Effects of calcium propionate seed treatments and foliar sprays of potatoes

Abstract

Potatoes provide a significant economical value to the New Zealand economy, contributing over $1 billion per year. Candidatus Liberibacter solanacearum (CLso) which causes zebra chip disease and is vectored by tomato potato psyllid (Bactericera cockerelli) (TPP) causes several million dollars of damage to the potato industry. Calcium propionate (Ca prop) is used as a food additive to inhibit micro-organisms. In this series of trials, we investigated its use to prevent infection by CLso. Preliminary investigations in pots using ‘Moonlight’ seed potatoes showed no infection in potato plants, which received a single foliar treatment of 0.25, 0.5, 0.75 or 1% Ca prop or a 2% Ca prop soil drench were not infected. Only untreated tubers were infected with CaLSo after exposure to CLSo-infected TPP for 3 weeks. A second trial focussed on soil drench treatments with concentrations of 0.25, 0.5, 0.75, 1.0, and 2.0%. All soil drench treatments showed a 50 to 100% reduction in CLso infection compared to the control. A third trial using ‘Russet Burbank’ seed tubers treated with of 1% foliar treatment, 5% seed treatment in which tubers were dipped into Ca prop and a third treatment of the foliar and seed treatment combined did not show significant differences. More trials are needed to determine if success is related to potato variety, changes in cell wall strength, or psyllid feeding preferences.