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Quarterly Update: June 2006
Updated:22 April 2008
Final Report
The Waikato Fruitgrowers Association is planning to build on our developing grower chemical thinning guidelines, by extending our ability to confidently manage chemical thinning on key varieties in modern high density plantings, adapted to the warm moist climatic conditions of the northern North Island.
The group proposes to evaluate emerging new chemical thinners by select most favourable successful thinning treatments from our previous self funded trials over the past two years, for trial on dwarf rootstock/varieties combinations to include rootstocks M9, CG202, M26, M9/M26 interstem and modern apple varieties of relevance to the Northern North Island.
The Grower group will finalise best trial options and select grower trial sites for the years 2005/06 and 2006/07.
Quarterly update: June 2006
Key Outcomes
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.
Chemical Thinning : Three Year Summary
| Variety | Effective Thinners | No Thinning Response | ||||
| Season | 2003 | 2004 | 2005 | 2003 | 2004 | 2005 |
| Royal Gala |
Thin-It NAA | Thin-It |
NAA/BAPSol full or NAA/BAPSoL Half rate + Carbaryl Thin-It once intensive trees |
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 | - | Thin-It once | Thin-It once | - | |
| Variety | Return Bloom Enhanced | Return Bloom, Not Enhanced |
| Braeburn | Thin-It twice (1 trial) Ethrel then Thin-It |
Ethrel then Thin-It |
| Fuji | Ethrel |
| Variety | Fruit Sizing Effects | ||
| Season | 2003 | 2004 | 2005 |
| Royal Gala | No responses | BAPSoL increased fruit size | No responses |
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.
Introduction
Overview
In 2005/06, we have continued the chemical thinning trial programme to consider three areas.
Firstly, to look at NAA with secondary thinner options on intensive Royal Gala plantings.
Secondly, to explore cost-effective thinning on semi intensive Braeburn in variable flower load conditions
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 needs 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®, Thin-It (ammonium thiosulphate), NAA.
Secondary fruit thinners – BAPSoL® (benzyladenine).
Planned Trial Programme
- Focus on key regional varieties on typical semi intensive and intensive plant densities.
Repeat trials with:
- Thin-It on semi intensive Braeburn
- BAPSoL on semi intensive Pink Lady
- Ethrel on Braeburn
New Trials with:
- NAA/Thin it, or NAA/BAPSoL on intensive Royal Gala
- Ethrel/BAPSoL on Braeburn.
In total 12 trials were planned with two of these an assessment of return bloom only.
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 1.
Table 1: Orchard, Variety and Treatment
| No | Grower/Orchard | Variety | Thinning Challenge | Trial Treatment | Control |
| 1 |
Christey/ Bellevue | Royal Gala | Targeting specific crop load | NAA then Thin-It once | NAA |
| 2 |
Christey/ Bellevue | Royal Gala | Targeting specific crop load | NAA then Thin-It twice | NAA |
| 3 |
Glenn/ WRO | Royal Gala | Targeting specific crop load | NAA then full rate BAPSoL | NAA |
| 4 |
Glenn/ WRO | Royal Gala | Targeting specific crop load | NAA then half rate BAPSoL plus carbaryl | NAA |
| 5 |
Sunfruit/ Ingram | Aurora | Manage biennial bearing on year | Ethrel early | Ethrel later |
| 6* |
Insoll/ Eureka | Aurora | Manage biennial bearing on year | Ethrel followed by full rate BAPSoL | NAA |
| 7* |
Insoll/ Eureka | Aurora | Manage biennial bearing on year |
Ethrel followed by half rate BAPSoL plus cabaryl | NAA |
| 8 |
Sunfruit/ Ingram | Aurora | Thinning in light bloom | Thin It twice | NAA |
| 9* |
Reid/ Holmwood | Pink Lady | Manage heavy bloom for fruit set in twos and minimal fruit set in weak positions | Full rate BAPSoL | Untreated |
| 10* |
Reid/ Holmwood | Pink Lady | Manage heavy bloom for fruit set in twos and minimal fruit set in weak positions | Half rate BAPSoL plus carbaryl | Untreated |
| 11 | Gowanlea |
Braeburn Semi intensive | Thin It once compared with no thinner, in 2004 | Assess Return Bloom | |
| 12 | Eureka |
Braeburn Biennial off | Ethrel once then Thin It once compared with Ethrel only, in 2004 | Assess Return Bloom |
* Proposed trial did not proceed
- At Bellevue, Royal Gala bloom proceeded very rapidly after NAA application, which resulted in there being insufficient time to apply Thin It for a second time. As a result we ended up with two treated blocks, Area B and Area C.
- At Eureka, the manager reviewed bloom levels and considered secondary thinning after Ethrel application was not warranted.
- At Reid/Holmwood, Pink Lady flowered unexpectedly lightly, to the point where chemical thinning of any nature would have resulted in significant reduction in commercial crop.
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.
Pre-harvest fruit size was assessed on the NAA/Thin It treatment on Galaxy at Bellevue, and also on the NAA/BAPSoL treatments on Royal Gala at Waikato Research Orchard. Fruit diameter was measured on 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 2: Thinning Results Summary
For each trial, the results in the table below represent significant differences between the treated and control options, for Fruit/100Flower Clusters.
| Trial No. | Variety | Treated | Control | Fruit/100 Flower Clusters | |||||
| Treated | Control | ||||||||
|
Lower Tree |
Upper Tree |
Lower + Upper |
Lower Tree |
Upper Tree |
Lower + Upper |
||||
|
1 |
Royal Gala Intensive |
NAA/Thin It once; | No application | - | - | - | 57.4 | 66.1 | 62.0 |
| Area B | 28.6 | 31.7 | 30.1 | - | - | - | |||
| Area C | 42.9 | 39.3 | 41.2 | - | - | - | |||
| 3 |
Royal Gala Intensive | NAA/Full Rate BAPSoL | NAA only | 77.0 | 66.6 | 71.8 | 117.7 | 127.7 | 123.0 |
| 4 |
Royal Gala Intensive | NAA/Half Rate BAPSoL +Carbaryl | NAA only | 56.0 | 72.9 | 64.6 | 117.7 | 127.7 | 123.0 |
| 5 | Braeburn | Ethrel Early | Ethrel Later | 77.5 | 79.3 | 78.4 | 59.9 | 48.2 | 53.6 |
| 8 |
Braeburn Aurora |
Thin It twice | NAA | 41.0 | 51.6 | 45.9 | 69.1 | 68.8 | 68.9 |
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.
