Publication 360, Guide to Fruit Production:
Vegetative Growth Control in Apples


Excerpt from Ch. 4, Publication 360, Guide to Fruit Production 2012-2013,

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Cover of Publication 360, Guide to Fruit ProductionTable of Contents

  1. Vegetative Growth Control in Apples
  2. Other Information on Growth Regulators and Thinning
  3. Other Information on Apples
  4. Chapter 4: Apple Calendar - PDF 357 kb

Vegetative Growth Control in Apples

Apogee or prohexadione-calcium, is a plant growth regulator that reduces terminal shoot growth. Apogee inhibits the synthesis of gibberellins, the plant hormones responsible for cell elongation. Trees treated with Apogee often have the same number of shoots as untreated trees, but shoots from treated trees are thicker or greater in diameter and have compressed internodes.

When used properly in apple orchards, Apogee can:

  • reduce shoot growth by 20-60% and diminish the time required to dormant prune and/or summer prune
  • lead to improved fruit colour on red-coloured cultivars
  • result in a more open tree canopy, which will improve spray coverage
  • reduce the incidence and severity of fire blight on shoots, but not blossom blight infections

Apogee does not have activity against the fire blight bacteria. Trees with reduced shoot growth make the trees less susceptible to fire blight development. Apogee does not reduce the number of leaves or fruit size.

 

Time of application and rates

Patterns of terminal growth and fruit set differ among growing regions. Likewise, the response to Apogee appears to differ between regions. Therefore, the rate and calendar date of application may vary between regions.

Make the first application when terminal shoots (and/or bourse shoots) are no longer than 2.5-5.0 cm. Some cultivars show early bourse shoot development (see Figure 4-5. Diagram Indicating Bourse Shoot Development, below). Note: This first application timing may occur in late bloom or petal fall. Sufficient leaf area must be available for Apogee to be translocated into the leaf. Later timings will not provide satisfactory results.

Figure 4-5. Diagram Indicating Bourse Shoot Development

Figure 4-5. Diagram indicating bourse shoot development

Apogee is non-toxic to bees, so the first application can be made before bees are removed from the orchard.

Once applied, Apogee requires about 14 days to slow growth. It breaks down in the trees within a few weeks, so at least one additional application may be necessary to maintain growth control throughout the entire growing season.

See Table 4-21. Suggested Apogee Rates and Timings Based on a Tree-row Volume Dilute of 1,000 L/ha, for rates. The application rate is determined primarily by tree size, vigour, and whether protection against shoot blight is an objective.

  • for medium to high vigour trees, apply 45 g product per 100 L of dilute spray (125 ppm)
  • for low to medium vigour trees, apply 27 g product per 100 L of dilute spray (75 ppm)

Repeat application(s) should be made at 14-21 day intervals, based on the level of growth control required.

Follow the steps on the label to adjust rates for tree-row volume dilute applications. Table 4-21. Suggested Apogee Rates and Timings Based on a Tree-row Volume Dilute of 1,000 L/ha, shows various rates for sprays applied at 1,000 L/ha (dilute). Apogee has been used effectively when applied in more concentrated sprays provided thorough wetting of the canopy is achieved. Low-volume spraying of plant growth regulators and chemical thinners is not recommended.

Do not tank mix Apogee with calcium sprays like calcium chloride. In the presence of calcium, Apogee will precipitate in the tank, clog nozzles and screens, and reduce tree response.

Table 4-21a. Suggested Apogee Rates and Timings Based on Tree-Row Volume Dilute of 1,000 L/ha(use this chart in conjunction with the product label.)

1st Spray
2nd Spray
3rd Spray
4th Spray
Typical Date1, SW Ontario
25-May
8-Jun
22-Jun
6-Jul
Stage
Petal fall
Fruit set
June drop
Growth

* Make the first application when terminal shoots are no longer than 2.5-5.0 cm, which usually corresponds with late bloom to petal fall. This will vary with tree growth and development in your area and by cultivar. These are approximate dates in southwestern Ontario. Growers with orchards in other areas should note the appropriate tree phenology stage to time these applications correctly.

Table 4-21b. Suggested Apogee Rates and Timings Based on Tree-Row Volume Dilute of 1,000 L/ha- g Apogee/ha (use this chart in conjunction with the product label.)

(based on 1000L/ha Tree-Row Volume (TRV) Dilute)4

LevelTree Vigour1
1st Spray
(Petal fall)
2nd Spray
(Fruit set)
3rd Spray
(June drop)
4th Spray
(Growth)

Season Total2 (g/ha)

1
Low vigour - 1 spray
450
-
-
-
450
2

Low vigour - 2 sprays

270
270
-
-
540
3*
Medium vigour - 2 sprays+*
450*
450*
-*
-*
900*
4
Medium/High vigour - 3 sprays
450
450
270
-
1170
5
High vigour - 3 sprays
450
450
450
-
1350
6
High vigour - 4 sprays
450
450
450
270
1620

+- Suggested base rate. Move to next higher or lower level based on factors listed below.

* Shaded cells show the suggested base rate. Move to next higher or lower level based on factors listed below.
1 Make the first application when terminal shoots are no longer than 2.5-5 cm, which usually correspond with late bloom to petal fall. This will vary with tree growth and development in your area and by cultivar. These are appropriate dates in southwestern Ontario. Growers with orchards in other areas should note the appropriate tree phenology stage to time these applications correctly.
2 Vigour is defined as the total amount of shoot growth in a single season. Not to be confused with tree-row volume.
3 Tree-row volume (see OMAFRA Factsheet, Adjusting, Maintaining, and Collaborating Airblast Sprayers, order no. 10-069, for more details). Rates need to be increased when higher water volumes are required for adequate spray coverage.

4 Maximum seasonal rate should not exceed a total of 5.4 kg of Apogee.

Orchard and Environmental Factors to Adjust Apogee Rates and Number of Sprays

 
Heavy Dormant Pruning
increase rate by 10-20% per ha per spray
Longer Growing Season

add 3rd or 4th spray

Low Crop Load
Move Apogee program to next higher level
Questionable Coverage
Move Apogee program to next higher level
Fire Blight Suppression
Move Apogee program to next higher level or apply (650 g/1,000 L)initial rate

Adjuvants and Hard Water

Include the spray adjuvant, Agral 90, with Apogee to improve the uptake of the prohexadione-calcium molecule by the leaf. In addition, if the spray water source is hard water and contains high levels of calcium or magnesium, include an equal amount of ammonium sulphate (AMS) fertilizer by weight with Apogee. Use a high-quality, greenhouse grade of AMS to avoid plugging of nozzles. Obtain water hardness ratings from your municipal water supplier, or have well water tested for hardness. Consult www.ene.gov.on.ca/en/water/sdwa/licensedlabs.php for a list of accredited labs that conduct these tests.

Precautions when using Apogee

In some instances, Apogee may increase the strength of fruit set and make thinning more difficult. This response is not consistent but is more likely at concentrations above 125 ppm (45 g/100 L). Apogee-treated trees may require more aggressive chemical or hand thinning to reduce the crop load to the desired level.

Apogee can cause severe cracking on Empire and Stayman cultivars as stated on the product label. The cause is unclear, but may be related to environmental conditions. Reports of cracking damage of Empire when Apogee has been used are increasing. Compliance with the label is strongly advised. Apogee may result in decreased yield and marketable yield of Cortland. Despite this, clear benefits of the use of Apogee on tip bearing cultivars such as Cortland and Northern Spy have been observed in other regions of Canada where the shortened internodes of Apogee treated trees has produced a more compact tree habit.



For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 05 July 2007
Last Reviewed: 01 November 2010