Evaluation of Potassium Phosphite and Myclobutanil Combinations for Pear Scab (Venturia pirina) Suppression    (View PDF)

Glynn C. Percival and Kelly Noviss

Abstract: The purpose of this study was to investigate the use of potassium phosphite (Pi) alone and in combination with a reduced dose of synthetic fungicide (myclobutanil) to control pear scab (Venturia pirina) under field conditions. Irrespective of Pi and myclobutanil concentration, no leaf or fruit phytotoxic effects were observed throughout the 2006 and 2007 experiments. In both field experiments, Pi alone significantly reduced the incidence and severity of V. pirina on leaves and fruit compared to water-treated control with the degree of scab reduction similar to that of a reduced dose of myclobutanil. The efficacy of Pi at 20 ml per liter water in inhibiting V. pirina scab incidence and severity was superior than that of Pi at 10 ml per liter water and a reduced dose of myclobutanil in virtually all monthly assessments. Combining a reduced dose of myclobutanil with either Pi at 10 ml or 20 ml per liter significantly improved the efficacy of scab control compared to stand alone applications of each product at most monthly assessments. Data analyzed with Limpel’s formula indicated a positive synergistic effect between Pi and a reduced dose of myclobutanil. Greatest reductions in V. pirina incidence and severity on leaves and fruit were, however, achieved by stand alone applications of myclobutanil at manufacturers recommended strength. Irrespective of year, crown volume, number of fruit per tree, and total fruit yield were higher in Pi and myclobutanil treated trees irrespective of concentration applied compared to water-treated controls. A combined mix of Pi with a reduced dose of myclobutanil proved effective in increasing crown volume, number of fruit per tree and fruit yield compared to stand alone applications of each treatment. Greatest increases in crown volume, number of fruit per tree and fruit yield were achieved by applications of myclobutanil at the manufacturers recommended strength. In virtually all cases, Pi combined with a reduced dose of myclobutanil induced positive synergistic effects on crown volume and fruit yield greater than their additive effects alone. Mean fruit weight per tree were in all cases higher in Pi and myclobutanil treated trees irrespective of concentration applied compared to water-treated controls, however, these differences were not statistically significant in all cases.

Keywords: Fungicides, Integrated Disease Management; Orchard Management; Pathogen Control; Plant Health Care; Synergism; Urban Landscapes

https://doi.org/10.48044/jauf.2010.012