2017 ASHS Annual Conference

California produces about 90% of the nation’s avocado (Persea americana) crop and San Diego County grows about 40% of all the avocados grown in the state. Avocado trees are native to subtropical climates where rainfall is abundant so it is important to keep trees well irrigated to produce fruit and leach out salts from their sensitive root zone. Currently the cost of water in San Diego County is approximately $1,600/ac ft and avocados require 3.5 – 4 ac ft/ac to produce a commercial crop. Water costs are expected to increase. The cost of water is causing many growers to turn off their water because they can no longer make a profit. To adapt, growers need to dramatically increase yield per acre using the same amount of water or less. Higher yields have been achieved with high density spacing plantings in Chile. As an alternative to planting at the traditional spacing of 20’ x 20,’ trees for this project were planted at a high density spacing of 10’ x 10’. Also, in other trials in California it has been shown that Hass avocado yield can be improved by planting B-flowered avocado varieties nearby for cross-pollination. Therefore, in order to achieve the best yield possible, we planted nine 9-tree units (8 ‘Hass’ surrounding 1 B-flowered ‘Zutano’) in blocks of 72 ‘Hass’ and 72 ‘Lamb Hass’ avocados, all on ‘Dusa’ rootstalks, in August 2012. The actual trial consists of a comparison of two different methods of pruning (traditional all sides pruned and topped at 8 ft) and alternate side pruning (southwest side pruned every other year with the northeast side pruned in alternate years). We are comparing 5 alternate side pruned units to 4 traditional pruned units within each variety. In addition to heavy pruning after the harvest, twice within the year light pruning was done to keep the aisles cleared for a worker. Yield was collected on the third, fourth and fifth years after planting for ‘Hass” and on the third and fourth years for ‘Lamb Hass’. Results thus far have indicated no significant difference in yield between the two pruning styles, but taken as a whole the yields in the Hass block have been much higher than the county average yields for mature trees of 6,000-7,000 lbs/acre. In our trial from years 2014-2017 yield/ac in Hass has been 480 lb/ac, 13,246 lb/ac, 25,104 lb/ac and 5,641 respectively. The 2017 harvest was an off-year due to high temperatures in 2016. From years 2014-2016 yield/ac in Lamb Hass has been 975 lb/ac, 8,796 lb/ac and 15,243 lb/ac respectively. Lamb Hass has not yet been harvested in 2017. Because trees are being kept below 8 ft, ladders are not required and harvesting is much less expensive. Water costs are less than neighboring tall trees kept at 30 ft, but pruning costs are more. Pruning methods and costs still need to be further evaluated to gain the information that is needed to maximize production for California growers.