Articles
Preharvest efficacy of alternatives used in conjunction with registered fungicides in controlling heart rot in pomegranates
Article number
1464_37
Pages
271 – 276
Language
English
Abstract
Pomegranates (Punica granatum L.) is a minor crop in South Africa, with an industry that has grown by 25% in the last five years as reported in 2024, where more than 8,000 t were exported from South Africa to countries in the northern hemisphere during their off-season.
The aim of this preharvest trial was to gauge if two alternative products show potential to limit Alternaria sp. infections causing heart rot on P. granatum trees where the registered fungicides that contained azoxystrobin and difenoconazole were applied three times in 2-week intervals from full bloom.
In 2023/2024 a pilot trial on ‘Wonderful’ pomegranate trees was conducted during bloom where spray was applied using 0.03 mg L‑1 silver ions (Ag+) in 5% hydrogen peroxide (SHP). For a larger scale trial for the 2024/2025 season, another treatment was also tested, and it was a product containing 1.8 g L‑1 l-phenylalanine (LPA) and the trial was conducted on the cultivars ‘Acco’ and ‘Wonderful’. At harvest, all fruit was cut and evaluated for heart rot incidence.
Symptomatic fruit was sampled and fungi isolated.
For the 2023/2024 season the average heart rot incidence found on the SHP treated trees was 2% and for the untreated control 2.1%. For the 2024/2025 season, the average heart rot incidence in-orchard for the ‘Acco’ SHP treatment was 1.2, 2.3% for LPA, and 0.9% for the controls.
In ‘Wonderful’ SHP treated, fruit incidence was 0.4%, while in those treated with LPA and untreated was 0.7 and 1.0%, respectively.
From the pilot trial, fungi isolated from heart rot symptoms included species from the genus Alternaria, Aspergillus, and Penicillium. It is expected that the same genera of fungi will be isolated from the 2024/2025 trial, and that Alternaria sp. and Aspergillus sp. would be the causal agents of the heart rot in the pomegranates after species identification and pathogenicity trials.
The aim of this preharvest trial was to gauge if two alternative products show potential to limit Alternaria sp. infections causing heart rot on P. granatum trees where the registered fungicides that contained azoxystrobin and difenoconazole were applied three times in 2-week intervals from full bloom.
In 2023/2024 a pilot trial on ‘Wonderful’ pomegranate trees was conducted during bloom where spray was applied using 0.03 mg L‑1 silver ions (Ag+) in 5% hydrogen peroxide (SHP). For a larger scale trial for the 2024/2025 season, another treatment was also tested, and it was a product containing 1.8 g L‑1 l-phenylalanine (LPA) and the trial was conducted on the cultivars ‘Acco’ and ‘Wonderful’. At harvest, all fruit was cut and evaluated for heart rot incidence.
Symptomatic fruit was sampled and fungi isolated.
For the 2023/2024 season the average heart rot incidence found on the SHP treated trees was 2% and for the untreated control 2.1%. For the 2024/2025 season, the average heart rot incidence in-orchard for the ‘Acco’ SHP treatment was 1.2, 2.3% for LPA, and 0.9% for the controls.
In ‘Wonderful’ SHP treated, fruit incidence was 0.4%, while in those treated with LPA and untreated was 0.7 and 1.0%, respectively.
From the pilot trial, fungi isolated from heart rot symptoms included species from the genus Alternaria, Aspergillus, and Penicillium. It is expected that the same genera of fungi will be isolated from the 2024/2025 trial, and that Alternaria sp. and Aspergillus sp. would be the causal agents of the heart rot in the pomegranates after species identification and pathogenicity trials.
Authors
E. van Rooyen, E. Venter, J.C. Meitz-Hopkins, C.L. Lennox
Keywords
Alternaria, heart rot, alternatives, pomegranate (Punica granatum L.)
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