Captan-induced bronzing and inking of peach skin and mitigation strategies

The skin disorders known as ‘bronzing’ and to a lesser degree ‘inking’ have reduced marketable yield of peach fruit in South Carolina and Georgia over decades.
However, the causes of the disorders are largely unknown and mitigation strategies are not available.
Peaches with bronzing reveal discoloration of the skin in form of blotches that may be bronze, brown on yellow skin (bronzing) or dark purple to almost black on red skin (inking) depending on the background color.
Captan fungicide applied preharvest for brown rot control has long been suspected to cause skin discoloration, especially inking.
In this two-year study, captan was applied in form of Captan 80WDG at label rate and three times (3×) the label rate with or without adjuvant AG09075 ten days and one day before harvest and bronzing/inking incidence and severity were determined on fruit after storage.
Results indicate that Captan 80WDG applications induced bronzing/inking incidence and severity in both experimental years.
The adjuvant AG09075 significantly mitigated bronzing/inking occurrence and severity in the label-rate captan treatment (P<0.01), but not in the 3× label rate treatment.
Bronzing/inking incidence and severity were higher in all treatments (including the untreated control) in experimental year 2020 compared to 2019 and correlated with increased rainfall during preharvest season.
The data indicate that bronzing/inking can be induced by multiple factors, including (but not limited to) preharvest captan applications and increased rainfall during fruit maturation.
Limited mitigation of bronzing/inking was achieved with adjuvant AG09075.

X International Peach Symposium

J.M. Lawton, J.C. Melgar, G. Schnabel

Prunus persica, blotches, inking, bronzing, peach, skin disorder, environmental conditions

https://doi.org/10.17660/ActaHortic.2022.1352.6