CHEMICAL THINNING OF APPLE UNDER NORWEGIAN CONDITIONS. WHAT WORKS?

Transcription

1 CHEMICAL THINNING OF APPLE UNDER NORWEGIAN CONDITIONS. WHAT WORKS? Frank Maas & Mekjell Meland Norwegian Institute of Bioeconomy Research NIBIO Ullensvang

2 CONTENT PRESENTATION Introduction Frank Maas Background physiology of fruit set and fruit thinning Available methods for fruit thinning apples Recent experiences with some thinning agents in Norway Future of fruit thinning

3 WHO IS FRANK MAAS? Plant physiologist / Fruit scientist 2013 present: part time fruit scientist at NIBIO-Ullensvang : Horticultural scientist Wageningen University and Research centre Main research areas Fruit tree physiology Chemical thinning Regulation of tree vigour o o o Growth regulators Root pruning Rootstock selection and evaluation

4 NEED FOR REGULATION OF FRUIT LOAD IN APPLE To obtain the desired fruit quality (size, colour, sugar content) To avoid alternate bearing From flowers to 100 apples per tree

5 FACTORS AFFECTING FRUIT NUMBERS PER TREE Number of flowers per tree Pollination and fertilization of flowers Fruit set Carbohydrate availability and distribution (June drop) Competition between fruits Competition between fruits and shoots

6 ANNUAL CYCLE OF FRUIT PRODUCTION Thinning options ATS Ethephon (Cerone) Lime sulphur Mechanical thinning BA (MaxCel, Exilis) NAA Metamitron (Brevis) Artificial shading Hand thinning

7 PRINCIPLE OF BLOOM THINNING Reduction in fruit set of flowers by: Prevention of fertilization by inhibition of pollen germination and pollen tube growth Prevention of fertilization by enhancing senescence egg cells (= less time for pollen tube to reach egg cells in the ovary) 24 h after ATS 24 h after Ethephon

8 Hours FROM POLLINATION TO FERTILIZATION Time needed for pollen tube to reach ovary days days Temperature ( C) Source: Williams & Wilson (1970), Long Ashton Research Station

9 % fruit set EFFECT ATS ON FRUIT SET DEPENDS ON TIME BETWEEN POLLINATION AND ATS-APPLICATION kg/ha ATS, 200 L no pollination no ATS Source: Maas, Acta Hort. 1138: Time between pollination and ATS-application (hours)

10 APPLICATION OF ATS Critical, narrow window for application 1 st application at full bloom 1 day after full bloom old wood 2 nd application 1-3 days after full bloom old wood 3 rd application at full bloom 1 st year wood Critical, only apply on dry leaves to prevent leaf damage!

11 EXAMPLE OF TRIAL WITH ATS IN ELSTAR APPLE Used in many trials since 1996, widely used in practise Treatment in 1996 Flower clusters per tree Fruits per tree Average fruit weight (g) Untreated 311 a 146 a 135 a 31 a 0.5% ATS 303 a 118 a 145 ab 49 a 1.0% ATS 304 a 82 b 151 bc 44 a 1.5% ATS 317 a 43 c 152 bc 40 a 3.0% ATS 341 a 48 c 159 c 44 a 1% ATS = 10 kg/ha (spray volume = 1000 l/ha) Return bloom (%) Source: Balkhoven & Wertheim (1997). Acta Hort. 463:

12 APPLICATION OF ETHEPHON (CERONE) Application window: pink bud to ca. 2 weeks after full bloom Stronger thinning effect at earlier development stage Critical, thinning very temperature dependent Too small effect at low temperatures (T < 12 C) Risk of overthinning at high temperatures (T > 20 C) Not widely used in Netherlands Not a reliable thinning agent in cool climate

13 EFFECT THINNING WITH ETHEPHON ON FRUIT SET DELBLUSH TENTATION Source: Maas & van der Steeg, 2001

14 APPLICATION OF 6-BENZYLADENINE (BA) Fruitlet thinner Applied at fruit size 8 to 14 mm Critical, thinning temperature dependent Temperate > 18 C needed after application No thinning in weak growing trees or branches Commonly used thinning agent in Netherlands Not a reliable thinning agent in cool climate Advice: wait for the right temperature as BA thins better at 16 mm fruit size and 25 C than at 12 mm and 15 C

15 CURRENT STRATEGY FOR THINNING APPLES IN NL Ammonium thiosulphate (ATS) during bloom to prevent pollen germination and fertilization (12 to 15 kg/ha, 1 to 3 applications) Metamitron (Brevis ) at 8-16 mm (since 2016) (1.1 to 2.2 kg/ha, 1 or 2 applications) 6-benzyladenine (MaxCel, Exilis, Globaryll 100) at mm fruit diameter ( mg BA/liter = liter MaxCel/ha)

