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 (greater diameter) and have compressed internodes.

When used properly in apple orchards, Apogee can:

Apogee does not reduce the number of leaves or fruit size. 

Time of Application & Rates

Patterns of terminal growth and fruit set differ among growing regions. Likewise, the response to Apogee® appears to differ depending upon where it is used. Therefore, the rate and calendar date of application may vary from region to region.

Timing: Make the first application when terminal shoots are no longer than 2.5 - 5 cm. This typically coincides with late bloom or petal fall, when the bourse shoots are beginning to grow and sufficient leaf area has developed for Apogee to be translocated into the leaf. Later timings will not provide satisfactory results. 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.

Rates: See Table 1, Suggested Apogee rates and timings based on a tree-row volume dilute of 1000 L/ha. The application rate is determined primarily by tree size, vigour (influenced by rootstock, cultivar, soil, crop load, site) and whether protection against shoot blight is an objective.

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 1 shows various rates for sprays applied at 1000 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 (i.e. calcium chloride). In the presence of calcium, Apogee will precipitate in the tank, clog nozzles and screens, and reduce tree response.

Table 1(a). Suggested Apogee rates and timings based on a tree-row volume dilute of 1000 L/ha
(this chart is to be used in conjunction with the product label)

Table 1(b)

^† - suggested base rate. Move to next higher or lower level based on factors listed below.

Adjuvants and Hard Water

Obtain water hardness ratings from your municipal water supplier. Have well water tested for hardness. Consult the Ministry of the Environment for a list of accredited labs.

Precautions when using Apogee:

Increased Fruit Set: In some instances, Apogee may increase 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.

Fruit Cracking: Research in the U.S.A. suggests that Apogee can cause severe cracking on ‘Empire’ and ‘Stayman’ cultivars. The cause is unclear and it has not been observed in research blocks at the University of Guelph, Simcoe after treatment of ‘Empire’ trees for several years. Producers who wish to use Apogee on ‘Empire’ should be aware of this precaution, and perhaps use it on a limited acreage of their ‘Empire’ trees for a few years to determine the real risk of cracking in our region.

Tip-bearing cultivars: Apogee may result in decreased yield and marketable yield of ‘Cortland’. Despite this, clear benefits of using 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.

Suggested Strategy for Using Apogee®