Final Report
Key Outcomes
2006/2007
- On intensive Royal Gala on dwarf rootstock M9, NAA as a primary thinner followed by BAPSoL as a secondary thinner, with or without NAA added in to the secondary thinner, gave a very effective thinning result. Fruit numbers were significantly reduced and fruit size was significantly improved.
- On semi intensive Pink lady on MM102 rootstock, NAA as a primary thinner followed by BAPSoL as a secondary thinner gave a very effective thinning result.
- On Aurora, the full bloom Ethrel treatment that achieved better thinning in 2005/06 did not translate into an improvement in return bloom in 2006/07.
2005/2006
- Thin-It was an effective thinner for intensive Royal Gala but treatment did not lead to an increase in fruit size.
- On intensive Royal Gala, NAA followed by BAPSoL full rate or BAPSoL half rate plus carbaryl, is effective in increasing the proportion of flower sites cleared and as well, thinned within clusters on higher branches, but does not necessarily result in a measurable increase in fruit size, either in response to the actual reduction in crop load achieved by thinning, or in any direct effect
- On Braeburn, Thin It was applied in a two application programme at around 60-80% bloom and 80 % bloom can be an effective treatment on Braeburn
- On Braeburn, Ethrel was effective at thinning by completely clearing more flower clusters, when applied at about 80% full bloom compared with Ethrel applied slightly earlier at around 50 -70% full bloom
2004/2005
- Thin-It was an effective thinner for Royal Gala but treatment did not lead to an increase in fruit size.
- Thin-It and Ethrel followed by Thin-It gave a good thinning response in Braeburn this season.
- Pink Lady was not thinned by one application of Thin-It despite a noticeable burning of flower parts.
- Ethrel did not thin Aurora.
- BAPSoL did not thin Royal Gala but fruit size was increased by half a size count.
- Return bloom in Braeburn was improved after Thin-It application in 2003 in one trial but not another. Ethrel did not improve return bloom.
- Return bloom in Fuji was greatly improved following one application of Ethrel in the previous season.
2003/2004
- Both NAA and Thin-It in sequential applications can achieve significant reductions in crop load, particularly when Thin It is well timed.
- Thin-It applied twice on Pink Lady had a positive effect on thinning, which could be particularly useful for Waikato growers.
- Ethrel generally had beneficial thinning effects, but we are as yet uncertain as to the payoff from early thinning on return bloom.
- Biothinner did not thin to an adequate level by comparison with NAA on Brookfield.
- Cylex did thin effectively in the one trial undertaken, but not sufficiently to obviate the need for heavy hand thinning.
Four Year Summary
Table 1: Thinning
| Variety | Effective Thinners | No Thinning Response | ||||||
|---|---|---|---|---|---|---|---|---|
| Season | 03/04 | 04/05 | 05/06 | 06/07 | 03/04 | 04/05 | 05/06 | 06/07 |
| Royal Gala | Thin-It NAA |
Thin-It | NAA/BAPSol full rate or NAA/BAPSoL half rate + Carbaryl Thin It once intensive trees |
NAA then BAPSoL or NAA then BAPSoL+NAA |
Biothinner | BAPSoL | - | - |
| Braeburn | Thin-It twice (1 trial only) | Thin-It once; Ethrel then Thin-It |
Thin-It twice Ethrel |
- | Thin-It (3 trials) |
- | - | |
| Fuji | Ethrel Cylex |
N/A | - | - | - | - | - | N/A |
| Pink Lady | Thin-It twice | - | - | NAA then BAPSoL | Thin-It once | Thin-It once | ||
Table 2: Return Bloom
| Variety | Return Bloom Enhanced | Return Bloom Not Enhanced |
|---|---|---|
| Braeburn | Thin-It twice (one trial) Ethrel then Thin It |
Ethrel then Thin It Ethrel |
| Fuji | Ethrel |
Table 3: Fruit Size
| Variety | Fruit Sizing Effects | |||
|---|---|---|---|---|
| Season | 2003 | 2004 | 2005 | 2006 |
| Royal Gala | No responses | BAPSoL increased fruit size |
No responses | NAA / BAPSoL better than NAA / BAPSoL + NAA, better than NAA |
Introduction
Overview
Successful chemical thinning requires having a clear understanding of the status of each block to be thinned, such as cropping history and tree vigour, the desired outcomes of thinning for each block, the range of tools available to achieve those outcomes and a plan on how to use those tools, on a block by block basis.
