The effects of Cyclone Gabrielle on fruit tree health in Hawke’s Bay

Stephen Trolove1*, Emily Husband1, Isabelle Sorensen1, Michael White2, Josh van der Weyden1, Nathan Arnold1, Jim Walker1, Mary Horner1, Jonathan Brookes3
1 Bioeconomy Science Institute, Hawke’s Bay, New Zealand
2 Fruition Horticulture (Hawke’s Bay) Limited, New Zealand
3 AgFirst, Hawke’s Bay, New Zealand
Stephen.Trolove@PlantandFood.co.nz

Cyclone Gabrielle struck New Zealand in February 2023, causing widespread flooding that affected approximately 2500 of the 7000 ha of pipfruit orchards in the Hastings region. The cyclone came during a season that was already very wet, with high soil moisture readings recorded from spring 2022 until late spring 2023. There is little published information about how to manage pipfruit orchards affected by large amounts of sediment and ponded water, therefore transects were established in selected orchards to monitor soil and tree health post-cyclone to provide information for future growers who may face similar challenges.

Flooded orchards were divided into three categories based on the best knowledge at the time:

  1. Sediment >30 cm – tree survival unlikely and sediment removal would be very expensive
  2. Sediment 0–30 cm or ponded water for ≥1 week – tree survival uncertain
  3. No sediment or ponded water – tree survival highly likely.

Soil, sediment and tree health measurements were taken 2–4 weeks after the cyclone in 29 orchards across the Heretaunga Plains where tree survival was uncertain (Category 2). The health of nine trees was scored at seven sites along a transect. Holes were also augered and the depth of mottles, gleying and waterlogging measured. Further tree health scoring was conducted in May 2023, and in the subsequent growing season at flowering and just before harvest. A grower survey was conducted in May 2023 regarding management practices, and for yield data after the harvests of 2024 and 2025.

Flowering was abundant in the season following the cyclone. Some growers were uncertain how their trees would respond to chemical thinners so used lighter rates, and reported large hand-thinning costs. By harvest 2024, tree deaths averaged 12%, with an average ill-thrift score post cyclone of 0.24 (where 0 was healthy and 4 was dead). Much higher losses were seen in young trees, especially 1-year-old trees, than in mature trees. Good drainage was essential to tree survival, with trees on gleyed soils or a high-water table <45 cm below the surface 2 weeks post cyclone experiencing higher tree losses.

Seventy-five percent of orchard managers from the surveyed blocks reported reduced fruit yields in 2024, with 91% of these stating that the yield loss was at least partly attributable to the cyclone. Possible explanations for the cyclone-related yield loss included root damage, tree loss, poorer bud quality including Phytophthora infection in buds, and difficulties in completing necessary management practices due to the cyclone.

By harvest 2025 most of the orchards surveyed had recovered from the cyclone, with only 27% of growers reporting a yield decrease that they attributed to the cyclone. The size of the yield loss was typically estimated at 5–25%, apart from one block where losses of 79% were reported. This block was located on a poorly drained loam where water had ponded for >4 weeks after the cyclone, and tree losses from Phytophthora had been high.

Most growers removed the sediment within two months of the cyclone in the blocks studied. In one orchard where the sediment had not been removed from around the trunk, 13% of trees had developed trunk fungal lesions when assessed at flowering, whereas the incidence of trunk lesions was <2.5% at other the orchards. Although not included in this survey, growers reported very high tree losses in blocks inundated with ≥50 cm of sediment. In blocks where sediment was left above the graft union, growers noted a marked increase in tree vigour in the second season after the cyclone because of scion rooting.

Management recommendations post flooding included:

  • Dig holes to 60 cm to check for gleying or a high-water table
  • Have drains checked and working
  • Prioritise draining water and removing sediment from young trees over mature trees
  • Apply phosphorous acid to reduce Phytophthora risk
  • Remove sediment to below the graft union (taking care to avoid trunk damage)
  • Cultivate the sediment into the underlying soil and sow understorey species
  • Conduct soil and leaf tests the following season and fertilise accordingly.

Funding sources:
This work was made possible by the Strategic Science Investment Fund administered by The New Zealand Institute for Plant & Food Research Ltd (now part of the Bioeconomy Science Institute), with the Grower Survey funded by New Zealand Apples and Pears Inc.

For more information regarding this work:

PowerPoint presentation

Proceedings paper (AI generated from transcript and abstract)