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Crop load management of apples by chemical thinning

In modern apple production systems, chemical thinning of young fruitlets within the first four weeks after petal fall has become a key management element. Inadequate thinning of fruit during this period increases the need for hand thinning, which is generally more laborious and expensive. On the other side, if trees are left without thinning at all, the chances of having low quality fruits and less return bloom in the following year are very high. To achieve adequate thinning using chemical thinners, many factors should be taken into consideration. These include, but are not limited to, fruit size, carbohydrate reserve status of the tree, weather conditions and -to a lesser extent- variety sensitivity. As a general rule, sunny days and cold nights promote the accumulation of photoassimilates and consequently trees become less prone to shed any of their fruits and are less sensitive to thinning applications. Whereas, cloudy days and warm nights lead to carbohydrate deficit and therefore trees tend to retain only a limited number of fruits and become more sensitive to chemical thinning. This associating between weather conditions and the total carbohydrate reserve has encouraged scientists (Alan Lakso and Terance Robinson) at Cornell University to establish a model known as “The Cornell Apple Carbohydrate-Thinning Model” that provides instructions on the dose and timing of thinning applications based on the solar radiation, temperature and day length records acquired from a weather station in a grower’s orchard blocks. This model can be accessed online through the Network for Environmental and Weather Applications (NEWA)(http://newa.cornell.edu/index.php?page=apple-thin).
It is a good practice to visit the NEWA website and make yourself familiar with the inputs and outputs of this model, especially if you have a weather station in your orchard that is connected with NEWA server, or you know the one that is close to your operation and that you can depend on.
As we are moving toward a heavy crop load and, luckily, less frost damage for apples this year, we have to consider looking at the outputs of the carbohydrate model in order to decide the timing and the dose of the chemical thinner. Typically, the efficiency of thinning applications applied from petal fall until a fruit size of 20 mm correlates well with the carbohydrate reserve of the tree and these are the times where the model outputs will serve as useful guidelines.
This year, we, at AHS Jr. AREC, Winchester, will run the model weekly and provide the outputs of this model as graphs that show the carbohydrate reserve of apple trees, and the recommended applications. The following table (Table 1) describes the recommended dose of chemical thinners based on the carbohydrate balance of the tree.
Table (1): Decision rules for using the output of the carbohydrate model to adjust chemical thinning rate.

Fruit size is another major factor that determines the efficiency of chemical thinning. When fruits are young (~ 6 mm), their demand of carbohydrate is not much and hence thinning becomes relatively challenging. However, chemical thinners such as naphthaleneacetic acid (NAA) and Sevin (carbaryl) and, to some extent, naphthaleneacetamide (NAD; Amid-Thin) can be successfully used at this stage. As fruits grow to the size of 7-14 mm, their cells divide rapidly and their demand of carbohydrate becomes more than what vegetative tissues can supply, especially if weather conditions do not largely support photoassimilation. At this stage, fruits become more sensitive to chemical thinners such as 6-benzyladenine (6-BA), NAA and NAD. However, if thinning is not adequate at this stage due to unsuitable weather conditions, then another round of thinning application will be essential. As fruit develops to the size above 20 mm, the chemical thinning becomes a tangible challenge. At such an advanced stage of development, fruits become more tolerant to abscission as they have more carbohydrate reserve and the seeds produce auxin which interferes with ethylene action preventing abscission. Chemical thinning at this stage (known as delayed/ rescue thinning), relies mostly on the combined application of 2-chloroethylphosphonic acid (ethephon) and 1-naphthyl methylcarbamate (carbaryl). The following table (Table 2) shows the recommended thinning applications in each stage of flower/fruit development and the dose of each application.
Table (2): Materials, rates and timing of chemical thinning application (Source:2017 Spray Bulletin for commercial tree fruit growers).

Snow is not bad after all…keep it dry.

Having some snow on trees and ground, even if it is not that heavy like the one we had last night, is not bad at all. Having a layer of dry snow on the ground should provide good insulation for soil and roots against the expected low temperatures we will face tonight and tomorrow morning. Also, large limbs that are still loaded with snow should get some protection. Using sprinklers will worsen the situation as wet snow works as a good thermal conductor and will transfer these freezing temperatures to roots much faster than dry snow.

Sprinklers for frost protection: are they worth using?

The simple and direct answer is YES, BUT you have to consider the right time/conditions.
When you use sprinklers to reduce frost damage, you are simply using the internal (latent) energy of water molecules as a source of heat to your trees. Simply, water exists in three forms (liquid, solid (ice) and gas (vapor), and the transition among these forms can produce energy (exothermic) or consume energy (endothermic) as appears in the diagram below. So, when the air temperature is below freezing points (< 32 oF), and you use sprinklers, you indeed encourage the transition of water from its liquid phase into ice in order to release the latent energy into sensible energy (heat) that plant tissues can use to warm up. Great! Where is the problem?

