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Can vitamin sprays control almond disease?
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Almond hulls make up 54% of the whole nut, and in Australia they go mainly to animal feed and bioenergy. That makes pesticide residues in the hulls a real concern for the industry. A Federation University Australia team wanted to know whether foliar vitamin sprays could control disease in a commercial almond orchard as well as the grower's usual chemical program, so that fewer pesticides would end up in the hulls (Udagepolage Don et al., 2026).
What this means for your grow
For almond growers, this is one to watch rather than act on yet. In one commercial orchard in north-west Victoria, over two seasons, every vitamin spray tested cut leaf and nut disease compared with unsprayed trees, and none differed significantly from the grower's chemical program. Kernel yield, leaf chlorophyll and flower-to-nut conversion were not significantly affected. The authors say studies across other regions, seasons and orchard management systems are needed before broader recommendations can be made, and the trial was run in a commercial orchard, not a home garden.
What did the team do?
The trial ran on almond farms in the main Australian almond-growing region, in north-west Victoria between Swan Hill and Robinvale, and the authors describe it as a single commercial orchard. It covered two complete growing seasons, over three years from 2021 to 2024, on three varieties: Monterey, Carmel and Nonpareil.
There were eight vitamin sprays: vitamin B1 (thiamine) on its own, a commercial vitamin B complex, B complex with vitamin E, and B complex with vitamins C and E, each at 50 and 250 micrograms per millilitre. Each formulation also contained 5% plant-derived amino acids and 5% biologically active organic molecules, added to help absorption, and no spray adjuvant was used. Trees were sprayed twice, once while the nuts were developing and once as they matured, to the point of drip.
The sprays were compared with two kinds of trees: an untreated control that got neither vitamins nor pesticides, and a grower standard that got the orchard's normal fungicide and insecticide program. Irrigation, fertilising and other orchard work were kept the same across all treatments.
The team counted disease damage on samples of 20 leaves and 20 nuts, looking at shot-hole, bacterial spot and leaf rust. They also measured leaf chlorophyll with a SPAD meter, flower-to-nut conversion (how many flowers become harvestable nuts), kernel nutrients, kernel damage from insects and from aborted or gummy kernels, and the oven-dried weight of the kernels, and screened hull and kernel samples for pesticide residues.
What did they find?
- Less leaf disease than unsprayed trees. All the treatments had significantly less leaf disease than the untreated control in both seasons, and there was no significant difference between the grower standard and any of the vitamin sprays.
- Season one leaves. The untreated control accounted for 20.22% of all the leaf damage counted that season. B1-50 (vitamin B1 at 50 micrograms per millilitre) and BcCE-50 (B complex with vitamins C and E at the same strength) had the lowest share, 7.01% each, and the grower standard 8.09%.
- Season two leaves. No visible leaf disease damage was recorded on trees sprayed with B1-50, in any of the three varieties. The untreated control accounted for 28.81% of the season's leaf damage and the grower standard 11.86%.
- Less disease on the nuts too. Whole-nut disease was also significantly lower than the untreated control for every treatment, with no significant difference between the grower standard and the vitamin sprays. In season one the untreated control accounted for 24.57% of the nut damage, BcCE-50 6.57% and the grower standard 7.27%. In season two the figures were 29.76% for the control, 1.09% for BcE-50 (B complex with vitamin E at 50 micrograms per millilitre) and 11.60% for the grower standard.
- No cost to the crop. Oven-dried kernel weight showed no significant treatment effect in either season (p = 0.181 and p = 0.211). Chlorophyll did not differ significantly between the control and treated trees, and flower-to-nut conversion showed no significant difference between the grower standard and the vitamin sprays.
- Kernel damage stayed low. Insect damage from carob moth and Carpophilus beetle affected one of 1920 kernels in season one and 19 in season two, and aborted or gummy kernels numbered 8 and 31 of 1920. Neither showed significant differences between treatments.
- Residues in the chemical program. A screen of 280 analytes found residues mainly in samples from the grower standard. The highest reported was the fungicide azoxystrobin, at up to 7.43 mg/kg in season two. No elevated pesticide residues were detected in the kernels in either season.
Disease pressure was higher in season one than season two, with 371 against 118 leaf disease incidents and 578 against 457 on the nuts.
What could it mean?
The authors conclude that several treatments performed at a level comparable to the grower standard chemical program, and that vitamin-based biostimulants have the potential to become a useful part of integrated disease management in commercial almond production. Because the sprays did not raise kernel yield, they describe the benefit as lower disease pressure without compromising productivity, along with a lower risk of pesticide residues in hulls meant for livestock feed. They also estimated the cost of the vitamin applications at approximately five times lower than conventional chemical pesticide applications for disease management, while calling for a comprehensive cost-benefit analysis.
Right now this is a result for commercial almond growers and researchers to follow, not a proven replacement for a spray program.
What were the limitations?
- The trial was run at a single commercial orchard in one almond-growing region of Australia, on a defined range of vitamin formulations, over two growing seasons.
- Disease pressure stayed low enough that it did not translate into a detectable yield penalty. The authors say trials under greater disease pressure, across more sites and seasons, are needed to find out whether disease suppression can give a measurable yield advantage.
- Application timing, frequency, best rates and long-term economic performance still need to be worked out.
- The lower disease in season two may have been due to the season or to the season-one treatments carrying over; the authors say this needs more research.
