By Erica Faber – Technical Manager
Watch out for sunburn on the exposed tender green stems as well as the base of the trunk upwards. The young trees are extremely prone to sunburn resulting in poor vegetative growth, stem splitting and secondary fungal disease or even ringbarking and death. Either include sunburn products (e.g. Surround) monthly throughout summer or until the stems are protected by the new flush. Apply with your foliar sprays or paint the exposed stems with a 1:1 mixture of white water based acrylic paint and water.
Newly planted trees need regular watering. If mother nature isn’t supplying it and you don’t have irrigation, then a water tank or bucket may be required. Work on around 30-50L of water through rain or irrigation or a combination thereof, per week depending on the weather. The trees will lose more water in hot, dry and windy conditions than in warm, humid conditions and water requirements can be adjusted accordingly using either the lower or higher range.
Even though the trees are receiving adequate water they may appear wilted on really hot days. Don’t be tempted to over irrigate as this will cause overly wet soils and anaerobic conditions which can lead to root dieback or Phytophthora Root Rot. The wilting is the trees way of trying to minimize moisture loss. You can support the tree in these conditions and reduce the stress on the tree by adding an antitranspirant (eg. Vapor Gard) to your foliar spray. This reduces the rate of transpiration (moisture loss) the tree experiences and keeps them happier on those very hot days.
Insects need to be monitored and controlled. Insects will be eyeing up the new buffet you have just provided – keep an eye out for Leafroller, Passion Vine Hopper, Cicadas, Fullers RoseWeevil and Bronze Beetle.
Apply compost to your planting hole. I have been working with Revital and together we have come up with a compost planting mix. This blend includes compost, vermicast, chicken manure, lime and phosphorus and is bio certified. It has a NPK of 12.5:9.5:3 and includes Magnesium and Calcium. Apply to your planting hole at 10% (e.g. 60L of compost for a 0.6m3 hole) and mix evenly with the soil. Just Avocados growers receive a discounted price! For those that are yet to plant, refer to our planting guide.
TREE STRUCTURE MANAGEMENT
Even though the chainsaws should be packed away, the hand pruning saws can make an appearance. Doing any major structural pruning this time of year on mature trees may disrupt the fruit set causing a higher fruitlet drop than normal. This happens due to a hormonal shift in the tree with the vegetative response to structural pruning. Summer pruning also reduces late-season photosynthesis, and theoretically reduces the accumulation of reserve carbohydrates within the tree that Irrigation and monitoring soil moisture is key over summer. are used for early season growth in the following Spring. However, if this is not a concern to you for whatever reason and you want to continue pruning then ensure adequate sunburn prevention on exposed limbs during the hot summer months.
For those who are guarding their fruit set and working towards improving production then read on.If you are trying to improve the bearing capacity of your trees and have large voids off the main trunk where there is no lateral branching then this is the time of year when you can try initiate dormant (also known as latent) buds to shoot by taking advantage of the high sap flow, evidence of which can be seen by the active vegetative flush. By cincturing (a xylem and phloem interruption technique), you temporarily restrict and redirect the flow of reserves. Done in late spring or early summer you can initiate dormant vegetative buds below your cincture and done in autumn or winter can improve flowering or fruit set by increasing photosynthates to the flowers.
How to cinture.
This technique can also be used on young trees to initiate a lateral branch where there is none. In this case use a sharp budding/grafting or similar knife and make a light incision through the cambium above a node.
Remember to always sanitise your tools with a bleach solution when moving from tree to tree. Please contact your technical adviser or grower rep. before attempting this if you are unsure of what to do.
How a cinturing cut should look.