There are three things you have to understand and consider in order to get this positive effect of sprinklers and not to harm your plants. First, you have to watch the wind. The Wind encourages the transition of the water from the liquid phase into the gaseous phase (vapor) and while this happens, heat in the air and around your plants will be consumed in an endothermic reaction. So, it’s always recommended that you don’t use sprinklers if the wind is above (10 mph). The table below (Table 1) should help you decide the amount of water needed (inches/h) under different wind conditions (mph) and under different temperatures.
Table (1): Amount of water (inches/h) that should be provided for frost protection under different wind speeds (mph). (U of Florida Ext. Circ. 287)

Second is the dew point: without putting complication to the topic, low dew points implies low humidity and if the dew point is too low, the water you add through sprinklers will be soon evaporated to compensate for the low air humidity and consequently cools down air around your plants. So, under moderate dew points, a part of water you add through sprinklers will turn into vapor and consumes heat and another part will turn into ice and produces heat, but AFTER SOME TIME, the net energy will be positive and you will get the benefit of using sprinklers. However, if the dew point is too low, it means that the air is too dry and it will take MUCH TIME to be saturated with vapor. During this time, the air temperature might reach to the critical temperature at which your buds/flowers will be damaged. In this case, sprinklers will cause more damage to your plants than without sprinklers. To help you decide whether sprinklers will be useful for your case or not, use the following table (Table 2) to determine the temperature at which you should turn on/off your sprinklers. If the dew point and the critical damage temperatures are not in the range shown in the table, don’t use sprinklers.
Table (2) shows the minimum temperature at which sprinklers should be turned on/off (UC-Davis, FP005 Quick Answers).
Simply, select the critical temperature for frost damage (the columns) and the dew-point temperature (the rows). The temperature where the row value crosses with the column value is the minimum air temperature at which you can turn on/off your sprinklers.

– you can use this tool to determine the dew point (https://www.weather.gov/epz/wxcalc_rh).
Or, you can get the dew points from Intellicase (use your zip code) http://www.intellicast.com/Local/Weather.aspx?location=USVA0837

The third thing to consider is the amount of water that your sprinklers can provide. If you are not sure that your sprinklers can provide sufficient amount of water, don’t use them at all. Table (1) should help you determine the amount of water required under different conditions.

What’s important to look at if concerned about potential frost?

Two things-the developmental stage of your buds and the critical temperature for frost damage
– For deciduous like pome and stone fruits, dormant buds are protected enough and not too much affected by the frost and freeze conditions. However, once the buds swell and become ready to burst, low temperatures are a major threat for the developing floral organs and the fresh vegetative tissues. For the northern parts of Virginia, and from what I see in our apple orchard at AHS Jr. AREC, I would not raise any red flags regarding the frost that might occur tonight (March 10) or over the weekend. Why? because most apple varieties are still between the silver tip and the green tip stage and we would need some degrees between 5-10 F or below to worry about bud damage, which is not the case based on the weather forecasting for this period.
Here is the table that has been developed by WSU for the critical temperatures that might cause damage to apple and other fruit trees.

To download the whole table, use the link https://extension.usu.edu/files/publications/factsheet/pub__5191779.pdf

– Another source that may be useful for some of you is the apple freeze risk tool developed by Cornell University. Link:

CSF Apple Stage / Freeze Damage Probability

In this tool, you can select the location (using ZIP code), the variety (only three apple varieties), and whether you would like to see the full season trend (choose full season) or the current (this is the default setting). The tool takes into consideration the minimum temp., the developmental stage, and the temp. where 50% buds could be killed due to frost. If the minimum temp line (the blue line), crosses with the critical temp (the orange line), then the expectation is 50% bud damage.
If you look at the chart above, you can easily realize why I am stating that it might be useful for SOME (not all), because we at Winchester area are not even close to the tight cluster in Red Delicious (or any other variety) as this tool suggests; and hence the prediction of the 50% damage during the weekend (March 11, 12) is unrealistic. However, if this tool hits the right stage for you, I would say use it as a reliable source for frost prediction. Otherwise, use the above-mentioned table to assess the damage, if any.