In 2006/07, we have focussed on thinning in Royal Gala, Braeburn and Pink Lady. Growers by and large now have the tools to thin these varieties
We have worked on younger and higher density plantings reflecting the mix of varieties and tree ages planted in the region.
Three key areas were explored.
Firstly, to look at NAA with secondary thinner of BAPSoL® on intensive Royal Gala plantings.
Secondly, to look at NAA with secondary thinner of BAPSoL® on high performing Pink Lady plantings.
Thirdly, to follow up on the return bloom effects of treatments applied in the previous seasons on Braeburn.
The performance of these options under local conditions needed to be evaluated to gain a better understanding of how these might be integrated into thinning programmes.
Trial products were used either as replacements for the conventional thinners NAA (ANA) or Carbaryl, or as secondary thinners after NAA had been applied.
Chemical Thinners Trialled
- Primary blossom thinners - Ethrel®, NAA.
- Secondary fruit thinners - BAPSoL® (benzyladenine).
Planned Trial Programme 2006/07
- NAA or NAA/BAPSoL on intensive Royal Gala
- NAA or NAA/BAPSoL on high performing Pink lady
- Ethrel return bloom effects on Braeburn
It is expected that BAPSoL will perform in exactly the same way as CyLex®, since these are both 6 - benzyl adenine products.
Materials and Methods
The trials were planned for grower properties. The orchards, varieties and treatments as proposed are summarised in Table 4.
Table 4: Orchard, Variety and Treatment
| No | Grower; Orchard |
Variety | Thinning Challenge | Trial Treatments | Control |
|---|---|---|---|---|---|
| 1 | Christey/ Bellevue |
Royal Gala M9 rootstock |
Targeting specific crop load. | NAA 10ppm + 125ml Spray Aid/100L NAA10ppm/ |
No thinning |
| 2 | Sunfruit/ Ingram |
Aurora | Return Bloom assessment from 2005/06 treatment | Ethrel Early Ethrel Later |
|
| 3 | Reid/ Holmwood |
Pink Lady | Manage heavy bloom for fruit set in twos and minimal fruit set in weak positions |
BAPSoL 9L/ha NAA10ppm/ BAPSoL 9L/ha |
No thinning |
*10ppm =10ml/100L
/ denotes that treatments were applied in sequence, rather than in combination in the same tank mix
+ denotes that treatment was applied as a tank mix
Trial methods
Either of two options was used to ensure that control trees were available for comparison against treated trees.
Either: both the control and the trial treatments were applied in the same block. Trees were selected for counts where we could be sure there had been no drift effects within the block, between treated and control areas.
Or: the treatment was applied on one block and the control was applied on another block of the same variety, rootstock, growing conditions and orchard management.
For each treatment, 10 typical treated trees and 10 typical control trees were selected. On each of these trees, a typical upper and lower branch was tagged for monitoring. At or before treatment time, the total number of flower clusters on each tagged branch was counted and recorded.
In spring, trunk circumference was measured at 10cm above the graft and then measured again in the winter following, once leaf fall was complete. This measure of trunk circumference was used to calculate trunk cross sectional area (TCA). TCA can be used to make meaningful comparisons of crop loads and performance between different blocks, ages, rootstock/scion combinations, management and other factors, for a variety.
In December, after natural and thinning drop, but before hand thinning, the same tagged branches were revisited. At this time, the number of fruit at each fruiting site were counted and recorded.
Fruit size was assessed immediately at the start of commercial harvest on the NAA/BAPSoL treatments on dwarf Royal Gala at Bellevue. Fruit diameter and fruit weight was measured on about 200 fruit/treatment and 200 fruit/control.
