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Avocado

Impact of Peroxsil® on (Cercospora) Black Spot

Silver as an Effective Disinfectant: Silver possesses natural antimicrobial properties due to its ions binding to the DNA of viruses, fungi and bacteria, preventing their replication. When combined with (unstable) hydrogen peroxide, which corrodes cell walls, silver forms a stable product with dual action. This results in a highly effective disinfectant that is not only biodegradable but also eco-friendly.

Avocado Disease Management:

Cercospora (Black Spot), caused by fungus Cercospora purpurea, is a prevalent pre-harvest disease effecting avocado fruit. It leads to lesions that impact the fruit’s aesthetic quality. Fungal spores spread through wind, water, contaminated tools, and insects. While the disease primarily affects the fruit skin (peel), severe infections can affect the flesh. Control measures often involve copper-containing fungicides. However, excessive use of this heavy metal has negatively affected soil biodiversity, and plant health.

Investigating Peroxsil’ s Impact on Cercospora Black Spot – A Case Study:

A study was conducted by RDAgric (Estelle Louw MSc) to determine the impact of Peroxsil® on Cercospora Black Spot, a common pre-harvest disease affecting avocado fruit. The research focused on the cv. Fuerte and took place within the Greater Tzaneen municipal district in South Africa’s Limpopo Province. To ensure infections (for a successful study), Copper Oxychloride was applied only twice during the initial stages of the 2023/24 avocado growing season – in late October and late November 2023 (approximately monthly intervals).

Peroxsil® was applied as a pre-harvest foliar spray at three different concentrations: 0.5%, 1%, and 2%. The corrective, medium cover foliar spray was applied on 24/02/2024, when disease manifestations were already prominent. The aim was to conduct a pre-count assessment, allowing researchers to gauge disease spread and severity across the study area. Finally, a single assessment was conducted just before the commercial harvest, on March 4,2024.

Conclusion:

Applying Peroxsil® towards the end of the season, when reducing the number of Copper Oxychloride applications, can mitigate possibility of residues. Additionally, this approach may help minimise potential adverse impacts on soil biodiversity and plant health. An increase in the number of pre-harvest foliar sprays would prominently reduce latent post-harvest infections in the orchard, which, in turn, can enhance the efficacy of the Peroxsil® post-harvest dip treatment.

Download the full trial details (pdf).