- The study looked at field performance only, so how the vitamins work was not investigated. Storage life of the nuts was not measured.
- The commercial B complex product's concentrations of each individual B vitamin were not verified.
- The paper is not always consistent. Its abstract credits a formulation of vitamin B complex together with vitamin B1 at 50 micrograms per millilitre, but no treatment in Table 1 combines the two: B1-50 is vitamin B1 alone. One passage names BcE-50 as having the lowest leaf damage in season one, while Table 2 gives the lowest share to B1-50 and BcCE-50. One methods passage also says the control trees received the grower's chemical sprays, while Table 1 and the description of the grower standard say the untreated control received neither vitamins nor pesticides. This post follows Table 1 and the results tables.
Trial details
- Who and where: Federation University Australia (The Future Regions Research Centre, Mount Helen, Ballarat), with authors also from RMIT University and Ag Analytics. The trial was in a commercial almond orchard in the main almond-growing region of north-west Victoria, Australia, between Swan Hill and Robinvale. Facility type: field (commercial orchard).
- When: two complete consecutive growing seasons over three years, from 2021 to 2024.
- Crop: almond (Prunus dulcis), varieties Monterey, Carmel and Nonpareil. Sprays applied at the nut development stage and the nut maturation stage.
- Treatments: vitamin B1 (B1), commercial vitamin B complex (Bc), vitamin B complex + E at 1:1 (BcE) and vitamin B complex + C + E at 1:1:1 (BcCE), each at 50 and 250 µg mL−1; each formulation with 5% plant-derived amino acids and 5% biologically active organic molecules (BAOMs); no spray adjuvant. Compared with an untreated control (no chemical or vitamin treatments) and the grower standard (the orchard's routine fungicide and insecticide program).
- Application: foliar spray with a motorised 12v spray unit, 5 litres of tank mix per plant, to the point of drip, at a water rate of 1250 L/Ha; applied once during nut development and once during nut maturation.
- Design: randomised complete block design on 66 rows of 138 almond trees across two neighbouring plots; 72 treated replicates, 12 control replicates and 12 grower standard replicates. Each replicate comprised three groups of 3 trees; replicates were separated by buffers of approximately 12 m (two to three rows, or a buffer area).
- Sampling and measurements: 20 mature nuts per replicate, picked from shoulder height one week before harvest, and 20 mature leaves per replicate; 96 leaf samples and 96 whole-nut samples. Nut samples were incubated for 14 days in sealed plastic bags at 4.0 °C to assess fungal disease. Chlorophyll by SPAD-502 Plus over 1920 leaves. Kernels and hulls dried at 70 °C to constant weight. Kernel nutrients by ICP-OES and ICP-MS; residues by multi-residue screening (280 analytes) at Analytical Laboratories and Technical Services Australia Pty Ltd.
- Statistics: linear mixed model in IBM SPSS (versions 29.0.0.0 and 30.0.0.0), with Bonferroni correction. Treatment effect on leaf disease p < 0.001 in both seasons; on whole-nut disease p < 0.001 (season one) and p = 0.040 (season two).
- Results: leaf damage as a share of the season's total: season one control 20.22%, grower standard 8.09%, B1-50 and BcCE-50 7.01%; season two control 28.81%, grower standard 11.86%, B1-50 0.00%. Whole-nut damage share: season one control 24.57%, grower standard 7.27%, BcCE-50 6.57%; season two control 29.76%, grower standard 11.60%, BcE-50 1.09%. Oven-dried kernel weight: no significant treatment effect (p = 0.181 and 0.211). Chlorophyll: no significant difference between control and treated trees (p = 0.996 in season one, p = 0.527 in season two). Insect-damaged kernels: 1 of 1920 (0.052%) and 19 (0.989%); aborted and gummy kernels: 8 of 1920 (0.416%) and 31 of 1920 (1.614%), not significant. Grower standard residues included azoxystrobin up to 7.43 mg/kg and methoxyfenozide up to 3.65 mg/kg.
- Funding and conflicts of interest: funded by the Australian Government Research Training Program (RTP) Fee-Offset Scholarship through Federation University Australia and by Dual Investment Group, via Dual Chelate Fertilizer Pty Ltd. Redox Pty Ltd supplied the commercially available vitamin formulations, and Dual Chelate Fertilizer Australia Pty Ltd and Olam Edible Nuts Australia gave in-kind support. One author was employed by Ag Analytics Pty Ltd; the others declare no conflicts of interest.
- Publication: Plants 15(17), 2606, published 26 August 2026, https://doi.org/10.3390/plants15172606. Licence: CC BY 4.0.
- Not reported in the paper: the exact dates of each spray, tree age and rootstock, the per-component concentrations in the B complex product, weather and climate data, irrigation and fertiliser details, the products and rates in the grower standard program, and residue figures for the vitamin-treated and untreated trees.
Links
- The study: Evaluation of Vitamin-Based Biostimulants for Disease Suppression and Sustainable Almond Production Under Commercial Orchard Conditions
- The institution: Future Regions Research Centre, Federation University Australia
References
- Udagepolage Don, M. N., Florentine, S., Turville, C., & Dassanayake, K. (2026). Evaluation of vitamin-based biostimulants for disease suppression and sustainable almond production under commercial orchard conditions. Plants, 15(17), 2606. https://doi.org/10.3390/plants15172606