Research on Dithianon to Evaluate Suspects of Reduced Sensitivity of &amp;lt;i&amp;gt;Venturia inaequalis&amp;lt;/i&amp;gt; with Different Methodologies in Italian Apple Areas

Fiaccadori Riccardo

doi:10.4236/ajps.2021.123026

Abstract

Dithianon is a multi-site fungicide and has never been object of suspects and reports of reduced sensitivity and activity. Italian IFP technicians had the suspect of reductions of activity by this fungicide on Venturia inaequalis. Methodologies, in vitro and in vivo were carried out to verify this suspect. Populations poorly controlled with suspects on dithianon and sensible ones were utilized. The tests in vitro permitted to evidence light and non-significant reductions of sensitivity of poorly controlled populations with respect to sensible ones. In vivo tests on seedlings were non-reliable for a general low activity of dithianon. On the contrary, the original in vivo methodology on grafted apple plants showed several reductions of activity, with moderate levels and a spot distribution in orchards. The cause was probably due to the increased treatments with dithianon caused by problems on other groups of fungicides and by a high infective pressure in some years. It is discussed if this reduction can be considered a resistance phenomenon or a temporary modification of the interactions of plant-fungus-fungicide.

Highlights

The cause was probably due to the increased treatments with dithianon caused by problems on other groups of fungicides and by a high infective pressure in some years
The different types were collected from: - Trees in uncultivated and untreated areas. - Orchards often treated with dithianon where the control of V.inaequalis was good
The results showed that there are no statistical differences among the three types of populations, especially when we compare well and poorly controlled ones in commercial orchards

Summary

Introduction

Dithianon is a fungicide commercialized since 1963 with a broad spectrum of activity on many phytopathogen fungi belonging to Ascomycetes or Deuteromycetes [1] that infect crops all over the world [2] and is registered on many diseases, comprehending on Venturia (inaequalis and pirina). In the control of V. inaequalis, dithianon has often acquired an important role and it is active mostly in preventive applications, 3 - 5 day before infection [5] [6], and in timely post-infection sprays, better 12 hours after the beginning of the infection [7] [8] It is utilized during a long vegetative period (from “mouse ears” to “fruit set”), generally with a rather high number of treatments. The importance of this fungicide is increased by the fact that regulations of European Community [9] revoked or limited many pesticides, reducing those with multiside action and favoring the news, more toxicologically sure but with a much higher risk of resistance

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