The establishment of an avocado orchard is a long-term undertaking, and it is up to the grower to ensure that his orchard gets off to a good start by purchasing high-quality trees.
Site selection is of prime importance and soil should be deep and well drained, with high organic matter content. Apply lime / gypsum / phosphate according to the soil analysis and then deep rip to a depth of 60cm. As avocado trees are highly susceptible to both water logging and Phytophthora root rot disease, a 10cm mound should be made to increase the soil depth for improved drainage.
Alternatively planting can be done on ridges. Dig a hole 60x60x60cm, backfill with topsoil, irrigate and allow soil to settle. DO NOT PLANT THE TREE WHILE THE SOIL IS WET!
Water the planting basins a week before planting. The trees should be well irrigated before planting.
In the orchard the trees should be kept upright and out of direct sunlight until planted in the soil to prevent sunburn to the leaves, stems and roots. The planting bag becomes very hot and can kill the root tips
Dig a hole slightly shallower and wider than the bag.
To remove the plant from the bag, cut the bag along the base and remove the base. Now cut along the length of the bag without removing the bag. This should be done carefully so as to avoid damage to the roots. An adjustable utility knife set to the first notch works well.
Place the tree in the hole, positioning it so that the top of the potting mix is higher than the top of the hole. (See the attached diagram). Position the tree in such a way that most of the branches and leaves face in the direction of the hottest sun in order to protect the tree against sunburn.
Only now remove the bag taking care not to disturb or damage the roots.
Inspect the roots at this stage to ensure that they are healthy.
Fill the hole with the topsoil and build a mound around the protruding top of the root ball, gently pressing the soil into contact with the root ball from the sides towards the centre. Care must be taken at this stage as the roots of avocado trees are very brittle and break easily. DO NOT STAMP THE SOIL DOWN WITH YOUR FEET.
It is VERY IMPORTANT to check the planting depth as planting too deep will result in collar rot and planting too shallow will expose the unpainted stem and the roots to sun burn.
Irrigate well immediately after planting as this helps to bring the soil into close contact with the root ball.
Proper irrigation of young trees is very important! Tensiometers or other moisture meters must be used for accurate irrigation scheduling. A 15cm tensiometer should be installed into the nursery medium immediately after planting to monitor the moisture in the root zone; and a 30cm tensiometer should be placed away from the first, outside the nursery medium to monitor moisture in the surrounding soil. Read the tensiometers early in the morning. When the 15cm tensiometer reads 20kPa for sandy soils and 30-40kPa for loam and clay soils, start watering. Stop watering when the reading falls to 10kPa. If readings on the 30cm tensiometer continue to rise immediately after irrigation, not enough water has been applied. If readings however fall to less than 10kPa soon after irrigation then too much water has been applied. Regularly remove any accumulated air and check that gauges are working by using the vacuum pump. Refill the tensiometers with clean water. Once the roots have grown into the surrounding soil (1-2 months after planting), the 30cm and 60cm tensiometers should be placed in the major root zone and the 15 cm tensiometer can be removed. If tensiometers are not used, the general rule would be that a small tree should not get more than 10ℓ of water per week. In extremely hot weather this can be increased to 7ℓ twice a week. It is preferred that you scratch in the soil next to the tree to check the moisture. BEWARE: more trees die due to too much water than too little! If irrigation is by bucket, make a dam 60cm in diameter to contain the water. Pour the water onto the empty planting bag to stop the soil from being washed away. If micros are used, fit spreaders to limit the irrigation area.
Although the stems are painted with PVA before leaving the nursery, it may be necessary to touch up at the base of the stem and any branches exposed to direct sunlight with white PVA paint. Renew the paint often until the stems and branches are protected by leaves. BEWARE: settling soil will expose the unpainted section of the stem! Prevent the paint from running down the stem. It will harden into a ring which will girdle the young tree eventually.
Mulch trees well to increase the organic matter, improve the soil structure and reduce evaporation and fluctuations in root temperature. Keep the mulch around the stems to protect it against sun burn and to prevent the soil from getting hot. Remember to also apply mulch around the tensiometers.
Soon after planting the young trees should be supported with a stronger wooden stake. Place the stake at an angle facing into the prevailing wind direction. Do not push this stake into the nursery growing medium as this will damage the roots. Use untreated sisal twine to tie the tree to the stick in at least two places. The nursery stake can be removed after four to six months. Regularly check the sisal twine and loosen it to prevent it from girdling the tree. Re-tying should be done regularly – every four to six weeks.
Trees should be protected against Phytophthora with Aliette WP foliar sprays every 4-6 weeks at 275g/100ℓ or alternatively buffered H3PO3 at 3g/ℓ. (Joe Darvas’s M5 foliar spray can be used instead with great success.) If the trees are planted in an old orchard, the treatment should commence as soon as possible after planting. The foliar sprays should be applied in the late afternoon only and continued until trees can be injected. Even trees on Dusa™ rootstock must be protected against this disease to ensure development of strong, healthy roots. This rootstock is root rot tolerant, not resistant.
Weeding is important to prevent competition with the avocado tree roots. By handweeding, keep an area of 1m diameter around the trees free from weeds. Herbicides are not recommended at this stage unless the trees are protected with stem protectors. Even then a spray hood should be attached to the sprayer to contain drift.
Fertilising by foliar feeding (leaf sprays) with Nitrosol or a similar fertiliser is advisable for 1-2 months after planting until the roots have started to grow into the soil. Thereafter granular fertiliser can be applied to the soil 20cm around the stem, being careful to avoid contact with the stem. A good granular fertiliser to apply is a 2:2:1 mix of LAN:MAP:KNO3 applied at 20g/tree. Continue with foliar feeding once a month with Nitrosol and Zinc (2g Zinc oxide/ℓ water). Boron (1g Solubor/ℓ water) should be applied every two months. Suspend all fertilising in winter. Increase the quantity of fertiliser as the size of the trees increases.
Pest and disease management is mainly against Phytophthora root rot although young trees should be regularly inspected for insect pests such as mites, scale, mealy bugs, thrips, leaf rollers, beetles, locusts and grasshoppers.
Protecting the trees against damage from buck is very important. In the winter months when natural food is scarce buck will feed on the leaves and stems of young avocado trees causing extensive damage that may result in the tree dying back completely!
If planting in a cold region it is necessary to protect the young trees against frost.
USE THE ATTACHED CHECKLIST TO AID IN THE MANAGEMENT OF YOUR SMALL TREES
IF YOU HAVE ANY FURTHER QUESTIONS PLEASE SPEAK TO HERMAN ERASMUS