Significant information about walnut cultivar performance in New Zealand.
Heather North, on behalf of the New Zealand Walnut Industry Group, December 2021
Background: The New Zealand Tree Crops Association undertook walnut cultivar trials in the late 1980s to early 1990s, resulting in several good local selections including ‘Rex’ and ‘Meyric’. By the early 2000s these were widely planted by New Zealand growers. The New Zealand Walnut Industry Group decided to continue this progress and broaden the range of high-performing cultivars available, so organised a new cultivar trial that was planted in 2005.
The trial: Nine candidate cultivars were chosen, including ‘wild’ trees identified as having excellent nuts, a candidate from a previous trial deserving of a second chance, and promising selections discovered by propagators. ‘Rex’ and ‘Meyric’ were also included for comparison. There were four trial sites: one in Otago (near Wanaka), two in Canterbury (Kirwee and Springston areas, respectively), and one in Whanganui (near Kai Iwi). On each site were five replicates of each candidate (i.e. 55 trees on each site), planted in a randomised block layout. The candidates were known only by code numbers during the trial and data analysis.
Data collection and analysis: Measurements were collected at the trial sites until 2015, including tree growth, timing of budburst and flowering, and walnut yield and quality. Ideally, data analysis would have been completed at that time, with results published for growers. However, time constraints in the voluntary NZWIG research committee delayed the final analysis and report until 2021. This document is the brief/summary version of the report; for details, please see the full-length version.
Results: The table below summarises the performance of the candidate cultivars across all the assessment metrics – tree growth, flowering and pollination times, yield, and nut quality. These are overall results, averaged across all sites. The full version of this report also includes per-site results – there are some differences in which cultivars were best on each site, though the general patterns hold across the sites.
The orange shading indicates significantly poorer performance than average (amongst the candidates), the green shading indicates significantly better performance than average, and the unshaded (white) cells show where performance was about average. In general, the candidates with multiple metrics shaded orange are those with many poor characteristics, and those with multiple metrics shaded green are our top-performing candidates. However, all candidates have some positive and some negative factors, and choice of a new variety is a trade-off between these factors.
In addition, some judgements are site- or situation-dependent. For example, a variety with poor shell seal could be acceptable where the nuts are harvested by hand and sold in-shell as table nuts. Likewise, a variety that flowers early (which we have judged to be ‘bad’ here) would be fine in a warm climate with low frost risk.
‘Shannon’: Strong tree growth and good survival. Highest yielding of the varieties trialled, with excellent appearance of both shell and kernel. However, slightly below-average crackout, with very poor shell seal and strength. Early budburst and flowering, so could be susceptible to spring frost.
‘Rex’: Second highest yield in the trial overall (though not in Whanganui), but only average in tree growth and survival. Budburst and flowering are late, reducing frost susceptibility. Attractive kernel appearance, with strong shell and seal. However, the nut is small, with poor crackout.
‘1340’, ‘Diana’ and ‘Serr’ all have many good characteristics. They are the next-best group for yield – each does well in some locations and not others – and generally have high nut quality. ‘1340’ is the largest of the nuts, with the best in-shell appearance, and strong shell seal, but low crackout. Budburst and flowering are late, so is likely to be less frost-prone, but tree growth is slow. ‘Diana’ has high nut weight with attractive in-shell appearance, but the kernel appearance is not as good. Tree growth and survival are high, but budburst and female flowering are early. ‘Serr’ has good shell seal, very good survival, and is late for female flowering, but is early for budburst. It is variable for appearance, depending on site.
The next group comprises ‘Rangiora’, ‘Meyric’ and ‘Blenheim’ which are low-average for yield. ‘Rangiora’ has very good tree growth and survival, late budburst and excellent crackout, with no strongly negative characteristics, though its relative yield is the lowest of this group of three. ‘Meyric’ has the highest relative yield of this group, and has late female flowering, but has low nut weight, and its other characteristics are average. ‘Blenheim’ has excellent crackout and very good kernel appearance, but has early budburst and flowering, a low nut weight, and the shell seal is poor.
Candidates ‘DSIR-121’, ‘Coleridge’ and ‘Cashmere’ are not recommended as they exhibited: (a) poor tree growth and survival; (b) poor yield; and (c) poor appearance of both kernel and shell. Other characteristics are mixed.
The team who worked on the trial
Those who organised the trial, recommended the walnut selections for trialling, and screened the selections – Clive Marsh, Jenny Lawrence, Ross Jamieson, Heather North, John Blanchard, Tim Jenkins, David Murdoch, Nick Nelson Parker, Vernon Harrison, Diana Loader
Owners of parent trees, and those who collected scion wood from them
Propagator – Darrell Johnston, River Terrace Nurseries, Brightwater, Nelson
Trial block owners – Mike & Margaret Caldwell, Jeffrey & Margaret Feint, Diana & Walter
Loader, Hel Loader & Scott Wilson, Barbara & Graeme Nicholas, Karen Savage & Roger Slee,
Sonya Olykan & Steve Thomas
Those who recorded trial data on tree growth, yield and timing of budburst and flowering –
including the organising committee, the trial block owners, Hugh Stevenson, Selwyn Adams,
Basil & Trudi Meyer, and several students
Those who carried out nut assessment measurements – Hugh & Jill Stevenson, Anna Brenmuhl,
Dave Malcolm, Nelson Hubber, Barbara Nicholas, Margaret Brenmuhl, Heather North
Data analysis and write-up – Heather North.
‘Shannon’ and ‘1340’ – selected by Manawatū propagator Vernon Harrison
‘Serr’ – a cultivar imported from USA in the 1970s, preferred by walnut industry pioneer Bernard
Vavasour in Marlborough, which we felt deserved further trial
‘DSIR-121’: the selection ‘121 Chch’ that did well at the old DSIR/NZ Tree Crops Association
(NZTCA) trial block (late 1970s/early 1980s) in Lincoln
Four seedling trees on the properties of walnut suppliers which processors Jenny and Malcolm
Lawrence noted for good nut quality: ‘Coleridge’, ‘Blenheim’, ‘Cashmere’ and ‘Rangiora’ (named
here according to their location)
One seedling selection ‘Diana’ put forward by Whanganui grower Diana Loader.
The trees were grafted in the winters of 2004 and 2005, using cultivar ‘Serr’ as rootstock. The Whanganui growers found the use of ‘Serr’ as a rootstock was problematic, as it produced excessive growth of suckers from the rootstock at that site. There were multiple spring frosts in the early years of the trial (2007, 2008, 2009) particularly affecting the Canterbury sites, which limited early growth rates and caused some tree deaths.