Apogee® - A new plant bioregulator for cherries

Introduction

Registration was approved for the 2013 growing season for Apogee®, a new growth retardant for use on sweet and tart cherries in Canada. The purpose of this article is to provide producers with timely information to help determine how this product can be used in their orchards. Apogee® will reduce shoot growth on sweet and tart cherries, and may be particularly beneficial to those planting at higher densities or beneath tree covers. It is especially important to read the product label for the recommended use and precautions associated with Apogee®. The label can be found on-line at BASF Canada Inc. website (www.agsolutions.ca) or by searching the PMRA website.

Apogee® contains 27.5% (w/w) prohexadione-calcium, a gibberellin biosynthesis inhibitor. Prohexidione-calcium reduces terminal growth by inhibiting the synthesis of growth-specific gibberellins, a group of plant hormones that are primarily responsible for regulation of terminal growth in cherry trees. Once applied, Apogee® requires about 14 days to slow growth. It degrades within the tree within a few weeks, so a repeat application may be necessary to extend growth control.

Patterns of terminal growth and fruit set characteristics differ among growing regions. Likewise, the response to Apogee® may differ depending upon the where it is used. Therefore, a regional interpretation of the label is likely necessary to obtain maximum response and satisfaction from this compound.

Consider using Apogee® if short-term seasonal growth control is desired. Since tree vigor is also influenced by rootstock, cultivar, orchard system, soil type, climate, and soil moisture, these factors should be considered initially for long-term vigor control of sweet cherries (see my previous reported research on size controlling rootstocks in the TFGV). Some may question using plant bioregulators to reduce shoot extension growth given the availability of size-controlling rootstocks on the market. However observations that size-controlling rootstocks have led to poor tree anchorage, excessive fruit set, or poor fruit size, especially when self-fruitful cultivars are grown have been made, particularly in suboptimal tree growth conditions. 'Mazzard' and 'Mahaleb' remain the most common (seedling) rootstocks in use in Ontario today for sweet and tart cherries, respectively and therefore Apogee® can play a role in the management of these orchards.

Research at the University of Guelph, Simcoe and Agriculture and Agri-Food Canada, Summerland, as well as in the Pacific Northwest and Europe, has demonstrated that Apogee® can reduce current season extension shoot growth of sweet cherry trees. Much of this research was conducted using separate and combination sprays of prohexadione-calcium and Ethephon. While Ethephon is commonly used as a ripening agent to aid in mechanical harvesting of tart cherries, combination sprays for growth control with Apogee® are not currently approved for use on the Canadian product label.

For sweet cherries, growers can expect a significant reduction in terminal shoot growth - ranging from 20-50% in a given season by using Apogee® at the proper timing and concentration. This should help reduce the time required to dormant prune as well as open up the tree canopy leading to improved spray coverage and reduced disease pressure. As limited research is available on the response of Montmorency tart cherries to Apogee®, the recommendations in this article are limited to sweet cherries.

Time of Application and Rates

Terminal shoot growth in Ontario proceeds rapidly usually during the first six weeks of the season. Since two weeks are required for Apogee® to slow growth effectively, it is essential to make the first application when terminal shoots are no longer than 2.5 - 5 cm. This typically coincides with late bloom, when sufficient leaf area has developed for prohexadione- calcium to be translocated into the leaf. Satisfaction from the use of Apogee® will depend upon making the first application at this time, and no later. It reportedly has no detrimental effects on bees, so the first application can be made before bees are removed from the orchard.

The label recommends 45 g formulated product per 100 litres of dilute spray (which equates to 125 ppm or 125 mg/L of active ingredient) and spraying dilute (up to 3000 L/ha). A repeat application should be made 14-21 days later -- this is important. Sprays are limited to a maximum of two sprays per season and a total of 2.7 kg of formulated product/ha/season. Based on the 125 ppm rate and a tree row volume dilute rate of 2000 litres/ha, 1.8 Kg of product per hectare (728 g/acre) will be required.

Follow the steps in the product label to adjust rates for tree-row volume dilute applications. Apogee® has been used effectively on apples when applied in water volumes less that TRV, provided thorough coverage is achieved. However, spraying of concentrated plant bioregulators beyond 1X TRV is not generally recommended.

