budbreak percentages more than a single one in the same non-netted cultivar. In the present study, under the adopted schemes, there were no significant differences in budbreak between trees treated with one or two applications (Figures 1 and 2).
Terminal budbreak of hail-netted ‘Baigent’ (a, c) and ‘Fuji Kiku 8’ (b, d) apple trees submitted to a single application of budbreak promoters and different sequential ones. Data from the lower and upper portions of the canopy in the 2017/18 (a, b) and 2018/19 (c, d) seasons. Vacaria-RS, Brazil, 2024.1 Break-thru® 0.05% was added in all chemical treatments. DAFA: days after the first application. HC: hydrogen cyanamide.MO: mineral oil. FA, SA: first and second applications, respectively. ns: not significant (p>0.05). **, *: significant at p=0.01 and p=0.05, respectively.
Differences in the effectiveness of sequential applications, where they may induce greater budbreak compared to single treatments, can be attributed to the intervals adopted, particularly in relation to weather conditions.
Specifically, the initiation of chemical reactions required for budburst depends on the accumulation of low air temperatures followed by adequate water availability and higher temperatures (MALAGI et al., 2015).
Therefore, the limited success observed could be linked to a significant dry period early in the 2017/18 season and delayed temperature increases in 2018/19, resulting in insufficient accumulation of heat units post-application (Table 1).
Terminal budbreak of ‘Baigent’ trees ranged from 71 to 92.9%, while ‘Fuji Kiku 8’ ones presented an interval of 86.8 to 98.4% between the lower and upper portions of the canopy at 62 DAFA in the 2017/18 season (Figure 2).
At 63 DAFA, these percentages were nearly 100% in 2018/19. There was no consistent response of both canopy portions, and any initial differences were subsequently offset. The lowest terminal budbreak at the end of the evaluation time was exhibited by control (no spray) trees, usually significantly inferior to those treated with budbreak promoters for both cvs.in both seasons (Figure 2).
Terminal buds have lower chilling requirement than axillaries, a well-known fact in dormancy research that underscores the importance of studying sequential treatments to increase axillary budbreak, particularly in years with low chilling during dormancy, such as 2017.
Apple trees trained as a central leader and in a high-density planting receive less PAR as their canopy portions approach the ground, which is intensified by hail nets (BOSCO et al., 2017).
Increased incident PAR in the upper part favors the development of more fertile buds, potentially explaining higher fruiting attributes observed in both cultivars during the 2017/18 and 2018/19 seasons (Table 3).
The upper portion of ‘Fuji Kiku 8’ trees averaged 21.2 fruits in 2017/18 and 60.6 in 2018/19, marking increases of 194% and 197% compared to the lower portion, respectively. Similarly, ‘Baigent’ trees produced 63.3 fruits in the first season and 28.6 in the second, reflecting increases of 79% and 218%, respectively.
Fruit production decreased for ‘Baigent’ and increased for ‘Fuji Kiku 8’ from 2017/18 to 2018/19. Low intensity and high heterogeneity of flowering were manifested by ‘Fuji Kiku 8’ trees in the 2017/18 season, and this could have reduced the fruiting of ‘Baigent’ ones (Table 3).
Since their number of clusters with fruit and fruits per tree can be considered elevated, this cultivar was not or was minimally affected.
However, ‘Baigent’apple trees exhibited reduced fruiting in the 2018/19 growing season, likely due to diminished bud fertility caused by a significant drought period and high fruit load in 2017/18 growing season, in addition to low axillary budbreak. Additionally, the fast/ high budbreak and high rainfall amounts (Sept. and Oct. - Table 1) likely intensified competition between vegetative and reproductive sink and reduced pollinator activity in the second season.
Petri et al. (2016) demonstrated that a single application of budbreak promoters decreased fruit set in non-netted ‘Maxi Gala’ apple trees. Similarly, significant reductions in number of clusters with fruit and fruits per tree were observed in the two cultivars (Table 3).
However, ‘Baigent’ trees were affected during the 2017/18 season, whereas ‘Fuji Kiku 8’ ones showed impacts in 2018/19. In 2017/18, HC 0.17% and 0.34% + MO 3.5% as a sequential application resulted in higher and lower fruit counts compared to MO 3.5% in ‘Baigent’ and ‘Fuji Kiku 8’ trees, respectively. For Fuji Kiku 8’, the use of Erger® and Syncron® 1.5% + MO 3.5% provided the same effects and these responses probably result from axillary budbreak and fruiting on axillary buds.
Trees treated with either one or two applications did not show significant differences in fructification variables, contrary to the expected lower fruit set from sequential treatments (Table 3). This outcome was probably not obtained because of the similarities in budbreak. Besides, the limited effects may also be explained by the high chilling during the winter of 2016, which heightened the relative contribution of terminal buds in the 2017/18 season.
Number of clusters with fruit per tree, mean number of fruits per cluster and number of fruits per tree of hail-netted ‘Baigent’ and ‘Fuji Kiku 8’ apple trees submitted to a single application of budbreak promoters and different sequential ones. Data from the lower and upper canopy in the 2017/18 and 2018/19 seasons. Vacaria-RS, Brazil, 2024.
