Asian soybean rust management based on leaf area index and multisite fungicide¹

Manejo da ferrugem asiática da soja baseado no índice de área foliar e fungicida multissítio

HIGHLIGHTS:

Based on the leaf area index (LAI), a new approach was proposed to start the fungicide applications to control Asian soybean rust.

Fungicide application started at 3.6 LAI proved to be the best option to control Asian soybean rust.

An increase in carrier volume does not benefit the spray deposition on soybean leaves.

ABSTRACT

Soybean foliar diseases negatively affect leaf area index (LAI) and compromise the main structure for photosynthesis and grain yield. The objective of this study was to propose a new methodology to determine the commencement of fungicide application based on the soybean LAI, spray volumes, and the inclusion of a multisite fungicide to control Asian soybean rust (ASR). The study was implemented in a randomized block design at two locations, with four replicates in a factorial scheme plus one additional treatment (4 × 2 × 2 + 1) - four soybean LAI (0.9, 1.8, 3.6, and 6.1) indicating the initiation stages of fungicide applications, two spray volumes (70 and 120 L ha^-1), with or without multisite fungicide (mancozeb), and a control treatment without fungicide. The spray deposition on plants did not differ between the treatments for 1.8 and 3.6 LAI. Treatments including the multisite fungicide for LAI between 3.6 and 6.1 for both spray volumes presented superior ASR control results. The highest soybean yields were observed when fungicide application started at 3.6 LAI for both spray volumes. The best correlation between disease control and grain yield occurred when the applications started at 3.6 LAI with 70 L ha^-1 spray volume and the multisite fungicide.

Key words:
Glycine max; Phakopsora pachyrhizi; application timing; spray volume; plant protection