16 THINNING TRIAL ELSTAR 2006 Treatment Elstar 2006 Flower clusters per tree Fruits per 100 flower clusters Average fruit weight (g) Flower clusters per tree 2007 (% of 2006) Untreated c 120 a 45 a (19%) Hand thinning a 176 c 80 a (32%) BA bc 166 bc 175 b (71%) ATS + BA ab 181 c 81 a (33%)

17 SIZE DISTRIBUTION ELSTAR APPLES 100 % 80 % >85 > % % % 0 % < Untreated control Hand thinned ATS + BA BA % kg >70 mm

18 SUMMARY & CONCLUSIONS Chemical fruit thinning in The Netherlands relies on only a few products In case of many flower clusters growers are adviced to start thinning during bloom by using ATS or Ethefon. ATS is the preferred product ATS application is difficult (narrow time window and often non optimal weather conditions during bloom) Approx. 4 weeks after bloom (10-12 mm fruit diameter) BA or Brevis (since 2016) may be used for additional fruit thinning. ATS and BA on their own are less effective and usually not sufficient to obtain the desired level of thinning. ATS followed by BA is the preferred and most commenly used thinning strategy Fruit size, fruit quality and return bloom are all positively affected by ATS + BA Optimum thinning strategy with Brevis is still under evalutation in practise

19 EXPERIMENTAL FIELD ULLENSVANG Summerred / M.9 planted May 2012 Pollinizers: Dolgo and Everest

20 TRIAL LAYOUT 2014 Randomized block design 8 Treatments 4 replicated blocks of plots of 2 trees 1. Untreated control 2. Hand thinning after June drop kg/ha Brevis at 15 mm fruit ø kg/ha Brevis at 15 mm fruit ø kg/ha Brevis at 15 mm and 19 mm kg/ha Brevis at 15 mm and 19 mm 2 year old trees planted in 2012 Planting distance: 4.0 x 1.0 m Ø Flower clusters per tree 2014: 96

21 COURSE FRUIT SET SUMMERRED IN ULLENSVANG

22 RESULTS BREVIS THINNING TRIAL 2014 Too strong thinning at 2.2 kg Brevis and 2x 1.1 kg and 2x 2.2 kg Brevis per ha Return bloom low even in case of severe overthinning

23 TRIAL LAYOUT 2016 Randomized block design 8 Treatments 4 replicated blocks of plots of 2 (Ullensvang) to 4 trees each (Lier) 1. Untreated control 2. Hand thinning after June drop kg/ha Brevis at 8-10 mm kg/ha Brevis at 8-10 mm kg/ha Brevis at 8-10 mm and mm kg/ha Brevis at 8-10 mm and mm L/ha Cerone (240 mg/l ethephon) at full bloom (May 12, 2016) kg/ha ATS at full bloom (May 12, 2016) Ø Flower clusters per tree 2016: 94 (Ullensvang), 131 (Lier)

24 WEATHER DATA 2016 LOFTHUS-ULLENSVANG Brevis application dates: May 31 and June 8

25 COURSE FRUIT SET SUMMERRED IN ULLENSVANG

26 RESULT THINNING TRIAL ULLENSVANG 2016 No significant effects of Brevis in 2016 on: fruit set average fruit weight Possible explanation for lack of thinning efficacy: high natural fruit drop

27 WEATHER DATA 2016 LIER (EASTERN NORWAY) Brevis application dates: May 28 and June 6

28 FRUIT SET AND WEIGHT SUMMERRED IN LIER Trial in commercial orchard in cooperation with local advisor Summerred / M.9 planted in 2008

29 YIELD (KG/TREE) SUMMERRED IN LIER Trial in commercial orchard in cooperation with local advisor Summerred / M.9 planted in 2008

30 FRUIT QUALITY SUMMERRED IN LIER Treatment Back-ground colour Blush colour Firmness (kg) No. seeds Brix Starch index Control Hand thinned kg Brevis kg Brevis x 1.1 kg Brevis x 2.2 kg Brevis L Cerone kg ATS F-test N.S. N.S. N.S. N.S. No significant effect of thinning treatment on fruit quality parameters Fruit very ripe at time of harvest (almost no starch left) 11.5 N.S. 9.4 N.S.

31 CONCLUDING REMARKS No good explanation for lack of thinning efficacy Brevis, ethephon and ATS on Summerred apple in Ullensvang trial in 2016 (strong natural fruit drop?) Single application of Brevis at 8-10 mm gave adequate thinning in trial in Lier. Twofold applications of 1.1 and 2.2 kg/ha resulted in overthinning. ATS gave adequate thinning in Lier Ethephon resulted in overthinning in Lier No effects of thinning treatments were observed on fruit quality. Fruits were picked too ripe at both locations Experiment will be repeated in 2017

32 FUTURE OF FRUIT THINNING APPLES New thinning products and methods in development ABA plant growth regulator ACC precursor of plant growth regulator ethylene Armocarb (registered in CH as thinning agent for organic apple production) Mechanical thinning on basis of flower density measured by camera

33 Thank you for your attention NIBIO Ullensvang