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et al., 2013 ). With the vast majority of weed seeds exiting in the chaff fraction dur-
ing harvest a number of commercially available systems are now available that tar-
get this weed seed bearing fraction. These include, chaff collection and subsequent
burning, grazing or mulching (chaff cart), concentration in a narrow windrow with
straw residues for subsequent burning (narrow windrow burning), concentration of
chaff into narrow rows (chaff lining), chaff collected and baled along with straw
residues (Bale Direct System) and mechanical destruction during harvest (Harrington
Seed Destructor)
As HWSC systems target the weed seed bearing chaff fraction, these will all be
similarly effective in in targeting weed seed during crop harvest. With the assump-
tion of efficient harvester setup and operation, weed seeds will predominantly exit
the harvester in the chaff fraction which logically then is the focus for HWSC sys-
tems. An extensive evaluation of three HWSC systems (chaff cart, narrow windrow
burn and HSD) for their efficacy on annual ryegrass was conducted across the
Australian dryland cropping region in 2010 and 2011. These treatments, imposed
during harvest, were assessed for their efficacy on subsequent autumn emergence of
annual ryegrass. Across 25 sites chaff cart, narrow windrow burning and HSD treat-
ments similarly reduced (p < 0.05) annual ryegrass emergence in comparison to the
control treatment (Table 1 ). In this study the overall impact of HWSC treatments
was varied and likely influenced by pre-harvest seed shed as well as pre-existing
seed banks and early season rainfall. When averaged across all 25 sites, HWSC
treatments resulted in a 56 % reduction in subsequent autumn annual of ryegrass
emergence. However, there was considerable variation in HWSC efficacy between
sites with large reductions in annual ryegrass emergence of up to 90 % (Arthurton)
contrasting with reductions as low as 29 % (Rand) (Table 1 ). Thus although HWSC
systems will be similarly effective on annual ryegrass populations, large variations
in population responses can be expected due to seasonal conditions and background
seedbank levels
HWSC is now established as an effective weed control practice with Australian
crop producers. It is estimated that currently almost one-third of Australian growers
are routinely using some form of HWSC to target their crop weed problems.
However, although these systems have proven their efficacy on annual ryegrass and
wild radish (Walsh et al. 2013 ) their efficacy on the other dominant weed species of
Australian cropping, wild oats and brome grass, may be limited by poor seed reten-
tion at crop harvest (Walsh and Powles 2014 ). Therefore, given that HWSC is now
a routine form of weed control the challenge for researchers and the industry is to
increase the efficacy of these systems on other weed species.
5 Weed Management in Future Crop Production Systems
The opportunity for substantial cost savings combined with the potential for intro-
ducing novel weed control technologies is driving the demand for site-specific weed
management control. However, this approach to weed control requires suitable
weed detection and identification technology that currently is not commercially
M. Wa lsh