Storm damage

Based on knowledge from growers that have experienced several severe storms, a “Storm Damage Decision Guide” has been developed. The guide explains how to assess damaged trees and what to do with them to minimise the effects on orchard productivity. The strategy and goals of each individual orchard will of course need to be factored into any final decisions. See the guide in the resources section below along with videos showing the outcome of discussion with growers on how to assess and manage storm damaged avocado trees.

We would like your feedback on the guide to make it relevant, as comprehensive as possible, and easy to use. We would also like to hear about your success with mitigating storm damage using shelter management, increased drainage, pruning, or any other method. Please contact info@nzavocado.co.nz for any feedback.

Development of the Decision Guide involved growers that have experienced several severe storms visiting a damaged orchard in Whangarei in 2014 and discussing what they would do when presented with different situations.

NZ Avocado would like to acknowledge John Wiessing, Dave Alderton, Mark West and Sue Culham for the time they spent with us at the orchard and the effort made to create this information.

Guideline: Storm damage decision guide

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See below for videos on storm damage:

• Pruning a windblown avocado pollinizer tree
• Managing avocado trees with saturated roots
• Pruning a split avocado tree
• Dealing with avocados on the ground after a storm
• Recovery of small avocado trees after storm damage
• Assessing windblown avocado trees

Learnings from Hale, Gabrielle and a difficult Spring, Summer

Phillip West – Research Manager, NZ Avocado

16^th March 2023

We’ve had one of the wettest summers on record in 2022-23 following from a very dry summer in 2020-21, where fruit size was impacted for growers.  Information is already available about storm damage mitigation and recovery on the NZ Avocado website but what can we learn from the most recent extreme weather. This is under the umbrella of many growers realigning their orchards for more frequent extreme weather events and seek to maximise profitability?

Ex-tropical cyclone’s Hale and Gabrielle made landfall on 11 Jan 2023 and 13 Feb 2023 respectively. Hale did not significantly affect the Far North but brought significant rain to the Mid North (224mm) and Bay of Plenty (180mm – 160mm). Gabrielle brought significant rain and wind to Northland (85mm – Far North, 372mm Mid North) and while delivered less rain to parts of Bay of Plenty (114mm Katikati, 64mm Te Puke), Eastern Bay of Plenty was more significantly affected. Significant rain events also arrived in between the two ex-cyclones exacerbating the damage.

Variable tree loss was reported in Northland with damage less severe in the Far North. Some Mid North growers reported ~1 productive tree/ha lost due to wind. Shelter damage was variable but shelter tree loss was common in reports received from the Mid North. The Bay of Plenty also lost trees but waterlogging was more evident in reports rather than wind.

Early fruit loss was estimated at 1-8% in the Far North and was as high as 20% on Mid North orchards. Fruit quality downgrading is also expected to be significant.

A late October 2022 frost had significant negative impact on predominately Bay of Plenty and Mid North fruit set.

What can we learn?

Shelter

• Establish shelter on young orchards as soon as possible.
  • Several new orchards with living shelter have suffered very low packouts and tree damage as a result of the shelter not being mature. Young orchards are at significant risk under shelter trees establish.
• Ensure mature trees are pruned below the height of shelter.
  • Shelter is ineffective if productive trees are taller than the surrounding shelter
• Adequate shelter on all aspect of orchard blocks is important.
  • Cyclones brought wind from North and North east before swinging around to the South. Orchards with minimal Northern shelter suffered damage that may have been preventable.

Orchard/planting set up

• Hump and hollow where possible ensuring humps do not act as dams to heavy rain runoff.
  • Having trees on humped rows provides greater drainage and aeration in the soil. One orchard in the Bay of Plenty pumped out a block that was humped and hollowed and trees showed very limited impact of the flooding.
• Consider use of weedmat on young trees.
  • Some weedmats may help direct excess rainfall away from roots.
  • Weed mats often have specific infiltration rates meaning very heavy rain is shed away from root zones.
• Consider additional drainage
  • Drainage will speed the removal of excess water from blocks without reducing the amount of useful water a soil can hold.
  • Simple swale drains helped direct water away from production blocks. Some were gouged out to 2.5m deep trenches with the amount of rain but still helped direct water away from trees.
  • Novaflow with coarse gravel backfill to soil level were effective in orchards but adequate spacing between drainage lines and size of piping is important.

Crop load managment

• Reduce clusters of fruit
  • Reducing the amount of fruit clusters reduces stress on the tree from excessive crop loading, making it more resilient.
  • Less clusters means less ideal thrip and leaf roller habit, helping reduce pest pressure.
• Flower pruning in excessive flowering years but caution required if you are frost/cold prone
  • Flower pruning means more resources are preserved to support fruit and new flush development as early as possible.
  • Late spring frosts can make it risky in that pollination success is not guaranteed. Consider a multi visit approach if labour resource allows that removes some flower with fruit thinning carried out if required as well.