The avocado is an oil-rich fruit that requires a large energy investment for the fruit to mature. Apart from the oily flesh, the fruit also has a large central seed that accounts for an even larger energy expenditure.
Well, the avocado trees are under a lot of pressure to photosynthesize in order to supply the developing fruit with carbohydrates. This results in very low fruit set, as low as 0.001% in some cases, and more importantly, a phenomenon known as ‘alternate bearing’.
This is the tendency of many fruit trees to have irregular yields year on year. In other words, in one year, the tree will produce an above average crop yield (image on the right above). However, the stress placed on the tree sends it into a recovery phase the following year, where below average yields are received (image on the left above). These are commonly known as ‘on’ and ‘off’ years in the industry.
It is believed that alternate bearing can be triggered by factors hindering fruit production, like frost or drought, which dramatically decreases crop load in the first year, and the problem snowballs from there.
Alternate bearing is observed in species like apples, mangoes and nut trees. However, because the avocado fruit demands a huge energy investment, alternate bearing can be especially problematic, especially if the trees are mismanaged.
In the avocados specifically, on years are characterized by heavy blooms and increased crop loads, but the fruit are smaller and therefore less valuable. Off years have decreased blooming and very low yields, but the fruit are larger. Therefore, it is extremely important for commercial farmers to manage their trees to minimize the stark contrasts between on and off years in order to maintain economic stability.
Management practices to mitigate the issue include culling excess fruit during on years, pruning trees to lower the number of flowering sites and the using growth regulators to manipulate production cycles.