By Erica Faber – Orchard Productivity Manager
As our trees start to gear up for flowering, it is important to supply them with the correct resources at the right time.
In order to supply our trees with the correct resources it needs when it needs it, we need to first understand the tree phenology so that we can be two steps ahead.
With the seasonal change of lower temperatures and shorter day lengths, flower initiation is being triggered within the tree. Hormones trigger the transition from vegetative to floral buds but it is the nutrient levels and balances that drive this reaction and the carbohydrate levels that determine the stamina of this reaction.
This pre-flowering and flowering stage is one of those critical stages that we as growers need to ensure the tree has all the resources it needs, in order to optimise production.
Actions to be implementing now to support the imminent flower initiation and the current crop:
✓ Firstly, ensure correct nitrogen levels. Too much of a good thing is not always a good thing! Excessive nitrogen in the tree at this time will swing the balance in favour of vegetative growth, thereby compromising potential flowering and fruit set.
✓ Low cytokinin levels in relation to other hormones will inhibit floral bud development. As cytokinins are produced in root tips, trees with fewer healthy roots or an imbalanced root to shoot ratio, are likely to have reduced cytokinin levels. A heavy prior crop will also most likely have exhausted most of the tree’s resources, resulting in amongst other things, reduced root mass and also reduced cytokinin levels. Apply products to boost root health and vigour and soil health and fertility. Foliar sprays of seaweed products will boost cytokinin levels as seaweed extracts are particularly rich in cytokinins.
✓ Boron is a highly-undervalued element. It increases flower production and retention, pollen tube elongation and germination and seed and fruit development. In order for fertilisation to take place, the pollen grain, needs to first be transferred to the stigma. It then has to germinate and a pollen tube needs to grow all the way down the style to the ovule to transfer the male gametes. Boron improves the pollen germination and increases the length and vigour of the pollen tube, greatly enhancing fertilisation. Boron tends to have restricted mobility in plants and is also one of the most leachable elements which often contribute to a deficit at the important draw-down time at reproduction.
Avocados are an incredibly boron-hungry crop and their low flower to fruit ratio can be substantially improved with a foliar spray of boron at the pre-flowering stage. Boron also plays an important role in regulating the plant hormone levels responsible for flower initiation and fruit development. Another reason to ensure the all-important pre-flowering boron spray is applied.
✓ Calcium and boron work in such close synergy that in the absence of sufficient calcium, boron toxicity can even occur. Calcium also fulfills many essential roles in the sexual reproduction of flowering plants. It is also called the “trucker of all minerals” because it directly affects all mineral uptake. It is therefore advisable to apply calcium at this stage as well, not only for the flower development and fruit set but also for its role in the current developing crop. Calcium governs cell wall strength and not only improves fruit quality but also aids in resistance to anthracnose and post-harvest rots. The most critical time and our window of opportunity for accumulating calcium levels in the fruit is in the period when the young fruit are still developing.
✓ Potassium is extremely important during this fruit-fill stage. Insufficient levels of potassium reduce the yield potential and quality of the crop and ultimately our pockets!
✓ Zinc is one of the most important elements in carbohydrate metabolism in plants. Most enzymes that play a role in carbohydrate metabolism are activated by zinc. Zinc is also an essential micronutrient for protein production in plants. One of the sites of protein synthesis is the pollen tube. So once again an often-neglected micronutrient plays a big role in carbohydrate metabolism which in turn determines the stamina of critical reactions at this important reproductive phase and also in improving the flower to fruit ratio.
✓ Lastly but definitely not least, are our all-important pollinators. Without these guys, all the pruning and
fertilising and money you’ve been spending will all be in vain. Remember to book your hives now for the start of delivery at about 10% open flower. In our climate, we rely heavily on pollinators. Without the bees, the pollen cannot get transferred onto the stigma, fertilisation cannot take place and fruit cannot develop. So, more bees mean raising your odds on a higher fruit set, higher crop, higher returns!
Remember to ensure compatibility when mixing your chemicals and fertilisers. If you are concerned about any incompatibility or phytotoxicity, contact the manufacturers or do a jar or spray test.