Adjuvants and Hard Water

A spray adjuvant (Agral 90, LI-700) should be included to improve plant uptake of the prohexadione-calcium molecule. In addition, where a high calcium 'or magnesium water source (hard water) is used, it is important to include an equal amount of ammonium sulphate (AMS) fertilizer by weight with Apogee®. A high-quality grade of AMS (ie, greenhouse grade) is recommended to avoid plugging of nozzles. This is readily available form suppliers such as Vineland Growers and Plant Products for around $25 per 25 kg bag, representing inexpensive "insurance" to ensure product efficacy. If you do not know the hardness of your water and are on a municipal water system, the water supplier can tell you the hardness level of the water they deliver. If you have a private water supply, you can have the water tested for hardness for a fee. See http://www.ene.gov.on.ca/environment/en/resources/STDPROD_096104.html for a list of accredited labs and use the last column in the table to determine which labs are accredited for inorganic analysis.

Tank Mixing

The Apogee® label recommends that calcium sprays should not be tank mixed with Apogee®. This warning is especially appropriate for calcium chloride and other calcium-containing products. In the presence of calcium, Apogee® may precipitate in the tank, clog nozzles and screens, and reduce tree response.

Other Precautions

Effects of Apogee on fruit set, fruit size and yield are inconsistent based on results reported in the literature. Several studies have reported a resurgence in late season growth in some situations when marked suppression of growth was achieved early in the season. Furthermore, some resurgence in growth the year following application has been observed. Therefore, fine-tuning of treatment timings and concentrations may need to be considered.

Suggested Strategy for Using Apogee® on Cherries in 2013

  • Consider using Apogee® on the most vigorous growing cultivars first
  • Document all dates of application and measure shoot growth at the time of application (for your records)
  • Compare your dormant pruning costs with the cost of using Apogee®. Count on about 40% reduction in vegetative growth.
  • Apply the first application early - no later than petal fall.
  • Don't forget to add a surfactant and AMS if you have/suspect hard water. A second spray 14-21 days later is almost always required.
  • Direct spray/adjust nozzles to apply more spray to the tops of trees.
  • Be sure to leave several unsprayed trees for comparison purposes (and flag them)
  • Consider measuring the length of ~100 randomly-selected extension shoots per cultivar (from treated and untreated trees) on a 7 or 10 day basis until terminal bud set. This will reveal when trees start and stop growing. I would really value this data in order to adjust Ontario recommendation for the use of Apogee® on a regional and cultivar specific basis. This data would be a great value to input into the Ontario recommendations.

Selected References

  1. Basak, A. and W. Rademacher. 2000. Growth regulation of pome and stone fruit trees by use of prohexadione-calcium. Acta Hort. 514, 41-50.
  2. Byers, R.E., and K.S. Yoder. 1999. Prohexadione-calcium inhibits apple but not peach, tree growth, but has little influence on apple fruit thinning and quality. HortScience, 34, 1205-1209.
  3. Byers, R.E., and D.H. Carbaugh and L.D. Combs. 2004. Prohexadione-calcium suppression of apple tree shoot growth as affected by spray additives. HortScience, 39, 115-119.
  4. Elfving, D.C. and G.A. Lang. 2005. Effects of prohexadione calcium and ethephon on growth and flowering of 'Bing' sweet cherry. Acta Hort., 667, 439-446.
  5. Elfving, D.C., G. A. Lang, and D.B. Visser. 2003. Prohexadione- Ca and ethephon reduce shoot growth and increase flowering in young vigorous sweet cherry trees. HortScience, 38, 293-298.
  6. Elfving, D. C., D.B Visser, and M.D.Whiting. 2004. Growth and flowering responses of sweet cherry cultivars to prohexadione- calcium and ethephon. Acta Hort., 636, 75-81.
  7. Facteau, T. J. and K. E. Rowe. 1979. Growth, flowering, and fruit set responses of sweet cherries to daminozide and ethephon. HortScience, 14, 234-236.
  8. Guak, S. M. Beulak, and N. Looney. 2005. Controlling growth of sweet cherry trees with prohexadione-calcium: its effect its effect on cropping and fruit quality. Acta Hort. 667, 433-437.
  9. Jacyna, T., W. ,Wokcik and T. Lipa. 2011. Effects of different pH sprays on the efficiency of prohexadione-Ca in sweet cherry trees. Folia Horticulturae, 23, 43-47.
  10. Jacyna, T, J. Barnard, J, and M. Wielgus. 2012. Immediate and residual effects of prohexadione-calcium, with or without ethephon, applied in a low-pH solution on vegetative and reproductive growth of sweet cherry trees (Prunus avium L.). J. Hort. Sci. and Biotech. 87:577-582
  11. Manriquez, D., B. Defilippi, and J. Retamales. 2005. Prohexadione-calcium, a gibberellin biosynthesis inhibitor can reduce vegetative growth in 'Bing' sweet cherries. Acta Horticulturae, 667, 447-451.

For further information or questions, feel free to contact Dr. John Cline, Pomologist, University of Guelph, (Tel: 519-426-7127 Ext 331; Email:jcline@uoguelph.ca).


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