Growth Regulators for Apples

Excerpt from Chapter 7, Publication 360, Fruit Production Recommendations, Order this publication

1. Promalin to Improve Fruit Shape of Delicious
• Precautions
• Application Notes
2. Ethephon to Promote Fruit Colouring
3. Chemical Control of Preharvest Drop in Apples
• Recommendations for Use of NAA
• Recommendations for Use of ReTain
  • Precautions
  • Additional Information
4. Prevention of Heat Stress and Sunburn in Apples
• Precautions When Using Surround
5. Vegetative Growth Control in Apples (Apogee)
• Time of Application and Rates
• Table 7-21. Suggested Apogee Rates and Timings Based on a Tree-row Volume Dilute of 1000 L/ha
• Adjuvants and Hard Water
• Precautions when using Apogee
6. Pub 360 Chapter 7 - Apples - Apple Calendar - (Pdf format 1.17 Mb)
7. Related Links
8. For more information

• If Promalin is applied at higher rates or volumes than those recommended on the label or where blooms are weak or frost-injured, fruit thinning may occur. Promalin use may also increase the amount of thinning achieved with subsequent blossom thinning sprays.
• Apples may not respond to Promalin if spur vigour is low or the king blossoms have been damaged by frost.
• Do not apply Promalin if rain is expected within six hours.
• Do not apply when air temperatures are lower than 24C or greater than 32C.

Application Notes

• For optimimuim results, apply Promalin between full king bloom and early petal fall. Applications earlier or later are likely to produce unsatisfactory response.
• High relative humidity and slow drying conditions favour maximum absorption. It is preferable to apply in morning or evening.

Ethephon to Promote Fruit Colouring

Ethephon (Ethrel) has the following effects on trees and fruit, depending upon the timing and rate of application:

• Ethrel stimulates ripening, colour development and fruit drop. To prevent excessive premature drop following the use of Ethrel, apply a suitable stop-drop product such as naphthaleneacetic acid (NAA). Two applications are required: 1 as a tank-mix at the time Ethrel is applied and the second 5 days later. Apply the stop-drop at the normal rate recommended on the label.
• Spray just the number of trees that can be harvested over a 2 or 3 day period. Depending on cultivar and air temperature, fruit will be ready to harvest 5-10 days after the spray is applied. After spraying, check the maturity of the apples on a daily basis (e.g., pressure, starch, flavour, colour). A few trees sprayed at 3-4 day intervals are easier to manage than a large number sprayed at one time. Make sure a market is available for the treated apples before you spray, especially with early cultivars.
• Rates of application depend on cultivar, date of application, tree vigour, temperature, weather conditions and degree of response required. The response to Ethrel is a chemical reaction and therefore depends on temperature. For this reason early cultivars, such as Jerseymac and Paulared, require less material than later cultivars. On early cultivars use 0.75-1.5 L of Ethrel/ha with sufficient water to wet the trees thoroughly. McIntosh requires 1.5-4.25 L/ha. Use the higher rate early in the season on trees high in nitrogen, or on poorly-pruned trees. Lower rates may be better nearer normal harvest on young, well-pruned trees, or on trees low in nitrogen.
• Best results are obtained when Ethrel is applied 2-3 weeks before harvesting. Be sure and apply Ethrel uniformly, since it works only where the spray touches.

Chemical Control of Preharvest Drop

Recommendations for use of ReTain

ReTain is a plant growth regulator and an effective preharvest drop control agent for apples, such as Honeycrisp, Red Delicious and Northern Spy. It inhibits the production of ethylene in maturing apples.

• Apply this material 4 weeks before anticipated harvest date. ReTain may delay maturity of apples on the tree and allow a longer harvest window for a particular variety. Although ripening in ReTain-treated fruit is temporarily delayed, treatment with ReTain may increase soluble solids, colour, fruit size, fruit firmness and reduce the increase of water core.
• Pick fruit treated with ReTain st the same time internal maturity, based on starch-iodine tests, as untreated fruit. There may be a 7 to 10 day delay from predicted harvest date of untreated fruit to the start of the harvest date of untreated fruit to the start of the harvest of ReTain treated fruit.

Recommended use 4-5 weeks before anticipated harvest

• Use one, 333 gram pouch (50g active ingredient) of ReTain/ 0.40 ha (1 ac). Use with Slygard 309 (organosilicone surfactant) at 0.5-1.0 L of Slygard 309/ 1000 L of water.
• Apply four weeks before anticipated harvest, adjusted for any seasonal differences that have advanced or delayed the "normal" harvest date for that year. If this date is uncertain, it is better to be early, such as five weeks, rather than late like three weeks. Late applications will not perform well because ethylene production within the plant may have already begun and this is difficult to suppress once initiated. To help determine the start of the "normal" harvest period, refer to historical trends for harvest date for each cultivar in your area.

