Table of Contents
Catch’em Blushing
As harvest nears it’s time to pull out all of the blush-worthy tricks. Feed the trees and cue the growth regulators to fire up that red pigmentation. Snip a few leaves and roll out the reflective runway so your apples can strut their stuff in full colour.
The best option for ideal colouration is to have an open canopy to allow light penetration throughout the tree.
Options that may be of interest to growers include an open canopy, reflective ground covers, leaf removal, plant growth regulators and nutrients.
Remember that:
timing is critical for all colouring technologies
AND
cool nights are still needed for the success of any colour aid.
Reflective Ground Covers
This includes reflective materials that are placed underneath the trees and into the alleyways to encourage sunlight reflection in the bottom of the canopy. These covers range in material (film or fabric) and colour (white or metallic), providing different timings of setup (3 weeks to 10 days before harvest) and different options for use. Some materials can be moved throughout the harvest season, driven over, and re-used year after year, while others cannot. Reflective materials used in apples include:
- Extenday – CoolColorUp Film
- Extenday – Reflective Fabric
- Proline – ColorIt Reflective Cloth
- Proline – EasyColor Reflective Foil
- Lumilys – Smart Reflective Groundcover
Cornell conducted a study comparing various ground cover materials, where all materials showed varied success in apple colouration. The study also looked at the economics of the materials, which can be found here – Reflective Ground Cover – Cornell – keep in mind that this study was conducted in 2018.
Leaf Removal
Refers to manual and mechanical defoliation. Timing of the removal of leaves is critical to the success of apple colouration, as removal too soon can lead to sunburn damage and removal too late doesn’t aid in colouration (meaning a loss in time and money).
Leaf pruning commonly occurs in higher return cultivars, taking place 2 to 3 weeks before harvest. Leaf pruning can be costly as it is labour intensive, which is why growers utilize this approach in better returning apples.
Pneumatic defoliators such as the REDpulse aren’t as common within Ontario, but are available. Companies that sell pneumatic defoliators include Fruit Tec, Olmi, and Blueline. The timing of these defoliators is also important, often taking place 10 to 8 days before harvest, with strong suggestions to not go earlier than 14 days before harvest.
Researchers, Christian Andergassen and Daniel Pichler, at the Laimburg Research Centre based in Italy compared manual pruning, mechanical defoliation and control. They found that leaf removal, no matter the method, improved colour and were comparable in success.
Plant Growth Regulators (PGRs)
PGRs can be used in 2 different methods to improve colour of apples. One method is applying products to enhance fruit colour and the other is to delay fruit maturation to encourage more time for fruit colouration.
Product | Active Ingredient | Use | Timing | PHI |
|---|---|---|---|---|
Blush | Prohydrojasmon 5.25% | Improves colour | 7 to 28 days before harvest | 7 days |
Blush 2X | Prohydrojasmon 10% | Improves colour | First application 28 to 21 days before harvest. Second application 10 to 7 days before harvest. | 7 days |
Harvista 1.3 SC | 1-Methylcyclopropene 1.3% | Keeps fruit on tree. Delays fruit maturation encouraging more time for colouration | Apply 3 to 21 days before harvest. Delays maturation by 7 to 14 days. | 3 days |
ReTain | Aviglycine hydrochloride 15% | Keeps fruit on tree. Delays fruit maturation encouraging more time for colouration | Apply 3 to 4 weeks prior for single pick cultivars. Apply 1 to 2 weeks prior to multiple pick cultivars. Delays maturation by 7 to 10 days. | 7 days |
For more product specific information check out the Crop Protection Hub.
Nutrients
Nutrients support colouration through the accumulation of anthocyanins (red pigmentation). Below is a breakdown of nutrients and their roles in colouring:
- Potassium is involved in sugar transport which can enhance colouring. It is critical that calcium is balanced with potassium for effective fruit colouration – especially due to the risk of bitter pit with high potassium levels.
- Phosphorus aids in energy transfer, root and shoot vigour, along with enzyme production – indirectly helping colouration. Foliar applications of phosphorus with magnesium or phosphorus with calcium have shown to aid in apple colouration.
- Magnesium is critical for chlorophyll and in turn photosynthesis. Magnesium indirectly supports colouring through healthy leaf tissues, but is important to keep balanced when encouraging colouration.
- Boron relates to cell wall integrity and sugar transport. Boron indirectly aids in fruit colouration.
- Less direct, but still important nutrients related to colour include, zinc and manganese.
Excessive nitrogen inhibits colouration of apples.
Avoid using calcium nitrate or chloride foliar sprays in the final 3 weeks leading up to harvest, as they can interfere with colouring and leave residue on the fruit skin.
Erika DeBrouwer
OMAFA Tree Fruit Specialist