2017 Tree Fruit Research Priorities Questionnaire

Orchard management and profitable production of tree fruits has become driven by robust science and thorough research. In light of this fact, this multidisciplinary questionnaire has been put together by a group of AHS Jr.-AREC scientists to help them identify and set research questions that reflect the interests of Virginia tree fruit growers and stakeholders. A similar questionnaire was distributed 6 years ago and has served to guide AHS Jr.-AREC scientists designing their field-blocks and shaping their research directions. Based on this survey, many experiments in pomology, plant pathology and entomology have been initiated. This includes, but is not limited to, experiments on crop load management practices, orchard tree planting density, variety and rootstock evaluation, physiological disorders, fungicides and insecticide efficacy trials, mating disruption trials and organic practices. This year’s questionnaire is meant to investigate the new trends and interests of Virginia fruit producers that may ignite new ideas or further promote researching the existing ones.

We are expecting responses from tree fruit growers, private agricultural consultants, agribusiness field representatives, VCE specialists and VCE extension educators in Virginia. An online version of the 2017 questionnaire can be accessed here (https://virginiatech.qualtrics.com/SE/?SID=SV_ezHdupTmKNcdO05). Please complete before March 15th.

A paper version of this questionnaire will be distributed during the upcoming fruit school meetings (Feb 13-17).

2017 Tree Fruit Schools

Carroll Patrick Fruit School in Cana, Virginia: Monday, February 13, 2017 – agenda and registration details: ( carroll-patrick-fruit-school )

Botetourt-Roanoke Fruit School : Tuesday, February 14, 2017 – agenda and details ( roanoke-area-fruit-school )

Southside Fruit School in Blackstone, Virginia: Wednesday, February 15, 2017 – agenda and registration details: ( southside-fruit-school )

Nelson-Albemarle (Central Virginia ) Fruit School : Wednesday, February 15, 2017 – agenda and details ( 2017-fruit-school-registration-lovingston )

Rappahannock-Madison Fruit School in Syria, Virginia: Thursday, February 16, 2017 – agenda and details: ( rappahannock-madison-fruit-school )

Winchester Fruit School in Winchester, Virginia: Friday, February 17, 2017 – agenda and registration details: ( winchester-fruit-school )

2016 Spring Tree Fruit Meetings – Central Virginia

Central Virginia Tree Fruit Meetings:

Our first technical production meeting of the 2016 Central Virginia Orchard Meeting series begins on Tuesday, April 5th.  It will be hosted by Henry Chiles and everyone at Crown Orchard.  We will be meeting at the Johnson Purvis orchard block which is located just south of the village of Covesville.  DIRECTIONS:  From Charlottesville: Travel on Route 29 south for 15 miles (about 20 minutes). Approximately one mile south of Covesville turn left on Route 632 (Faber Road). From Lynchburg: Travel on Route 29 north. Approximately 1 mile north of the Nelson County line, at the top of the hill, turn right on Route 632 (Faber Road).

The orchard entrance is less than a quarter mile down the road.  Turn left and cross the wooded railway trestle. The orchard is on the other side.

After the in-orchard portion of the program we will be provided lunch by the Chiles family.  Since this is a catered lunch please let us know how many people are planning to attend by calling the Extension office at (434) 263-4035 or replying directly to this email. We owe many thanks to Mr. Chiles and his family for once again providing their hospitality to kick off another season of apple production.

This and all subsequent meetings will begin at 11:00 a.m.  Please come to discuss fruit production issues and concerns with other fruit growers and Extension fruit specialists.  Once again, please bring a bag lunch to our other meetings.  Cold drinks will be provided by the host orchard.

 

2016 Orchard Meeting Schedule

Date                       Orchard

April   5th                 Crown Orchard

April 19th                 Silver Creek Orchard

May    3rd                 Saunders Brothers Orchard

May  17th                 Dickie Bros. Orchard

May  31st                 Fitzgerald Orchard

 

Sincerely,

Michael W. Lachance

Extension Agent

 

Lucinda A MacRae

Unit Administrative Assistant

Virginia Cooperative Extension

Nelson County Office

P.O. Box 298

8445 Thomas Nelson Hwy.

Lovingston, VA 22949

Tel 434-263-4035

Fax 434-263-4367

Email lmacrae@vt.edu

 

2016 Winter Fruit Schools – Save the Dates

The Patrick-Carroll school (Mt. Airy) will be held on Monday, Feb 8. The Botetourt-Roanoke school will be held on the morning of Wednesday, Feb 9, starting at 8:00 AM. A Blackstone school will be held this year, morning of Feb 10. The Nelson-Albemarle (Central Virginia) school will be held in the late afternoon-evening of that Wednesday, Feb 10, starting at 3:00 PM. The Madison-Rappahannock school will beheld on Thursday, Feb 11, and the Winchester school will be held on Friday, Feb 12. Details on the agendas will be posted when available.

http://www.virginiafruit.ento.vt.edu/HotApple.html

 

Annual End-of-August Maturity Testing

This it the 28th year that researchers at the Alson H. Smith, Jr. AREC have recorded Golden Delicious and Red Delicious apple maturity data from orchards based in and around Winchester. Including 2013, data for Empire has been taken for twelve years and Gala for six years. In recent years, we have also added other commercially important cultivars to the analyses in order to generate long term averages. These data provide an interesting insight into the current season’s harvest, and can help growers make decisions on when to pick different blocks.