Precautions

• When you mix ReTain with the surfactant, keep agitation to a minimum because Slygard 309 has a tendancy to foam.
• To minimize foam, add Slygard 309 last, when the tank is full. Compatibility and performance data for ReTain with antifoam products are not available.
• Do not use surfactants other than Slygard 309 because they are not registered with Retain in Canada. If the rate of ReTain is reduced, maintain the Slygard rate at 0.05%- 0.1% v/v ratio.
• Discard any unused spray material at the end of each day.
• Do not tank-mix with other products except Dipel or Foray. Combination effects and potential interactions between ReTain and NAA (naothaleneacetic acid) or Ethephon products have not been thoroughly evaluated. Use of these products on ReTain-treated blocks may negate or reduce the benefits of ReTain.
• Do not overhead irrigate for eight hours after applying.
• Adjust spray water volumes based on tree size and spacing. Do not apply to the point of runoff but wet the tree under slow drying conditions. Use tree row volume (TRV) reductions cautiously and test on a few rows or small blocks to gain a level of comfort with this techniques. For many orchards, 1000L/ water/ ha is adequate for size control in rootstocks.
• For best results, have spray water at a pH of between 6 and 8.

Note: For best storage performance of ReTain, segregate treated fruit to reduce exposure to ethylene.

Additional Considerations When Using ReTain

• Spray only trees that are healthy and not under severe drought, insect, disease, or nutritional stress.
• Apply treatments to Gala strains, Golden Delicious types and Honeycrisp with caustion These cultivars appear to be more responsive to ReTain compared to McIntosh. Using ReTain on these sensitive cultivars can significantly impede crop maturity and development.
• For multiple pick cultivars such as Royal Gala, for best results time application four weeks from the second harvest pick date.
• The harvest window for treated cultivars, which includes Gala, is shorter but delayed and results in fewer pickings. This can increase harvest efficiency.

Preventing Heat Stress and Fruit Sunburn on Apple and Pear Trees

Surround WP Crop Protectant is a highly refined kaolin clay. Appled to the tree canopy, it forms a uniform microscopic particle film that protects both leaves and fruit from high UV light and heat.Because excessive heat and high UV can slow the photosynthetic rate in a tree canopy, untreated trees assimilate less carbon in the heat of the day.

The use of Surround WP on young apple and pear trees during their establishment can provide several benefits to growth and development. It can:

• increase net accumulation of carbon from photosynthesis
• enhance fruit bud initiation
• increase trunk diameter
• increase shoot growth

In established orchards, trees treated with Surround have shown better foliage health through to leaf drop and plant dormancy is not affected. Improvements in fruit finish and marketable yield have been documented on several cultivars.

To prevent heat stress, make two applications of Surround WP, seven days apart, using 50 kg/ha. Begin spraying before heat stress is likely to occur. Continue applications at 7-14 day intervals and use a reduced rate of 25 kg/ha to maintain even coverage.

Surround WP is made of an inert, non-reactive grade of kaolin that is not absorbed by plant tissues. The kaolin is food grade quality and approved by both PMRA and EPA. Surround WP is OMRI listed, highly refined and suitable for reduced risk programs.

Precautions When Using Surround

• Do not mix Surround with spreaders, stickers or anti-foaming agents.
• Do not spray when bees are active.
• Do not re-enter the orchard for four hours after application.

In orchards treated with Surround. monitor fruit maturity carefully and use starch iodine tests in the last two weeks of crop development.

For detailed application instructions, see the product label and Using Surround as a pest management tool, on page 105, for more information.

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 amore open tree canopy, which will improve spray coverage
• reduce the indicence 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. For more information see Fire Blight, on page 116 in the apple notes.

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 depending upon where it is used. Therefore, the rate and calendar date of application may vary from region to region.

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 begin to grow and suficient 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 neccessary to maintain growth control throughout the entire growing season.

See Table 7-21. Suggested Apogee Rates and Timings Based on a Tree-row Volume Dilute of 1000 L/ha, on Page 139 for rates. The application rate is determined primarily by tree size, vigour, which is influenced by rootstock, cultivar, soil, crop load and site, and whether protection against shoot blight is an objective.

• for medium to high vigour trees apply 45g product per 100 L of dilute spray (125 ppm)
• for low to medium vigour trees apply 27g 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 7-21. Suggested Apogee Rates and Timings Based on a Tree-row Volume DIlute of 1000 L/ha, on page 139, shows various rates for sprays applied at 10000 L/ha (dilute). Apogee has been used effectively when applied in more concentrated sprays provided through wetting 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 nozzels and screens, and reduce tree response.

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

• Heavy dormant pruning- increase rate by 10-20% per hectare per spray
• Longer growing season- add 3rd or 4th spray
• Low crop load- move Apogee Program to next higher level (i.e., tree size)
• Questionable coverage- move Apogee Program to next higher level (i.e., tree size)
• Fire blight suppression- move Apogee Program to next higher level (i.e., tree size)

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 nozzles.

Obtain water hardness ratings from your municipal water supplier. Have well water tested for hardness. Consult www.ene.gov.on.ca/envision/water/sdwa/licensedlabs.htm for a list of accredited labs.

Precautions when using Apogee:

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 (45g/ 100L). Apogee-treated trees may require more aggressive chemical or hand thinning to reduce the crop load to the desired level.

Research in the United States 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 in Ontario after treatment of Empire trees for several years. Producers who wish to use Apogee on Empire should be aware of this precaution and use it on limited acerage of their Empire trees for a few years to determine the real risk of cracking in our region.

Apogee may result in decreased yield and marketable yeild 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 produces a more compact tree habit.

• Guide for Spraying Tree Fruit, (Order No. 00-035)
• Publication 360- Fruit Production Recommendations
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