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.
Past trial results
-
Effects of Thin-It on Return Bloom
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.
-
Effects of Ethrel on Return Bloom
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.
Effects of Thin it and Ethrel 2005/2006 trials
In 2005/06, the use of Ethrel and Thin-It in spring 2004 on Braeburn 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.
-
Braeburn Gowanlea
In spring 2004 the Thin-It treated trees had an improved return bloom. In spring 2005 the Ethrel/Thin-It treated trees had less return bloom than the untreated controls (Table 3), 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.
The graph left demonstrates the smoothing effect on flowering that Ethrel and Thin-It has achieved on these trees.
A similar pattern was also considered to be the case over commercial blocks at Eureka, but not supported on our trial plots.
Table 3: Return Bloom after Ethrel/Thin-It thinning, Braeburn: Gowanlea
|
Average Number of Flower Clusters Per Branch |
||||||
| 2003 | 2004 | Change (%) | 2005 | Change (%) | ||
| Treated | Lower | 124 | 82 | - 34 | 107 | + 30.5 |
| Upper | 64 | 70 | + 9 | 93 | + 32.9 | |
| Whole tree | 188 | 152 | - 19.2 | 200 | +31.6 | |
| Control | Lower | 112 | 49 | - 56 | 94 | + 91.8 |
| Upper | 96 | 71 | - 26 | 134 | + 88.7 | |
| Whole tree | 208 | 120 | - 42.3 | 228 | +90.0 | |
The percentage change should ideally be close to zero from one year to the next, as this means that mature trees are consistently carrying a similar crop load from one year to the next.
A percentage change figure which is negative shows a reduction in flower load from one year to the next, and conversely a positive figure shows an increase in flower load from one year to the next.
-
Braeburn Eureka
At Eureka, Ethrel followed by Thin It on Braeburn 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 (Table 4).
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.
Table 4: Return Bloom after Ethrel/Thin-It thinning, Braeburn: Eureka
| Average Number of Flower Clusters Per Branch | ||||
| 2004 | 2005 | Change (%) | ||
| Treated | Lower | 126.8 | 78.4 | - 38.2 |
| Upper | 64.5 | 37.9 | - 41.2 | |
| Whole tree | 191.3 | 116.3 | - 39.2 | |
| Control | Lower | 123.8 | 84.3 | - 31.9 |
| Upper | 50.6 | 42.2 | - 16.6 | |
| Whole tree | 174.4 | 126.5 | - 27.5 | |
We have carried out trials in the last three seasons and have obtained some interesting, worthwhile and in some cases unexpected results.
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. This was a light cropping season as a general trend in the Waikato and elsewhere, and some over-thinning may have occurred 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. This year 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
Yet again as for 2004/05, we have seen a lack of fruit sizing response to chemical thinning treatments which reduced crop load.
This consistent pattern of lack of fruit sizing response to thinning is not what we expected for Royal Gala and indicates that factors other than crop load are limiting fruit sizing on the trial blocks. Similar results have been found on Royal Gala thinning trials in Hawkes Bay.
Tree Growth
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.
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 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.
Future Work Options
Our trial results over the past three seasons have demonstrated effective thinning options for intensively grown Royal Gala, Braeburn and Pink Lady. However, the ideal chemical thinner combinations in terms of thinning out fruit clusters, selective thinning on annual wood and evening out return bloom have not been fully determined.
For Royal Gala, the challenge has been to get a fruit size response to chemical thinning and to avoid the removal of too much fruit.
Future trials should look at getting a better fruit sizing response using BAPSOL/Cylex, and at expressing thinning responses as fruit numbers per tree (for growers to relate to expected crop loads). Half rate BAPSOL/Cylex has been shown to be as effective as full rates in other regions, and full/half rate comparisons should be done here.
For Braeburn, the effectiveness of BAPSOL/Cylex as a secondary thinner following Ethrel and Thin It blossom thinning needs further trialling. Return bloom could be assessed on the 2005/06 trials where there was a thinning response.
For Pink Lady, further work is needed on secondary thinners. The trial planned last year should be attempted again.
In assessing fruit size effects, it may be worth measuring both individual fruit diameter and weight, as both measurements together provide a better indication of the thinner effects on crop load and consequent fruit size than either factor alone.
We may also consider utilising more trees, separating out counting in spur versus annual wood and recording treatment effects on one branch only per tree, as well as carrying out some whole tree counts.
Acknowledgements
The authors would like to thank:
- Waikato Fruitgrowers Association, MAF Sustainable Farming Fund and Farmlands for funding this project.
- Fruitgrowers: Richard Glenn, Paul Christey, Jack Jenkins, Brian Insoll, Martin Reid, and John Altham for their willingness to host trials in their orchards.
- Ken Johnson, Ken Holroyd, Adrienne Turner, Chris Bennett, Tom Hewitson and Orr Boonsrithanich for assistance with flower and fruit counting.
- GroChem for supply of Thin It, BAPSoL 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.