As discussed in a previous post, bloom date was about three weeks later than in 2012 and fairly close to the long-term averages. This should mean that harvest dates will be relatively “normal” or at least more similar to harvest dates in the late 1990’s through early 2000’s than they have been in the last several years.

As of this week, most growers in the Northern Shenandoah region are finishing up picking Ginger Golds, and have started picking Gala and Honeycrisp. Some growers in Central Virginia are finishing Gala and starting with Golden Delicious.

Many of the Golden Delicious blocks that we tested this week had very nice fruit finish, with minimal russet. Golden Delicious maturity was quite variable in the blocks that we tested, and it appears that some blocks will be ready to harvest within the next week, while others are probably 7-10 days away from being ready to harvest. The use of ReTain by some growers may explain some of this variability.

With the cool nights that we have experienced in August, red skinned cultivars have developed better than average color. However, be sure to check the starch and sugar levels before picking to be sure that the apples are mature enough to pick. Many Red Delicious apples that we tested this week had great color but very little starch degradation and soluble solids were only at 9-10 Brix.

Below are the data from this year’s end-of-August apple maturity sampling. In each year, the samples were taken around August 25 (August 26 this year) and consist of apples from the AREC and a few local growers. Thanks to Dave Carbaugh and Abby Kowalski for collecting and testing the fruit. Please refer to my post from last year if you need help interpreting the different maturity indices. You can also download a pdf of the 2013 Annual August Maturity Report.

Golden Delicious Maturity Report 1986-2013

 

 
Year

Background Color (1-4)*

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)**

Ethylene (ppm)

Bloom Date

1986

2.2

19.5

12.7

1987

20.0

12.2

1988

18.6

11.0

1.5

1989

17.7

10.3

2.0

1990

18.0

10.5

1.6

1991

1.8

19.7

12.0

2.1

1992

1.8

20.1

12.0

1.6

1993

1.9

19.8

11.6

1.5

1994

2.3

19.8

12.0

1.7

1995

0.9

18.8

10.9

2.1

1996

2.9

19.6

11.2

2.9

1997

2.0

21.8

11.7

2.0

1998

2.5

19.2

12.2

2.1

1999

1.9

20.3

11.7

1.4

2000

1.8

17.5

11.9

2.5

2001

1.9

20.1

11.0

1.4

2002

2.2

21.2

11.4

2.1

2003

2.6

20.3

11.1

1.2

2004

2.3

18.2

12.3

2.0

2005

1.8

20.1

11.4

1.7

2006

1.9

18.5

12.4

1.8

2007

1.6

18.0

12.3

1.6

2008

2.1

18.3

12.9

1.6

22-23 Apr

2009

1.8

17.2

12.4

1.7

22-Apr

2010

1.6

18.6

12.9

1.4

13-Apr

2011

2.1

20.1

12.9

1.2

20-Apr

2012

2.5

18.5

13.0

1.3

0.00

2-Apr

2013

2.2

18.3

11.9

2.2

0.17

25-Apr

Mean

2.0

19.2

11.9

1.8

17-Apr

Max

2.9

21.8

13.0

2.9

25-Apr

Min

0.9

17.2

10.3

1.2

2-Apr

* 1 = green, 2 = light green, 3 = yellowish green, 4 = yellow.
** 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

Red Delicious Maturity Report 1986-2013

Year

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

Ethylene (ppm)

