- Author: Sonia Rios
Dr. Gary Bender, UC Cooperative Extension (UCCE) Farm Advisor Emeritus, is the lead instructor for a six-week course entitled “Avocado Production for New Growers.” Co-instructor, Sonia Rios, current subtropical Farm Advisor, Riverside/San Diego Counties will also be teaching in the course. The course is designed for new avocado growers, as well as those interested in learning more about avocado production best practices and meeting fellow growers.
The six-week course consists of six, two-hour sessions and will be held in Fallbrook, CA this year. The fee for the course is $105 and includes two avocado books, an IPM book and a post-harvest handbook. Final dates and the location will be announced soon. The always fills up, so please register A.S.A.P.
- Introduction to Agriculture in San Diego County, History of Avocado Production in California
- Botany, Flowering, Varieties, Harvest Dates, Rootstocks
- Irrigation Systems, Irrigation Scheduling, Salinity Management
- Fertilization, Organic Production
- Weed, Insect and Mite Control, Disease Control
- Ag Waiver Water School Training (Dr. Loretta Bates)
- Canopy Management, Tree Spacing, Frost Management
- Field trip to High Density Trial grove and a commercial grove
For more information, contact Erin Thompson at 858.822.7919 or firstname.lastname@example.org.
Here is a system of avocado pruning that seems to be working for the grower. He has been keeping his 12 year old ‘Hass' planted on 16 x 16 to 8 feet high by pruning out center limbs each year. He leaves some to flower and fruit the next year, then removes those with the fruit once they pass maturity in January. The cost of the pruning and chipping is about the value of the fruit that is harvested off those limbs. On older trees that were planted in the 1970's are treated in a similar manner. The trees were scaffolded to 5 feet and once tamed, have been allowed to grow in a similar fashion as the 12 year old trees. Both tree ages are productive throughout the canopy. In the spring, the trees are size picked from the ground with picking poles and as necessary with short ladders. In the summer they are stripped. The key is yearly pruning. I have been somewhat disenchanted with this style in the past because the centers would fill up so fast. In this case, the trees are kept short to keep light throughout the tree and the yearly pruning keeps opening it up.
12 year old center pruned trees
Fruit hanging in the interior
40 year old, scaffolded then center pruned trees
Transpiration is essentially a function of the amount of leaves present. With no leaves, there is no transpiration and no water use. The extreme case is tree removal. If canopies are pruned there is reduced water use. The more canopy reduction, the more transpiration reduction. Most citrus produces terminal flowers, so there is also a reduction in yield, but there is also typically an increase in fruit size as competitive fruit growing points are removed. There is a balance between yield reduction and tree water use, but typically a 25% canopy reduction results in a 25% decrease in tree water use (Romero, 2006).
The severity of the drought will determine how drastic the canopy should be trimmed. The trees can be skeletonized so that only the main structural branches are left. The tree is whitewashed to prevent sunburn and the water is turned off. As the tree gradually leafs out, the water is gradually reapplied in small amounts. It's important to check soil moisture to make sure the tree do not get too much or too little water. The trees if pruned in the winter will often flower a year later in the spring, but normal production will often take three years for the trees to recover their previous yields.
Skeletonizing should first be practiced on orchards that are the poorest producing. In those areas that get too much wind and have lots of wind scarring or elevated water use, those areas that are most prone to frost damage, those areas that have been always problematic, such as fruit theft. In areas that are healthy and a new variety has been contemplated, this is the time to topwork and replace that old variety. In areas that have been poor producing from disease, this is the time to get rid of those trees.
Canopy sprays of kaolinite clay have shown some promise in reducing transpiration with negligible yield reduction (Skewes, 2013; Wright, 2000). If these are used, they should be done under the advisement of the packing house to make sure the clay can be removed in the packing house.
With a reduced canopy, there are often other benefits besides water reduction. There is better spray coverage for pest control. There is also reduced fertilizer use. New growth is normally coming from nutrients that are now being mined by a large root system and fertilizer applications can be significantly reduced or eliminated altogether for a year until fruit set recommences.
Kerns, D. and G. Wright. 2000. Protective and Yield Enhancement qualities of yield of kaolin on lemon. In: Eds. G. Wright and D. Kilby, AZ1178: "2000 Citrus and Deciduous Fruit and Nut Research Report," College of Agriculture and Life Sciences, University of Arizona. http://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1178_3.pdf
Skewes, M. 2013 Citrus Drought Survival and Recovery Trial. HAL Project Number CT08014 (16/12/2013). SARDI. http://pir.sa.gov.au/__data/assets/pdf_file/0004/238414/SARDI-Citrus-Drought-Survival-Recovery-Trial.pdf
Navel trees skelotinized and topworked, ready for rain and more profits in the future.
A recent trip to Spain was an opportunity to look at their cherimoya production practices. One of the most interesting is their ability to manage the tree through pruning to produce fruit off-season (in spring) when the prices are the highest. IN California our low period of production is in the summer. The climate in Spain along the Mediterranean coast is warmer and more humid than coastal California, so most tree crops are about two months advanced in their production. So in the text I refer to a period when something is done and then follow it with another date. The one in parenthesis is the probable time in California if the date in Spain is used. So, to produce fruit in spring (summer) in March/April when prices are high:
Remove all shoots from the previous year in March (May)
With the new shoots, prune them back 6 inches in length around July 15 (September 15)
Pollinate the flowers that are produced in the period of August to September (Sept/Nov)
Pick fruit in March/April (June/Aug)
Fruit is produced when prices are higher
Generally fewer seeds than at other periods
In some cases there is higher sugar content in the off-season frui
Not always consistent with all cultivars
Off-season fruit often has black spots in the pulp
May see increased leaf drop
In some cultivars, the skin is more prone to abrasion, and this is already a very delicate fruit
There are other fruit species that fruiting date can be manipulated by pruning, such as evergreen blueberries, guava, lime, mango and carambola (star fruit). Always it is to find a better market for the fruit.
A general rule of thumb about pruning trees is that only healthy trees should be pruned. Pruning is a devitalizing practice that comes at the expense of the roots. If an avocado has root rot, make sure the tree has been treated with one of the phosphite products to get the root system healthy. A common pruning method is stumping to 3 feet and allowing regrowth to occur. A common phenomenon after stumping is that the tree puts on vigorous growth for two or three years and then collapses. All that canopy regrowth was coming from a large root system that was brought into balance with a smaller canopy. Energy is diverted from the root to fight off disease. Gradually the root system gets out of balance with a larger canopy that it can no longer support. Often when a severely impaired root system tree is pruned, it often does not have energy to push a new canopy and the tree dies. Make sure you only prune healthy trees.