Using the Avocado Tree Growth Cycle to Manage Groves

Each avocado grove is unique — as are the trees within the grove. Avocado growers are very aware that even within a grove there can be high variability — avocado trees in one section of the grove may bloom earlier or later than in other sections, for example. Understanding the avocado tree growth cycle is useful because it helps avocado growers:

• make cultural management decisions based upon the current or previous growth of the avocado trees rather than the time of year
• comprehend the competition for resources between the various avocado tree cycles
• time cultural-management activity in order to provide the optimum balance among shoot growth, fruiting and root growth
• determine avocado tree problems

Avocado tree growth (phenology) cycle

The avocado seasonal-growth changes that consistently occur, within a year, are:

• Flowering
• Shoot growth
• Root growth
• Fruit set
• Fruit growth
• Harvest

Avocado tree growth cycles are dynamic

Ideally, an avocado tree would produce a similar crop each year. But avocado trees tend to adopt an alternate bearing cycle — an on-crop year (a large crop of fruit that is usually smaller in size) followed by an off-crop year (less fruit that is generally larger in size). Once started, an alternate bearing cycle can be self-perpetuating. A large on-crop inhibits fruit set and flowering, leading to a smaller crop next year. Likewise, a small off-crop leads to robust fruit set and flowering and a large crop the following year.

Avocado crop load, shoot growth and flowering are interrelated, and the timing and duration of these phenological events can change each year depending on the avocado tree’s history.

Avocado growth cycles compete for resources

An avocado has three two-year cycles occurring simultaneously:

• Developing the current year’s fruit — providing nutrients and resources that mature the fruit for harvest.
• Supporting the needs of the year two fruit set that will be harvested the following year.
• Producing new shoots and buds that will produce either vegetative or floral buds for the year three harvest.

That means branches in one part of the growth cycle are competing for resources (nutrients, water, sun) with branches in other parts of the cycle. Fruit and flowers require a lot of resources (sugars, starch, water, minerals and chemicals) from the tree. If there is an abundance of fruit or flowers, the tree may shed some fruit and may conserve resources by inhibiting the growth of new shoots, flowers, fruit set or roots. Because avocado trees only flower, set fruit and bear fruit on peripheral new shoots, having just a few new shoots in the current year means a smaller crop next year.

The challenge, for the grower, is to establish the correct balance among various shoot-growth cycles, ensuring the tree always has good cropping potential. Ultimately, the amount of fruit harvested in the current year is a result of cumulative weather and cultural management influences in the preceding two years, so understanding the avocado tree growth cycle is important to help growers manage the difference between on-crop and off-crop years.

Applying the avocado tree growth cycle to cultural management decisions

When a portion of the tree is actively growing, it acts as a “sink” for the raw materials and draws the majority of the tree’s resources and raw materials. Sink strength changes annually — in an off-crop year, the tree will devote most of its resources to flowers and fruit, while in an on-crop year the majority of resources will be devoted to avocado tree growth.

A key horticultural skill for avocado growers is knowing proper application amounts of raw materials and when to adjust such materials, in relation to primary sink.

Correct cultural-management timing, in relation to the growth cycle, is critical for:

• Water management
• Root-rot control
• Fruit quality (calcium uptake)
• Pruning
• Girdling
• Fertilizer
• Harvest strategy

Following are a few examples of cultural management timing mapped to avocado tree growth cycles and their primary sinks.

• Timing phytophthora control
• Examine the growth cycle, and identify when roots are the primary sink. You can tell roots are in a growth phase by looking under the leaf litter for new white roots. There will also be low shoot growth, flowering or fruit development occurring. Apply phytophthora control twice a year — in anticipation of root growth so the new roots are protected.
• Timing calcium application to optimize avocado fruit quality
• Review your trees’ growth cycles and determine when fruit is the primary sink. The first 6 – 8 weeks of fruit growth are critical for accumulating calcium because the fruit have stomata that allow water (and the calcium in it) to move easily through the fruit and deposit there. This improves the quality of the fruit.
• Managing avocado shoot growth when competing with avocado fruit set
• During flowering, a fine balance exists between resources used for fruit set or shoot growth. Avoid high-nitrogen applications when shoot bud break and flowering occur because nitrogen can tip the balance to shoot growth at the expense of fruit set.