More details of trial procedures are given in ‘Chemical Thinning Trial 2005 Specifications’ Waikato Fruitgrowers Association.
Records were also kept of application details including
- Application date (s)
- Product application rate and concentration
- Weather conditions on application date and for two days afterwards
Thinning Results
Table 5: Thinning Results Summary 2006/07
| Trial No. | Variety | Treated | Fruit/100 Flower Clusters |
|---|---|---|---|
| 1 | Royal Gala (on M9) | Untreated | 82.3 |
| NAA only | 61.4 | ||
| NAA/BAPSoL | 39.5 | ||
| NAA/BAPSoL+ NAA | 39.7 | ||
| 2 | Pink Lady | Untreated | 74.16 |
| NAA/BAPSoL | 55.44 |
For each trial, the results in the table above represent significant differences between the treated and control options, for Fruit/100 Flower Clusters. Detailed trial summaries are available on request.
Thin It
Royal Gala, Galaxy
In 2003/04, we found that both NAA and Thin It in sequential applications can achieve significant reductions in crop load, particularly when Thin It is well timed. The reduction in crop load did not result in an increase in average fruit size, suggesting that some other factors on the trees are influencing final fruit size in addition to the crop loads carried.
In 2004/05, Thin-It application after NAA resulted in a significantly lower crop load compared with NAA alone. Again though, the reduction in crop load did not lead to a significant increase in fruit size. Crop load was evidently not limiting to fruit sizing.
In 2005/06, Thin It applied once only as a bloom thinner on dwarf trees was very effective in increasing the proportion of flower sites cleared. On these trees, bloom was relatively compressed this year.
There was a reduction in fruit/100 flower clusters, between one third and one half; as a result of the Thin It application compared to the untreated control.
Thin-It had the same thinning effect on annual wood as spur wood.
Braeburn
In 2004/05, Thin-It was used on two different trials on Braeburn blocks. Where Thin-It was used once just after full bloom to target bloom on annual wood, Thin-It increased the number of flower sites cleared in both lower and upper parts of the tree, giving a significant and useful thinning result. Where Ethrel was applied at 600 ml/ha followed by one Thin-It targeted at the tops, the main thinning effect was an increase in the proportion of cleared flower clusters.
In 2005/06, Thin It was applied in a two application programme at around 60-80% bloom and 80 % bloom compared with NAA applied on the same date as the first Thin It.
This trial showed that the two programme Thin It applications application achieved a higher degree of thinning.
This was mainly as a result of completely clearing more flower clusters, by comparison with the NAA only treatment.
Pink Lady
In 2004/05, despite the impressive burning of flowers and leaves, Thin-It application did not result in a reduction in fruit set in two separate trials. From both trials, the implication is that the Thin-It application was not effective or that the late flower did not set fruit regardless of thinner use.
BAPSoL
In 2004/05, BAPSoL was used on semi dwarf Royal Gala trees and although there was no thinning effect from the BAPSoL applied as a secondary thinner, fruit size was significantly bigger on the treated trees at 69.0 mm diameter compared with 67.6mm on control fruit. This is roughly equivalent to half a count size difference.
There was a direct effect of the BAPSoL treatment on fruit size unaffected by crop load.
In 2005/06, NAA followed by BAPSoL full rate or BAPSoL half rate plus carbaryl, was also effective in increasing the proportion of flower sites cleared and as well, thinned within clusters on higher branches.
Unlike the previous season’s trial results, however, there was no measurable increase in fruit size, neither in response to the actual reduction in crop load achieved by thinning, nor in any direct effect on fruit size as a result of applying BAPSoL.
In 2006/07, on dwarf Royal Gala trees, NAA followed by BAPSoL alone or by BAPSoL plus NAA, also achieved effective thinning. These trees were selected for treatment as they were considered hard to thin.
The treatments resulted in lower numbers of fruit per cluster and more flower sites cleared, combining to give greater thinning compared with the untreated trees.
The average number of fruit per cluster was significantly lower in the NAA/BAPSoL, and NAA /BAPSoL + NAA treatments.
