Growers should strive to produce flowers of high quality with an Effective Pollination Period (EPP) of 3 days or more. For optimum flower bud quality:
- Trees should be thinned early in the previous season to optimum crop loads.
- Fruit harvesting should not be delayed too long, as late picking may reduce flower quality on varieties such as Bramley and Braeburn.
- Maintain good tree health status by judicious use of pest and disease control measures.
- Use nitrogenous fertilisers sparingly in the spring and summer prior to harvesting so as to reduce shoot growth which competes with developing flower buds.
- Consider foliar or ground (taking into account Nitrate Vulnerable Zone restrictions) applications of nitrogen in the autumn following harvesting, but before leaf fall, to improve the quality of flowers in the subsequent spring.
- Adopt winter pruning techniques that improve light distribution through the tree but do not encourage excessive growth. This is best achieved by making a few larger cuts.
- Summer prune to allow adequate light into the centres of the trees.
- Bend shoots towards the horizontal or below, but this should not be carried out to excess or the optimal balance of new renewal shoot growth and flower bud production will be lost.
- Growers should take note of the average maximum temperatures in February, March and April in their Cox orchards, as these have a significant bearing on flower quality: Where temperatures are higher than desired average maxima (i.e.10oC or higher), they are advised to intensify their efforts to secure good pollination and flower fertilisation. This can be achieved by supplementing bee populations, providing increased shelter and controlling early growth straight after petal fall using an approved growth regulator. Where temperatures are of the desired average maximum, or lower, growers will need to consider implementing appropriate thinning procedures.
Delaying flowering in the spring using plant growth regulators and other spray treatments
Pollination and fruit set are often reduced severely by spring frost damage to the flowers. One possible strategy that has been investigated in attempts to reduce this risk is delaying flowering in the spring using plant growth regulators or other spray treatments.
- Although sprays of various chemicals can influence the time of spring flowering in the previous autumn or winter, none of these treatments are approved for use in UK apple orchards.
- Further research may be warranted, examining misting techniques to delay flowering times of apple varieties.