Chemical Regulation of Crop Load in Apples: Present Options and Future Possibilities. Steven McArtney Southeast Apple Specialist

Transcription

1 Chemical Regulation of Crop Load in Apples: Present Options and Future Possibilities Steven McArtney Southeast Apple Specialist

2 Critical Components of the Thinning Process Orchard design Spraying technology Chemistry Management Decision Tools

3 Currently Available Thinning Chemicals Sevin NAA and NAAm Ethrel 6-BA Potential New Thinning Chemicals ACC Metamitron Abscisic acid Banned in EU?????????

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5 Pictures taken 3 days after application of 400 mg/l ACC To Cameo at 19 mm

6 Pictures taken 3 days after application of 400 mg/l ACC To Cameo at 19 mm

7 So what exactly is ACC? SAM ACC Ethylene ACC synthase ACC oxidase ACC is naturally occurring in all plants ACC is the precursor of ethylene ACC is not Ethrel Ethylene is derived from ACC by a biochemical reaction vs. a physicochemical response for Ethrel Could ACC be an organic thinner? Fruit Abscission

8 NAA ± ACC (Goldrush, 2009, 2010) Treatments Whole tree sprays of 5 ppm NAA with an airblast sprayer Individual spurs sprayed with 0, 50, 100, 200 ppm ACC Split-plot design experiment with NAA as the main plot Measurements Fruit set (fruit per spur) Ethylene evolution 1 d and 4 d after treatment Spur leaf number at harvest (in 2009 only)

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10 Set (fruit/spur) The ACC Response is Concentration Dependent (GoldRush, 2009 and 2010) No NAA NAA 5 mg L No NAA NAA 5 mg L ACC (ppm) ACC (ppm)

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12 nl C 2 H 4 /g fr.wt./hr Ethylene evolution following application of ACC to Pink Lady at full bloom (A), 10 mm fruit diam. (B) or 20 mm fruit diam. (C) Control A B C Days after full bloom

13 nl C 2 H 4 /g fr.wt./hr Ethylene evolution following application of ACC to Pink Lady (2010) at full bloom (A), 10 mm fruit diam. (B) or 20 mm fruit diam. (C) Some time between 10 mm fruit diameter 60 (17 days after bloom) and Control 20 mm fruit 50 diameter (32 days after bloom) ACC 200 the mg L-1 ability 40 to convert ACC to ethylene was lost 30 ACC 400 mg L A B C Days after full bloom

14 Fruit set (no. per spur) Ethylene (nl g -1 FW h -1 ) ACC responses are reduced over time (GoldRush, 2011) Effects of fruit diameter at time of ACC (200 mg L -1 ) application on ethylene evolution from detached fruit (A) and final fruit set (B) of GoldRush apples in Ethylene evolution was measured 1 d after each time of ACC application *** *** a ** a Control ACC *** 11 mm 17 mm 23 mm 27 mm 31 mm a NS a A B 1.5 Perhaps the inability to thin fruit >20 mm in size is related to the loss of ACC oxidase activity? b c Control 11 mm 17 mm 23 mm 27 mm 31 mm Fruit diameter when ACC applied (mm)

15 Why do apple fruit become more difficult to thin with time there is an increasing carbohydrate surplus in the tree, or the fruit lose the ability to convert ACC to ethylene, or both of the above

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22 Metamitron is a photosynthetic inhibitor Binds to the Q B -binding site in PSII, Interrupting photosynthetic electron transport

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24 Control Metamitron 300 mg L-1

25 Light sat. leaf P n (% control Braeburn is more sensitive to Lime Sulfur than other cultivars What if apple cultivars responded differently to Metamitron? nd 3rd Royal Gala Pacific Rose Fuji Braeburn Days after 1st spray application Data from Jens Wünsche

26 Fv/Fm Fv/Fm Metamitron Creates a transient carbohydrate stress, as measured by chlorophyll fluorescence, 0.84 SunCrisp apples 0.85 Contender peaches Control 0.72 Metamitron 350 mg L Days after first application Control Metamitron 300 Terbacil Days after first treatment

27 ETR (µmol m -2 s -1 ) Metamitron Activity can be greatly increased by adding a surfactant a b a b a a a a b b c c Control Metamitron Addition of a surfactant (Silwet L-77) greatly Metamitron + Silwet L77 0 increased the effects of metamitron on Days after treatment chlorophyll fluorescence in Cameo

28 Use of Combinations of ACC and Metamitron for Re-thinning

29 Abscisic Acid (ABA) Control S-ABA [Protone]

30 Abscisic Acid (ABA)

31 Cross-section through an apple leaf stomata stomata/mm 2

32 Stomatal conductanc (% control) Is Abscisic Acid an Apple Thinner? Control ABA (250 mg L -1 ) (+)-8 -acetylene ABA (25 mg L -1 ) Days from treatment

33 Phytotoxicity from Abscisic Acid (ABA)

34 Carbohydrate Stress in the Fruit Integrates the Effects of Environment and Chemical Thinners on Fruit Set ABA

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36 You can make a big apple small but you can t make a small apple big

37 Typical Hand Thinning Instructions 1. Damaged or misshapen fruit removed first 2. Fruit number per spur reduced 3. Remaining fruit spaced 6-8 inches apart Notice! Fruit number per tree or fruit size were not considered during this process!

38 Frequency (%) Traditional Hand Thinning Methods do not Consider Fruit Size Fruit on the tree Fruit on the ground A lot of big apples ended up on the ground Fruit diameter (mm)

39 Size Thinning Method The size thinning method uses fruit size (diameter) as the primary basis for deciding which fruit to remove It places a lower priority on the number of fruit per spur and on spacing between fruit

40 Size Thinning Method You will need to do three things 1. Count how many fruit you have on each tree 2. Have an idea how many fruit you want to have (TARGET CROP LOAD) 3. Measure the diameter of 100 random fruit in mm and sort in order from smallest to largest

41 Example Size Thinning Method 1. Actual crop load = 450 fruit per tree 2. Target crop load = 300 fruit per tree You will need to remove 150 fruit from each tree or 33 % of the fruit to reach your TARGET CROP LOAD 3. To make sure you remove the smallest 150 fruit (33%) you will need to check the diameter of the 33 rd smallest fruit in the sorted size data

42 Fruit diameter (mm) Size Thinning Method Example mm Give your thinning crew a fruit that is 34 mm in diameter and instruct them to remove all fruit this size and smaller from the tree % Fruit number Size Thinning achieves two things ensure that only the smallest fruit are removed, and ensure a crop load target is met

43 Frequency (%) Size Thinning Method Traditional Method A Fruit on the tree Fruit on the ground Fruit diameter (mm) Size-Thinned B Fruit on the tree Fruit on the ground Fruit diameter (mm)

44 Critical Components of the Thinning Process Orchard design Spraying technology Chemistry Management Decision Tools

45 Acknowledgements JD Obermiller, NCSU Duane Greene, U.Mass Greg Clarke, Valent BioSciences Peter Petracek, Valent BioSciences