Budbreak promoters can be used to anticipate budbreak, flowering, and harvest to capture preferential market times (GEORGE et al., 2002). Due to fruit aspects related to genetics, central leader training, and the frequent phenology heterogeneity in most apple-producing areas, the main cvs. present hampered harvest in southern Brazil.
Thus, three or more pickings to harvest them at their commercial maturity might be needed. This study checked the potential to enhance uniform ripening of ‘Baigent’ apples through a sequential application in 2017, a year characterized by low winter chill accumulation (Figure 3).
Relative contributions of the first and second picking to the total mass of fruits per tree were not significantly affected by budbreak promoter (Figure 3). Two applications tended to increase the percentages, which may be partly justified by the lower role of the third picking in these trees than in HC 0.34% + MO 3.5% ones.
Earlier flowering does not provide, in the same proportion, anticipations of fruit ripening (PETRI et al., 2006). Despite delayed flowering in the upper canopy, 56.7% of the total mass of fruits per tree was obtained in the first picking. Such an outcome is probably linked to the higher incident PAR at the upper part than at the lower one (BOSCO et al., 2017).
Relative contribution of the first, second and third pickings to the total mass of fruits per tree, mass of fruits per tree and average fruit mass of hail-netted ‘Baigent’ (a, c) and ‘Fuji Kiku 8’ (b, d) apple trees submitted to a single application of budbreak promoters and different sequential ones. Data from the lower and upper canopy in the 2017/18 (a, b) and 2018/19 (c, d) seasons. Vacaria-RS, Brazil, 2024.1 Break-thru® 0.05% was added in all chemical treatments. HC: hydrogen cyanamide. MO: mineral oil. FA, SA: first and second applications, respectively. ns: not significant (p>0.05). **, *: significant at p=0.01 and p=0.05, respectively.
One of the most beneficial effects of budbreak promoters is their ability to increase the number of reproductive structures for future years (PASA et al., 2018; PETRI et al., 2021b). Specific comparisons between the two seasons could not be conducted because of contrasting conditions, such as using different trees to discern treatment impacts without residual effects.
Nonetheless, budbreak promoters almost always increased budbreak percentages in both years, indicating their potential to boost production. In the cultivar Baigent during 2018/19, there were no significant alterations in the mass of fruits per tree or average fruit mass (Figure 3).
Similarly, the average fruit mass in ‘Fuji Kiku 8’ trees remained unaffected, although differences were noted in fruit mass per tree between the two seasons.
During two seasons, Fenili et al. (2017) found variable results on fruit production attributes using their scheme with a sequential application of MO in non-netted ‘Fuji Suprema’ apple trees.
In the first year, the effects of budbreak promoters highly depend on meteorological conditions during spring/summer, and no significant influences have been found under adequate conditions for fruit growth (PETRI et al., 2006).
These findings may justify the overall average fruit mass results. Conversely, likely a consequence of reducing fruiting in the 2018/19 season, the budbreak promoters also reduced mass of fruits per tree in ‘Fuji Kiku 8’ trees, which tended to increase average fruit mass.
In the 2017/18 season, ‘Fuji Kiku 8’ trees yielded less than a total of 3.5 kg, while in 2018/19, ‘Baigent’ trees averaged about 5.5 kg (Figure 3), which is insufficient for profitability in southern Brazil.
However, insufficient amounts do not invariably occur. Fruit yield is closely tied to fructification, explaining the higher averages observed in the upper canopy. A higher number of fruits typically results in lower individual fruit mass due to increased competition for carbohydrates (VERMA et al., 2022).
Interestingly,no significant differences or even inverse relationships were noted between canopy portions, possibly attributed to more favorable meteorological conditions in the upper canopy compared to the lower (BOSCO et al., 2017). In this regard, variations in tree densities, management practices, and the use of hail nets could also contribute to differing results.
Conclusions
A sequential application of budbreak promoters is commonly adopted in many apple orchards in southern Brazil.
Nevertheless,the use of mineral oil (3.5%) and its combinations with hydrogen cyanamide (0.17%, 0.34%), Erger® (1.5%), and Syncron® (1.5%), can provide similar phenology, budbreak, fructification, and fruit production to hydrogen cyanamide 0.34% + mineral oil 3.5%, the standard treatment with one application.
The upper part of the canopy showed delayed phenology but earlier fruit ripening compared to the lower one in ‘Baigent’ trees. A higher fruit amount is provided by the former in ‘Baigent’ and ‘Fuji Kiku 8’.
The sequential application strategy of budbreak promoters is not effective under adverse conditions for budbreak in these economically important hail-netted apple trees in southern Brazil.
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Edited by
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Scientific Editor
Alexandre Pio Viana
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Associate Editor
Luis Eduardo Correa Antunes
Data citations
IBGE. Produção agrícola municipal: sistema IBGE de recuperação automática - SIDRA. Base de Dados. Rio de Janeiro, 2024. Disponível em: https://sidra.ibge.gov.br/pesquisa/pam/tabelas Acesso em: 13 out. 2024.