Thinning and tipping any regrowth emerging from the autumn and winter pruning on mature trees should also be done now. These shoots should be thinned out when they are about 50- 60cm long, soft, coppery and easy to break out by hand. As a general rule, remove all shoots growing from the top or underside of the pruned branch as well as any shoots emerging on or very close to the pruning cut. Aim to leave a lateral shoot at a 10 and 2 o’clock angle. When regrowth is controlled and the trees have adequate resources, flowering and fruit set should occur on the new growth minimizing production loss and the structure of the tree is improved thereby optimizing bearing structure and capacity.
Regrowth that isn’t managed results in poor tree structure and regrowth that remains vegetative and apical dominant.
Regrowth that is thinned and tipped ensures quick return to productive wood as well as good lateral branching as opposed to apical growth.
Remove any shoots below the graft union.
You should be experiencing the first of two main fruitlet drop periods. This is quite normal. However, additional fruitlet drop can be experienced in the following scenarios:
- When there is very strong vegetative growth stimulated by excess nitrogen. This strong vegetative growth competes for resources and as the tree only has so much to go around, will shed some of the fruitlets. High nitrogen levels will also inhibit efficient calcium uptake which is important during the first three months of fruit set and sizing to strengthen the cell walls and increase levels in the pulp. High
levels of calcium in fruit is associated with resistance to fungal infection, improved shelf life and reduced incidences of grey pulp which is also the result of excess nitrogen. The higher than ideal nitrogen levels will also result in higher pest pressure as the leaves and fruit are soft and palatable.
- The trees experience a water deficit. As the rate of transpiration (water loss) increases with the increase in daily temperatures and the additional vegetative flush and sizing fruit, the demand for the uptake of water to restore the balance increases as well. This increased demand often coincides with our lower rainfall months resulting in not only inadequate soil moisture but also a shrinking in the root mass due to them drying out, further exacerbating the stress the tree undergoes. In order to reduce the overload, the tree will shed fruit. Not only does the hotter, drier conditions result in low available soil moisture but also results in inadequate nutrition uptake as there is not enough soil moisture etc to dissolve the solid fertilizer into a readily available form. Fortunately, the soft new vegetative flush which coincides at this time absorbs foliar sprays effectively and can be applied to overcome the soil limitations. Monitor soil moisture and irrigate as necessary.
DETERMINATE AND INDETERMINATE FRUIT SET
Action is required if you are experiencing mostly determinate set where the fruitlets are exposed with no spring flush extending beyond them. This can be as a result of:
- Hanging your crop late when the tree does not have enough resources to hold crop, set and size the new crop as well as push vegetative flush.
- Not having adequate resources despite the crop having been harvested.
- Poor tree health.
- Dry soil conditions and little to no available soil water for root uptake or inadequate fertilser/nutrition uptake due to the dry soil conditions.
- Very heavy flowering and fruit set resulting in an overload on resources and not enough to push the vegetative flush.
- Under fertilisation.
- Winter leaf drop through mite damage.
- Not pruning enough the previous seasons. Pruning ensures a balance between vegetative and productive wood ensuring more balanced flowering as well as renewing flowering wood. It is important to take steps to remedy this as the spring flush not only protects the fruit set from sunburn and provides valuable resources to the sizing fruitlet through photosynthesis but it is also next year’s flowering wood and ensures next year’s return crop.
Take the following steps to encourage vegetative flush:
- Take leaf samples to ascertain the current nutrient status and correct deficiencies or low nutrient levels with foliar fertiliser sprays. This is especially important if you do not have irrigation and the soil moisture levels are low resulting in poor solid fertiliser uptake.
- Should you have irrigation, monitor soil moisture levels and irrigate as necessary.
- Increase solid fertiliser to these trees if and when there is adequate soil moisture.
- Reduce the resource load on the tree by harvesting your current crop.
- Reduce the resource load by thinning out the new fruit set or by removing about 25-30% by cutting back to 2cm wood.
There will always be a percentage of determinate set. In this instance, ensure you protect any exposed fruit with products (Surround or Bud Mate) that help prevent sunburn and ensure return value for this fruit.
Determinate (left) and indeterminant (right) panicles.