Integrated disease management update:
By Tonya Wiechel and Simone Kreidl Agriculture Victoria Research, AgriBio Centre for AgriBiosciences, Bundoora
AGRICULTURE Victoria researchers have been busy collecting this season's hull rot data as part of the Integrated disease management project AL22002. In February, two field trials at the Almond Centre of Excellence at Loxton were assessed for hull rot. SARDI Trial 3, the Low to Medium Density Optimisation Trial, evaluates four almond varieties, including three potential replacements for ‘Nonpareil.’
This large-scale (5 ha) planting was established in July 2018 using four varieties—Nonpareil, Carina, Vela, and Shasta—all grafted to Garnem rootstock. The trial is designed to assess tree performance across a range of planting densities, with trees established in 6.5m rows and spacing between trees varying from 5.0m to 2.5m. This results in six different density treatments ranging from 308 to 615 trees per hectare, with each treatment replicated six times to ensure reliable data on growth, yield, and orchard efficiency.
SARDI Trial 5 focuses on evaluating rootstock compatibility and planting density for new self-fertile, ‘Nonpareillike’ replacement varieties. The trial aims to assess these new varieties on a diverse selection of recently available rootstocks with varying vigour levels, including Nemaguard, Cornerstone, Garnem, Felinem, Monegro, Atlas, Krymsk, Barrier1, RootPacR, RootPac40, RootPac20, Controller6, Controller7, and Controller9.5. ‘Nonpareil’ is included as a comparator to provide a benchmark for performance. The trees are planted at both medium (H2 - 6.5m x 3m spacing) and high (H3 - 4.5m x 2m spacing) densities to determine the most effective combinations for optimal growth and productivity.
Agriculture Victoria’s IDM team is using these plantings to investigate the relationship between tree density, rootstocks and hull rot disease expression under Australian conditions. The first season of hull rot disease assessment data from Non pareil trees has recently been collected (Figure 1 and 2). Although conditions this season were not conducive for the disease with only 8.2mm of rainfall prior to hull split there was still disease apparent in the orchard, probably due to humidity. In SARDI Trial 3, the highest average number of hull rot strikes occurred at a density of 342 trees per hectare (20 strikes).
Figure 1. Hull rot strikes on Non pareil on Felinem at ACE orchard.
Table 1 - Hull rot strikes on NP across 14 rootstocks in SARDI Trial 5.
This density also exhibited the largest maximum value (92 strikes), indicating potential vulnerability to hull rot at moderate planting densities. All other planting densities had relatively low average strike numbers ranging from 4-10. The minimum and maximum values were more consistent at the lower density plantings suggesting that lower density may help reduce hull rot. However, the highest maximum number of strikes in the denser plantings (440, 513, and 615 trees per hectare) did not exceed 20, and in some cases, the minimum was as low as zero.
Figure 2. Hull rot strike on Non pareil with Rhizopus spores between the hull and the shell.
In SARDI Trial 5, the average number of hull rot strikes for H2 was 17, while it is significantly higher at 31 for H3, indicating that hull rot was greater in the denser H3 planting system. In the H2 system, RootPac40 (37) and Controller6 (28) had the highest number of hull rot strikes. For H3, Monegro (81) and Cornerstone (80) had the highest number of hull rot strikes, showing that the rootstocks perform differently in the different planting systems.
Rootstocks like Barrier 1, Garnem, and Controller9.5 had similar numbers of hull rot strikes across both planting systems. These rootstocks may offer reliable performance regardless of planting density. Monegro, RootPac20, Controller7 and Krymsk86 had less than 10 hull rot strikes in the H2 system while in H3, Krymsk86, RootPac40, RootPac20 and Controller6 had less than 10 hull rot strikes (Table 1).
Previous research has shown that rootstocks can influence hull rot strikes. Growers should consider the planting density when selecting rootstocks. For tighter plant spacing (H3), Monegro and Cornerstone developed more hull rot strikes, while RootPac40 and Controller6 had more in wider spacings (H2).