The NAA at flowering treatment also gave a significantly reduced average number of fruit per cluster compared with the control treatment.
The % of cleared flower sites was significantly higher in the NAA/BAPSoL and the NAA/ BAPSoL + NAA treatments.
The NAA at flowering treatment also gave a significantly higher % of cleared flower sites compared with the control treatment.
A similar treatment effect was found with the number of fruit/100 flower sites.
In 2006/07, on semi intensive Pink lady trees, NAA followed by BAPSoL was effective at increasing the proportion of flower sites cleared by comparison with BAPSoL alone.
The average number of fruit per cluster was statistically similar on the untreated trees compared with the two treatments.
The treatments did not appear to contribute much to thinning within clusters, but the NAA followed by BAPSoL treatment did remove a significant number of clusters.
The overall result was a higher level of thinning achieved by the NAA followed by BAPSoL programme.
Ethrel
In 2004/05, Ethrel on semi intensive Aurora MM106 trees of moderate vigour did result in a lower crop load expressed in fruit/100 flower clusters compared to the untreated control.
In 2005/06, optimal Ethrel timing was investigated. Ethrel was effective at thinning by completely clearing more flower clusters when applied at about 80% full bloom, compared with Ethrel applied slightly earlier at around 50 -70% full bloom. However, the earlier application timing resulted in more thinning within flower clusters.
The combined result of both of these measures of thinning efficacy, when expressed as Fruit/100 Flower Clusters showed that the later application of Ethrel resulted in higher overall thinning.
Return Bloom Results
Return bloom is expressed as the number of flower clusters in spring of one year as a percentage of the number in spring of the previous year, on the same trial trees. Gaining improved return bloom in the following season can give a significant benefit on top of thinning effects in the current season.
Thin-It
Thin It can enhance return bloom on Braeburn, but not always. In one trial, Thin-It applied twice in 2003 gave a significant increase in return bloom in 2004.
In another trial on strongly biennial ‘on’ Braeburn trees, Thin-It applied twice after Ethrel, did not result in an increase in return bloom in the following season.
Ethrel
On Braeburn, Ethrel applied twice on a Braeburn block with some ‘on’ flowering trees in the 2003 Trial 10 Eureka Orchard, did not result in a significant increase in return bloom in the following season. Ethrel did thin significantly in 2004 by increasing the number of flower sites cleared of fruit, particularly in the bottom branches.
On Fuji, Ethrel applied once in an ‘on’ year in 2003 achieved both a positive thinning effect in the year that it was applied and an improvement in return bloom in the following year.
On Braeburn, Ethrel applied in 2004 did not give consistent return bloom effects in our trials. The following summaries shows that at one site there was a definite improvement in return bloom as a result of Ethrel/Thin it application the previous spring. At the other site, this was not the case.
On Braeburn at Gowanlea orchard, the Thin-It treated trees of had an improved return bloom. In spring 2005 the Ethrel/Thin-It treated trees had less return bloom than the untreated controls despite a significant fruit thinning effect from this thinner combination in the previous season. The control trees, which have received no chemical thinning over two seasons, have developed a stronger biennial flowering pattern than the chemically thinned trees.
On Braeburn at Eureka, Ethrel followed by Thin It resulted in significant fruit thinning in spring 2004, but this did not follow through to give significantly different return bloom on these treated trees in spring 2005, compared with the untreated trees.
The orchard manager has noticed a general trend over the past 4 years towards more regular Braeburn cropping on the orchard, which he attributes to the ongoing use of Ethrel as a blossom thinner.
On Aurora at Sunfruit Ingram, Ethrel used either earlier or later in bloom did not improve return bloom on the trial trees in 2006.
The orchard manager commented that the block had a mix of trees on and off in 2006. The trial trees were all off in 2006 but this was not representative of the whole block where overall return bloom was considered to be good, by comparison with what was expected with whole rows or whole block being off in flower level.
Discussion
We have carried out trials in the last four seasons and have obtained some interesting, worthwhile and in some cases unexpected results.
