Agriculture Reference
In-Depth Information
Chapter 10
Site-Specifi c Weed Control
Roland Gerhards
Abstract
Spatial and temporal variations in weed seedling distributions in arable
fi elds are analysed. It is described how weed distributions can be assessed by manual
grid sampling and by using sensor technologies from the near range. The potential
for herbicide savings using site-specifi c weed management in different crops is
calculated. Two different approaches for site-specifi c weed control are presented.
First, an offl ine-approach based on georeferenced weed distribution maps and sec-
ondly a real-time approach combining sensor- and patch spraying technologies.
The decision rules for patch spraying should take into account density, coverage and
yield loss effects by weed species, its growth stages and costs of weed control.
Herbicide savings using precision weed control varied from 20 to 70 %. Real-time
patch spraying is the most economic treatment followed by map-based site-specifi c
weed control. Uniform herbicide applications and uncontrolled treatments gave the
lowest economic return. Several studies showed that weed species distribution
remained stable over time when site-specifi c herbicide applications were realized
based on economic weed thresholds.
Keywords
Direct injection system • Distribution • Image analysis • Mapping
• Multiple fi eld sprayer • Patches • Shape features • Site-specifi c control
10.1
Introduction
Weed seedling distribution changes spatially and temporally within agricultural
fi elds. It often presents itself in
aggregated patches
of varying size or in stripes
along the direction of cultivation (Marshall
1988
; Gerhards et al.
1997
; Christensen
