This means yields are inconsistent, which has an effect on the price, particularly in a low-crop year when demand for each fruit is high.
This is where Plant & Food Research comes in, partnering with NZ Avocado to tackle the most pressing challenges, including a big focus on irregular bearing.
In one example of this, Gould’s team trialled pruning shoots carrying flowers and fruit at different times to see how avocado trees respond.
“We’ve been able to show that the earlier you prune a tree in the reproductive cycle, the easier it is to balance the crop carried by the trees year to year,” he said.
But encouraging more flower growth is only part of the story.
“The other part is getting more fruit. An avocado tree might have more than one million flowers, but even in a good year, only 0.1 per cent of them turn into fruit.”
Gould said the key to achieving sustainable crop loads was to get well-resourced, healthy flowers that had a good rate of pollen transfer.
“We’re working to understand the local climate on flower health, flower timing and pollen transfer to develop orchard management systems that improve fruit set.”
Rot is the other bane of avocado growers.
Phil Elmer, who leads the Plant & Food Research plant pathology team, said it was a complex problem to solve, mostly because five different pathogens were involved.
As part of the Avovantage research programme funded by NZ Avocado, Elmer’s team has been trying to understand how rot takes hold – and how this could be mitigated through orchard management practices.
Getting to grips with the issue is complicated by the fact avocado rot only manifests post-harvest.
Plant & Food Research’s plant pathologists began their investigation by tapping into NZ Avocado’s database to see which of the avocado blocks identified for the research had a history of being rot-challenged and which had a history of low rots.
Elmer said it turned out the orchard block wasn’t the problem - it was the trees within the block.
“There is huge variability between individual trees.
“That finding allowed us to really start drilling down to figure out what was happening in canopies and under the trees.
“Now we know the individual rot-challenged trees in a block, so we can throw everything we know about best practice at these trees to turn them around.”
Elmer cautioned there won’t be a “silver bullet”.
Reducing canopy density and pathogen establishment in the tree with well-timed bio fungicides is one of the supposed best practices that will be evaluated.
Plant & Food Research is also working with NZ Avocado to identify an alternative to copper sprays, and a suite of other orchard practices are likely to be needed.
The key will be to find a practical cost-effective combination and prove to orchard managers it works.
“Our goal is to show that control of post-harvest rot is possible in an orchard by using best practices,” Elmer said.
“But it has to be pragmatic and cost-effective, or growers won’t do it.”
Even if an avocado leaves its orchard in good condition, it may not ultimately be that way by the time it gets to consumers’ toast.
For that reason, Plant & Food Research is also working on new approaches to handling fruit from the orchard to the cool store and storing fruit during transport.