We have shown that the newer thinning options can work alone, in tank combinations and in sequence.
We need to carefully consider, when deciding on use of chemical thinners, the likely natural fruit set under the influence of factors like tree age, pollination conditions and cropping history. We have observed both over and under thinning with chemical thinning treatments.
Thinning option(s) should be selected in relation to desired outcomes from thinning. For example, there is considerable advantage in chemically thinning Royal Gala within clusters, with the winter pruning programme having already set the maximum number of flower buds on the tree.
Thin-It
Thin It has achieved effective thinning from a single application on intensively planted 4th leaf Royal Gala.
The product has also achieved some worthwhile results on Braeburn. For example, Thin-It once; Ethrel followed by Thin-It; and Thin It in a two application programme have all given worthwhile thinning on Braeburn. Thin-It and Ethrel/Thin-It combinations provide useful chemical thinning options for Braeburn, at least in some seasons.
In 2003/04, Thin-It applications did a good fruit thinning job on Pink Lady. In 2004/05, one application of Thin-It did no thinning on Pink Lady despite impressive flower burning on late blossom. In 2005/06 it was not appropriate to use any thinner on Pink Lady.
Careful consideration should be given to the use of Thin It, which appears to mainly thin flowers open at the time of application, removing entire clusters if these are all open, as compared with other thinners which may thin better within clusters.
Fruit Sizing
This year, on dwarf Royal Gala trees, we have seen significant fruit sizing response to chemical thinning treatments which reduced crop load.
The BAPSoL treatments used in this trial produced a very effective and economically useful thinning job in terms of the number of fruit removed and in the fruit growth response. The best treatment (NAA >> BAPSoL) resulted in fruit with an average size count of 120 compared with 155 size count where no thinner was used and 135 count when only NAA was used. Note that these results were achieved without any hand thinning in the trial areas.
It may be that on such vigour reducing rootstocks, crop load as a result of thinning, produces a fruit sizing response. In previous years trials on Royal Gala, we have not seen fruit size responses where thinning responses have been obtained.
Tree Growth
In 2005/06, the trunk growth of the untreated intensive Royal Gala trees, which carried a heavier crop load, was greater than the trees in the two treated blocks. The heavier crop did not reduce tree growth. An explanation for this could be that the control trees are growing in a better site, despite being close to the treated trees. Crop load was not limiting tree growth in these blocks.
In 2006/07, the trunk growth measured over this period increased in parallel with the crop thinning effect; however, these differences were not statistically significant.
BAPSoL results
BAPSoL used as a secondary thinner at either the full rate or at half rate with carbaryl, when used after NAA, was effective at reducing fruit set per 100 flower clusters. However, there is not always a fruit size response, despite the reduction in crop load. For example, in the previous season we obtained a probable fruit size response to BAPSoL itself as a promoter of cell division, rather than the effect of BAPSoL on crop load. We have not always seen a consistent fruit sizing response to chemical thinning treatments with BAPSoL whether it reduced crop load or not.
Again, factors other than crop load are limiting fruit sizing on the trial blocks.
We consider that the positive thinning responses we have obtained from BAPSoL in 2006/07 are a result of the product being used under optimum conditions. I.e. where there was a window of warm temperature on the day of application and a rising daily average temperature for two to three days after application.
Acknowledgements
The authors would like to thank:
- Waikato Fruitgrowers Association, MAF Sustainable Farming Fund and Farmlands for funding this project.
- Fruitgrowers: Paul Christey, Martin Reid and John Altham for their willingness to host trials in their orchards.
- David Hart, Martin Reid, Dianne June and Orr Boonsrithanich for assistance with flower and fruit counting and fruit size measurement and trunk measurement.
- GroChem for supply of Thin It, BAPSoL, Spray Aid, Ethrel and advice.
Disclaimer
Because of the large number of factors involved in horticulture, Lynda Hawes, Horticultural Consultant and Selwyn June, Horticultural Consultant are not liable for any claims, losses or demands whatsoever whether in tort or contract, which may arise from information given by them or included in this and associated reports.
