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Avocado growing trial results in higher yields

Growing avocados in California has become a risky business over the last several years with drought and the rising cost of water making it a less than profitable endeavor. A University of California avocado specialist and farm advisor, Dr. Gary Bender has been working on methods to help the avocado industry thrive again in San Diego County.

While there have been many obstacles in the way of avocado growers, Bender said he has been working on better ways to grow the fruit as this area has the perfect climate for growing them. He would also like to see avocados treated "like real agriculture."

For more than four years, he has been conducting an experimental "Avocado High Density Trial" funded by the California Avocado Commission.

Although he has been a Fallbrook resident since 1985, the location of this project is high on a hill in Valley Center at Nick Stehly's farm. Bender supervised the planting of the avocado trees in August 2012.

The project title is "Improvement of yield per acre by close spacing, pruning of close-spacing Hass and Lamb Hass trees".

The project's features also include the specialized use of bees and the use of moisture meters.

Instead of the traditional 20 foot spacing of avocado trees, Bender planted the experimental grove with 10' x 10' spacing of small Hass trees grafted to Dusa rootstock from South Africa which is root rot tolerant and high producing.

He also planted a Zutano tree in the middle of every nine trees. The Zutano avocado tree, like bacon and Fuerte trees, are all pollinator trees, Bender said. He previously observed that Hass trees located near Zutanos were heavy with fruit. "Nobody else does this," he added, about planting Hass trees so close to a pollinator tree.

While some people might be leery of having a lot of bees around their trees with the possibility of attracting Africanized bees, Bender explained that a "beekeeper can requeen the hive with a European queen bee to calm down the hive if the queen bee mates with an African bee" (and produces African drones/male bees).

Besides the spacing of trees, the trial compares two pruning styles. Instead of the traditional pruning of one side of all the trees (the southwest side one year, the northeast side the next), Bender has had some of the trees pruned on all sides as well as the tops.

The trees were cut to 8' tall in the beginning but grew back so fast that they have tried topping them at 6 1/2 to 7'. They also skirt prune the trees to keep all branches about 16" off the ground.

Bender said that many people don't want to prune their trees because there is always fruit or flowers on them. However, if the tree is allowed to continue growing, he explained, the top will shade the bottom of the tree and the leaves at the bottom will fall off.

The trees need light coming through the branches in order to grow and produce fruit. If the bottom of the tree is bare, all the fruit will be growing up near the top. This makes the avocados harder to pick. So far, the two methods of pruning have not produced a noticeable difference in the amount of fruit produced.

At the project farm, a moisture meter is stuck into the soil so they know when to water. This year, the farm has used 2.8 acre feet of water per acre versus the 4 acre feet per acre to irrigate without the moisture meter. Last year, 3.3 acre feet per acre was used.

Keeping the trees shorter also cuts down on water usage as wind blowing through the tree tops makes the trees need more water. So, the farmer is better off keeping the trees low to the hill sides.

The average production of avocado trees in California, according to Bender, is 6,500 lbs per acre. The year 3 totals for the trial farm were 15,000 lbs per acre.

In contrast, the project activity report from September 2016 included Bender's figures for the July 8, 2016 harvest. "The average yield per Lamb Hass tree was 40.7 lbs/tree...At 387 Lamb Hass trees/acre, we produced at the rate of 15,743 lbs/acre. At 23,165.8 fruit per acre, the average size per fruit was 0.68 lbs/fruit."

In the March 17, 2016 Hass harvest, Bender's report continues, "the average yield per tree was 64.9 lbs/tree. At 387 trees per acre (on the 10 x 10 spacing) we produced at the rate of 25,104.7 lbs/acre. This is phenomenal yield for this age of tree..."

Bender also noted that the trees were going into alternate bearing years with a heavy harvest one year and lighter the next year, "The trial is not over yet, and our yield this year for Hass avocado was low ( 5,100 lbs/acre) in 2017. This shows that the grove is in an On/Off cycle. We have heavy bloom right now, so we expect a large crop again in 2018 when the crop is On."

The five year grant from the California Avocado Commission ends in October so the harvest this summer will be the last funded one. However, Stehly wants to keep using the methods Bender has developed.

Meanwhile, Bender is continuing to teach classes for avocado growers, getting new students all the time. Many of those students have bought property with avocado trees already on them and need to learn the basics of the industry.

The class includes History of Avocado Production in California; Botany, flowering, varieties, harvest dates, rootstocks; Irrigation systems, irrigation scheduling, salinity management; Fertilization, organic production; Canopy management, tree spacing, diseases and root rot control; Insects and mites, shothole borer; and a Saturday field trip to a high density grove.

To register, call the UC Cooperative Extension office at (858) 822-7933 or (858) 822-7919. More information can be found on the UC Cooperative Extension website,


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