Bloom Date

1986

72.0

18.8

11.2

1987

68.0

19.8

10.8

1988

54.0

18.4

10.0

1.6

1989

69.0

18.6

8.7

1.6

1990

73.0

18.1

8.9

1.5

1991

69.0

18.8

10.4

1.6

1992

76.0

20.8

10.2

1.3

1993

68.0

21.7

9.5

1.7

1994

68.0

19.7

9.5

1.9

1995

68.0

19.2

9.1

1.6

1996

62.5

19.3

8.9

2.0

25-Apr

1997

66.7

22.4

9.4

1.2

25-Apr

1998

81.9

19.3

9.9

2.5

15-Apr

1999

65.5

19.8

10.5

1.9

28-Apr

2000

87.4

16.2

9.6

2.3

11-Apr

2001

61.0

20.5

8.3

1.8

28-Apr

2002

60.2

21.4

9.4

2.1

22-Apr

2003

58.4

20.4

8.5

1.9

22-Apr

2004

88.2

16.7

10.0

2.3

20-Apr

2005

73.7

18.7

9.2

2.0

24-Apr

2006

63.8

18.7

10.7

2.0

16-Apr

2007

81.1

18.1

11.0

1.7

22-Apr

2008

86.6

18.1

9.4

2.0

22-Apr

2009

79.2

17.5

10.2

1.9

24-Apr

2010

65.9

18.2

11.5

1.7

8-Apr

2011

67.5

19.8

11.5

2.1

21-Apr

2012

92.1

18.2

11.9

1.8

0.03

29-30-Mar

2013

91.3

18.4

9.8

2.0

0.25

23-Apr

Mean

72.1

19.1

9.9

1.8

0.1

20-Apr

Max

92.1

22.4

11.9

2.5

0.3

28-Apr

Min

54.0

16.2

8.3

1.2

0.0

29-30-Mar

* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

 

Gala Maturity Report 2008-2013

 

 
Year

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

Ethylene (ppm)

Bloom Date

2008

93.5

18.3

13.6

5.6

21-Apr

2009

86.8

17.5

13.4

4.5

22-Apr

2010

78.0

16.3

14.9

6.4

9-Apr

2011

77.5

19.4

13.7

4.9

19-Apr

2012

91.1

18.0

13.2

4.1

7.13

29-30-Mar

2013

91.1

18.0

12.4

5.4

1.71

23-Apr

Mean

86.3

17.9

13.5

5.2

4.4

15-Apr

Max

93.5

19.4

14.9

6.4

7.1

23-Apr

Min

77.5

16.3

12.4

4.1

1.7

29-30-Mar

* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

 

Empire Maturity Report 2002-2013

 

 
Year

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

Ethylene (ppm)

Bloom Date

2002

42.0

25.3

10.4

2.1

2003

60.4

21.9

9.6

1.7

2004

78.1

17.2

10.9

2.2

2005

55.3

20.3

10.1

1.9

2006

46.0

19.7

10.7

2.1

2007

64.0

17.9

10.6

2.1

2008

66.3

18.2

11.0

2.1

21-Apr

2009

52.4

16.6

10.9

1.1

20-Apr

2010

44.3

18.1

10.7

1.8

2011

49.8

19.7

11.2

2.0

2012

85.9

19.2

12.5

1.7

0.01

29-Mar

2013

63.0

18.6

10.6

1.5

0.04

21-Apr

Mean

59.0

19.4

10.8

1.9

0.0

15-Apr

Max

85.9

25.3

12.5

2.2

0.0

21-Apr

Min

42.0

16.6

9.6

1.1

0.0

29-Mar

* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

 

Maturity Report – Other Varieties 2011

Cultivar

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

HoneyCrisp

66.2

15.8

13.0

5.1

Idared

17.0

19.9

11.1

1.2

* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

Maturity Report – Other Varieties 2012

 

 

Cultivar

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

Ethylene (ppm)

Bloom Date

Fuji Early Strain

65.5

16.7

14.7

4.1

0.03

5-Apr

Fuji Late Strain

26.0

20.9

12.1

2.1

0.03

5-Apr

Idared

36.7

17.0

12.3

1.3

0.00

2-Apr

Rome

39.8

22.5

12.3

1.5

.

12-Apr

York

41.8

22.4

10.7

1.0

0.00

3-Apr

* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.

Maturity Report – Other Varieties 2013

 

 

Cultivar (number of orchards tested)

Red Color (%)

Firmness (lbs)

Soluble Solids (ºBrix)

Starch-iodine Index (1-8)*

Ethylene (ppm)

Bloom Date

Cameo (1)

33.5

18.1

10.2

1.7

0.53

N/A

Fuji Early Strain (2)

80.3

16.3

13.6

4.3

1.51

25-Apr

Ginger Gold (2)

3.9**

16.0

12.8

3.5

0.00

24-Apr

Idared (6)

41.1

17.5

10.1

1.2

0.12

23-Apr

Jonagold (1)

35.5

18.7

11.8

2.8

0.00

23-Apr

Rome (1)

21.2

24.6

9.2

2

0.00

1-May

York (1)

53.5

24.4

9.4

1

1.20

25-Apr

* 1 = 100% starch, 5 = 60% starch, 8 = 0% starch.
** 1 = green, 2 = light green, 3 = yellowish green, 4 = yellow.